why is climate change happening essay

ENCYCLOPEDIC ENTRY

Climate change.

Climate change is a long-term shift in global or regional climate patterns. Often climate change refers specifically to the rise in global temperatures from the mid-20th century to present.

Earth Science, Climatology

Fracking tower

Fracking is a controversial form of drilling that uses high-pressure liquid to create cracks in underground shale to extract natural gas and petroleum. Carbon emissions from fossils fuels like these have been linked to global warming and climate change.

Photograph by Mark Thiessen / National Geographic

Climate is sometimes mistaken for weather. But climate is different from weather because it is measured over a long period of time, whereas weather can change from day to day, or from year to year. The climate of an area includes seasonal temperature and rainfall averages, and wind patterns. Different places have different climates. A desert, for example, is referred to as an arid climate because little water falls, as rain or snow, during the year. Other types of climate include tropical climates, which are hot and humid , and temperate climates, which have warm summers and cooler winters.

Climate change is the long-term alteration of temperature and typical weather patterns in a place. Climate change could refer to a particular location or the planet as a whole. Climate change may cause weather patterns to be less predictable. These unexpected weather patterns can make it difficult to maintain and grow crops in regions that rely on farming because expected temperature and rainfall levels can no longer be relied on. Climate change has also been connected with other damaging weather events such as more frequent and more intense hurricanes, floods, downpours, and winter storms.

In polar regions, the warming global temperatures associated with climate change have meant ice sheets and glaciers are melting at an accelerated rate from season to season. This contributes to sea levels rising in different regions of the planet. Together with expanding ocean waters due to rising temperatures, the resulting rise in sea level has begun to damage coastlines as a result of increased flooding and erosion.

The cause of current climate change is largely human activity, like burning fossil fuels , like natural gas, oil, and coal. Burning these materials releases what are called greenhouse gases into Earth’s atmosphere . There, these gases trap heat from the sun’s rays inside the atmosphere causing Earth’s average temperature to rise. This rise in the planet's temperature is called global warming. The warming of the planet impacts local and regional climates. Throughout Earth's history, climate has continually changed. When occuring naturally, this is a slow process that has taken place over hundreds and thousands of years. The human influenced climate change that is happening now is occuring at a much faster rate.

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Why is climate change happening and what are the causes?

There are many “natural” and “anthropogenic” (human-induced) factors that contribute to climate change. Climate change has always happened on Earth, which is clearly seen in the geological record; it is the rapid rate and the magnitude of climate change occurring now that is of great concern worldwide. Greenhouse gases in the atmosphere absorb heat radiation. Human activity has increased greenhouse gases in the atmosphere since the Industrial Revolution, leading to more heat retention and an increase in surface temperatures. Atmospheric aerosols alter climate by scattering and absorbing solar and infrared radiation and they may also change the microphysical and chemical properties of clouds. Finally, land-use changes, such as deforestation have led to changes in the amount of sunlight reflected from the ground back into space (the surface albedo).

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At the root of climate change is the phenomenon known as the greenhouse effect , the term scientists use to describe the way that certain atmospheric gases “trap” heat that would otherwise radiate upward, from the planet’s surface, into outer space. On the one hand, we have the greenhouse effect to thank for the presence of life on earth; without it, our planet would be cold and unlivable.

But beginning in the mid- to late-19th century, human activity began pushing the greenhouse effect to new levels. The result? A planet that’s warmer right now than at any other point in human history, and getting ever warmer. This global warming has, in turn, dramatically altered natural cycles and weather patterns, with impacts that include extreme heat, protracted drought, increased flooding, more intense storms, and rising sea levels. Taken together, these miserable and sometimes deadly effects are what have come to be known as climate change .

Detailing and discussing the human causes of climate change isn’t about shaming people, or trying to make them feel guilty for their choices. It’s about defining the problem so that we can arrive at effective solutions. And we must honestly address its origins—even though it can sometimes be difficult, or even uncomfortable, to do so. Human civilization has made extraordinary productivity leaps, some of which have led to our currently overheated planet. But by harnessing that same ability to innovate and attaching it to a renewed sense of shared responsibility, we can find ways to cool the planet down, fight climate change , and chart a course toward a more just, equitable, and sustainable future.

Here’s a rough breakdown of the factors that are driving climate change.

Natural causes of climate change

Human-driven causes of climate change, transportation, electricity generation, industry & manufacturing, agriculture, oil & gas development, deforestation, our lifestyle choices.

Some amount of climate change can be attributed to natural phenomena. Over the course of Earth’s existence, volcanic eruptions , fluctuations in solar radiation , tectonic shifts , and even small changes in our orbit have all had observable effects on planetary warming and cooling patterns.

But climate records are able to show that today’s global warming—particularly what has occured since the start of the industrial revolution—is happening much, much faster than ever before. According to NASA , “[t]hese natural causes are still in play today, but their influence is too small or they occur too slowly to explain the rapid warming seen in recent decades.” And the records refute the misinformation that natural causes are the main culprits behind climate change, as some in the fossil fuel industry and conservative think tanks would like us to believe.

Chemical manufacturing plants emit fumes along Onondaga Lake in Solvay, New York, in the late-19th century. Over time, industrial development severely polluted the local area.

Library of Congress, Prints & Photographs Division, Detroit Publishing Company Collection

Scientists agree that human activity is the primary driver of what we’re seeing now worldwide. (This type of climate change is sometimes referred to as anthropogenic , which is just a way of saying “caused by human beings.”) The unchecked burning of fossil fuels over the past 150 years has drastically increased the presence of atmospheric greenhouse gases, most notably carbon dioxide . At the same time, logging and development have led to the widespread destruction of forests, wetlands, and other carbon sinks —natural resources that store carbon dioxide and prevent it from being released into the atmosphere.

Right now, atmospheric concentrations of greenhouse gases like carbon dioxide, methane , and nitrous oxide are the highest they’ve been in the last 800,000 years . Some greenhouse gases, like hydrochlorofluorocarbons (HFCs) , do not even exist in nature. By continuously pumping these gases into the air, we helped raise the earth’s average temperature by about 1.9 degrees Fahrenheit during the 20th century—which has brought us to our current era of deadly, and increasingly routine, weather extremes. And it’s important to note that while climate change affects everyone in some way, it doesn’t do so equally: All over the world, people of color and those living in economically disadvantaged or politically marginalized communities bear a much larger burden , despite the fact that these communities play a much smaller role in warming the planet.

Our ways of generating power for electricity, heat, and transportation, our built environment and industries, our ways of interacting with the land, and our consumption habits together serve as the primary drivers of climate change. While the percentages of greenhouse gases stemming from each source may fluctuate, the sources themselves remain relatively consistent.

Traffic on Interstate 25 in Denver

David Parsons/iStock

The cars, trucks, ships, and planes that we use to transport ourselves and our goods are a major source of global greenhouse gas emissions. (In the United States, they actually constitute the single-largest source.) Burning petroleum-based fuel in combustion engines releases massive amounts of carbon dioxide into the atmosphere. Passenger cars account for 41 percent of those emissions, with the typical passenger vehicle emitting about 4.6 metric tons of carbon dioxide per year. And trucks are by far the worst polluters on the road. They run almost constantly and largely burn diesel fuel, which is why, despite accounting for just 4 percent of U.S. vehicles, trucks emit 23 percent of all greenhouse gas emissions from transportation.

We can get these numbers down, but we need large-scale investments to get more zero-emission vehicles on the road and increase access to reliable public transit .

As of 2021, nearly 60 percent of the electricity used in the United States comes from the burning of coal, natural gas , and other fossil fuels . Because of the electricity sector’s historical investment in these dirty energy sources, it accounts for roughly a quarter of U.S. greenhouse gas emissions, including carbon dioxide, methane, and nitrous oxide.

That history is undergoing a major change, however: As renewable energy sources like wind and solar become cheaper and easier to develop, utilities are turning to them more frequently. The percentage of clean, renewable energy is growing every year—and with that growth comes a corresponding decrease in pollutants.

But while things are moving in the right direction, they’re not moving fast enough. If we’re to keep the earth’s average temperature from rising more than 1.5 degrees Celsius, which scientists say we must do in order to avoid the very worst impacts of climate change, we have to take every available opportunity to speed up the shift from fossil fuels to renewables in the electricity sector.

The factories and facilities that produce our goods are significant sources of greenhouse gases; in 2020, they were responsible for fully 24 percent of U.S. emissions. Most industrial emissions come from the production of a small set of carbon-intensive products, including basic chemicals, iron and steel, cement and concrete, aluminum, glass, and paper. To manufacture the building blocks of our infrastructure and the vast array of products demanded by consumers, producers must burn through massive amounts of energy. In addition, older facilities in need of efficiency upgrades frequently leak these gases, along with other harmful forms of air pollution .

One way to reduce the industrial sector’s carbon footprint is to increase efficiency through improved technology and stronger enforcement of pollution regulations. Another way is to rethink our attitudes toward consumption (particularly when it comes to plastics ), recycling , and reuse —so that we don’t need to be producing so many things in the first place. And, since major infrastructure projects rely heavily on industries like cement manufacturing (responsible for 7 percent of annual global greenhouse gas), policy mandates must leverage the government’s purchasing power to grow markets for cleaner alternatives, and ensure that state and federal agencies procure more sustainably produced materials for these projects. Hastening the switch from fossil fuels to renewables will also go a long way toward cleaning up this energy-intensive sector.

The advent of modern, industrialized agriculture has significantly altered the vital but delicate relationship between soil and the climate—so much so that agriculture accounted for 11 percent of U.S. greenhouse gas emissions in 2020. This sector is especially notorious for giving off large amounts of nitrous oxide and methane, powerful gases that are highly effective at trapping heat. The widespread adoption of chemical fertilizers , combined with certain crop-management practices that prioritize high yields over soil health, means that agriculture accounts for nearly three-quarters of the nitrous oxide found in our atmosphere. Meanwhile, large-scale industrialized livestock production continues to be a significant source of atmospheric methane, which is emitted as a function of the digestive processes of cattle and other ruminants.

Stephen McComber holds a squash harvested from the community garden in Kahnawà:ke Mohawk Territory, a First Nations reserve of the Mohawks of Kahnawà:ke, in Quebec.

Stephanie Foden for NRDC

But farmers and ranchers—especially Indigenous farmers, who have been tending the land according to sustainable principles —are reminding us that there’s more than one way to feed the world. By adopting the philosophies and methods associated with regenerative agriculture , we can slash emissions from this sector while boosting our soil’s capacity for sequestering carbon from the atmosphere, and producing healthier foods.

A decades-old, plugged and abandoned oil well at a cattle ranch in Crane County, Texas, in June 2021, when it was found to be leaking brine water

Matthew Busch/Bloomberg via Getty Images

Oil and gas lead to emissions at every stage of their production and consumption—not only when they’re burned as fuel, but just as soon as we drill a hole in the ground to begin extracting them. Fossil fuel development is a major source of methane, which invariably leaks from oil and gas operations : drilling, fracking , transporting, and refining. And while methane isn’t as prevalent a greenhouse gas as carbon dioxide, it’s many times more potent at trapping heat during the first 20 years of its release into the atmosphere. Even abandoned and inoperative wells—sometimes known as “orphaned” wells —leak methane. More than 3 million of these old, defunct wells are spread across the country and were responsible for emitting more than 280,000 metric tons of methane in 2018.

Unsurprisingly, given how much time we spend inside of them, our buildings—both residential and commercial—emit a lot of greenhouse gases. Heating, cooling, cooking, running appliances, and maintaining other building-wide systems accounted for 13 percent of U.S. emissions overall in 2020. And even worse, some 30 percent of the energy used in U.S. buildings goes to waste, on average.

Every day, great strides are being made in energy efficiency , allowing us to achieve the same (or even better) results with less energy expended. By requiring all new buildings to employ the highest efficiency standards—and by retrofitting existing buildings with the most up-to-date technologies—we’ll reduce emissions in this sector while simultaneously making it easier and cheaper for people in all communities to heat, cool, and power their homes: a top goal of the environmental justice movement.

An aerial view of clearcut sections of boreal forest near Dryden in Northwestern Ontario, Canada, in June 2019

River Jordan for NRDC

Another way we’re injecting more greenhouse gas into the atmosphere is through the clearcutting of the world’s forests and the degradation of its wetlands . Vegetation and soil store carbon by keeping it at ground level or underground. Through logging and other forms of development, we’re cutting down or digging up vegetative biomass and releasing all of its stored carbon into the air. In Canada’s boreal forest alone, clearcutting is responsible for releasing more than 25 million metric tons of carbon dioxide into the atmosphere each year—the emissions equivalent of 5.5 million vehicles.

Government policies that emphasize sustainable practices, combined with shifts in consumer behavior , are needed to offset this dynamic and restore the planet’s carbon sinks .

The Yellow Line Metro train crossing over the Potomac River from Washington, DC, to Virginia on June 24, 2022

Sarah Baker

The decisions we make every day as individuals—which products we purchase, how much electricity we consume, how we get around, what we eat (and what we don’t—food waste makes up 4 percent of total U.S. greenhouse gas emissions)—add up to our single, unique carbon footprints . Put all of them together and you end up with humanity’s collective carbon footprint. The first step in reducing it is for us to acknowledge the uneven distribution of climate change’s causes and effects, and for those who bear the greatest responsibility for global greenhouse gas emissions to slash them without bringing further harm to those who are least responsible .

The big, climate-affecting decisions made by utilities, industries, and governments are shaped, in the end, by us : our needs, our demands, our priorities. Winning the fight against climate change will require us to rethink those needs, ramp up those demands , and reset those priorities. Short-term thinking of the sort that enriches corporations must give way to long-term planning that strengthens communities and secures the health and safety of all people. And our definition of climate advocacy must go beyond slogans and move, swiftly, into the realm of collective action—fueled by righteous anger, perhaps, but guided by faith in science and in our ability to change the world for the better.

If our activity has brought us to this dangerous point in human history, breaking old patterns can help us find a way out.

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What is climate change and why does it matter?

Climate change is the defining issue of our time . We have reached a pivotal moment in deciding our planet's future.

Find out what climate change is, why it matters and what it could mean for our collective future.

What are weather, climate and climate change?

Weather refers to atmospheric conditions, such as rain or snow, happening in a place at a specific moment in time. Climate is how much, on average, a type of weather will occur over a longer period.

Dr Joeri Rogelj is a climate scientist at Imperial College London's Grantham Institute who has contributed to and led several major climate change assessments. He explains, 'Climate change is how the characteristics of the weather we experience in a certain place change.

'It can get hotter or wetter on average or have more concentrated rain in a short period, but then get longer dry periods. All of that can be a result of climate change.'

Global warming is a term used interchangeably with climate change, although the latter is preferred because the warming atmosphere and oceans are just some of the effects we see.

'It's not just about temperature. Places are also becoming wetter or drier, and in some the seasons are moving. Most importantly, in a few regions and seasons, it may actually at times be cooler than we're used to. That's confusing if you just talk about global warming.'

This is Typhoon Utor, which affected the Philippines and China in 2013. It caused considerable damage and loss of life. Climate change influences most weather events, including tropical storms and hurricanes. © NASA Goddard Space Flight Center via Flickr ( CC BY 2.0 )

Causes of climate change

The main driver of current climate change is the emission of greenhouse gases, most importantly carbon dioxide and methane . These are primarily released when fossil fuels are burnt. Meat and dairy production, producing cement and some industrial processes, such as the production and use of fertilisers, also emit greenhouse gases.

Greenhouse gases trap heat in our atmosphere. Since the mid-nineteenth century , the world has emitted over 2.2 trillion tonnes of carbon dioxide.

Joeri explains, 'Energy from the Sun falls on our planet and normally gets reflected back as infrared radiation. But instead of escaping back out into space, this radiation gets absorbed by molecules of greenhouse gases, which then emit them in all directions.'

This process causes more heat to be kept near Earth's surface, warming our world.

How do we know climate is changing?

There are measuring stations all around the world that keep track of air and sea temperature. From these measurements it's clear that temperatures are rising.

'There are many more indicators that tell us that the Earth is warming. For example, on a warming planet we would expect polar ice caps and glaciers to melt. It is clearly observed that those are melting,' explains Joeri.

This image of an iceberg in McMurdo Sound was captured in 2017 as part of NASA's Operation IceBridge. This is an ongoing airborne mission to monitor changes in polar ice. © NASA Goddard Space Flight Center via Flickr ( CC BY 2.0 )

We know that greenhouse gases are causing change. Thanks to studies that look at how carbon dioxide absorbs infrared radiation, for example, there is a scientific understanding of how the planet would warm as a result of emissions. This has allowed climate scientists to discount the theory that global warming is being caused by an increase in the Sun's intensity, for example.

