Evidence Agains Natural Climate Change Causing Global Warming

Human and natural factors both influence the earth'southward climate, but the long-term tendency observed over the past century tin only exist explained past the event of human activities on climate. Source: U.Due south. Global Change Research Program, Fourth National Climate Assessment, Chapter 2: Our Changing Climate, 2017.

Since the Industrial Revolution, human activities have released large amounts of carbon dioxide and other greenhouse gases into the atmosphere, which has inverse the earth'southward climate. Natural processes, such as changes in the sun'south energy and volcanic eruptions, likewise bear upon the earth'due south climate. Even so, they do non explain the warming that we have observed over the last century.^ane

Human Versus Natural Causes

Scientists have pieced together a record of the earth's climate by analyzing a number of indirect measures of climate, such as water ice cores, tree rings, glacier lengths, pollen remains, and sea sediments, and past studying changes in the world'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 take 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

Oestrus-trapping Greenhouse Gases And The Earth'south Climate

Source: Smithsonian National Museum of Natural History, 2018

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 world'southward atmosphere than any time in the last 800,000 years.⁵ These greenhouse gas emissions have increased the greenhouse issue and caused the earth'due south surface temperature to rise. Called-for fossil fuels changes the climate more than than any other human activeness.

Carbon dioxide: Human activities currently release over thirty billion tons of carbon dioxide into the temper every year.⁶ Atmospheric carbon dioxide concentrations have increased past more than 40 percentage since pre-industrial times, from approximately 280 parts per million (ppm) in the 18th century⁷ to 414 ppm in 2020.⁸

Methyl hydride: Human being activities increased methane concentrations during most of the 20th century to more than ii.5 times the pre-industrial level, from approximately 722 parts per billion (ppb) in the 18th century⁹ to 1,867 ppb in 2019.¹⁰

Nitrous oxide: Nitrous oxide concentrations accept risen approximately twenty pct since the start of the Industrial Revolution, with a relatively rapid increment toward the finish of the 20th century. Nitrous oxide concentrations have increased from a pre-industrial level of 270 ppb¹¹ to 332 ppb in 2019.¹²

For more information on greenhouse gas emissions, come across the Greenhouse Gas Emissions website. To larn more than virtually actions that tin reduce these emissions, meet What You lot Tin Do.

This graph shows the increase in atmospheric concentrations of three of the fundamental greenhouse gases over the last ii,000 years. Increases in concentrations of these gases since 1750 are due to human activities in the industrial era. Source: U.S. EPA, Climate change Indicators in the United states: Atmospheric Concentrations of Greenhouse Gases, 2021.

Reflectivity or Assimilation of the Sun'southward Free energy

Activities such equally agriculture, road construction, and deforestation can change the reflectivity of the world's surface, leading to local warming or cooling. This issue is observed in heat islands, which are urban centers that are warmer than the surrounding, less populated areas. Ane 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 every bit crops, the net effect of all country-employ changes appears to exist a small cooling.¹³

Emissions of pocket-sized particles, known as aerosols, into the air tin also lead to reflection or absorption of the lord's day's free 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. Acquire more than virtually man-generated and natural aerosols.

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Natural Processes

Natural processes are always influencing the earth'south 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 World's Orbit and Rotation

Changes in the world's orbit and its axis of rotation accept had a big touch on climate in the past. For example, the amount of summertime sunshine on the Northern Hemisphere, which is affected past changes in the planet'south orbit, appears to exist the primary cause of by 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 concluding glacial period (or ice historic period), the boilerplate global temperature was about 11°F colder than it is today. At the peak of the last interglacial flow, however, the average global temperature was at well-nigh 2°F warmer than it is today.¹⁵

Variations in Solar Activity

Changes in the lord's day'due south energy output can touch the intensity of the sunlight that reaches the world'due south surface. While these changes tin can influence the earth's climate, solar variations have played footling role in the climate changes observed in recent decades.¹⁶ Satellites take 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

The lord's day follows a natural eleven-year cycle of small ups and downs in intensity (bottom chart), but the effect on the earth is minor. Over the same flow, the boilerplate global temperature has increased markedly (top nautical chart). Source: National Academy of Sciences, Climate Change Testify & Causes, 2020.

Changes in the Earth's Reflectivity

The amount of sunlight that is captivated or reflected by the planet depends on the earth's surface and temper. Dark objects and surfaces, like the sea, forests, and soil, tend to blot more sunlight. Low-cal-colored objects and surfaces, like snow and clouds, tend to reverberate sunlight. Almost 70 percent of the sunlight that reaches the world is absorbed.¹⁸ Natural changes in the earth'south surface, similar the melting of body of water ice, have contributed to climate alter in the by, often acting as feedbacks to other processes.

Volcanic Activity

Volcanoes have played a noticeable function in climate, and volcanic eruptions released large quantities of carbon dioxide in the distant past. Some explosive volcano eruptions can throw particles (east.g., SO₂) into the upper atmosphere, where they can reflect enough sunlight dorsum to space to cool the surface of the planet for several years.¹⁹ These particles are an case of cooling aerosols.

Volcanic particles from a unmarried eruption exercise not produce long-term climatic change because they remain in the atmosphere for a much shorter time than greenhouse gases. In addition, homo activities emit more than 100 times equally much carbon dioxide as volcanoes each yr.^xx

Changes in Naturally Occurring Carbon Dioxide Concentrations

Over the last several hundred grand 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 modify 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 globe's orbit.²³

Analyses of water ice core data extending back 800,000 years show that warmer periods on the world coincide with periods of relatively loftier atmospheric carbon dioxide concentrations. Source: Based on information actualization in NAS, Climate change Evidence & Causes, 2020.

