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Climate Change

Here we review the causes and effects of climate change, as well as adaptation as a response. See our broader energy discussion of solutions for emissions reductions and our discussion of geoengineering approaches.

The Climate Budget

Industrial activity has emitted about 2200 billion tons (Gt) of carbon dioxide (CO2) into the atmosphere. Meeting internationally agreed goals of 2 °C or 1.5 °C of global warming over preindustrial levels would require that no more than 1500 or 580 Gt additional CO2 respectively, which would require a sharp reversal of the trend of growing emissions 1.

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Figures are CO2 only; comparable rates of reductions in other greenhouse gases would also be required. Source: IPCC 1.

Source of Emissions

By sector, world greenhouse gas emissions are as follows as of 2016.

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Bunker fuels refer to emissions from international shipping or aviation. Source: World Resources Institute 2.

Following are overall greenhouse gas emissions from human activity.

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Sources: overall: IPCC 1, carbon dioxide (CO2): Le Quéré et al. 3, methane (CH4): Global Methane Initiative 4, nitrous oxide (N2O): Davidson and Kanter 5 and Winiwarter 6, and fluorinated gases (F-gases): Purohit and Höglund-Isaksson 7.

Addressing the major sources of emissions requires replacing most of the world's current energy production with low carbon sources; reforming agriculture to reduce CO2 emissions from land use, methane from enteric fermentation, and nitrous oxide emissions; preventing the release of methane from decomposing organic matter in landfills, and phasing out the use of F-gases in refrigeration and air conditioning 8.

Current Impact of Climate Change

As of 2020, the world has warmed about a degree Celcius from the 1850-1900 average.

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Source: IPCC 9.

Emissions from human activity are responsible for most of the warming. Aside from warmer temperatures, consequences of climate change include glacial retreat, sea level rise, likely increase heat waves and droughts, and possibly increased wildfires and flooding 9.

A 2021 study estimates that climate change will be responsible for 83 million deaths from 2020 to 2100 under the baseline scenario. This translates to one death for every 4,434 tons of CO2, or the lifetime emissions of 3.5 Americans, an a carbon cost of $37-258 from only mortality 10. An estimated 37% of heat-related deaths, or about 60,000 of the 166 thousand total deaths, have been attributed to climate change 11.

Future Impact of Climate Change

The International Panel on Climate Change has identified four future scenarios, based on how much global warming occurs. A brief summary of their impacts is as follows.

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Summary of the IPCC's Representative Concentration Pathway (RCP) scenarios. Radiative forcing, which gives rise to scenario names, refers to the amount of additional energy per square meter that will be captured by the greenhouse effect.

The IPCC 12 estimates warming levels and sea level rise. Lafakis et al. 13 report estimated atmospheric CO2 concentration; as of 2020, concentration is about 410 parts per million and was about 250 ppm in pre-industrial times. Estimates on GDP impact are drawn from Kompas et al. 14, Kahn et al. 15, and Burke et al. 16. Wiebe et al. 17 estimate impacts on crop yields. Their estimates may be pessimistic, as they do not account for CO2 fertilization.

The most likely scenario, based on current trends, is between RCP4.5 and RCP6. RCP8.5 is an unlikely worst case scenario and should not be presented as "business as usual" 18.

Under current policies, total warming should be around 3 °C, though with considerable uncertainty.

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Source: Hausfather 19.

The World Health Organization estimates that climate change will be responsible for about 250,000 deaths per year in 2030.

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Source: World Health Organization 20.

Climate change is also expected to cause deaths through coastal flooding and storms, but precise estimates of the number of deaths are lacking 20.

There are a number of potentially catastrophic outcomes from climate change whose likelihoods are unknown, including collapse of the West Antarctica Ice Sheet 21, release of large quantities of methane from the Arctic permafrost 22 or submerged methane hydrates 23, induced seismic events 24, and risks that are themselves unknown 25. The presence of unknown "fat tail" risks justifies a stronger response to climate change than consideration of only median or expected outcomes 26.

Impact of Emissions on Ecosystems

Over thousands of years, the oceans will absorb most excess carbon emissions; see our work on ocean acidification for more on this topic. In the short term, carbon emissions travel as follows.

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Source: Peters et al. 27.

A main effect of soil uptake of CO2 is fertilization of plant growth. Based on satellite data, world vegetation growth may have increased 1.3-4.3% from 1982 to 2011, mostly as a result of CO2 fertilization. The following crop yield increases have been observed.