It's also known that greenhouse gases are primarily emitted by fossil fuel combustion.

'To burn carbon and produce carbon dioxide, you need oxygen. The amount of oxygen that is in the atmosphere is reducing at exactly the right amount for the increase in carbon dioxide to be caused by combusting fossil fuels,' explains Joeri.

There is additional evidence in the ratios of different types of carbon. Fossil fuels are, essentially, ancient plants . Plants now and in the past preferentially take up carbon-12. In normal conditions, the ratio between carbon-12 and carbon-13 is constant.

'What we can see is that the ratio of carbon-13 in our atmosphere is going down at exactly the rate you would predict if the carbon dioxide increase was due to burning fossil fuels.'

Scientists predict that climate change will cause extreme weather events such as wildfires, floods and hurricanes to become worse ©  Quarrie Photography via Flickr ( CC BY-NC-ND 2.0 )

Effects of climate change

Climate change does not have the same effects everywhere. The planet is generally getting hotter, but some regions and seasons can at times be temporarily cooler. Some places will see drawn-out seasons, while others may experience concentrated bursts of extreme weather.

Extreme weather events - such as hurricanes, floods, heatwaves , drought and  wildfires  - are predicted to become more intense and frequent.

'Pretty much any weather event is influenced by climate change. As scientists we can estimate how much climate change has made a certain event more likely or more intense than it would have been without climate change,' explains Joeri.

When the world warms, ice melts. Arctic sea ice could disappear entirely in a warming world, and Greenland and Antarctica's ice sheets could be destabilised. This would result in large sections melting, which would add more liquid to the ocean. 

Sea level rise caused by climate change is a threat to low lying islands such as Panama's idyllic San Blas Islands, 49 of which are inhabited © Marc Veraart via Flickr ( CC BY-ND 2.0 )

Ice also reflects the Sun's energy, so without ice, more heat is absorbed by the ocean . Water expands as it warms - this is known as thermal expansion. This effect means that the ocean takes up more space, causing sea levels to rise. Even with rapid emission cuts, sea levels are expected to rise by around 26 to 53 centimetres by 2100.

Along with melting ice sheets and glaciers, rising global temperatures could cause rainforests to die and widespread species extinctions.

The effects of climate change on us

How climate change will affect you depends on who you are and where you live.

Around 190 million people currently live in areas that, due to rising sea levels, are expected to be under high tide levels by 2100. This could cause a massive displacement of populations. Low lying atoll nations such as Tuvalu and the Maldives are incredibly vulnerable to this change and could be lost to the sea.

Hundreds of millions of people rely on seafood as their main source of protein. Warming and more acidic waters could destroy marine food chains by affecting their base, such as krill or coral reefs .

Longer-lasting drought could devastate crops, threating food security. Reservoirs drying up , as well as the loss of glaciers, could make drinking water scarce. 

Pasterze Glacier is estimated to be receding at a rate of 10 metres per year. A sign shows where the glacier lay in 1995, with the ice having since dramatically retreated up the valley. ©  H Raab via Flickr ( CC BY-NC-ND 2.0 )

Increased precipitation can cause deadly flooding, as well as lowering indoor air quality. This could affect our health as dampness benefits moulds and fungi.

Around four billion people live in urban areas, and by 2050 this will have risen to an estimated 6.7 billion.

City dwellers are not exempt from climate change's effects. Urban populations usually rely on rural areas for inputs such as food and water. If climate change disrupts these important connections, it could heavily affect those in urban areas.

Natural disasters impact poor and vulnerable populations disproportionately hard and clearly expose the consequences of ignoring social inequalities . With extreme weather increasing, these populations face a heightened level of risk.

For example, the urban heat island effect amplifies the effects of temperature extremes in cities. Those unable to afford to buy and run air conditioning may find their health compromised.

The hazards of climate change also do  disproportionate harm to women and girls .

Joeri says, 'We don't know what will happen when, exactly. It's really hard to anticipate, particularly for populations that are already on the edge every year.'

People are also seeing climate change impact their mental health, experiencing a phenomenon known as eco-anxiety . 

Differences in wealth, ethnicity and health are just some of the inequalities that could determine a person's vulnerability to the effects of climate change © Kompas/Hendra A Setyawan via World Meteorological Organization Flickr ( CC BY-NC-ND 2.0 )

How does climate change affect biodiversity?

The natural world is delicately balanced . No species - including ours - is completely independent of all others. A 2019 report confirmed that over one million animal and plant species are now at risk of extinction as a result of human activities.

In the UK, an analysis of over 700 species has shown that more than 80% of trends between 1976 and 2005 indicate seasonal events are happening earlier. Differing rates of change could mean that species' lives are no longer synchronised with those they rely on.

Many plants are flowering earlier. Migrating birds arrive earlier, leave later and some even are getting smaller . Butterflies are emerging earlier . Birds and amphibians are laying their eggs earlier in the year. Some species are moving into new areas, such as kelps which form vital marine habitats.

Seaweeds are important for many reasons . They act as vital habitats. Some also help protect coastlines from erosion.

Insects are one of the most vulnerable groups, with less ability than mammals or birds to escape warmer temperatures. Loss of insects, which are a primary food source for many animals, a key pollinator of plants and whose numbers are already plummeting , could cause the ecosystem to collapse.

In aquatic ecosystems, activities to mitigate the side effects of climate change, such as building hard flood defences, can have negative effects. As sea levels rise, sea walls reduce the space for intertidal ecosystems. A rising sea could also damage important coastal habitats like sand dunes and cliffs.

Joeri says, 'The ocean looks homogenous, but it also experiences variations. There are ocean heatwaves, where if a particularly warm mass of water comes to an area like coral reefs, it induces loss and mass dieback.'

The loss of Arctic sea ice takes away a key habitat from animals including polar bears, seals and walruses. The ice is now declining at a rate of more than 12% per decade .

Climate change is just one of the stressors currently impacting nature. Sea use, invasive species, pollution and the exploitation of organisms are all factors in the threat to nature. Without drastic changes , it's expected that there will be devastating changes in biodiversity and ecosystems.

Find out more about the link between climate change and the biodiversity crisis . 

A warming planet and melting ice threatens the survival of iconic animals such as polar bears © Gary Kramer/USFWS via U.S. Fish and Wildlife Service Flick r ( CC BY 2.0 )

Is there any hope for the future?

Climate change has been a known problem for around 30 years. Starting to fix it earlier might have made this daunting task much easier.

Joeri says, 'We definitely know how to reduce emissions to a significant degree. We are seeing more impacts of climate change, but we can also see a heightened interest and concern in the general public.

'Ultimately, reducing emissions is really an issue of public and political will.'

By understanding more about the planet, such as by studying the poles, scientists are able to estimate the consequences climate change will have © NASA Goddard Space Flight Center via Flickr ( CC BY 2.0 )

Over the past decades, scientists have estimated the potential impacts of the planet's average temperature rising by different amounts.

'Based on that information, governments have come together and decided that they don't want to exceed a 2°C rise. They want to be well below that and pursue efforts to make it as close as possible to 1.5 °C.'

The difference in outcomes between 1.5 and 2°C are considerable. The impacts are the difference of 70% or 99% of coral reefs dying or a summer free of Arctic sea ice once every 100 or 10 years.

Scientists have determined how much carbon dioxide can still be emitted before this temperature rise limit will be exceeded. This is called the carbon budget and it's relatively small.

Joeri says, 'It's currently 420 to 580 billion tonnes of carbon dioxide for having a two-in-three or a one-in-two chance of limiting warming to 1.5°C, starting to count in 2018.

'Today we are roughly emitting 42 billion tonnes a year. So, if you start today and are going to net-zero emissions , if you want a one-in-two chance, we should there by around mid-century.

'These numbers define the geophysical requirement. Scientists then use engineering and economic models to understand how we can transform society to stay within that emission limit.'

There are many ways that you can help the planet . One way is by reducing the amount of meat and dairy you eat. © Theo Stikkelman via Flickr ( CC BY 2.0 )

This transformation could include changes such as increasing the share of energy produced by renewables , changing the way food is produced , changing our diets to have a lower carbon footprint and changing the way we build houses and design cities .

Moving to net-zero emissions will not be a perfectly co-ordinated transition . It will take some countries to lead and show the world that moving to this new way of living and functioning is both possible and beneficial for other sustainability objectives, such as public health and food security.

But on whether we'll ever see a change for the better, Joeri says he's hopeful.

'Preferably we would have started 25 or 30 years ago, but I will take any year at which we start declining steadily towards net-zero.'

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Responding to the Climate Threat: Essays on Humanity’s Greatest Challenge

A new book co-authored by MIT Joint Program Founding Co-Director Emeritus Henry Jacoby

From the Back Cover

This book demonstrates how robust and evolving science can be relevant to public discourse about climate policy. Fighting climate change is the ultimate societal challenge, and the difficulty is not just in the wrenching adjustments required to cut greenhouse emissions and to respond to change already under way. A second and equally important difficulty is ensuring widespread public understanding of the natural and social science. This understanding is essential for an effective risk management strategy at a planetary scale. The scientific, economic, and policy aspects of climate change are already a challenge to communicate, without factoring in the distractions and deflections from organized programs of misinformation and denial. 

Here, four scholars, each with decades of research on the climate threat, take on the task of explaining our current understanding of the climate threat and what can be done about it, in lay language―importantly, without losing critical  aspects of the natural and social science. In a series of essays, published during the 2020 presidential election, the COVID pandemic, and through the fall of 2021, they explain the essential components of the challenge, countering the forces of distrust of the science and opposition to a vigorous national response.  

Each of the essays provides an opportunity to learn about a particular aspect of climate science and policy within the complex context of current events. The overall volume is more than the sum of its individual articles. Proceeding each essay is an explanation of the context in which it was written, followed by observation of what has happened since its first publication. In addition to its discussion of topical issues in modern climate science, the book also explores science communication to a broad audience. Its authors are not only scientists – they are also teachers, using current events to teach when people are listening. For preserving Earth’s planetary life support system, science and teaching are essential. Advancing both is an unending task.

About the Authors

Gary Yohe is the Huffington Foundation Professor of Economics and Environmental Studies, Emeritus, at Wesleyan University in Connecticut. He served as convening lead author for multiple chapters and the Synthesis Report for the IPCC from 1990 through 2014 and was vice-chair of the Third U.S. National Climate Assessment.

Henry Jacoby is the William F. Pounds Professor of Management, Emeritus, in the MIT Sloan School of Management and former co-director of the MIT Joint Program on the Science and Policy of Global Change, which is focused on the integration of the natural and social sciences and policy analysis in application to the threat of global climate change.

Richard Richels directed climate change research at the Electric Power Research Institute (EPRI). He served as lead author for multiple chapters of the IPCC in the areas of mitigation, impacts and adaptation from 1992 through 2014. He also served on the National Assessment Synthesis Team for the first U.S. National Climate Assessment.

Ben Santer is a climate scientist and John D. and Catherine T. MacArthur Fellow. He contributed to all six IPCC reports. He was the lead author of Chapter 8 of the 1995 IPCC report which concluded that “the balance of evidence suggests a discernible human influence on global climate”. He is currently a Visiting Researcher at UCLA’s Joint Institute for Regional Earth System Science & Engineering.

Access the Book

View the book on the publisher's website  here .

Order the book from Amazon  here . 

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MIT Climate News in Your Inbox

There is unequivocal evidence that Earth is warming at an unprecedented rate. Human activity is the principal cause.

• While Earth’s climate has changed throughout its history , the current warming is happening at a rate not seen in the past 10,000 years.
• According to the Intergovernmental Panel on Climate Change ( IPCC ), "Since systematic scientific assessments began in the 1970s, the influence of human activity on the warming of the climate system has evolved from theory to established fact." 1
• Scientific information taken from natural sources (such as ice cores, rocks, and tree rings) and from modern equipment (like satellites and instruments) all show the signs of a changing climate.
• From global temperature rise to melting ice sheets, the evidence of a warming planet abounds.

The rate of change since the mid-20th century is unprecedented over millennia.

Earth's climate has changed throughout history. Just in the last 800,000 years, there have been eight cycles of ice ages and warmer periods, with the end of the last ice age about 11,700 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives.

The current warming trend is different because it is clearly the result of human activities since the mid-1800s, and is proceeding at a rate not seen over many recent millennia. 1 It is undeniable that human activities have produced the atmospheric gases that have trapped more of the Sun’s energy in the Earth system. This extra energy has warmed the atmosphere, ocean, and land, and widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred.

Earth-orbiting satellites and new technologies have helped scientists see the big picture, collecting many different types of information about our planet and its climate all over the world. These data, collected over many years, reveal the signs and patterns of a changing climate.

Scientists demonstrated the heat-trapping nature of carbon dioxide and other gases in the mid-19th century. 2 Many of the science instruments NASA uses to study our climate focus on how these gases affect the movement of infrared radiation through the atmosphere. From the measured impacts of increases in these gases, there is no question that increased greenhouse gas levels warm Earth in response.

Scientific evidence for warming of the climate system is unequivocal.

Intergovernmental Panel on Climate Change

Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that Earth’s climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly 10 times faster than the average rate of warming after an ice age. Carbon dioxide from human activities is increasing about 250 times faster than it did from natural sources after the last Ice Age. 3

The Evidence for Rapid Climate Change Is Compelling:

Global Temperature Is Rising

The planet's average surface temperature has risen about 2 degrees Fahrenheit (1 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide emissions into the atmosphere and other human activities. 4 Most of the warming occurred in the past 40 years, with the seven most recent years being the warmest. The years 2016 and 2020 are tied for the warmest year on record. 5 Image credit: Ashwin Kumar, Creative Commons Attribution-Share Alike 2.0 Generic.

The Ocean Is Getting Warmer

The ocean has absorbed much of this increased heat, with the top 100 meters (about 328 feet) of ocean showing warming of 0.67 degrees Fahrenheit (0.33 degrees Celsius) since 1969. 6 Earth stores 90% of the extra energy in the ocean. Image credit: Kelsey Roberts/USGS

The Ice Sheets Are Shrinking

The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA's Gravity Recovery and Climate Experiment show Greenland lost an average of 279 billion tons of ice per year between 1993 and 2019, while Antarctica lost about 148 billion tons of ice per year. 7 Image: The Antarctic Peninsula, Credit: NASA

Glaciers Are Retreating

Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska, and Africa. 8 Image: Miles Glacier, Alaska Image credit: NASA

Snow Cover Is Decreasing

Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and the snow is melting earlier. 9 Image credit: NASA/JPL-Caltech

Sea Level Is Rising

Global sea level rose about 8 inches (20 centimeters) in the last century. The rate in the last two decades, however, is nearly double that of the last century and accelerating slightly every year. 10 Image credit: U.S. Army Corps of Engineers Norfolk District

Arctic Sea Ice Is Declining

Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades. 11 Credit: NASA's Scientific Visualization Studio

Extreme Events Are Increasing in Frequency

The number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing, since 1950. The U.S. has also witnessed increasing numbers of intense rainfall events. 12 Image credit: Régine Fabri,  CC BY-SA 4.0 , via Wikimedia Commons

Ocean Acidification Is Increasing

Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30%. 13 , 14 This increase is due to humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the ocean. The ocean has absorbed between 20% and 30% of total anthropogenic carbon dioxide emissions in recent decades (7.2 to 10.8 billion metric tons per year). 1 5 , 16 Image credit: NOAA

1. IPCC Sixth Assessment Report, WGI, Technical Summary . B.D. Santer et.al., “A search for human influences on the thermal structure of the atmosphere.” Nature 382 (04 July 1996): 39-46. https://doi.org/10.1038/382039a0. Gabriele C. Hegerl et al., “Detecting Greenhouse-Gas-Induced Climate Change with an Optimal Fingerprint Method.” Journal of Climate 9 (October 1996): 2281-2306. https://doi.org/10.1175/1520-0442(1996)009<2281:DGGICC>2.0.CO;2. V. Ramaswamy, et al., “Anthropogenic and Natural Influences in the Evolution of Lower Stratospheric Cooling.” Science 311 (24 February 2006): 1138-1141. https://doi.org/10.1126/science.1122587. B.D. Santer et al., “Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes.” Science 301 (25 July 2003): 479-483. https://doi.org/10.1126/science.1084123. T. Westerhold et al., "An astronomically dated record of Earth’s climate and its predictability over the last 66 million years." Science 369 (11 Sept. 2020): 1383-1387. https://doi.org/10.1126/science.1094123

2. In 1824, Joseph Fourier calculated that an Earth-sized planet, at our distance from the Sun, ought to be much colder. He suggested something in the atmosphere must be acting like an insulating blanket. In 1856, Eunice Foote discovered that blanket, showing that carbon dioxide and water vapor in Earth's atmosphere trap escaping infrared (heat) radiation. In the 1860s, physicist John Tyndall recognized Earth's natural greenhouse effect and suggested that slight changes in the atmospheric composition could bring about climatic variations. In 1896, a seminal paper by Swedish scientist Svante Arrhenius first predicted that changes in atmospheric carbon dioxide levels could substantially alter the surface temperature through the greenhouse effect. In 1938, Guy Callendar connected carbon dioxide increases in Earth’s atmosphere to global warming. In 1941, Milutin Milankovic linked ice ages to Earth’s orbital characteristics. Gilbert Plass formulated the Carbon Dioxide Theory of Climate Change in 1956.

