natural causes of global warming essay

Essay on Global Warming – Causes and Solutions

500+ words essay on global warming.

Global Warming is a term almost everyone is familiar with. But, its meaning is still not clear to most of us. So, Global warming refers to the gradual rise in the overall temperature of the atmosphere of the Earth. There are various activities taking place which have been increasing the temperature gradually. Global warming is melting our ice glaciers rapidly. This is extremely harmful to the earth as well as humans. It is quite challenging to control global warming; however, it is not unmanageable. The first step in solving any problem is identifying the cause of the problem. Therefore, we need to first understand the causes of global warming that will help us proceed further in solving it. In this essay on Global Warming, we will see the causes and solutions of Global Warming.

Causes of Global Warming

Global warming has become a grave problem which needs undivided attention. It is not happening because of a single cause but several causes. These causes are both natural as well as manmade. The natural causes include the release of greenhouses gases which are not able to escape from earth, causing the temperature to increase.

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Further, volcanic eruptions are also responsible for global warming. That is to say, these eruptions release tons of carbon dioxide which contributes to global warming. Similarly, methane is also one big issue responsible for global warming.

So, when one of the biggest sources of absorption of carbon dioxide will only disappear, there will be nothing left to regulate the gas. Thus, it will result in global warming. Steps must be taken immediately to stop global warming and make the earth better again.

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Global Warming Solutions

As stated earlier, it might be challenging but it is not entirely impossible. Global warming can be stopped when combined efforts are put in. For that, individuals and governments, both have to take steps towards achieving it. We must begin with the reduction of greenhouse gas.

Furthermore, they need to monitor the consumption of gasoline. Switch to a hybrid car and reduce the release of carbon dioxide. Moreover, citizens can choose public transport or carpool together. Subsequently, recycling must also be encouraged.

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For instance, when you go shopping, carry your own cloth bag. Another step you can take is to limit the use of electricity which will prevent the release of carbon dioxide. On the government’s part, they must regulate industrial waste and ban them from emitting harmful gases in the air. Deforestation must be stopped immediately and planting of trees must be encouraged.

In short, all of us must realize the fact that our earth is not well. It needs to treatment and we can help it heal. The present generation must take up the responsibility of stopping global warming in order to prevent the suffering of future generations. Therefore, every little step, no matter how small carries a lot of weight and is quite significant in stopping global warming.

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FAQs on Global Warming

Q.1 List the causes of Global Warming.

A.1 There are various causes of global warming both natural and manmade. The natural one includes a greenhouse gas, volcanic eruption, methane gas and more. Next up, manmade causes are deforestation, mining, cattle rearing, fossil fuel burning and more.

Q.2 How can one stop Global Warming?

A.2 Global warming can be stopped by a joint effort by the individuals and the government. Deforestation must be banned and trees should be planted more. The use of automobiles must be limited and recycling must be encouraged.

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Causes of global warming, explained

Human activity is driving climate change, including global temperature rise.

The average temperature of the Earth is rising at nearly twice the rate it was 50 years ago. This rapid warming trend cannot be explained by natural cycles alone, scientists have concluded. The only way to explain the pattern is to include the effect of greenhouse gases (GHGs) emitted by humans.

Current levels of the greenhouse gases carbon dioxide, methane, and nitrous oxide in our atmosphere are higher than at any point over the past 800,000 years , and their ability to trap heat is changing our climate in multiple ways .

IPCC conclusions

To come to a scientific conclusion on climate change and what to do about it, the United Nations in 1988 formed a group called the Intergovernmental Panel on Climate Change , or IPCC. The IPCC meets every few years to review the latest scientific findings and write a report summarizing all that is known about global warming. Each report represents a consensus, or agreement, among hundreds of leading scientists.

One of the first things the IPCC concluded is that there are several greenhouse gases responsible for warming, and humans emit them in a variety of ways. Most come from the combustion of fossil fuels in cars, buildings, factories, and power plants. The gas responsible for the most warming is carbon dioxide, or CO2. Other contributors include methane released from landfills, natural gas and petroleum industries, and agriculture (especially from the digestive systems of grazing animals); nitrous oxide from fertilizers; gases used for refrigeration and industrial processes; and the loss of forests that would otherwise store CO2.