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Yield increases of major crops from CO2 fertilization, given an increase of 100 parts per million increase in atmospheric concentration. Figures are fertilization only and do not account for the impact of climate change. Source: McGrath and Lobell 28.

Extreme Weather

According to the International Panel on Climate Change 29, the coming decades should, as a result of climate change, see an increase in heat waves. However, the IPCC places low confidence in the rise of other kinds of natural disasters, including floods, tropical storms, and droughts.

Despite the IPCC's lack of clear observed evidence, it is suspected that warmer ocean surface temperatures may cause more intense but fewer tropical cyclones 30. Pausas and Keeley 31 assess weather patterns arising from climate change to be one of several risk factors behind wildfires, and while the prevalence of fire weather may increase in coming decades, there has not been a global trend toward increased wildfire in the recent past 32. Some modeling 33 suggests that under climate change, world precipitation will be more variable, which may increase the prevalence of both droughts and floods.

The Carbon Cycle

Most near-surface carbon is stored in the oceans.

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Storage of carbon near the Earth's surface. Far larger reserves of carbon are in the Earth's mantle, and this carbon is exchanged with the surface over geologic time via plate tectonics and volcanoes. Source: NASA 34.

Adaptation

Climate adaptation refers to efforts intended to reduce harms from climate change, as opposed to mitigation, which is intended to reduce climate change itself. Worldwide, adaptation spending is a fraction of mitigation spending.

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Major purposes of world business, government, and non-profit spending on climate change. Figures are averages of 2017 and 2018 totals and represent all spending the Climate Policy Initiative is able to track, which may not be all climate spending. Source: Buchner et al. 35.

The Global Commission on Adaptation has found $1.8 trillion of adaptation projects expected to have net benefits 36.

Problem:
Need for Climate Change Adaptation
Solution:
Increased Adaptation Investment - World

References

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  2. World Resources Institute. "CAIT Climate Data Explorer". Accessed April 5, 2020. ↩

  3. Le Quéré et al. "Global Carbon Budget 2018". ICOS Carbon Portal. 2018. ↩

  4. Global Methane Initiative. "Global Methane Emissions and Mitigation Opportunities". Accessed August 13, 2019. ↩

  5. Davidson, E., Kanter, D. "Inventories and scenarios of nitrous oxide emissions". Environmental Research Letters 9 105012. 2014. ↩

  6. Winiwarter, W. "Technical opportunities to reduce global anthropogenic emissions of nitrous oxide". Environmental Research Letters 13: 014011. 2018. ↩

  7. Purohit, P., Höglund-Isaksson, L. "Global emissions of fluorinated greenhouse gases 2005–2050 with abatement potentials and costs". Atmospheric Chemistry and Physics 17, pp. 2795–2816. February 2017. ↩

  8. U.S. Environmental Protection Agency. "Overview of Greenhouse Gases". Accessed April 18, 2019. ↩

  9. IPCC. "Summary for Policymakers". In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I 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 and B. Zhou (eds.)]:. Cambridge University Press. In Press. 2021. ↩ ↩2

  10. Bressler, R. D. "The mortality cost of carbon". Nature Communications 12: 4467. July 2021. ↩

  11. Vicedo-Cabrera, A. M. et al. "The burden of heat-related mortality attributable to recent human-induced climate change". Nature Climate Change 11, pp. 492-500. May 2021. ↩

  12. IPCC. "Summary for Policymakers". In Climate Change 2013: The Physical Science Basis. Contribution of Working Group I 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 and P.M. Midgley (eds.)]:. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. 2013. ↩

  13. Lafakis, C., Ratz, L., Fazio, E., Cosma, M. "The Economic Implications of Climate Change". Moody's Analytics. June 2019. ↩

  14. Kompas, T., Pham, V., Che, T. "The Effects of Climate Change on GDP by Country and the Global Economic Gains From Complying With the Paris Climate Accord". Earth's Future 6(8), pp. 1153-1173. July 2018. ↩

  15. Kahn, M., Kohaddes, M., Ng, R., Pesaran, M., Raissi, M., Yang, J. "Long-Term Macroeconomic Effects of Climate Change: A Cross-Country Analysis". International Monetary Fund. October 2019. ↩

  16. Burke, M., Davis, W., Diffenbaugh, N. "Large potential reduction in economic damages under UN mitigation targets". Nature 557, pp. 549-553. May 2018. ↩