3. IPCC Sixth Assessment Report, WG1, Chapter 2 Vostok ice core data; NOAA Mauna Loa CO2 record O. Gaffney, W. Steffen, "The Anthropocene Equation." The Anthropocene Review 4, issue 1 (April 2017): 53-61. https://doi.org/abs/10.1177/2053019616688022.

4. https://www.ncei.noaa.gov/monitoring https://crudata.uea.ac.uk/cru/data/temperature/ http://data.giss.nasa.gov/gistemp

5. https://www.giss.nasa.gov/research/news/20170118/

6. S. Levitus, J. Antonov, T. Boyer, O Baranova, H. Garcia, R. Locarnini, A. Mishonov, J. Reagan, D. Seidov, E. Yarosh, M. Zweng, " NCEI ocean heat content, temperature anomalies, salinity anomalies, thermosteric sea level anomalies, halosteric sea level anomalies, and total steric sea level anomalies from 1955 to present calculated from in situ oceanographic subsurface profile data (NCEI Accession 0164586), Version 4.4. (2017) NOAA National Centers for Environmental Information. https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/index3.html K. von Schuckmann, L. Cheng, L,. D. Palmer, J. Hansen, C. Tassone, V. Aich, S. Adusumilli, H. Beltrami, H., T. Boyer, F. Cuesta-Valero, D. Desbruyeres, C. Domingues, A. Garcia-Garcia, P. Gentine, J. Gilson, M. Gorfer, L. Haimberger, M. Ishii, M., G. Johnson, R. Killick, B. King, G. Kirchengast, N. Kolodziejczyk, J. Lyman, B. Marzeion, M. Mayer, M. Monier, D. Monselesan, S. Purkey, D. Roemmich, A. Schweiger, S. Seneviratne, A. Shepherd, D. Slater, A. Steiner, F. Straneo, M.L. Timmermans, S. Wijffels. "Heat stored in the Earth system: where does the energy go?" Earth System Science Data 12, Issue 3 (07 September 2020): 2013-2041. https://doi.org/10.5194/essd-12-2013-2020.

7. I. Velicogna, Yara Mohajerani, A. Geruo, F. Landerer, J. Mouginot, B. Noel, E. Rignot, T. Sutterly, M. van den Broeke, M. Wessem, D. Wiese, "Continuity of Ice Sheet Mass Loss in Greenland and Antarctica From the GRACE and GRACE Follow-On Missions." Geophysical Research Letters 47, Issue 8 (28 April 2020): e2020GL087291. https://doi.org/10.1029/2020GL087291.

8. National Snow and Ice Data Center World Glacier Monitoring Service

9. National Snow and Ice Data Center D.A. Robinson, D. K. Hall, and T. L. Mote, "MEaSUREs Northern Hemisphere Terrestrial Snow Cover Extent Daily 25km EASE-Grid 2.0, Version 1 (2017). Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/MEASURES/CRYOSPHERE/nsidc-0530.001 . http://nsidc.org/cryosphere/sotc/snow_extent.html Rutgers University Global Snow Lab. Data History

10. R.S. Nerem, B.D. Beckley, J. T. Fasullo, B.D. Hamlington, D. Masters, and G.T. Mitchum, "Climate-change–driven accelerated sea-level rise detected in the altimeter era." PNAS 15, no. 9 (12 Feb. 2018): 2022-2025. https://doi.org/10.1073/pnas.1717312115.

11. https://nsidc.org/cryosphere/sotc/sea_ice.html Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS, Zhang and Rothrock, 2003) http://psc.apl.washington.edu/research/projects/arctic-sea-ice-volume-anomaly/ http://psc.apl.uw.edu/research/projects/projections-of-an-ice-diminished-arctic-ocean/

12. USGCRP, 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp, https://doi.org/10.7930/j0j964j6 .

13. http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F

14. http://www.pmel.noaa.gov/co2/story/Ocean+Acidification

15. C.L. Sabine, et al., “The Oceanic Sink for Anthropogenic CO2.” Science 305 (16 July 2004): 367-371. https://doi.org/10.1126/science.1097403.

16. Special Report on the Ocean and Cryosphere in a Changing Climate , Technical Summary, Chapter TS.5, Changing Ocean, Marine Ecosystems, and Dependent Communities, Section 5.2.2.3. https://www.ipcc.ch/srocc/chapter/technical-summary/

Header image shows clouds imitating mountains as the sun sets after midnight as seen from Denali's backcountry Unit 13 on June 14, 2019. Credit: NPS/Emily Mesner Image credit in list of evidence: Ashwin Kumar, Creative Commons Attribution-Share Alike 2.0 Generic.

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Century of Science: Theme

Our climate change crisis

The climate change emergency.

Even in a world increasingly battered by weather extremes, the summer 2021 heat wave in the Pacific Northwest stood out. For several days in late June, cities such as Vancouver, Portland and Seattle baked in record temperatures that killed hundreds of people. On June 29 Lytton, a village in British Columbia, set an all-time heat record for Canada, at 121° Fahrenheit (49.6° Celsius); the next day, the village was incinerated by a wildfire.

Within a week, an international group of scientists had analyzed this extreme heat and concluded it would have been virtually impossible without climate change caused by humans. The planet’s average surface temperature has risen by at least 1.1 degree Celsius since preindustrial levels of 1850–1900 — because people are loading the atmosphere with heat-trapping gases produced during the burning of fossil fuels, such as coal and gas, and from cutting down forests.

A little over 1 degree of warming may not sound like a lot. But it has already been enough to fundamentally transform how energy flows around the planet. The pace of change is accelerating, and the consequences are everywhere. Ice sheets in Greenland and Antarctica are melting, raising sea levels and flooding low-lying island nations and coastal cities. Drought is parching farmlands and the rivers that feed them. Wildfires are raging. Rains are becoming more intense, and weather patterns are shifting .

The roots of understanding this climate emergency trace back more than a century and a half. But it wasn’t until the 1950s that scientists began the detailed measurements of atmospheric carbon dioxide that would prove how much carbon is pouring from human activities. Beginning in the 1960s, researchers began developing comprehensive computer models that now illuminate the severity of the changes ahead.

Global average temperature change, 1850–2021

Long-term climate datasets show that Earth’s average surface temperature (combined land and ocean) has increased by more than 1 degree Celsius since preindustrial times. Temperature change is the difference from the 1850–1900 average.

Today we know that climate change and its consequences are real, and we are responsible. The emissions that people have been putting into the air for centuries — the emissions that made long-distance travel, economic growth and our material lives possible — have put us squarely on a warming trajectory . Only drastic cuts in carbon emissions, backed by collective global will, can make a significant difference.

“What’s happening to the planet is not routine,” says Ralph Keeling, a geochemist at the Scripps Institution of Oceanography in La Jolla, Calif. “We’re in a planetary crisis.” — Alexandra Witze

Tracking a Greenland glacier

The calving front of Greenland’s Helheim Glacier, which flows toward the sea where it crumbles into icebergs, held roughly the same position from the 1970s until 2001 (left, the calving front is to the far right of the image). But by 2005 (right), it had retreated 7.5 kilometers toward its source. 

The first climate scientists

One day in the 1850s, Eunice Newton Foote, an amateur scientist and women’s rights activist living in upstate New York, put two glass jars in sunlight. One contained regular air — a mix of nitrogen, oxygen and other gases including carbon dioxide — while the other contained just CO 2 . Both had thermometers in them. As the sun’s rays beat down, Foote observed that the jar of CO 2 alone heated more quickly, and was slower to cool, than the one containing plain air.

The results prompted Foote to muse on the relationship between CO 2 , the planet and heat. “An atmosphere of that gas would give to our earth a high temperature,” she wrote in an 1856 paper summarizing her findings .

Three years later, working independently and apparently unaware of Foote’s discovery, Irish physicist John Tyndall showed the same basic idea in more detail. With a set of pipes and devices to study the transmission of heat, he found that CO 2 gas, as well as water vapor, absorbed more heat than air alone. He argued that such gases would trap heat in Earth’s atmosphere, much as panes of glass trap heat in a greenhouse, and thus modulate climate. “As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial rays, produces a local heightening of the temperature at the Earth’s surface,” he wrote in 1862.

Today Tyndall is widely credited with the discovery of how what are now called greenhouse gases heat the planet, earning him a prominent place in the history of climate science. Foote faded into relative obscurity — partly because of her gender, partly because her measurements were less sensitive. Yet their findings helped kick off broader scientific exploration of how the composition of gases in Earth’s atmosphere affects global temperatures.

Carbon floods in

Humans began substantially affecting the atmosphere around the turn of the 19th century, when the Industrial Revolution took off in Britain. Factories burned tons of coal; fueled by fossil fuels, the steam engine revolutionized transportation and other industries. In the decades since, fossil fuels including oil and natural gas have been harnessed to drive a global economy. All these activities belch gases into the air.

Yet Svante Arrhenius, a Swedish physical chemist, wasn’t worried about the Industrial Revolution when he began thinking in the late 1800s about changes in atmospheric CO 2 levels. He was instead curious about ice ages — including whether a decrease in volcanic eruptions, which can put CO 2 into the atmosphere, would lead to a future ice age. Bored and lonely in the wake of a divorce, Arrhenius set himself to months of laborious calculations involving moisture and heat transport in the atmosphere at different zones of latitude. In 1896 he reported that halving the amount of CO 2 in the atmosphere could indeed bring about an ice age — and that doubling CO 2 would raise global temperatures by around 5 to 6 degrees C.

It was a remarkably prescient finding for work that, out of necessity, had simplified Earth’s complex climate system down to just a few variables. Today, estimates for how much the planet will warm through a doubling of CO 2 — a measure known as climate sensitivity — range between 1.5 degrees and 4.5 degrees Celsius. (The range remains broad in part because scientists now incorporate their understanding of many more planetary feedbacks than were recognized in Arrhenius’ day.)  

But Arrhenius’ findings didn’t gain much traction with other scientists at the time. The climate system seemed too large, complex and inert to change in any meaningful way on a timescale that would be relevant to human society. Geologic evidence showed, for instance, that ice ages took thousands of years to start and end. What was there to worry about? And other laboratory experiments — later shown to be flawed — appeared to indicate that changing levels of CO 2 would have little impact on heat absorption in the atmosphere. Most scientists aware of the work came to believe that Arrhenius had been proved wrong.

One researcher, though, thought the idea was worth pursuing. Guy Stewart Callendar, a British engineer and amateur meteorologist, had tallied weather records over time, obsessively enough to determine that average temperatures were increasing at 147 weather stations around the globe. In 1938, in a paper in a Royal Meteorological Society journal , he linked this temperature rise to the burning of fossil fuels. Callendar estimated that fossil fuel burning had put around 150 billion metric tons of CO 2 into the atmosphere since the late 19th century.

Like many of his day, Callendar didn’t see global warming as a problem. Extra CO 2 would surely stimulate plants to grow and allow crops to be farmed in new regions. “In any case the return of the deadly glaciers should be delayed indefinitely,” he wrote. But his work revived discussions tracing back to Tyndall and Arrhenius about how the planetary system responds to changing levels of gases in the atmosphere. And it began steering the conversation toward how human activities might drive those changes.

When World War II broke out the following year, the global conflict redrew the landscape for scientific research. Hugely important wartime technologies, such as radar and the atomic bomb, set the stage for “big science” studies that brought nations together to tackle high-stakes questions of global reach. And that allowed modern climate science to emerge.

The Keeling curve and climate change

One major postwar effort was the International Geophysical Year, an 18-month push in 1957–1958 that involved a wide array of scientific field campaigns including exploration in the Arctic and Antarctica. Climate change wasn’t a high research priority during the IGY, but some scientists in California, led by Roger Revelle of the Scripps Institution of Oceanography in La Jolla, used the funding influx to begin a project they’d long wanted to do. The goal was to measure CO 2 levels at different locations around the world, accurately and consistently.

The job fell to geochemist Charles David Keeling, who put ultraprecise CO 2 monitors in Antarctica and on the Hawaiian volcano of Mauna Loa. Funds soon ran out to maintain the Antarctic record, but the Mauna Loa measurements continued. Thus was born one of the most iconic datasets in all of science — the “Keeling curve,” which tracks the rise of atmospheric CO 2 . When Keeling began his measurements in 1958, CO 2 made up 315 parts per million of the global atmosphere. Within just a few years it became clear that the number was increasing year by year. Because plants take up CO 2 as they grow in spring and summer and release it as they decompose in fall and winter, CO 2 concentrations rose and fell each year in a sawtooth pattern — but superimposed on that pattern was a steady march upward.  

Monthly average CO 2 concentrations at Mauna Loa Observatory

Atmospheric carbon dioxide measurements collected continuously since 1958 at Mauna Loa volcano in Hawaii show the rise due to human activities. The visible sawtooth pattern is due to seasonal plant growth: Plants take up CO 2 in the growing seasons, then release it as they decompose in fall and winter.

“The graph got flashed all over the place — it was just such a striking image,” says Ralph Keeling, who is Charles David Keeling’s son. Over the years, as the curve marched higher, “it had a really important role historically in waking people up to the problem of climate change.” The Keeling curve has been featured in countless earth science textbooks, congressional hearings and in Al Gore’s 2006 documentary on climate change, An Inconvenient Truth . Each year the curve keeps going up: In 2016 it passed 400 ppm of CO 2 in the atmosphere, as measured during its typical annual minimum in September. In 2021, the annual minimum was 413 ppm. (Before the Industrial Revolution, CO 2 levels in the atmosphere had been stable for centuries at around 280 ppm.)

Around the time that Keeling’s measurements were kicking off, Revelle also helped develop an important argument that the CO 2 from human activities was building up in Earth’s atmosphere. In 1957 he and Hans Suess, also at Scripps at the time, published a paper that traced the flow of radioactive carbon through the oceans and the atmosphere. They showed that the oceans were not capable of taking up as much CO 2 as previously thought; the implication was that much of the gas must be going into the atmosphere instead. “Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future,” Revelle and Suess wrote in the paper. It’s one of the most famous sentences in earth science history.

“Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future.”

Here was the insight underlying modern climate science: Atmosheric CO 2 is increasing, and humans are causing the buildup. Revelle and Suess became the final piece in a puzzle dating back to Svante Arrhenius and John Tyndall.

“I tell my students that to understand the basics of climate change, you need to have the cutting-edge science of the 1860s, the cutting-edge math of the 1890s and the cutting-edge chemistry of the 1950s,” says Joshua Howe, an environmental historian at Reed College in Portland, Ore.

Environmental awareness grows

As this scientific picture began to emerge in the late 1950s, Science News was on the story. A March 1, 1958 article in Science News Letter , “Weather May Be Warming,” described a warm winter month in the Northern Hemisphere. It posits three theories, including that “carbon dioxide poured into the atmosphere by a booming industrial civilization could have caused the increase. By burning up about 100 billion tons of coal and oil since 1900, man himself may be changing the climate.” By 1972, the magazine was reporting on efforts to expand global atmospheric greenhouse gas monitoring beyond Keeling’s work; two years later, the U.S. National Oceanic and Atmospheric Administration launched its own CO 2 monitoring network, now the biggest in the world.

Environmental awareness on other issues grew in the 1960s and 1970s. Rachel Carson catalyzed the modern U.S. environmental movement in 1962 when she published a magazine series and then a book, Silent Spring , condemning the pesticide DDT for its ecological impacts. 1970 saw the celebration of the first Earth Day , in the United States and elsewhere, and in India in 1973 a group of women led a series of widely publicized protests against deforestation. This Chipko movement explicitly linked environmental protection with protecting human communities, and helped seed other environmental movements.