Gaseous abilities

Different greenhouse gases have very different heat-trapping abilities. Some of them can trap more heat than an equivalent amount of CO2. A molecule of methane doesn't hang around the atmosphere as long as a molecule of carbon dioxide will, but it is at least 84 times more potent over two decades. Nitrous oxide is 264 times more powerful than CO2.

Other gases, such as chlorofluorocarbons, or CFCs—which have been banned in much of the world because they also degrade the ozone layer—have heat-trapping potential thousands of times greater than CO2. But because their emissions are much lower than CO2 , none of these gases trap as much heat in the atmosphere as CO2 does.

When those gases that humans are adding to Earth's atmosphere trap heat, it’s called the "greenhouse effect." The gases let light through but then keep much of the heat that radiates from the surface from escaping back into space, like the glass walls of a greenhouse. The more greenhouse gases in the atmosphere, the more dramatic the effect, and the more warming that happens.

Climate change continues

Despite global efforts to address climate change, including the landmark 2015 Paris climate agreement , carbon dioxide emissions from fossil fuels continue to rise, hitting record levels in 2018 .

Many people think of global warming and climate change as synonyms, but scientists prefer to use “climate change” when describing the complex shifts now affecting our planet’s weather and climate systems. Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and and habitats, rising seas , and a range of other impacts.

Read next: Global Warming Effects

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The Causes of Climate Change

Human activities are driving the global warming trend observed since the mid-20th century.

• The greenhouse effect is essential to life on Earth, but human-made emissions in the atmosphere are trapping and slowing heat loss to space.
• Five key greenhouse gases are carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and water vapor.
• While the Sun has played a role in past climate changes, the evidence shows the current warming cannot be explained by the Sun.

Increasing Greenhouses Gases Are Warming the Planet

Scientists attribute the global warming trend observed since the mid-20 th century to the human expansion of the "greenhouse effect" 1 — warming that results when the atmosphere traps heat radiating from Earth toward space.

Life on Earth depends on energy coming from the Sun. About half the light energy reaching Earth's atmosphere passes through the air and clouds to the surface, where it is absorbed and radiated in the form of infrared heat. About 90% of this heat is then absorbed by greenhouse gases and re-radiated, slowing heat loss to space.

Four Major Gases That Contribute to the Greenhouse Effect

Carbon dioxide.

A vital component of the atmosphere, carbon dioxide (CO 2 ) is released through natural processes (like volcanic eruptions) and through human activities, such as burning fossil fuels and deforestation.

Like many atmospheric gases, methane comes from both natural and human-caused sources. Methane comes from plant-matter breakdown in wetlands and is also released from landfills and rice farming. Livestock animals emit methane from their digestion and manure. Leaks from fossil fuel production and transportation are another major source of methane, and natural gas is 70% to 90% methane.

Nitrous Oxide

A potent greenhouse gas produced by farming practices, nitrous oxide is released during commercial and organic fertilizer production and use. Nitrous oxide also comes from burning fossil fuels and burning vegetation and has increased by 18% in the last 100 years.

Chlorofluorocarbons (CFCs)

These chemical compounds do not exist in nature – they are entirely of industrial origin. They were used as refrigerants, solvents (a substance that dissolves others), and spray can propellants.

FORCING:  Something acting upon Earth's climate that causes a change in how energy flows through it (such as long-lasting, heat-trapping gases - also known as greenhouse gases). These gases slow outgoing heat in the atmosphere and cause the planet to warm.

Another Gas That Contributes to the Greenhouse Effect:

Water vapor.

Water vapor is the most abundant greenhouse gas, but because the warming ocean increases the amount of it in our atmosphere, it is not a direct cause of climate change. Credit:  John Fowler  on  Unsplash

FEEDBACKS:  A process where something is either amplified or reduced as time goes on, such as water vapor increasing as Earth warms leading to even more warming.