  17. Wiebe, K. et al. "Climate change impacts on agriculture in 2050 under a range of plausible socioeconomic and emissions scenarios". Environmental Research Letters 10: 085010. 2015. ↩

  18. Hausfather, Z., Peters, G. P. "Emissions - the ‘business as usual’ story is misleading". Nature 577, pp. 618-620. January 2020. ↩

  19. Hausfather, Z. "Flattening the Curve of Future Emissions". The Breakthrough Institute. August 2021. ↩

  20. World Health Organization. "Quantitative risk assessment of the effects of climate change on selected causes of death, 2030s and 2050s". 2014. ↩ ↩2

  21. Banwell, A. "Ice-shelf stability questioned". Nature 544, pp. 306-307. April 2017. ↩

  22. Turetsky, M., Abbot, B., Jones, M., Anthony, K., Olefeldt, D., Schuur, E., Koven, C., McGuire, A., Grosse, G., Kuhry, P., Hugelius, G., Lawrence, D., Gibson, C., Sannel, A. "Permafrost collapse is accelerating carbon release". Nature 569, pp. 32-34. April 2019. ↩

  23. Maslin, M., Owen, M., Betts, R., Day, S., Jones, T., Ridgwell, A. "Gas hydrates: past and future geohazard?". Philosophical Transactions of the Royal Society A 368(1919). May 2010. ↩

  24. McGuire, B. Hazardous responses of the solid Earth to a changing climate. Climate Forcing of Geological Hazards, First Edition. Edited by Bill McGuire and Mark Maslin. The Royal Society and John Wiley & Sons, Ltd. by John Wiley & Sons, Ltd. 2013. ↩

  25. DeFries, R., Edenhofer, O., Halliday, A., Heal, G., Lenton, T., Puma, M., Rising, J., Rockström, J., Ruane, A., Schellnhuber, H., Stainforth, D., Stern, D., Tedesco, M., Ward, B. "The missing economic risks in assessments of climate change impacts". Policy insight, Grantham Research Institute on Climate Change and the Environment, The Earth Institute, Columbia University, Potsdam Institute for Climate Impact Research. September 2019. ↩

  26. Weitzman, M. "Fat Tails and the Social Cost of Carbon". American Economic Review 104(5), pp. 544-546. May 2014. ↩

  27. Peters, G., Le Quéré, C., Andrew, R., Canadell, J., Friedlingstein, P., Ilyina, T., Jackson, R., Joos, F., Korsbakken, J., McKinley, G., Sitch, S., Tans, P. "Towards real-time verification of CO2 emissions". Nature Climate Change 7, pp. 848–850. November 2017. ↩

  28. McGrath, J., Lobell, D. "Regional disparities in the CO2 fertilization effect and implications for crop yields". Environmental Research Letters 8(1) 014054. March 2013. ↩

  29. Ranasinghe, R., A.C. Ruane, R. Vautard, N. Arnell, E. Coppola, F.A. Cruz, S. Dessai, A.S. Islam, M. Rahimi, D. Ruiz Carrascal, J. Sillmann, M.B. Sylla, C. Tebaldi, W. Wang, and R. Zaaboul, 2021: "Climate Change Information for Regional Impact and for Risk Assessment". In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I 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, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1767–1926. ↩

  30. Kang, N.-Y., Elsner, J. B. "Trade-off between intensity and frequency ofglobal tropical cyclones". Nature Climate Change 5, pp. 661-664. May 2015. ↩

  31. Pausas, J. G., Keeley, J. E. "Wildfires and global change". Frontiers in Ecology and the Environment 19(7), pp. 387-395. September 2021. ↩

  32. Jones, M.W., Abatzoglou, J.T., Veraverbeke, S., Andela, N., Lasslop, G., Forkel, M., Smith, A.J., Burton, C., Betts, R.A., van der Werf, G.R., Sitch, S. "Global and regional trends and drivers of fire under climate change". Reviews of Geophysics 60(3): e2020RG000726. July 2022. ↩

  33. Pendergrass, A.G., Knutti, R., Lehner, F., Deser, C., Sanderson, B.M. "Precipitation variability increases in a warmer climate". Scientific reports 7(1): 17966. December 2017. ↩

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  35. Buchner, B., Clark, A., Falconer, A., Macquarie, R., Meattle, C., Wetherbee, C. "Global Landscape of Climate Finance 2019". Climate Policy Initiative. November 2019. ↩

  36. Global Commision on Adaptation. "Adapt Now: A Global Call for Leadership on Climate Resilience". September 2019. ↩