The fragility of global energy supplies was also becoming more obvious through the 1970s. The United States, heavily dependent on other countries for oil imports, entered a gas shortage in 1973–74 when Arab members of the Organization of the Petroleum Exporting Countries cut off oil supplies because of U.S. government support for Israel. The shortage prompted more people to think about the finiteness of natural resources and the possibility of overtaxing the planet. — Alexandra Witze

Climate change evidence piles up

Observational data collected throughout the second half of the 20th century helped researchers gradually build their understanding of how human activities were transforming the planet. “It was a sort of slow accretion of evidence and concern,” says historian Joshua Howe of Reed College.

Environmental records from the past, such as tree rings and ice cores, established that the current changes in climate are unusual compared with the recent past. Yet such paleoclimatology data also showed that climate has changed quickly in the deep past — driven by triggers other than human activity, but with lessons for how abrupt planetary transformations can be.

Ice cores pulled from ice sheets, such as that atop Greenland, offer some of the most telling insights for understanding past climate change. Each year snow falls atop the ice and compresses into a fresh layer of ice representing climate conditions at the time it formed. The abundance of certain forms, or isotopes, of oxygen and hydrogen in the ice allows scientists to calculate the temperature at which it formed, and air bubbles trapped within the ice reveal how much carbon dioxide and other greenhouse gases were in the atmosphere at that time. So drilling down into an ice sheet is like reading the pages of a history book that go back in time the deeper you go.

Scientists began reading these pages in the early 1960s, using ice cores drilled at a U.S. military base in northwest Greenland . Contrary to expectations that past climates were stable, the cores hinted that abrupt climate shifts had happened over the last 100,000 years. By 1979, an international group of researchers was pulling another deep ice core from a second location in Greenland — and it, too, showed that abrupt climate change had occurred in the past. In the late 1980s and early 1990s a pair of European- and U.S.-led drilling projects retrieved even deeper cores from near the top of the ice sheet, pushing the record of past temperatures back a quarter of a million years.

Together with other sources of information, such as sediment cores drilled from the seafloor and molecules preserved in ancient rocks, the ice cores allowed scientists to reconstruct past temperature changes in extraordinary detail. Many of those changes happened alarmingly fast. For instance, the climate in Greenland warmed abruptly more than 20 times in the last 80,000 years, with the changes occurring in a matter of decades. More recently, a cold spell that set in around 13,000 years ago suddenly came to an end around 11,500 years ago — and temperatures in Greenland rose 10 degrees Celsius in a decade.

Evidence for such dramatic climate shifts laid to rest any lingering ideas that global climate change would be slow and unlikely to occur on a timescale that humans should worry about. “It’s an important reminder of how ‘tippy’ things can be,” says Jessica Tierney, a paleoclimatologist at the University of Arizona in Tucson.

More evidence of global change came from Earth-observing satellites, which brought a new planet-wide perspective on global warming beginning in the 1960s. From their viewpoint in the sky, satellites have measured the steady rise in global sea level — currently 3.4 millimeters per year and accelerating, as warming water expands and as ice sheets melt — as well as the rapid decline in ice left floating on the Arctic Ocean each summer at the end of the melt season. Gravity-sensing satellites have ‘weighed’ the Antarctic and Greenlandic ice sheets from above since 2002, reporting that more than 400 billion metric tons of ice are lost each year.

Temperature observations taken at weather stations around the world also confirm that we are living in the hottest years on record. The 10 warmest years since record keeping began in 1880 have all occurred since 2005. And nine of those 10 have come since 2010.

What’s more, extreme weather is hammering the planet more and more frequently. That 2021 heat wave in the Pacific Northwest, for instance, is just a harbinger of what’s to come. — Alexandra Witze

Worrisome predictions from climate models

By the 1960s, there was no denying that the planet was warming. But understanding the consequences of those changes — including the threat to human health and well-being — would require more than observational data. Looking to the future depended on computer simulations: complex calculations of how energy flows through the planetary system. Such models of the climate system have been crucial to developing projections for what we can expect from greenhouse warming.

A first step in building climate models was to connect everyday observations of weather to the concept of forecasting future climate. During World War I, the British mathematician Lewis Fry Richardson imagined tens of thousands of meteorologists working to forecast the weather, each calculating conditions for a small part of the atmosphere but collectively piecing together a global forecast. Richardson published his work in 1922, to reviews that called the idea “of almost quixotic boldness.”

But it wasn’t until after World War II that computational power turned Richardson’s dream into reality. In the wake of the Allied victory, which relied on accurate weather forecasts for everything from planning D-Day to figuring out when and where to drop the atomic bombs, leading U.S. mathematicians acquired funding from the federal government to improve predictions. In 1950 a team led by Jule Charney, a meteorologist at the Institute for Advanced Study in Princeton, N.J., used the ENIAC, the first general-purpose, programmable electronic computer, to produce the first computer-driven regional weather forecast . The forecasting was slow and rudimentary, but it built on Richardson’s ideas of dividing the atmosphere into squares, or cells, and computing the weather for each of those. With the obscure title “Numerical integration of the barotropic vorticity equation,” the paper reporting the results set the stage for decades of climate modeling to follow.

By 1956 Norman Phillips, a member of Charney’s team, had produced the world’s first general circulation model, which captured how energy flows between the oceans, atmosphere and land. Phillips ran the calculations on a computer with just 5 kilobytes of memory, yet it was able to reproduce monthly and seasonal patterns in the lower atmosphere. That meant scientists could begin developing more realistic models of how the planet responds to factors such as increasing levels of greenhouse gases. The field of climate modeling was born.

The work was basic at first, because early computers simply didn’t have much computational power to simulate all aspects of the planetary system. “People thought that it was stupid to try to study this greenhouse-warming issue by three-dimensional model[s], because it cost so much computer time,” meteorologist Syukuro Manabe told physics historian Spencer Weart in a 1989 oral history .

Climate models have predicted how much ice the Ilulissat region of the Greenland ice sheet might lose by 2300 based on different scenarios for greenhouse gas emissions. The models are compared to 2008 (first image). In a best-case scenario, in which emissions peak by mid-century, the speed at which the glacier is sending ice out into the ocean is much lower (second image) than with a worst-case scenario, in which emissions rise at a high rate (third image).

An important breakthrough came in 1967, when Manabe and Richard Wetherald — both at the Geophysical Fluid Dynamics Laboratory in Princeton, a lab born from Charney’s group — published a paper in the Journal of the Atmospheric Sciences that modeled connections between Earth’s surface and atmosphere and calculated how changes in carbon dioxide would affect the planet’s temperature. Manabe and Wetherald were the first to build a computer model that captured the relevant processes that drive climate , and to accurately simulate how the Earth responds to those processes. (Manabe shared the 2021 Nobel Prize in physics for his work on climate modeling; Wetherald died in 2011.)

The rise of climate modeling allowed scientists to more accurately envision the impacts of global warming. In 1979, Charney and other experts met in Woods Hole, Mass., to try to put together a scientific consensus on what increasing levels of CO 2 would mean for the planet. They analyzed climate models from Manabe and from James Hansen of NASA. The resulting “Charney report” concluded that rising CO 2 in the atmosphere would lead to additional and significant climate change. The ocean might take up much of that heat, the scientists wrote — but “it appears that the warming will eventually occur, and the associated regional climatic changes so important to the assessment of socioeconomic consequence may well be significant.”

In the decades since, climate modeling has gotten increasingly sophisticated . Scientists have drawn up a variety of scenarios for how carbon emissions might change in the future, depending on the stringency of emissions cuts. Modelers use those scenarios to project how climate and weather will change around the globe, from hotter croplands in China to melting glaciers in the Himalayas. Climate simulations have also allowed researchers to identify the fingerprints of human impacts on extreme weather that is already happening, by comparing scenarios that include the influence of human activities with those that do not.

And as climate science firmed up and the most dramatic consequences became clear, the political battles raged. — Alexandra Witze

Climate science meets politics

With the development of climate science tracing back to the early Cold War, perhaps it shouldn’t be a surprise that the science of global warming became enmeshed in broader societal and political battles. A complex stew of political, national and business interests mired society in debates about the reality of climate change, and what to do about it, decades after the science became clear that humans are fundamentally altering the planet’s atmosphere.

Society has pulled itself together before to deal with global environmental problems, such as the Antarctic ozone hole. In 1974 chemists Mario Molina and F. Sherwood Rowland, both of the University of California, Irvine, reported that chlorofluorocarbon chemicals, used in products such as spray cans and refrigerants, caused a chain of reactions that gnawed away at the atmosphere’s protective ozone layer . The resulting ozone hole, which forms over Antarctica every spring, allows more ultraviolet radiation from the sun to make it through Earth’s atmosphere and reach the surface, where it can cause skin cancer and eye damage.

Governments ultimately worked under the auspices of the United Nations to craft the 1987 Montreal Protocol, which strictly limited the manufacture of chlorofluorocarbons . In the years following, the ozone hole began to heal. But fighting climate change would prove to be far more challenging. Chlorofluorocarbons were a suite of chemicals with relatively limited use and for which replacements could be found without too much trouble. But the greenhouse gases that cause global warming stem from a wide variety of human activities, from energy development to deforestation. And transforming entire energy sectors to reduce or eliminate carbon emissions is much more difficult than replacing a set of industrial chemicals.

In 1980, though, researchers took an important step toward banding together to synthesize the scientific understanding of climate change and bring it to the attention of international policy makers. It started at a small scientific conference in Villach, Austria. There, experts met under the auspices of the World Meteorological Organization, the International Council of Scientific Unions and the United Nations Environment Program to discuss the seriousness of climate change. On the train ride home from the meeting, Swedish meteorologist Bert Bolin talked with other participants about how a broader, deeper and more international analysis was needed. In 1985, a second conference was held at Villach to highlight the urgency, and in 1988, the Intergovernmental Panel on Climate Change, the IPCC, was born. Bolin was its first chairperson.

The IPCC became a highly influential and unique body. It performs no original scientific research; instead, it synthesizes and summarizes the vast literature of climate science for policy makers to consider — primarily through massive reports issued every couple of years. The first IPCC report , in 1990, predicted that the planet’s global mean temperature would rise more quickly in the following century than at any point in the last 10,000 years, due to increasing greenhouse gases in the atmosphere. Successive IPCC reports showed more and more confidence in the link between greenhouse emissions and rising global temperatures — and explored how society might mitigate and adapt to coming changes.

IPCC reports have played a key role in providing scientific information for nations discussing how to stabilize greenhouse gas concentrations. This process started with the Rio Earth Summit in 1992 , which resulted in the U.N. Framework Convention on Climate Change. Annual U.N. meetings to tackle climate change led to the first international commitments to reduce emissions, the Kyoto Protocol of 1997. Under it, developed countries committed to reduce emissions of CO 2 and other greenhouse gases. By 2007 the IPCC declared that the reality of climate warming is “unequivocal ”; the group received the Nobel Peace Prize that year along with Al Gore for their work on climate change.

The IPCC process ensured that policy makers had the best science at hand when they came to the table to discuss cutting emissions. “If you go back and look at the original U.N. framework on climate change, already you see the core of the science represented there,” says Rachel Cleetus, a climate policy expert with the Union of Concerned Scientists in Cambridge, Mass. Of course, nations did not have to abide by that science — and they often didn’t.

Throughout the 2000s and 2010s, international climate meetings discussed less hard-core science and more issues of equity. Countries such as China and India pointed out that they needed energy to develop their economies, and that nations responsible for the bulk of emissions through history, such as the United States, needed to lead the way in cutting greenhouse gases. Meanwhile, residents of some of the most vulnerable nations, such as low-lying islands that are threatened by sea level rise, gained visibility and clout at international negotiating forums. “The issues around equity have always been very uniquely challenging in this collective action problem,” says Cleetus.

By 2015, the world’s nations had made some progress on the emissions cuts laid out in the Kyoto Protocol, but it was still not enough to achieve substantial global reductions. That year, a key U.N. climate conference in Paris produced an international agreement to try to limit global warming to 2 degrees C , and preferably 1.5 degrees C, above preindustrial levels.

Every country has its own approach to the challenge of addressing climate change. In the United States, which gets approximately 80 percent of its energy from fossil fuels, sophisticated efforts to downplay and critique the science led to major delays in climate action. For decades U.S. fossil fuel companies such as ExxonMobil worked to influence politicians to take as little action on emissions reductions as possible. Working with a small group of influential scientists, this well-funded, well-orchestrated campaign took many of its tactics from earlier tobacco-industry efforts to cast doubt on the links between smoking and cancer, as historians Naomi Oreskes and Erik Conway documented in their book Merchants of Doubt.

Perhaps the peak of U.S. climate denialism came in the late 1980s and into the 1990s — roughly a century after Swedish physical chemist Svante Arrhenius laid out the consequences of putting too much carbon dioxide into the atmosphere. In 1988 NASA scientist James Hansen testified to lawmakers about the consequences of global warming. “It is already happening now,” Hansen said, summarizing what scientists had long known.

The high-profile nature of Hansen’s testimony, combined with his NASA expertise, vaulted global warming into the public eye in the United States like never before. “It really hit home with a public who could understand that there are reasons that Venus is hot and Mars is cold,” says Joshua Howe, a historian at Reed College. “And that if you use that same reasoning, we have some concerns about what is happening here on Earth.” But Hansen also kicked off a series of bitter public battles about the reality of human-caused climate change that raged for years.        

One common approach of climate skeptics was to attack the environmental data and models that underlie climate science. In 1998, scientist Michael Mann, then at the University of Massachusetts–Amherst, and colleagues published a detailed temperature record that formed the basis of what came to be known as the “hockey stick” graph, so named because the chart showed a sharp rise in temperatures (the hockey blade) at the end of a long, much flatter period (the hockey stick). Skeptics soon demanded the data and software processing tools Mann used to create the graph. Bloggers and self-proclaimed citizen scientists created a cottage industry of questioning new climate science papers under the guise of “audits.” In 2009 hackers broke into a server at the University of East Anglia, a leading climate-research hub in Norwich, England, and released more than 1,000 e-mails between climate scientists. This “Climategate” scandal purported to reveal misconduct on the part of the researchers, but several reviews largely exonerated the scientists.  

The graph that launched climate skeptic attacks

This famous graph, produced by scientist Michael Mann and colleagues, and then reproduced in a 2001 report by the Intergovernmental Panel on Climate Change, dramatically captures temperature change over time. Climate change skeptics made it the center of an all-out attack on climate science.

Such tactics undoubtedly succeeded in feeding politicians’ delay on climate action in the United States, most of it from Republicans. President George W. Bush withdrew the country from the Kyoto Protocol in 2001 ; Donald Trump similarly rejected the Paris accord in 2017 . As late as 2015, the chair of the Senate’s environment committee, James Inhofe of Oklahoma, brought a snowball into Congress on a cold winter’s day in order to continue his argument that human-caused global warming is a “hoax.” In Australia, a similar mix of right-wing denialism and fossil fuel interests has kept climate change commitments in flux, as prime ministers are voted in and out over fierce debates about how the nation should act on climate.

Yet other nations have moved forward. Some European countries such as Germany aggressively pursued renewable energies, such as wind and solar, while activists such as the Swedish teenager Greta Thunberg — the vanguard of a youth-action movement — pressured their governments for more.

In recent years the developing economies of China and India have taken center stage in discussions about climate action. Both nations argue that they must be allowed extra time to wean themselves off fossil fuels in order to continue economic growth. They note that historically speaking, the United States is the largest total emitter of carbon by far.

Total carbon dioxide emissions by country, 1850–2021

These 20 nations have emitted the largest cumulative amounts of carbon dioxide since 1850. Emissions are shown in in billions of metric tons and are broken down into subtotals from fossil fuel use and cement manufacturing (blue) as well as from land use and forestry (green).

China, whose annual CO 2 emissions surpassed those of the United States in 2006, declared several moderate steps in 2021 to reduce emissions, including that it would stop building coal-burning power plants overseas. India announced it would aim for net-zero emissions by 2070, the first time it has set a date for this goal.