Human Activity Is the Cause of Increased Greenhouse Gas Concentrations

Over the last century, burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO 2 ). This increase happens because the coal or oil burning process combines carbon with oxygen in the air to make CO 2 . To a lesser extent, clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases.

The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels by nearly 50% since 1750 2 . This increase is due to human activities, because scientists can see a distinctive isotopic fingerprint in the atmosphere.

In its Sixth Assessment Report, the Intergovernmental Panel on Climate Change, composed of scientific experts from countries all over the world, concluded that it is unequivocal that the increase of CO 2 , methane, and nitrous oxide in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver of many changes observed across the atmosphere, ocean, cryosphere and biosphere.

"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."

Intergovernmental Panel on Climate Change

The panel's AR6 Working Group I (WGI) Summary for Policymakers report is online at https://www.ipcc.ch/report/ar6/wg1/ .

Evidence Shows That Current Global Warming Cannot Be Explained by Solar Irradiance

Scientists use a metric called Total Solar Irradiance (TSI) to measure the changes in energy the Earth receives from the Sun. TSI incorporates the 11-year solar cycle and solar flares/storms from the Sun's surface.

Studies show that solar variability has played a role in past climate changes. For example, a decrease in solar activity coupled with increased volcanic activity helped trigger the Little Ice Age.

But several lines of evidence show that current global warming cannot be explained by changes in energy from the Sun:

• Since 1750, the average amount of energy from the Sun either remained constant or decreased slightly 3 .
• If a more active Sun caused the warming, scientists would expect warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere and a warming at the surface and lower parts of the atmosphere. That's because greenhouse gases are slowing heat loss from the lower atmosphere.
• Climate models that include solar irradiance changes can’t reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases.

1. IPCC 6 th Assessment Report, WG1, Summary for Policy Makers, Sections A, “ The Current State of the Climate ”

IPCC 6 th Assessment Report, WG1, Technical Summary, Sections TS.1.2, TS.2.1 and TS.3.1

2. P. Friedlingstein, et al., 2022: “Global Carbon Budget 2022”, Earth System Science Data ( 11 Nov 2022): 4811–4900. https://doi.org/10.5194/essd-14-4811-2022

3. IPCC 6 th Assessment Report, WG1, Chapter 2, Section 2.2.1, “ Solar and Orbital Forcing ” IPCC 6 th Assessment Report, WG1, Chapter 7, Sections 7.3.4.4, 7.3.5.2, Figure 7.6, “ Solar ” M. Lockwood and W.T. Ball, Placing limits on long-term variations in quiet-Sun irradiance and their contribution to total solar irradiance and solar radiative forcing of climate,” Proceedings of the Royal Society A , 476, issue 2228 (24 June 2020): https://doi 10.1098/rspa.2020.0077

Header image credit: Pixabay/stevepb Four Major Gases image credit: Adobe Stock/Ilya Glovatskiy

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Causes of Climate Change

Since the Industrial Revolution, human activities have released large amounts of carbon dioxide and other greenhouse gases into the atmosphere, which has changed the earth’s climate. Natural processes, such as changes in the sun's energy and volcanic eruptions, also affect the earth's climate. However, they do not explain the warming that we have observed over the last century. 1

Human Versus Natural Causes

It is unequivocal that human influence has warmed the atmosphere, ocean and land . - Intergovernmental Panel on Climate Change 4

Scientists have pieced together a record of the earth’s climate by analyzing a number of indirect measures of climate, such as ice cores, tree rings, glacier lengths, pollen remains, and ocean sediments, and by studying changes in the earth’s orbit around the sun. 2 This record shows that the climate varies naturally over a wide range of time scales, but this variability does not explain the observed warming since the 1950s. Rather, it is extremely likely (> 95%) that human activities have been the dominant cause of that warming. 3

Human activities have contributed substantially to climate change through:

• Greenhouse Gas Emissions

Reflectivity or Absorption of the Sun’s Energy

Heat-trapping greenhouse gases and the earth's climate, greenhouse gases.