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

²Wuebbles, D.J., D.Due west. Fahey, K.A. Hibbard, B. DeAngelo, S. Doherty, Yard. Hayhoe, R. Horton, J.P. Kossin, P.C. Taylor, A.M. Waple & C.P. Weaver. (2017). Executive summary. In: Climate science special report: 4th national climate cess, book I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.S. Global Change Inquiry Programme, Washington, DC, pp. 12–34, doi: 10.7930/J0DJ5CTG

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

³IPCC (2013). Climate change 2013: The physical science footing.Working Group I contribution to the 5th assessment written report of the Intergovernmental Panel on Climatic change [Stocker, T.F., D. Qin, One thousand.-K. Plattner, One thousand. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.G. Midgley (eds.)]. Cambridge Academy Press, Cambridge, United Kingdom and New York, NY, p. 869.

⁴IPCC. (2021). Climate change 2021: The physical scientific discipline basis. Working Group I contribution to the sixth assessment report of the Intergovernmental Console on Climate change [Masson-Delmotte, V., P. Zhai, A. Pirani, Southward.Fifty. Connors, C. Péan, South. Berger, N. Caud, Y. Chen, L. Goldfarb, Yard.I. Gomis, Chiliad. Huang, M. Leitzell, East. 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.

^fiveNational Academy of Sciences. (2020). Climatic change: Testify and causes: Update 2020. The National Academies Printing, Washington, DC, p. B-2. doi: 10.17226/25733

Fahey, D.W., Southward.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017).Physical drivers of climate change. In: Climate science special report: 4th national climate assessment, book I [Wuebbles, D.J., D.W. Fahey, Chiliad.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.Due south. Global Modify Enquiry Program, Washington, DC, p. 80, Effigy ii.four. doi: 10.7930/J0513WCR

⁶Hayhoe, K., D.J. Wuebbles, D.R. Easterling, D.W. Fahey, S. Doherty, J. Kossin, West. Sweet, R. Vose & M. Wehner. (2018). Our changing climate. In: Impacts, risks, and accommodation in the United States: Quaternary national climate assessment, volume II [Reidmiller, D.R., C.Due west. Avery, D.R. Easterling, K.E. Kunkel, Grand.L.1000. Lewis, T.K. Maycock & B.C. Stewart (eds.)]. U.Due south. Global Change Inquiry Program, Washington, DC, p. 76. doi: ten.7930/NCA4.2018

⁷IPCC. (2013). Climate change 2013: The physical science basis.Working Group I contribution to the 5th cess written report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, 1000.-Chiliad. Plattner, M. Tignor, S.Thou. Allen, J. Boschung, A. Nauels, Y. Xia, 5. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, p. 166.

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

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

^ten NOAA. (2021). Trends in atmospheric methyl hydride. Retrieved 3/25/2021. esrl.noaa.gov/gmd/ccgg/trends_ch4

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

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

^thirteen Fahey, D.Due west., South.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017). Physical drivers of climate modify. In: Climate science special written report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.Due west. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.Chiliad. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 78, Fig. 2.3 and p. 86. doi: 10.7930/J0513WCR

¹⁴ National University of Sciences. (2020). Climate modify: Testify and causes: Update 2020. The National Academies Printing, Washington, DC, p. 9. doi: x.17226/25733

¹⁵ Fahey, D.W., Due south.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017). Our globally changing climate. In: Climate science special written report: Fourth national climate assessment, book I [Wuebbles, D.J., D.Due west. Fahey, Chiliad.A. Hibbard, D.J. Dokken, B.C. Stewart & T.G. Maycock (eds.)]. U.Southward. Global Change Research Program, Washington, DC, p. 53. doi: 10.7930/J08S4N35

^sixteen National Academy of Sciences. (2020). Climate modify: Bear witness and causes: Update 2020. The National Academies Press, Washington, DC, p. 7. doi: 10.17226/25733

¹⁷ National Academy of Sciences. (2020). Climate change: Prove and causes: Update 2020. The National Academies Press, Washington, DC, p. seven. doi: ten.17226/25733

¹⁸ Fahey, D.W., S.J. Doherty, One thousand.A. Hibbard, A. Romanou, & P.C. Taylor. (2017). Physical drivers of climatic change. In: Climate scientific discipline special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.Due west. Fahey, Thou.A. Hibbard, D.J. Dokken, B.C. Stewart & T.M. Maycock (eds.)]. U.S. Global Change Inquiry Program, Washington, DC, p. ii. doi: 10.7930/J0513WCR

¹⁹ Fahey, D.West., S.J. Doherty, K.A. Hibbard, A. Romanou, & P.C. Taylor. (2017). Concrete drivers of climate change. In: Climate science special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.W. Fahey, G.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.South. Global Alter Research Plan, 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 scientific discipline special report: 4th national climate assessment, volume I [Wuebbles, D.J., D.Westward. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.South. Global Change Enquiry Programme, Washington, DC, p. 79. doi: 10.7930/J0513WCR

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

²² IPCC. (2013).Climate change 2013: The concrete science basis.Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Alter [Stocker, T.F., D. Qin, G.-K. Plattner, Thousand. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.Yard. Midgley (eds.)]. Cambridge University Press, Cambridge, United kingdom of great britain and northern ireland 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–x. doi: x.17226/25733

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Source: https://www.epa.gov/climatechange-science/causes-climate-change

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