Yet such pledges continue to be criticized. At the 2021 U.N. Climate Change Conference in Glasgow, Scotland, India was globally criticized for not committing to a complete phaseout of coal — although the two top emitters, China and the United States, have not themselves committed to phasing out coal. “There is no equity in this,” says Aayushi Awasthy, an energy economist at the University of East Anglia. — Alexandra Witze

Facing a warmer future

Climate change creeps up gradually on society, except when it doesn’t. The slow increase in sea level, for instance, causes waters to lap incrementally higher at shorelines year after year. But when a big storm comes along — which may be happening more frequently due to climate change — the consequences become much more obvious. Storm surge rapidly swamps communities and wreaks disproportionate havoc. That’s why New York City installed floodgates in its subway and tunnel system in the wake of 2012’s Superstorm Sandy , and why the Pacific island nation of Tuvalu has asked Australia and New Zealand to be prepared to take in refugees fleeing from rising sea levels.

The list of climate impacts goes on and on — and in many cases, changes are coming faster than scientists had envisioned a few decades ago. The oceans are becoming more acidic as they absorb carbon dioxide, harming tiny marine organisms that build protective calcium carbonate shells and are the base of the marine food web. Warmer waters are bleaching coral reefs. Higher temperatures are driving animal and plant species into areas in which they previously did not live, increasing the risk of extinction for many. “It’s no longer about impacts in the future,” says Rachel Cleetus, a climate policy expert at the Union of Concerned Scientists. “It’s about what’s happening in the U.S. here and now, and around the world.”

No place on the planet is unaffected. In many areas, higher temperatures have led to major droughts, which dry out vegetation and provide additional fuel for wildfires such as those that have devastated Australia , the Mediterranean and western North America in recent years. The Colorado River , the source of water for tens of millions of people in the western United States , came under a water-shortage alert in 2021 for the first time in history.

Then there’s the Arctic, where temperatures are rising at more than twice the global average and communities are at the forefront of change. Permafrost is thawing, destabilizing buildings, pipelines and roads. Caribou and reindeer herders worry about the increased risk of parasites to the health of their animals. With less sea ice available to buffer the coast from storm erosion, the Inupiat village of Shishmaref, Alaska, risks crumbling into the sea. It will need to move from its sand-barrier island to the mainland .

“We know these changes are happening and that the Titanic is sinking,” says Louise Farquharson, a geomorphologist at the University of Alaska in Fairbanks who monitors permafrost and coastal change around Alaska. Like many Arctic scientists, she is working with Indigenous communities to understand the shifts they’re experiencing and what can be done when buildings start to slump and water supplies start to drain away. “A big part is just listening to community members and understanding what they’re seeing change,” she says.

All around the planet, those who depend on intact ecosystems for their survival face the greatest threat from climate change. And those with the least resources to adapt to climate change are the ones who feel it first .

“We are going to warm,” says Claudia Tebaldi, a climate scientist at Lawrence Berkeley National Laboratory in California. “There is no question about it. The only thing that we can hope to do is to warm a little more slowly.”

That’s one reason why the IPCC report released in 2021 focuses on anticipated levels of global warming. There is a big difference between the planet warming 1.5 degrees versus 2 degrees or 2.5 degrees. Consider that we are now at least 1.1 degrees above preindustrial levels of CO 2 and are already seeing dramatic shifts in climate. Given that, keeping further global temperature increases as low as possible will make a big difference in the climate impacts the planet faces. “With every fraction of a degree of warming, everything gets a little more intense,” says paleoclimatologist Jessica Tierney. “There’s no more time to beat around the bush.”

Historical and projected global temperature change

Various scenarios for how greenhouse gas emissions might change going forward help scientists predict future climate change. This graph shows the simulated historical temperature trend along with future projections of global surface temperature based on five scenarios from the Intergovernmental Panel on Climate Change. Temperature change is the difference from the 1850–1900 average.

The future rests on how much nations are willing to commit to cutting emissions and whether they will stick to those commitments. It’s a geopolitical balancing act the likes of which the world has never seen.

Science can and must play a role going forward. Improved climate models will illuminate what changes are expected at the regional scale, helping officials prepare. Governments and industry have crucial parts to play as well. They can invest in technologies, such as carbon sequestration, to help decarbonize the economy and shift society toward more renewable sources of energy. “We can solve these problems — most of the tools are already there,” says Cascade Tuholske, a geographer at Columbia University. “We just have to do it.”

Huge questions remain. Do voters have the will to demand significant energy transitions from their governments? How can business and military leaders play a bigger role in driving climate action? What should be the role of low-carbon energy sources that come with downsides, such as nuclear energy ? How can developing nations achieve a better standard of living for their people while not becoming big greenhouse gas emitters? How can we keep the most vulnerable from being disproportionately harmed during extreme events, and incorporate environmental and social justice into our future?

These questions become more pressing each year, as CO 2 accumulates in our atmosphere. The planet is now at higher levels of CO 2 than at any time in the last 3 million years. Yet Ralph Keeling, keeper of the iconic Mauna Loa record tracking the rise in atmospheric CO 2 , is already optimistically thinking about how scientists would be able to detect a slowdown, should the world actually start cutting emissions by a few percent per year. “That’s what the policy makers want to see — that there’s been some large-scale impact of what they did,” he says.

At the 2021 U.N. climate meeting in Glasgow diplomats from around the world agreed to work more urgently to shift away from using fossil fuels. They did not, however, adopt targets strict enough to keep the world below a warming of 1.5 degrees Celsius. It’s been well over a century since Svante Arrhenius recognized the consequences of putting extra carbon dioxide into the atmosphere, and yet world leaders have yet to pull together to avoid the most dangerous consequences of climate change.

Time is running out. — Alexandra Witze

Climate change facts

We know that climate change and its consequences are real, and we are responsible. Here’s what the science tells us.

How much has the planet warmed over the past century?

The planet’s average surface temperature has risen by at least 1.1 degree Celsius since preindustrial levels of 1850–1900.

What is causing climate change?

People are loading the atmosphere with carbon dioxide and other heat-trapping gases produced during the burning of fossil fuels, such as coal and gas, and cutting down forests.

What are some of the effects of climate change?

Ice sheets in Greenland and Antarctica are melting, raising sea levels and flooding low-lying island nations and coastal cities. Drought is parching farmlands and the rivers that feed them. Wildfires are raging. Rains are becoming more intense, and weather patterns are shifting.

What is the greenhouse effect?

In the 19th century, Irish physicist John Tyndall found that carbon dioxide gas, as well as water vapor, absorbed more heat than air alone. He argued that such gases would trap heat in Earth’s atmosphere, much as panes of glass trap heat in a greenhouse, and thus modulate climate.

What is the Keeling curve?

One of the most iconic datasets in all of science, the Keeling curve tracks the rise of atmospheric CO 2 . When geochemist Charles David Keeling began his measurements in 1958 on the Hawaiian volcano of Mauna Loa, CO 2 made up 315 parts per million of the global atmosphere. Each year the curve keeps going up: In 2016 it passed 400 ppm of CO 2 in the atmosphere, as measured during its typical annual minimum in September. In 2021, the annual minimum was 413 ppm.

Does it get hotter every year?

Average global temperatures fluctuate from year to year, but temperature observations taken at weather stations around the world confirm that we are living in the hottest years on record. The 10 warmest years since record keeping began in 1880 have all occurred since 2005. And nine of those 10 have come since 2010.

What countries emit the most carbon dioxide?

The United States has been the largest total emitter of carbon dioxide by far, followed by China and Russia. China’s annual CO 2 emissions surpassed those of the United States in 2006.

What places are impacted by climate change?

No place on the planet is unaffected. Higher temperatures have led to major droughts, providing fuel for wildfires such as those that have devastated Australia , the Mediterranean and western North America in recent years. The Colorado River came under a water-shortage alert in 2021 for the first time in history. In the Arctic, where temperatures are rising at more than twice the global average, permafrost is thawing, destabilizing buildings, pipelines and roads. With less sea ice available to buffer the coast from storm erosion, the Inupiat village of Shishmaref, Alaska, risks crumbling into the sea. All around the planet, those who depend on intact ecosystems for their survival face the greatest threat from climate change. And those with the least resources to adapt to climate change are the ones who feel it first .

Editor’s note: This story was published March 10, 2022.

British mathematician Lewis Fry Richardson (shown at center) proposes forecasting the weather by piecing together the calculations of tens of thousands of meteorologists working on small parts of the atmosphere.

Geochemist Charles David Keeling (shown in 1988) begins tracking the rise in atmospheric carbon dioxide at Mauna Loa in Hawaii. The record, which continues through today, has become one of the most iconic datasets in all of science.

Rachel Carson (shown) publishes the book Silent Spring , raising alarm over the ecological impacts of the pesticide DDT. The book helps catalyze the modern U.S. environmental movement.

The first Earth Day, organized by U.S. senator Gaylord Nelson and graduate student Denis Hayes, is celebrated.

The first Landsat satellite launched (shown), opening the door to continuous monitoring of Earth and its features from above.

A powerful eruption from the Philippines’ Mount Pinatubo (shown) ejects millions of tons of sulfur dioxide into the stratosphere, temporarily cooling the planet.  

World leaders gathered (shown) at the United Nations Conference on Environment and Development in Rio de Janeiro to address how to pursue economic development while also protecting the Earth. The meeting resulted in an international convention on climate change.

Activist Greta Thunberg initiates the “School Strike for Climate” movement by protesting outside the Swedish parliament. Soon, students around the world join a growing movement demanding action on climate change . (Activists at the 2021 U.N. Climate Change Conference are shown.)

From the archive

Climate change foreseen.

In an early mention of climate change in Science News-Letter , the predecessor of Science News , British meteorologist C.E.P. Brooks warns that present warming trends could lead to “important economic and political effects.”

IGY Brings Many Discoveries

Science News Letter lists the Top 8 accomplishments of the International Geophysical Year.

Chilling possibilities

Science News explores the tentative idea that global temperatures are cooling and that a new ice age could be imminent, which is later shown to be inaccurate.

Long Hot Future: Warmer Earth Appears Inevitable

“The planet earth will be a warmer place in the 21st century, and there is no realistic strategy that can prevent the change,” Science News reports.

Ozone and Global Warming: What to Do?

Policy makers discuss how to solve the dual problems of ozone depletion and global warming.

Looking for Mr. Greenhouse

Science writer Richard Monastersky reports on scientists’ efforts to evaluate how to connect increasing greenhouse gases and a warming climate.

World Climate Panel Charts Path for Action

The Intergovernmental Panel on Climate Change reports that “the fingerprint of man in the past temperature record” is now apparent.

Animals on the Move

A warming climate means shifting ranges and ecosystem disruptions for a lot of species, Nancy Ross-Flanigan reports.

Changing climate: 10 years after ‘An Inconvenient Truth’

A decade after former vice president Al Gore releases the documentary film An Inconvenient Truth , Science News looks back at how climate science has advanced.

With nowhere to hide from rising seas, Boston prepares for a wetter future

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Yale Climate Connections

Scientists agree: Climate change is real and caused by people

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The scientific consensus that climate change is happening and that it is human-caused is strong. Scientific investigation of global warming began in the 19th century , and by the early 2000s, this research began to coalesce into confidence about the reality, causes, and general range of adverse effects of global warming. This conclusion was drawn from studying air and ocean temperatures, the atmosphere’s composition, satellite records, ice cores, modeling, and more.

In 1988 the United Nations and World Meteorological Organization founded the Intergovernmental Panel on Climate Change, IPCC, to provide regular updates on the scientific evidence on global warming. In a 2013 report , the IPCC concluded that scientific evidence of warming is “unequivocal” and that the largest cause is an increase of carbon dioxide in the atmosphere as a result of humans burning fossil fuels. The IPCC continues to assess this science, periodically issuing new reports.

Climate change is real and caused by humans

The IPCC is not the only scientific group that has reached a clear consensus on the scientific evidence of human-caused global warming. As this NASA page points out, 200 global scientific organizations, 11 international science academies, and 18 American science associations have released statements in alignment with this consensus.

Amanda Staudt is the senior director for climate, atmospheric and polar sciences at the National Academies of Science, Engineering and Medicine, where she has worked since 2001. The Academies, she said, first began studying climate change in 1979, researching how much warming would likely happen if the amount of carbon dioxide concentrations in the atmosphere were doubled.

Four decades later, those findings have held up and have been strengthened based on scores of continued studies and analysis. “The remarkable thing about that study,” she said, “is that they basically got the right answer” from the start. This 1979 study by the National Research Council, Staudt said, led to investment in climate science in the U.S. 

Though this consensus has been thoroughly established, scientific research and new findings continue. Staudt said countless attempted rebuttals of climate science findings have been researched and disproved.

“We did a lot of studies in that time period, looking at those questions,” she said, ”and one by one, putting them to bed and convincing ourselves over and over again, that humans were affecting climate, and that we could document that effect.”

At the National Academies, reaching consensus requires open sessions and dialogue with scientists and agreement from committees, which typically consist of 12-15 experts. Their draft reports go through peer review, and reviewers’ concerns are resolved before publication is approved. The goal is for the complex science of climate change to become as thoroughly researched and substantiated as possible.

“One of the things I think about scientists is that we’re all inherently skeptics at some level,” Staudt said. “That’s what drives us to science, that we have questions about the world around us. And we want to prove that for ourselves.”

Scientists consistently reaffirm evidence that climate change is happening

Climate scientists worldwide go through similar processes before their findings are published. And their research papers, too, show a strong consensus about global warming. As NASA states on its website , “Multiple studies published in peer-reviewed scientific journals show that 97 percent or more of actively publishing climate scientists agree: Climate-warming trends over the past century are extremely likely due to human activities.” (By sound practice, scientists resist saying science is for all times “certain” or that its findings are “final,” and the “extremely likely” language respects that practice.)

One of the studies about the consensus was led by John Cook, a fellow at the Climate Change Communication Research Hub at Monash University in Melbourne, Australia. Cook and colleagues reviewed nearly 12,000 scientific papers to examine how aligned published research is on major findings on climate change. That study found that 97 percent of scholarly papers that take a position on climate change do endorse the consensus. The papers that rejected the consensus position contained errors, according to subsequent research .

In reviewing the papers, Cook has said he and his colleagues found the consensus to have been so widely accepted by 2013 that many researchers by then no longer felt a need to mention or reaffirm it in their research papers.

Also see: Causes of global warming: How scientists know that humans are responsible

Samantha Harrington

Samantha Harrington, director of audience experience for Yale Climate Connections, is a journalist and graphic designer with a background in digital media and entrepreneurship. Sam is especially interested... More by Samantha Harrington

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Why does climate change matter we asked a nasa scientist: episode 23.

Emily Furfaro

Why does climate change matter?

Well, it’s happening. We look at the Earth from space and we measure it on the ground. And what we see is that the planet’s climate is changing. The last years have been the warmest since modern record-keeping began.

It’s serious. Even a little change in temperature can have big effects. And we’re seeing some of those effects now. Sea levels are rising. We’re seeing more extreme events like heatwaves and heavy rainfall and wildfire. And we know that a lot of those effects are going to increase with more warming. These changes are impacting decisions that some people make every day, like a farmer thinking about what crops to grow or a homeowner thinking about flood risk.

But there’s hope. There are scientists at NASA and around the world that are researching this. We know more about our planet than we have ever before, and we learn more every day.

So we know why climate is changing. We know that it’s due to increasing greenhouse gases from human activity. We also have tools that can help us better understand and better prepare for future climate change. So we develop computer models that help us understand how much it might change in the future. And we’re also developing technologies here at NASA and around the world that can help us limit future warming or respond to the warming that we’re experiencing.

So why does climate change matter? It’s real. It’s serious, and it’s here. Learn more: www.nasa.gov/earth  

[END VIDEO TRANSCRIPT]

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Why climate change is still the greatest threat to human health

Polluted air and steadily rising temperatures are linked to health effects ranging from increased heart attacks and strokes to the spread of infectious diseases and psychological trauma.

People around the world are witnessing firsthand how climate change can wreak havoc on the planet. Steadily rising average temperatures fuel increasingly intense wildfires, hurricanes, and other disasters that are now impossible to ignore. And while the world has been plunged into a deadly pandemic, scientists are sounding the alarm once more that climate change is still the greatest threat to human health in recorded history .

As recently as August—when wildfires raged in the United States, Europe, and Siberia—World Health Organization Director-General Tedros Adhanom Ghebreyesus said in a statement that “the risks posed by climate change could dwarf those of any single disease.”

On September 5, more than 200 medical journals released an unprecedented joint editorial that urged world leaders to act. “The science is unequivocal,” they write. “A global increase of 1.5°C above the pre-industrial average and the continued loss of biodiversity risk catastrophic harm to health that will be impossible to reverse.”