Concentrations of the key greenhouse gases have all increased since the Industrial Revolution due to human activities. Carbon dioxide, methane, and nitrous oxide concentrations are now more abundant in the earth’s atmosphere than any time in the last 800,000 years. 5 These greenhouse gas emissions have increased the greenhouse effect and caused the earth’s surface temperature to rise . Burning fossil fuels changes the climate more than any other human activity.

Carbon dioxide: Human activities currently release over 30 billion tons of carbon dioxide into the atmosphere every year. 6 Atmospheric carbon dioxide concentrations have increased by more than 40 percent since pre-industrial times, from approximately 280 parts per million (ppm) in the 18th century 7 to 414 ppm in 2020. 8

Methane: Human activities increased methane concentrations during most of the 20th century to more than 2.5 times the pre-industrial level, from approximately 722 parts per billion (ppb) in the 18th century 9 to 1,867 ppb in 2019. 10

Nitrous oxide: Nitrous oxide concentrations have risen approximately 20 percent since the start of the Industrial Revolution, with a relatively rapid increase toward the end of the 20th century. Nitrous oxide concentrations have increased from a pre-industrial level of 270 ppb 11 to 332 ppb in 2019. 12

For more information on greenhouse gas emissions, see the Greenhouse Gas Emissions website. To learn more about actions that can reduce these emissions, see What You Can Do . To translate abstract greenhouse gas emissions measurements into concrete terms, try using EPA's Greenhouse Gas Equivalencies Calculator .

Activities such as agriculture, road construction, and deforestation can change the reflectivity of the earth's surface, leading to local warming or cooling. This effect is observed in heat islands , which are urban centers that are warmer than the surrounding, less populated areas. One reason that these areas are warmer is that buildings, pavement, and roofs tend to reflect less sunlight than natural surfaces. While deforestation can increase the earth’s reflectivity globally by replacing dark trees with lighter surfaces such as crops, the net effect of all land-use changes appears to be a small cooling. 13

Emissions of small particles, known as aerosols, into the air can also lead to reflection or absorption of the sun's energy. Many types of air pollutants undergo chemical reactions in the atmosphere to create aerosols. Overall, human-generated aerosols have a net cooling effect on the earth. Learn more about human-generated and natural aerosols .

Natural Processes

Natural processes are always influencing the earth’s climate and can explain climate changes prior to the Industrial Revolution in the 1700s. However, recent climate changes cannot be explained by natural causes alone.

Changes in the Earth’s Orbit and Rotation

Changes in the earth’s orbit and its axis of rotation have had a big impact on climate in the past. For example, the amount of summer sunshine on the Northern Hemisphere, which is affected by changes in the planet’s orbit, appears to be the primary cause of past cycles of ice ages, in which the earth has experienced long periods of cold temperatures (ice ages), as well as shorter interglacial periods (periods between ice ages) of relatively warmer temperatures. 14   At the coldest part of the last glacial period (or ice age), the average global temperature was about 11°F colder than it is today. At the peak of the last interglacial period, however, the average global temperature was at most 2°F warmer than it is today. 15

Variations in Solar Activity

Changes in the sun’s energy output can affect the intensity of the sunlight that reaches the earth’s surface. While these changes can influence the earth’s climate, solar variations have played little role in the climate changes observed in recent decades. 16 Satellites have been measuring the amount of energy the earth receives from the sun since 1978. These measurements show no net increase in the sun’s output, even as global surface temperatures have risen. 17

Changes in the Earth’s Reflectivity

The amount of sunlight that is absorbed or reflected by the planet depends on the earth’s surface and atmosphere. Dark objects and surfaces, like the ocean, forests, and soil, tend to absorb more sunlight. Light-colored objects and surfaces, like snow and clouds, tend to reflect sunlight. About 70 percent of the sunlight that reaches the earth is absorbed. 18 Natural changes in the earth’s surface, like the melting of sea ice , have contributed to climate change in the past, often acting as feedbacks  to other processes.