Despite the acute dangers posed by COVID-19, the authors of the joint op-ed write that world governments “cannot wait for the pandemic to pass to rapidly reduce emissions.” Instead, they argue, everyone must treat climate change with the same urgency as they have COVID-19.

Here’s a look at the ways that climate change can affect your health—including some less obvious but still insidious effects—and why scientists say it’s not too late to avert catastrophe.

Air pollution

Climate change is caused by an increase of carbon dioxide and other greenhouse gases in Earth’s atmosphere, mostly from fossil fuel emissions. But burning fossil fuels can also have direct consequences for human health. That’s because the polluted air contains small particles that can induce stroke and heart attacks by penetrating the lungs and heart and even traveling into the bloodstream. Those particles might harm the organs directly or provoke an inflammatory response from the immune system as it tries to fight them off. Estimates suggest that air pollution causes anywhere between 3.6 million and nine million premature deaths a year.

“The numbers do vary,” says Andy Haines , professor of environmental change and public health at the London School of Hygiene and Tropical Medicine and author of the recently published book Planetary Health . “But they all agree that it’s a big public health burden.”

People over the age of 65 are most susceptible to the harmful effects of air pollution, but many others are at risk too, says Kari Nadeau , director of the Sean N. Parker Center for Allergy and Asthma Research at Stanford University. People who smoke or vape are at increased risk, as are children with asthma.

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Air pollution also has consequences for those with allergies. Carbon dioxide increases the acidity of the air, which then pulls more pollen out from plants. For some people, this might just mean that they face annoyingly long bouts of seasonal allergies. But for others, it could be life-threatening.

“For people who already have respiratory disease, boy is that a problem,” Nadeau says. When pollen gets into the respiratory pathway, the body creates mucus to get rid of it, which can then fill up and suffocate the lungs.

Even healthy people can have similar outcomes if pollen levels are especially intense. In 2016, in the Australian state of Victoria, a severe thunderstorm combined with high levels of pollen to induce what The Lancet has described as “the world’s largest and most catastrophic epidemic of thunderstorm asthma.” So many residents suffered asthma attacks that emergency rooms were overwhelmed—and at least 10 people died as a result.

Climate change is also causing wildfires to get worse, and wildfire smoke is especially toxic. As one recent study showed, fires can account for 25 percent of dangerous air pollution in the U.S. Nadeau explains that the smoke contains particles of everything that the fire has consumed along its path—from rubber tires to harmful chemicals. These particles are tiny and can penetrate even deeper into a person’s lungs and organs. ( Here’s how breathing wildfire smoke affects the body .)

Extreme heat

Heat waves are deadly, but researchers at first didn’t see direct links between climate change and the harmful impacts of heat waves and other extreme weather events. Haines says the evidence base has been growing. “We have now got a number of studies which has shown that we can with high confidence attribute health outcomes to climate change,” he says.

Most recently, Haines points to a study published earlier this year in Nature Climate Change that attributes more than a third of heat-related deaths to climate change. As National Geographic reported at the time , the study found that the human toll was even higher in some countries with less access to air conditioning or other factors that render people more vulnerable to heat. ( How climate change is making heat waves even deadlier .)

That’s because the human body was not designed to cope with temperatures above 98.6°F, Nadeau says. Heat can break down muscles. The body does have some ways to deal with the heat—such as sweating. “But when it’s hot outside all the time, you cannot cope with that, and your heart muscles and cells start to literally die and degrade,” she says.

If you’re exposed to extreme heat for too long and are unable to adequately release that heat, the stress can cause a cascade of problems throughout the body. The heart has to work harder to pump blood to the rest of the organs, while sweat leeches the body of necessary minerals such as sodium and potassium. The combination can result in heart attacks and strokes .

Dehydration from heat exposure can also cause serious damage to the kidneys, which rely on water to function properly. For people whose kidneys are already beginning to fail—particularly older adults—Nadeau says that extreme heat can be a death sentence. “This is happening more and more,” she says.

Studies have also drawn links between higher temperatures and preterm birth and other pregnancy complications. It’s unclear why, but Haines says that one hypothesis is that extreme heat reduces blood flow to the fetus.

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Food insecurity.

One of the less direct—but no less harmful—ways that climate change can affect health is by disrupting the world’s supply of food.

Climate change both reduces the amount of food that’s available and makes it less nutritious.   According to an Intergovernmental Panel on Climate Change (IPCC) special report , crop yields have already begun to decline as a result of rising temperatures, changing precipitation patterns, and extreme weather events. Meanwhile, studies have shown that increased carbon dioxide in the atmosphere can leech plants of zinc, iron, and protein—nutrients that humans need to survive.

Malnutrition is linked to a variety of illnesses, including heart disease, cancer, and diabetes. It can also increase the risk of stunting, or impaired growth , in children, which can harm cognitive function.

Climate change also imperils what we eat from the sea. Rising ocean temperatures have led many fish species to migrate toward Earth’s poles in search of cooler waters. Haines says that the resulting decline of fish stocks in subtropic regions “has big implications for nutrition,” because many of those coastal communities depend on fish for a substantial amount of the protein in their diets.

This effect is likely to be particularly harmful for Indigenous communities, says Tiff-Annie Kenny, a professor in the faculty of medicine at Laval University in Quebec who studies climate change and food security in the Canadian Arctic. It’s much more difficult for these communities to find alternative sources of protein, she says, either because it’s not there or because it’s too expensive. “So what are people going to eat instead?” she asks.

Infectious diseases  

As the planet gets hotter, the geographic region where ticks and mosquitoes like to live is getting wider. These animals are well-known vectors of diseases such as the Zika virus, dengue fever, and malaria. As they cross the tropics of Cancer and Capricorn, Nadeau says, mosquitoes and ticks bring more opportunities for these diseases to infect greater swaths of the world.

“It used to be that they stayed in those little sectors near the Equator, but now unfortunately because of the warming of northern Europe and Canada, you can find Zika in places you wouldn’t have expected,” Nadeau says.

In addition, climate conditions such as temperature and humidity can impact the life cycle of mosquitoes. Haines says there’s particularly good evidence showing that, in some regions, climate change has altered these conditions in ways that increase the risk of mosquitos transmitting dengue .

There are also several ways in which climate change is increasing the risk of diseases that can be transmitted through water, such as cholera, typhoid fever, and parasites. Sometimes that’s fairly direct, such as when people interact with dirty floodwaters. But Haines says that drought can have indirect impacts when people, say, can’t wash their hands or are forced to drink from dodgier sources of freshwater.

Mental health

A common result of any climate-linked disaster is the toll on mental health. The distress caused by drastic environmental change is so significant that it has been given its own name— solastalgia .

Nadeau says that the effects on mental health have been apparent in her studies of emergency room visits arising from wildfires in the western U.S. People lose their homes, their jobs, and sometimes their loved ones, and that takes an immediate toll. “What’s the fastest acute issue that develops? It’s psychological,” she says. Extreme weather events such as wildfires and hurricanes cause so much stress and anxiety that they can lead to post-traumatic stress disorder and even suicide in the long run.

Another common factor is that climate change causes disproportionate harm to the world’s most vulnerable people. On September 2, the Environmental Protection Agency (EPA) released an analysis showing that racial and ethnic minority communities are particularly at risk . According to the report, if temperatures rise by 2°C (3.6°F), Black people are 40 percent more likely to live in areas with the highest projected increases in related deaths. Another 34 percent are more likely to live in areas with a rise in childhood asthma.

Further, the effects of climate change don’t occur in isolation. At any given time, a community might face air pollution, food insecurity, disease, and extreme heat all at once. Kenny says that’s particularly devastating in communities where the prevalence of food insecurity and poverty are already high. This situation hasn’t been adequately studied, she says, because “it’s difficult to capture these shocks that climate can bring.”

Why there’s reason for hope

In recent years, scientists and environmental activists have begun to push for more research into the myriad health effects of climate change. “One of the striking things is there’s been a real dearth of funding for climate change and health,” Haines says. “For that reason, some of the evidence we have is still fragmentary.”

Still, hope is not lost. In the Paris Agreement, countries around the world have pledged to limit global warming to below 2°C (3.6°F)—and preferably to 1.5°C (2.7°F)—by cutting their emissions. “When you reduce those emissions, you benefit health as well as the planet,” Haines says.

Meanwhile, scientists and environmental activists have put forward solutions that can help people adapt to the health effects of climate change. These include early heat warnings and dedicated cooling centers, more resilient supply chains, and freeing healthcare facilities from dependence on the electric grid.

Nadeau argues that the COVID-19 pandemic also presents an opportunity for world leaders to think bigger and more strategically. For example, the pandemic has laid bare problems with efficiency and equity that have many countries restructuring their healthcare facilities. In the process, she says, they can look for new ways to reduce waste and emissions, such as getting more hospitals using renewable energy.

“This is in our hands to do,” Nadeau says. “If we don’t do anything, that would be cataclysmic.”

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Our Future Is Now - A Climate Change Essay by Francesca Minicozzi, '21

Francesca Minicozzi (class of 2021) is a Writing/Biology major who plans to study medicine after graduation. She wrote this essay on climate change for WR 355/Travel Writing, which she took while studying abroad in Newcastle in spring 2020. Although the coronavirus pandemic curtailed Francesca’s time abroad, her months in Newcastle prompted her to learn more about climate change. Terre Ryan Associate Professor, Writing Department

Our Future Is Now

By Francesca Minicozzi, '21 Writing and Biology Major

 “If you don’t mind me asking, how is the United States preparing for climate change?” my flat mate, Zac, asked me back in March, when we were both still in Newcastle. He and I were accustomed to asking each other about the differences between our home countries; he came from Cambridge, while I originated in Long Island, New York. This was one of our numerous conversations about issues that impact our generation, which we usually discussed while cooking dinner in our communal kitchen. In the moment of our conversation, I did not have as strong an answer for him as I would have liked. Instead, I informed him of the few changes I had witnessed within my home state of New York.

Zac’s response was consistent with his normal, diplomatic self. “I have been following the BBC news in terms of the climate crisis for the past few years. The U.K. has been working hard to transition to renewable energy sources. Similar to the United States, here in the United Kingdom we have converted over to solar panels too. My home does not have solar panels, but a lot of our neighbors have switched to solar energy in the past few years.”

“Our two countries are similar, yet so different,” I thought. Our conversation continued as we prepared our meals, with topics ranging from climate change to the upcoming presidential election to Britain’s exit from the European Union. However, I could not shake the fact that I knew so little about a topic so crucial to my generation.

After I abruptly returned home from the United Kingdom because of the global pandemic, my conversation with my flat mate lingered in my mind. Before the coronavirus surpassed climate change headlines, I had seen the number of internet postings regarding protests to protect the planet dramatically increase. Yet the idea of our planet becoming barren and unlivable in a not-so-distant future had previously upset me to the point where a part of me refused to deal with it. After I returned from studying abroad, I decided to educate myself on the climate crisis.

My quest for climate change knowledge required a thorough understanding of the difference between “climate change” and “global warming.” Climate change is defined as “a pattern of change affecting global or regional climate,” based on “average temperature and rainfall measurements” as well as the frequency of extreme weather events. 1   These varied temperature and weather events link back to both natural incidents and human activity. 2   Likewise, the term global warming was coined “to describe climate change caused by humans.” 3   Not only that, but global warming is most recently attributed to an increase in “global average temperature,” mainly due to greenhouse gas emissions produced by humans. 4

I next questioned why the term “climate change” seemed to take over the term “global warming” in the United States. According to Frank Luntz, a leading Republican consultant, the term “global warming” functions as a rather intimidating phrase. During George W. Bush’s first presidential term, Luntz argued in favor of using the less daunting phrase “climate change” in an attempt to overcome the environmental battle amongst Democrats and Republicans. 5   Since President Bush’s term, Luntz remains just one political consultant out of many politicians who has recognized the need to address climate change. In an article from 2019, Luntz proclaimed that political parties aside, the climate crisis affects everyone. Luntz argued that politicians should steer clear of trying to communicate “the complicated science of climate change,” and instead engage voters by explaining how climate change personally impacts citizens with natural disasters such as hurricanes, tornadoes, and forest fires. 6   He even suggested that a shift away from words like “sustainability” would gear Americans towards what they really want: a “cleaner, safer, healthier” environment. 7

The idea of a cleaner and heathier environment remains easier said than done. The Paris Climate Agreement, introduced in 2015, began the United Nations’ “effort to combat global climate change.” 8   This agreement marked a global initiative to “limit global temperature increase in this century to 2 degrees Celsius above preindustrial levels,” while simultaneously “pursuing means to limit the increase to 1.5 degrees.” 9    Every country on earth has joined together in this agreement for the common purpose of saving our planet. 10   So, what could go wrong here? As much as this sounds like a compelling step in the right direction for climate change, President Donald Trump thought otherwise. In June 2017, President Trump announced the withdrawal of the United States from the Paris Agreement with his proclamation of climate change as a “’hoax’ perpetrated by China.” 11   President Trump continued to question the scientific facts behind climate change, remaining an advocate for the expansion of domestic fossil fuel production. 12   He reversed environmental policies implemented by former President Barack Obama to reduce fossil fuel use. 13

Trump’s actions against the Paris Agreement, however, fail to represent the beliefs of Americans as a whole. The majority of American citizens feel passionate about the fight against climate change. To demonstrate their support, some have gone as far as creating initiatives including America’s Pledge and We Are Still In. 14   Although the United States officially exited the Paris Agreement on November 4, 2020, this withdrawal may not survive permanently. 15   According to experts, our new president “could rejoin in as short as a month’s time.” 16   This offers a glimmer of hope.

The Paris Agreement declares that the United States will reduce greenhouse gas emission levels by 26 to 28 percent by the year 2025. 17   As a leader in greenhouse gas emissions, the United States needs to accept the climate crisis for the serious challenge that it presents and work together with other nations. The concept of working coherently with all nations remains rather tricky; however, I remain optimistic. I think we can learn from how other countries have adapted to the increased heating of our planet. During my recent study abroad experience in the United Kingdom, I was struck by Great Britain’s commitment to combating climate change.

Since the United Kingdom joined the Paris Agreement, the country targets a “net-zero” greenhouse gas emission for 2050. 18   This substantial alteration would mark an 80% reduction of greenhouse gases from 1990, if “clear, stable, and well-designed policies are implemented without interruption.” 19   In order to stay on top of reducing emissions, the United Kingdom tracks electricity and car emissions, “size of onshore and offshore wind farms,” amount of homes and “walls insulated, and boilers upgraded,” as well as the development of government policies, including grants for electric vehicles. 20   A strong grip on this data allows the United Kingdom to target necessary modifications that keep the country on track for 2050. In my brief semester in Newcastle, I took note of these significant changes. The city of Newcastle is small enough that many students and faculty are able to walk or bike to campus and nearby essential shops. However, when driving is unavoidable, the majority of the vehicles used are electric, and many British citizens place a strong emphasis on carpooling to further reduce emissions. The United Kingdom’s determination to severely reduce greenhouse emissions is ambitious and particularly admirable, especially as the United States struggles to shy away from its dependence on fossil fuels.

So how can we, as Americans, stand together to combat global climate change? Here are five adjustments Americans can make to their homes and daily routines that can dramatically make a difference:

• Stay cautious of food waste. Studies demonstrate that “Americans throw away up to 40 percent of the food they buy.” 21   By being more mindful of the foods we purchase, opting for leftovers, composting wastes, and donating surplus food to those in need, we can make an individual difference that impacts the greater good. 22   
• Insulate your home. Insulation functions as a “cost-effective and accessible” method to combat climate change. 23   Homes with modern insulation reduce energy required to heat them, leading to a reduction of emissions and an overall savings; in comparison, older homes can “lose up to 35 percent of heat through their walls.” 24   
• Switch to LED Lighting. LED stands for “light-emitting diodes,” which use “90 percent less energy than incandescent bulbs and half as much as compact fluorescents.” 25   LED lights create light without producing heat, and therefore do not waste energy. Additionally, these lights have a longer duration than other bulbs, which means they offer a continuing savings. 26  
• Choose transportation wisely. Choose to walk or bike whenever the option presents itself. If walking or biking is not an option, use an electric or hybrid vehicle which emits less harmful gases. Furthermore, reduce the number of car trips taken, and carpool with others when applicable. 
• Finally, make your voice heard. The future of our planet remains in our hands, so we might as well use our voices to our advantage. Social media serves as a great platform for this. Moreover, using social media to share helpful hints to combat climate change within your community or to promote an upcoming protest proves beneficial in the long run. If we collectively put our voices to good use, together we can advocate for change.

As many of us are stuck at home due to the COVID-19 pandemic, these suggestions are slightly easier to put into place. With numerous “stay-at-home” orders in effect, Americans have the opportunity to make significant achievements for climate change. Personally, I have taken more precautions towards the amount of food consumed within my household during this pandemic. I have been more aware of food waste, opting for leftovers when too much food remains. Additionally, I have realized how powerful my voice is as a young college student. Now is the opportunity for Americans to share how they feel about climate change. During this unprecedented time, our voice is needed now more than ever in order to make a difference.

However, on a much larger scale, the coronavirus outbreak has shed light on reducing global energy consumption. Reductions in travel, both on the roads and in the air, have triggered a drop in emission rates. In fact, the International Energy Agency predicts a 6 percent decrease in energy consumption around the globe for this year alone. 27   This drop is “equivalent to losing the entire energy demand of India.” 28   Complete lockdowns have lowered the global demand for electricity and slashed CO2 emissions. However, in New York City, the shutdown has only decreased carbon dioxide emissions by 10 percent. 29   This proves that a shift in personal behavior is simply not enough to “fix the carbon emission problem.” 30   Climate policies aimed to reduce fossil fuel production and promote clean technology will be crucial steppingstones to ameliorating climate change effects. Our current reduction of greenhouse gas emissions serves as “the sort of reduction we need every year until net-zero emissions are reached around 2050.” 31   From the start of the coronavirus pandemic, politicians came together for the common good of protecting humanity; this demonstrates that when necessary, global leaders are capable of putting humankind above the economy. 32

After researching statistics comparing the coronavirus to climate change, I thought back to the moment the virus reached pandemic status. I knew that a greater reason underlay all of this global turmoil. Our globe is in dire need of help, and the coronavirus reminds the world of what it means to work together. This pandemic marks a turning point in global efforts to slow down climate change. The methods we enact towards not only stopping the spread of the virus, but slowing down climate change, will ultimately depict how humanity will arise once this pandemic is suppressed. The future of our home planet lies in how we treat it right now. 

• “Climate Change: What Do All the Terms Mean?,” BBC News (BBC, May 1, 2019), https://www.bbc.com/news/science-environment-48057733 )
• Ibid. 
• Kate Yoder, “Frank Luntz, the GOP's Message Master, Calls for Climate Action,” Grist (Grist, July 26, 2019), https://grist.org/article/the-gops-most-famous-messaging-strategist-calls-for-climate-action
• Melissa Denchak, “Paris Climate Agreement: Everything You Need to Know,” NRDC, April 29, 2020, https://www.nrdc.org/stories/paris-climate-agreement-everything-you-need-know)
• “Donald J. Trump's Foreign Policy Positions,” Council on Foreign Relations (Council on Foreign Relations), accessed May 7, 2020, https://www.cfr.org/election2020/candidate-tracker/donald-j.-trump?gclid=CjwKCAjw4871BRAjEiwAbxXi21cneTRft_doA5if60euC6QCL7sr-Jwwv76IkgWaUTuyJNx9EzZzRBoCdjsQAvD_BwE#climate and energy )
• David Doniger, “Paris Climate Agreement Explained: Does Congress Need to Sign Off?,” NRDC, December 15, 2016, https://www.nrdc.org/experts/david-doniger/paris-climate-agreement-explained-does-congress-need-sign )
• “How the UK Is Progressing,” Committee on Climate Change, March 9, 2020, https://www.theccc.org.uk/what-is-climate-change/reducing-carbon-emissions/how-the-uk-is-progressing/)
• Ibid.  
• “Top 10 Ways You Can Fight Climate Change,” Green America, accessed May 7, 2020, https://www.greenamerica.org/your-green-life/10-ways-you-can-fight-climate-change )
• Matt McGrath, “Climate Change and Coronavirus: Five Charts about the Biggest Carbon Crash,” BBC News (BBC, May 5, 2020), https://www.bbc.com/news/amp/science-environment-52485712 )
• Natural & Applied Sciences
• Social Sciences

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Climate change is already altering everything, from fertility choices to insuring our homes

Climate change is already changing the way many of us live or think. Image:  Unsplash/Alexander Tsang

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Stay up to date:, climate change.

• Climate change is already affecting people’s lives in a variety of ways.
• Global warming is the biggest health threat facing humanity, the World Health Organization says.
• It’s also making people rethink family planning choices and putting properties at risk of becoming uninsurable.
• Disruptions to supply chains because of extreme weather are shaking the global economy.

How is climate change affecting you?

You may think the biggest impacts lie far away – in terms of time or geography. But global warming is already changing the way many of us live or think.

1. Health suffers because of climate change

Climate change is the biggest health threat facing humanity , the World Health Organization says, estimating that it will cause around a quarter of a million additional deaths each year in 2030-50. These will mainly be from malnutrition, malaria, diarrhoea and heat stress.

However, climate change is already having more subtle effects on health and wellbeing. Spring is beginning earlier in many places, meaning there’s a higher pollen count. This is bad news for allergy sufferers. Higher temperatures in the United States made the pollen season 11-27 days longer between 1995 and 2011, the Asthma and Allergy Foundation of America says.

Rising temperatures also contribute to worsening air quality, which can increase the risk and severity of asthma attacks .

2. Climate change is raising the cost of living

COVID-19 has received most of the blame for recent global supply chain problems, but climate change is also having an impact. When supply chains are shaken, this impacts the availability and cost of goods.

Freezing weather in Texas in February 2021 triggered the United States’ most severe energy blackout of all time, leading to shutdowns at three major semiconductor plants and adding to the global shortage of microchips.

The cost of living is also soaring because of the global surge in energy prices. While Russia’s war on Ukraine is driving much of this now, climate change is also a factor.

“ Companies face up to $120 billion in costs from environmental risks in their supply chains by 2026,” according to research published in 2021 by CDP, a nonprofit that runs the world's largest environmental disclosure system. This will include increased costs for raw materials, and because of regulatory changes such as carbon pricing as the world addresses environmental crises, the report says.

In 2021, more than 20% of American adults lived in households unable to pay their utility bills .

3. Warming oceans are threatening our way of life

Sea level rises could pose the biggest threat to global supply chains , potentially putting ports and coastal infrastructure out of action. Higher sea temperatures may also cause more severe storms in tropical parts of the world, posing a threat to life and infrastructure.

The sea is home to most of our biodiversity, and 3 billion people globally rely on it for their livelihoods, according to the UN. However, carbon emissions from human activity are causing ocean warming, acidification and oxygen loss , putting large numbers of marine-related jobs at risk, it says.

Climate change poses an urgent threat demanding decisive action. Communities around the world are already experiencing increased climate impacts, from droughts to floods to rising seas. The World Economic Forum's Global Risks Report continues to rank these environmental threats at the top of the list.

To limit global temperature rise to well below 2°C and as close as possible to 1.5°C above pre-industrial levels, it is essential that businesses, policy-makers, and civil society advance comprehensive near- and long-term climate actions in line with the goals of the Paris Agreement on climate change.

The World Economic Forum's Climate Initiative supports the scaling and acceleration of global climate action through public and private-sector collaboration. The Initiative works across several workstreams to develop and implement inclusive and ambitious solutions.

This includes the Alliance of CEO Climate Leaders, a global network of business leaders from various industries developing cost-effective solutions to transitioning to a low-carbon, climate-resilient economy. CEOs use their position and influence with policy-makers and corporate partners to accelerate the transition and realize the economic benefits of delivering a safer climate.

Contact us to get involved.

4. People might have fewer babies

People are increasingly citing the climate crisis as a major reason why they may decide to have fewer or even no children. According to a study in the United States, a third of women said they will reduce their anticipated family size because of it.

However a similar number of the more than 2,800 American women surveyed by Modernfertility.com said the issue has made them decide to have children sooner . The study says this is because it’s either made them focus more on what’s important to them or given them a sense of urgency.

5. Your property could become uninsurable

Insurance is something that nearly everyone has, but climate change poses a “systemic risk” to the sector, according to professional services company Grant Thornton.

Extreme weather events led to insured losses of $105 billion in 2021 , the fourth-highest level since 1970, according to preliminary estimates by Swiss Re, one of the world's leading providers of reinsurance and insurance.

This not only potentially makes insurance more expensive for everyone, but it also means some assets could become uninsurable . One in 25 Australian homes could be uninsurable by 2030 , according to the Climate Council.

6. Increased chance of another pandemic

Climate change makes new pandemics more likely, because as temperatures increase, wild animals will be forced to change habitats. This could lead to them living nearer to human populations, increasing the chances of a virus jumping between species and causing the next pandemic, according to a report published by the scientific journal Nature.

“Geographic range shifts” will mean mammals encounter each other for the first time, and in doing so will share thousands of viruses, the report says. Even keeping global warming under 2°C this century “will not reduce future viral sharing”, the scientists note.

What is the World Economic Forum doing about fighting pandemics?

The first human trial of a COVID-19 vaccine was administered this week.

CEPI, launched at the World Economic Forum, provided funding support for the Phase 1 study. The organization this week announced their seventh COVID-19 vaccine project in the fight against the pandemic.

The Coalition for Epidemic Preparedness Innovations (CEPI) was launched in 2017 at the Forum's Annual Meeting – bringing together experts from government, business, health, academia and civil society to accelerate the development of vaccines against emerging infectious diseases and to enable access to these vaccines during outbreaks.

Coalitions like CEPI are made possible through public-private partnerships. The World Economic Forum is the trusted global platform for stakeholder engagement, bringing together a range of multistakeholders from business, government and civil society to improve the state of the world.

Organizations can partner with the Forum to contribute to global health solutions. Contact us to find out how.

The World Economic Forum is committed to helping limit global warming to 1.5°C above pre-industrial levels to stave off catastrophe. It aims to work with leaders to increase climate commitments, collaborate with partners to develop private initiatives, and provide a platform for innovators to realize their ambition and contribute solutions.

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10 reasons why climate change is an important issue

We’re all concerned about climate change, but when it looks like a problem for future generations, you ask yourself, ‘will climate change even affect me?’ No matter what you care about, climate change is already affecting our world today. While we still have time to limit the worst impact, here are ten great reasons why we should all care about climate change:

Climate change will mean big changes for animals around the world. So if we care about incredible species, we must care about how a changing climate will make it harder for them to find food, and decrease their habitats – from forest to sea ice to the UK’s rivers and chalk streams .

2. Because you need your morning coffee fix

If you’re one of those people who need a coffee hit to get going, mornings may become grim. The effects of climate change on coffee are well-documented and coffee producers are already seeing reduced harvests, and more pests, because of it. Even if you’re caffeine-free you’re not in the clear – wine production may also be hit.

Finding Nemo or Dory may become harder as their beautiful homes crumble under the stress of our changing climate. Warmer air and ocean temperatures cause coral bleaching, where corals lose their colour and may die. Ocean acidification – from increased CO2 in the atmosphere – compounds the problem. Today, the ocean is 26% more acidic than it was in 1990, and the Great Barrier Reef has just experienced unprecedented back-to-back bleaching events in 2016 and 2017. Climate change is very bad news for anyone hoping to see the Great Barrier Reef one day.

4. Because we all need clean water

Did you know that 2 in every 3 people worldwide live in regions of severe water scarcity? Even a small increase in global temperatures will destabilise the water cycle and could make water scarcity much worse. Climate change affects rainfall patterns, meaning both drought and flooding will be more common, and more intense. And although it’s hardly comparable with life-threatening floods, climate change may already be making you late for work .

Globally temperature records  have been broken in recent years, and flooding in the UK gets worse. Year after year we’ve seen politicians wading through floods in Somerset, hopping into dinghies in Cornwall and arguing with each other in Westminster. More frequent and more intense extreme weather is a documented result of our greenhouse gas emissions, and the annual cost of flooding in the UK could increase 15-fold by the 2080s. We need to see politicians taking serious action on reducing the UK's carbon footprint, not looking for the next photo opportunity.

6. Because rainforests are incredible

Unique, irreplaceable, and often described as ‘the world’s lungs’, rainforests are some of the most precious habitats on the planet. They really are amazing; the Amazon, for example, is home to an astonishing 1 in 10 of all the known species on Earth. Yet over a third of the Amazon rainforest is already threatened by climate change. It’s a double-edged sword too: worldwide, forest destruction – mainly for agriculture – is a major cause of climate change, generating an incredible amount of greenhouse gases.

With increasing carbon emissions, it stands to reason that we face compromised air quality. This affects human health, especially children. Air pollution can lead to asthma, heart and lung disease. Beijing’s insidious smog is a visible reminder of this, but bad air quality is also making headlines in the UK, and has been labelled a ‘public health emergency’ by MPs.

8. Because clean tech is exciting

It’s not all bad news. Some of the biggest advancements in technology over the past few years have come from trying to limit, and come up with alternatives to, humanity’s CO2 dependency. Solar panels, wave-energy conversion and wind farms are allowing us to harness the power of nature in a clean way, harvesting energy without harming our environment or destroying habitats. Meanwhile nifty gadgets – like the Wall-E sized robot that can insulate your house to save energy – are helping to cut carbon in unexpected places. More of this technology could mean a cleaner, healthier future for us and our planet – because clean tech doesn’t just help nature, it also has the potential to build better, more accessible and people-friendly cities.

Climate change won’t just impact forest, or coral reefs, or even people in far-off countries – it will affect all of us. From more extreme weather to increasing food prices, to recreation and decreased opportunities to appreciate the natural world, people everywhere will feel its effects. Reducing our carbon footprint is fundamentally necessary to create a world where people and nature thrive – and that’s why WWF is working on it .

10. Because of future generations

We are fortunate to live in a beautiful, diverse, nurturing, awe-inspiring planet. Our children, and all future generations, deserve the same.

If you’re feeling worried by now, you’re not alone. Millions of people are working together for our planet. Events like Earth Hour are a brilliant reminder that together, humanity is capable of great things, and we can make change happen for the right reasons.

Already, so much has changed since we first heard about the possible effect of climate change. Beginning with the Rio Earth Summit, then the Kyoto Protocol and the Paris Agreement, action on a global scale is speeding up. Now it is more important than ever that we use our action, our votes and our voices to tell political and business leaders that action on climate is absolutely essential.

What can you do? You could start with taking our carbon footprint calculator, to look at how your lifestyle impacts the environment and where you can reduce your footprint.

The Economic Consequences of Climate Change: An Interview with Nobel Laureate William Nordhaus

William Nordhaus and Lint Barrage (PhD ’13)

What are the economic consequences and opportunities of climate change? How do you integrate economic analysis with the science of climate change?

These questions are at the heart of Nobel laureate William Nordhaus ’s career, and in research released this week in the Proceedings of the National Academy of Sciences (PNAS), he and coauthor Lint Barrage (PhD ’13) present new findings from the updated DICE-2023 model, with major implications for global climate policy.

The DICE model (the Dynamic Integrated model for Climate and the Economy) is one of the first integrated assessment models or IAMs . This approach provides policy-relevant insights into global environmental issues through quantitative descriptions of key processes in human and earth systems. IAMs model the climate problem from end to end, from economy to emissions to atmospheric chemistry to climate dynamics, then on to impacts such as sea-level rise, wildfire, and health impacts, and finally closing the loop by including policies to bend the curve of CO2 emissions. The outputs of these models play a key role in understanding key relationships and formulating efficient policies to slow or reverse the trends.

One important finding is that international climate policy has set ambitious goals but has failed to establish an architecture for implementation…Additionally, we estimate that current policies will lead the global mean temperature increase (above pre-industrial levels) to pass the 1.5 °C target later in this decade, while without major policy changes, the globe will surpass the 2 °C goal of the Paris Accord by mid-century.” - William Nordhaus

The original DICE model was developed and published at Yale in 1992 and is the most widely used climate-change integrated assessment model. The US and other governments employ it to calculate the social cost of carbon, as well as create consistent scenarios and evaluate policies and uncertainties. The new study updates the 2016 DICE model with revised treatments of the carbon cycle, damages, discounting, and also includes results on the Paris Accord and temperature-limited scenarios.

Among the key findings from the new study, the authors note that both current policies and the extended Paris Accord fall far short of limiting global warming to 2 °C. They also highlight the substantial economic stakes at play in global climate policy: in the efficient scenario, where climate change policies maximize economic welfare according to the principles of cost–benefit analysis—they estimate a net present value of economic benefits of around $120 trillion.

Journal Publication

In the Q&A below, author and Nobel laureate William Nordhaus discusses the key findings and implications of this new research.