Volcanic Activity

Volcanoes have played a noticeable role in climate, and volcanic eruptions released large quantities of carbon dioxide in the distant past. Some explosive volcano eruptions can throw particles (e.g., SO 2 ) into the upper atmosphere, where they can reflect enough sunlight back to space to cool the surface of the planet for several years. 19 These particles are an example of cooling aerosols .

Volcanic particles from a single eruption do not produce long-term climate change because they remain in the atmosphere for a much shorter time than greenhouse gases. In addition, human activities emit more than 100 times as much carbon dioxide as volcanoes each year. 20

Changes in Naturally Occurring Carbon Dioxide Concentrations

Over the last several hundred thousand years, carbon dioxide levels varied in tandem with the glacial cycles. During warm interglacial periods, carbon dioxide levels were higher. During cool glacial periods, carbon dioxide levels were lower. 21 The heating or cooling of the earth’s surface and oceans can cause changes in the natural sources and sinks of these gases, and thus change greenhouse gas concentrations in the atmosphere. 22 These changing concentrations have acted as a positive climate feedback , amplifying the temperature changes caused by long-term shifts in the earth’s orbit. 23

1  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020 . The National Academies Press, Washington, DC, p. 5. doi: 10.17226/25733

2  Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, B. DeAngelo, S. Doherty, K. Hayhoe, R. Horton, J.P. Kossin, P.C. Taylor, A.M. Waple & C.P. Weaver. (2017). Executive summary. In: 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 & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, pp. 12–34, doi: 10.7930/J0DJ5CTG

National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020 . The National Academies Press, Washington, DC, p. 5. doi: 10.17226/25733

3  IPCC (2013). Climate change 2013: The physical science basis .  Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, p. 869.

4  IPCC. (2021). Climate change 2021: The physical science basis . Working Group I contribution to the sixth assessment report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu & B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom, p. SPM-5.

5  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020 . The National Academies Press, Washington, DC, p. B-2. doi: 10.17226/25733

Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017).  Physical drivers of climate change . In: 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 & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 80, Figure 2.4. doi: 10.7930/J0513WCR

6  Hayhoe, K., D.J. Wuebbles, D.R. Easterling, D.W. Fahey, S. Doherty, J. Kossin, W. Sweet, R. Vose & M. Wehner. (2018). Our changing climate . In: Impacts, risks, and adaptation in the United States: Fourth national climate assessment, volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock & B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 76. doi: 10.7930/NCA4.2018

7  IPCC. (2013). Climate change 2013: The physical science basis . Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, p. 166.

8 NOAA. (2021). Trends in atmospheric carbon dioxide . Retrieved 3/25/2021. esrl.noaa.gov/gmd/ccgg/trends/mlo.html

9 IPCC. (2013).  Climate change 2013: The physical science basis . Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, p. 167.

10 NOAA. (2021). Trends in atmospheric methane . Retrieved 3/25/2021. esrl.noaa.gov/gmd/ccgg/trends_ch4

11 IPCC. (2013).  Climate change 2013: The physical science basis . Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, p. 168.

12 NOAA. (2021). Trends in nitrous oxide . Retrieved 3/25/2021. esrl.noaa.gov/gmd/ccgg/trends_n2o/

13 Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017). Physical drivers of climate change . In: 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 & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 78, Fig. 2.3 and p. 86. doi: 10.7930/J0513WCR

14  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, p. 9. doi: 10.17226/25733

15  Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017). Our globally changing climate . In: 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 & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 53. doi: 10.7930/J08S4N35

16  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, p. 7. doi: 10.17226/25733

17  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, p. 7. doi: 10.17226/25733

18  Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou, & P.C. Taylor. (2017). Physical drivers of climate change . In: 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 & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 2. doi: 10.7930/J0513WCR

19  Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou, & P.C. Taylor. (2017). Physical drivers of climate change . In: 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 & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 79. doi: 10.7930/J0513WCR

20  Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017). Physical drivers of climate change . In: 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 & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 79. doi: 10.7930/J0513WCR

21  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, pp. 9–10. doi: 10.17226/25733

22  IPCC. (2013).  Climate change 2013: The physical science basis .  Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, p. 399.

23  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, pp. 9–10. doi: 10.17226/25733

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