What are the major new findings today? What are the major surprises?

One important finding is that international climate policy has set ambitious goals but has failed to establish a realistic architecture for implementation. This is seen in the “price of carbon” (or the cost to polluters of emitting CO2 into the atmosphere) that is far below the level necessary to reach international goals. We estimate that a global carbon price of $80 per ton of CO2 would be necessary to reach the goals of the 2015 Paris Accord. Yet, the World Bank estimates that the current global price is only a tiny $3 per ton.

Additionally, we estimate that current policies will lead the global mean temperature increase (above pre-industrial levels) to pass the 1.5 °C target later in this decade, while the globe will surpass the 2 °C goal of the Paris Accord by mid-century without major policy changes. All this might not be a big surprise – perhaps alarm is a better word. Professor Barrage and I emphasize that it is critically important to recognize how countries’ climate policies fall so far short of their rhetoric and goals, and this is borne out by the recent release of DICE 2023.

What does this new study say about the “social cost of carbon”?

This critical measure (“SCC” for short) is the most important single economic concept in the economics of climate change. It designates the current and future damages caused by an additional ton of carbon dioxide emissions or its equivalent. The SCC has become a central tool used in climate change policy, particularly in the determination of regulatory policies that involve greenhouse gas emissions. The SCC has been used by the US government in rules that provide more than $1 trillion in benefits. Integrated models like DICE are essential to the calculation of the SCC and have been used by many governments in their formulation of climate policies.

We estimate that the SCC is around $80 per ton of CO2 in today’s dollars. With about 5 billion tons annually of emissions, this represents a debit of about $400 billion for the US economy (out of a total output of $28 trillion). This is a useful finding because it shows again how inadequate climate policy is because current carbon prices are so far below our estimates of SCC. The figure below shows alternative estimates of the SCC from the publication.

Figure 4 from the article shows the relationship between the social cost of carbon and the discount rate for different scenarios of the DICE-2023 and several other models. 

What suggestions for climate policy emerge from your work?

Looking at the landscape of climate policy, we see three necessary aspects of an effective policy.

The first , mentioned above, is that countries need to raise carbon prices sharply to provide appropriate incentives for the private and public sectors to reduce emissions. This cannot be done overnight, obviously, but we need to move forward with this critical step as soon as possible. Here in the United States, there is an unusual opportunity because major tax provisions expire next year, and we face the need to either raise income taxes substantially or find other revenue sources. This would be a good time to replace the scheduled increases in income taxes with taxes on carbon emissions.

The second step is to replace the flawed international architecture on climate policy with a structure with carrots and sticks for incentivizing countries to participate in strong policies. I have called this the “climate club” to suggest a structure of pricing policies along with penalties for countries who do not participate. The flawed structure of current international agreements is a major reason why so little progress has been made to curtail carbon emissions to date.

The final step is to recognize that a policy of decarbonizing our economies will require major new technologies – ones that are only in the laboratories or at small scale – and that these need strong government fiscal support. Examples of such technologies are advanced renewables, negative-emissions technologies, and futuristic technologies such as fusion, advanced nuclear, and superconducting networks.

The most important support would be government subsidies for fundamental and applied research on green energy technologies. It is striking how little governments have recognized the importance of this aspect of climate policy. Major countries today provide only $40 billion of support for green energy R&D. This is less than half of the money that companies in the United States devote to research and development in pharmaceuticals. We do not have a prayer of reaching our climate goals without strong government research support.

These three steps are hardly revolutionary in concept, but they are awesomely challenging politically. They are the best chance for the community of nations to prevent the growing threats to humans and the global environment of rapid climate change.

The modeling behind DICE-2023 sounds like a major enterprise. Are these models complex to code and calculate?

The models themselves are relatively small compared to many scientific studies (you can see some representative code below). But they have a particularly complex structure because they are “optimization models,” which means that they solve for the least-cost or highest-value path of the variables.

If you excuse a little excursion into geekiness, I will explain a bit more. The simplest version of DICE has 1475 variables and 1381 linear and nonlinear constraints.

Solving this problem would not have been remotely possible without modern mathematics, software, and hardware, but today’s PCs can solve it in only 1.3 seconds. One interesting feature is that the solution is so fast and robust because of the development of an algorithm known as “linear programming,” by Yale economist Tjalling Koopmans, for which he won the 1974 Nobel Prize in Economics.

What has been Yale's role in the development of integrated models like DICE?

Yale has been in the forefront of integrated climate-economic modeling for decades. Contributors to earlier DICE-related studies over the years have been Yale scholars such as Robert Mendelsohn and Ken Gillingham at the Environment School and Economics Department faculty such as Tony Smith (Chair of Economics) and Sam Kortum . Yale-derived work has pioneered DICE spinoffs, such as multi-region versions, ones introducing uncertainty, approaches with research and development, and learning by doing.

I would emphasize, however, that each new study and every passing year reveal new complexities and challenges. A world aflame with wildfires, and New Yorkers sheltering from record-setting pollution from Canadian fires, are the surprises that await us in the years ahead if unchecked warming continues.

John Kerry’s Four Decades of Raising Climate Awareness on the World Stage

S itting in a taxi in Munich in February, stuck in traffic, John Kerry wrestled with an idea. The U.S. climate envoy was in southern Germany to attend an annual security conference, spending his days pushing world leaders to work together to fight global warming . But in a few hours, the former Secretary of State would receive an award named in honor of a well-known Nazi resister, Ewald von Kleist. As he ruminated on his remarks, he worked to connect what he called the “echoes of the 1930s” in today’s geopolitics with the need for unity on climate action.

By the time he took the stage to accept the award that night, Kerry had found the words to make the connection in a blunt speech lasting less than 15 minutes. “On climate, on Ukraine , and on so much more, the whole world needs to come together,” he told the dignitaries gathered in the ornate Bavarian palace where the ceremony was being held. “I hate to say it, and it’s not an exaggeration—but we do stand next to another abyss. It is the test of our own times, a test as acute and as existential as any previous one.”

Read More: It’s a New Era of Climate Geopolitics. And It’s Not Just For Policy Wonks

Over the past 40 years, Kerry has used his positions as U.S. Senator, Democratic nominee for President, and top American diplomat to bring climate action to the highest levels of international relations, using his stature and knack for persuasion to push the issue at home and abroad. As a Senator, he showed up at global climate meetings to keep the U.S. engaged. He would eventually piece together a bold, if ultimately unsuccessful, congressional effort to price carbon. Running for President, he leaned into the climate message with a commitment unlike any major-party nominee before him. And as Secretary of State he made the issue a State Department priority, created a global oceans conference that continues to this day, and helped broker the landmark Paris Agreement.

As the issue has risen on the global agenda in recent years, Kerry has been among the most influential voices shaping the tone and substance of the conversation. And despite the dark overtones of his Munich speech, devotees and critics alike often say Kerry’s defining characteristic is his optimism. He is able to look at the most dire situations , from climate change to the Middle East , and identify a path for everyone to come to their senses—often against the odds.

Read More: John Kerry’s Next Move

That optimism was tested from the start in his role as President Joe Biden’s climate envoy . Kerry entered the job in the middle of the pandemic and in the wake of an Administration that had effectively withdrawn the U.S. from international climate discussions. He immediately began hopping around the world calling on Presidents and princes to deliver the message that the U.S. could be trusted. By the end of the first year, he was launching coalitions and helping broker key international climate deals. “I know that people criticize the optimism,” says Amos Hochstein, a key international energy adviser to Biden who worked closely with Kerry. “I think it’s his superpower.”

That approach panned out at last year’s U.N. climate conference in Dubai , where Kerry held firm in his support of the oil CEO charged with leading the summit even as many climate advocates called for the executive to step down. “He sticks with his convictions,” says Sue Biniaz, a longtime adviser who served as his deputy climate envoy.

Kerry now begins a new chapter. He resigned from his role as climate envoy on March 6, but at the age of 80, after nearly 40 years in government, he is not retiring. Instead, he plans to join the private sector, drumming up money to finance climate efforts in the places that need it the most. It’s a fitting move. Kerry named his memoir Every Day Is Extra after a saying he and his buddies used as a touchstone during the Vietnam War. It’s a reminder to himself—and everyone else—not to sit on the sidelines when problems need solving.

Why Gabriela Hearst Considers Sustainable Fashion to Be the Ultimate Luxury

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Climate change is happening too fast for migrating birds

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 “In discussing climate change, we often focus on warming, but the length and timing of seasons — like when winter ends and spring begins — are some of the most dramatic effects of climate change.”

“A lot of these birds were tracking long-term averages of green-up more closely than they were current green-up.”

The awe-inspiring feat of migration has captivated humans for millennia, yet scientists know very little about how birds manage to fly as far as they do, up to tens of thousands of miles per trip, or why exactly they leave when they do. The migratory cues that birds rely on are myriad: temperature, day length, landforms, the stars — even the Earth’s magnetic field, as well as the instructions coded in their genetics. Some of the environmental cues, like temperature, are likely impacted by climate change. But others, like day length, are not. “That might be one reason some (migratory) birds are more affected by climate change (than others),” Robertson said.

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by Natalia Mesa, High Country News March 25, 2024

This <a target="_blank" href="https://www.hcn.org/articles/climate-change-is-happening-too-fast-for-migrating-birds/">article</a> first appeared on <a target="_blank" href="https://www.hcn.org">High Country News</a> and is republished here under a Creative Commons license.<img src="https://i0.wp.com/www.hcn.org/wp-content/uploads/2023/05/cropped-HCN_Logo-Monogram_White_Sq-2.png?fit=150%2C150&amp;ssl=1" style="width:1em;height:1em;margin-left:10px;"><img id="republication-tracker-tool-source" src="https://www.hcn.org/?republication-pixel=true&post=323597" style="width:1px;height:1px;">

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What to know about the crisis of violence, politics and hunger engulfing Haiti

A long-simmering crisis over Haiti’s ability to govern itself, particularly after a series of natural disasters and an increasingly dire humanitarian emergency, has come to a head in the Caribbean nation, as its de facto president remains stranded in Puerto Rico and its people starve and live in fear of rampant violence. 

The chaos engulfing the country has been bubbling for more than a year, only for it to spill over on the global stage on Monday night, as Haiti’s unpopular prime minister, Ariel Henry, agreed to resign once a transitional government is brokered by other Caribbean nations and parties, including the U.S.

But the very idea of a transitional government brokered not by Haitians but by outsiders is one of the main reasons Haiti, a nation of 11 million, is on the brink, according to humanitarian workers and residents who have called for Haitian-led solutions. 

“What we’re seeing in Haiti has been building since the 2010 earthquake,” said Greg Beckett, an associate professor of anthropology at Western University in Canada. 

What is happening in Haiti and why?

In the power vacuum that followed the assassination of democratically elected President Jovenel Moïse in 2021, Henry, who was prime minister under Moïse, assumed power, with the support of several nations, including the U.S. 

When Haiti failed to hold elections multiple times — Henry said it was due to logistical problems or violence — protests rang out against him. By the time Henry announced last year that elections would be postponed again, to 2025, armed groups that were already active in Port-au-Prince, the capital, dialed up the violence.

Even before Moïse’s assassination, these militias and armed groups existed alongside politicians who used them to do their bidding, including everything from intimidating the opposition to collecting votes . With the dwindling of the country’s elected officials, though, many of these rebel forces have engaged in excessively violent acts, and have taken control of at least 80% of the capital, according to a United Nations estimate. 

Those groups, which include paramilitary and former police officers who pose as community leaders, have been responsible for the increase in killings, kidnappings and rapes since Moïse’s death, according to the Uppsala Conflict Data Program at Uppsala University in Sweden. According to a report from the U.N . released in January, more than 8,400 people were killed, injured or kidnapped in 2023, an increase of 122% increase from 2022.

“January and February have been the most violent months in the recent crisis, with thousands of people killed, or injured, or raped,” Beckett said.

Armed groups who had been calling for Henry’s resignation have already attacked airports, police stations, sea ports, the Central Bank and the country’s national soccer stadium. The situation reached critical mass earlier this month when the country’s two main prisons were raided , leading to the escape of about 4,000 prisoners. The beleaguered government called a 72-hour state of emergency, including a night-time curfew — but its authority had evaporated by then.

Aside from human-made catastrophes, Haiti still has not fully recovered from the devastating earthquake in 2010 that killed about 220,000 people and left 1.5 million homeless, many of them living in poorly built and exposed housing. More earthquakes, hurricanes and floods have followed, exacerbating efforts to rebuild infrastructure and a sense of national unity.

Since the earthquake, “there have been groups in Haiti trying to control that reconstruction process and the funding, the billions of dollars coming into the country to rebuild it,” said Beckett, who specializes in the Caribbean, particularly Haiti. 

Beckett said that control initially came from politicians and subsequently from armed groups supported by those politicians. Political “parties that controlled the government used the government for corruption to steal that money. We’re seeing the fallout from that.”

Many armed groups have formed in recent years claiming to be community groups carrying out essential work in underprivileged neighborhoods, but they have instead been accused of violence, even murder . One of the two main groups, G-9, is led by a former elite police officer, Jimmy Chérizier — also known as “Barbecue” — who has become the public face of the unrest and claimed credit for various attacks on public institutions. He has openly called for Henry to step down and called his campaign an “armed revolution.”

But caught in the crossfire are the residents of Haiti. In just one week, 15,000 people have been displaced from Port-au-Prince, according to a U.N. estimate. But people have been trying to flee the capital for well over a year, with one woman telling NBC News that she is currently hiding in a church with her three children and another family with eight children. The U.N. said about 160,000 people have left Port-au-Prince because of the swell of violence in the last several months. 

Deep poverty and famine are also a serious danger. Gangs have cut off access to the country’s largest port, Autorité Portuaire Nationale, and food could soon become scarce.

Haiti's uncertain future

A new transitional government may dismay the Haitians and their supporters who call for Haitian-led solutions to the crisis. 

But the creation of such a government would come after years of democratic disruption and the crumbling of Haiti’s political leadership. The country hasn’t held an election in eight years. 

Haitian advocates and scholars like Jemima Pierre, a professor at the University of British Columbia, Vancouver, say foreign intervention, including from the U.S., is partially to blame for Haiti’s turmoil. The U.S. has routinely sent thousands of troops to Haiti , intervened in its government and supported unpopular leaders like Henry.

“What you have over the last 20 years is the consistent dismantling of the Haitian state,” Pierre said. “What intervention means for Haiti, what it has always meant, is death and destruction.”

In fact, the country’s situation was so dire that Henry was forced to travel abroad in the hope of securing a U.N. peacekeeping deal. He went to Kenya, which agreed to send 1,000 troops to coordinate an East African and U.N.-backed alliance to help restore order in Haiti, but the plan is now on hold . Kenya agreed last October to send a U.N.-sanctioned security force to Haiti, but Kenya’s courts decided it was unconstitutional. The result has been Haiti fending for itself. 

“A force like Kenya, they don’t speak Kreyòl, they don’t speak French,” Pierre said. “The Kenyan police are known for human rights abuses . So what does it tell us as Haitians that the only thing that you see that we deserve are not schools, not reparations for the cholera the U.N. brought , but more military with the mandate to use all kinds of force on our population? That is unacceptable.”  

Henry was forced to announce his planned resignation from Puerto Rico, as threats of violence — and armed groups taking over the airports — have prevented him from returning to his country.  

Now that Henry is to stand down, it is far from clear what the armed groups will do or demand next, aside from the right to govern. 

“It’s the Haitian people who know what they’re going through. It’s the Haitian people who are going to take destiny into their own hands. Haitian people will choose who will govern them,” Chérizier said recently, according to The Associated Press .

Haitians and their supporters have put forth their own solutions over the years, holding that foreign intervention routinely ignores the voices and desires of Haitians. 

In 2021, both Haitian and non-Haitian church leaders, women’s rights groups, lawyers, humanitarian workers, the Voodoo Sector and more created the Commission to Search for a Haitian Solution to the Crisis . The commission has proposed the “ Montana Accord ,” outlining a two-year interim government with oversight committees tasked with restoring order, eradicating corruption and establishing fair elections. 

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CORRECTION (March 15, 2024, 9:58 a.m. ET): An earlier version of this article misstated which university Jemima Pierre is affiliated with. She is a professor at the University of British Columbia, Vancouver, not the University of California, Los Angeles, (or Columbia University, as an earlier correction misstated).

Patrick Smith is a London-based editor and reporter for NBC News Digital.

Char Adams is a reporter for NBC BLK who writes about race.

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