Global surface temperature reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue.[1] Directly observed data is in red.[2]

In earth science, global surface temperature (GST; sometimes referred to as global mean surface temperature, GMST, or global average surface temperature) is calculated by averaging the temperatures over sea (sea surface temperature) and land (surface air temperature).

Series of reliable global temperature measurements began in the 1850—1880 time frame (this is called the instrumental temperature record). Through 1940, the average annual temperature increased, but was relatively stable between 1940 and 1975. Since 1975, it has increased by roughly 0.15 °C to 0.20 °C per decade, to at least 1.1 °C (1.9 °F) above 1880 levels.[3] The current annual GMST is about 15 °C (59 °F),[4] though monthly temperatures can vary almost 2 °C (4 °F) above or below this figure.[5]

Definition

The IPCC Sixth Assessment Report defines global mean surface temperature (GMST) as follows: GMST is the "estimated global average of near-surface air temperatures over land and sea ice, and sea surface temperature (SST) over ice-free ocean regions, with changes normally expressed as departures from a value over a specified reference period".[6]: 2231 

In comparison, the global mean surface air temperature (GSAT) is the "global average of near-surface air temperatures over land, oceans and sea ice. Changes in GSAT are often used as a measure of global temperature change in climate models."[6]: 2231 

Relevance

Changes in global temperatures over the past century provide evidence for the effects of increasing greenhouse gasses. When the climate system reacts to such changes, climate change follows. Measurement of the GST(global surface temperature) is one of the many lines of evidence supporting the scientific consensus on climate change, which is that humans are causing warming of Earth's climate system.

Projected global surface temperature changes relative to 1850–1900, based on CMIP6 multi-model mean changes

Measurement and calculation

The global surface temperature (GST) is calculated by averaging the temperatures over sea (sea surface temperature) and land (surface air temperature).

This section is an excerpt from Instrumental temperature record § Methods.[edit]
Surface air temperature change over the past 50 years.[7]

Instrumental temperature records are based on direct, instrument-based measurements of air temperature and ocean temperature, unlike indirect reconstructions using climate proxy data such as from tree rings and ocean sediments.[8] The longest-running temperature record is the Central England temperature data series, which starts in 1659. The longest-running quasi-global records start in 1850.[9] Temperatures on other time scales are explained in global temperature record.

"Global temperature" can have different definitions. There is a small difference between air and surface temperatures.[10]: 12 

Observations

This section is an excerpt from Effects of climate change § Changes in temperature.[edit]
Surface air temperature change over the past 50 years.[11]

Global warming affects all parts of Earth's climate system.[12] Global surface temperatures have risen by 1.1 °C (2.0 °F). Scientists say they will rise further in the future.[13][14] The changes in climate are not uniform across the Earth. In particular, most land areas have warmed faster than most ocean areas. The Arctic is warming faster than most other regions.[15] Night-time temperatures have increased faster than daytime temperatures.[16] The impact on nature and people depends on how much more the Earth warms.[17]: 787 

Scientists use several methods to predict the effects of human-caused climate change. One is to investigate past natural changes in climate.[18] To assess changes in Earth's past climate scientists have studied tree rings, ice cores, corals, and ocean and lake sediments.[19] These show that recent temperatures have surpassed anything in the last 2,000 years.[20] By the end of the 21st century, temperatures may increase to a level last seen in the mid-Pliocene. This was around 3 million years ago.[21]: 322  At that time, mean global temperatures were about 2–4 °C (3.6–7.2 °F) warmer than pre-industrial temperatures. The global mean sea level was up to 25 metres (82 ft) higher than it is today.[22]: 323  The modern observed rise in temperature and CO2 concentrations has been rapid. even abrupt geophysical events in Earth's history do not approach current rates.[23]: 54 

Effects

Thick orange-brown smoke blocks half a blue sky, with conifers in the foreground
A few grey fish swim over grey coral with white spikes
Desert sand half covers a village of small flat-roofed houses with scattered green trees
large areas of still water behind riverside buildings
Some climate change effects: wildfire caused by heat and dryness, bleached coral caused by ocean acidification and heating, environmental migration caused by desertification, and coastal flooding caused by storms and sea level rise.
This section is an excerpt from Effects of climate change.[edit]

Climate change affects the physical environment, ecosystems and human societies. Changes in the climate system include an overall warming trend, more extreme weather and rising sea levels. These in turn impact nature and wildlife, as well as human settlements and societies.[24] The effects of human-caused climate change are broad and far-reaching. This is especially so if there is no significant climate action. Experts sometimes describe the projected and observed negative impacts of climate change as the climate crisis.

The changes in climate are not uniform across the Earth. In particular, most land areas have warmed faster than most ocean areas. The Arctic is warming faster than most other regions.[15] There are many effects of climate change on oceans. These include an increase in ocean temperatures, a rise in sea level from ocean warming and ice sheet melting. They include increased ocean stratification. They also include changes to ocean currents including a weakening of the Atlantic meridional overturning circulation.[25]: 10  Carbon dioxide from the atmosphere is acidifiying the ocean.[26]

Recent warming has had a big effect on natural biological systems.[27] It has degraded land by raising temperatures, drying soils and increasing wildfire risk.[28]: 9  Species all over the world are migrating towards the poles to colder areas. On land, many species move to higher ground, whereas marine species seek colder water at greater depths.[29] At 2 °C (3.6 °F) of warming, around 10% of species on land would become critically endangered.[30]: 259 

See also

References

  1. ↑ PAGES 2k Consortium (2019). "Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era". Nature Geoscience. 12 (8): 643–649. doi:10.1038/s41561-019-0400-0. ISSN 1752-0894. PMC 6675609. PMID 31372180.
  2. ↑ "Global Annual Mean Surface Air Temperature Change". NASA. Retrieved 23 February 2020.
  3. ↑ World of change: Global Temperatures Archived 2019-09-03 at the Wayback Machine The global mean surface air temperature for the period 1951-1980 was estimated to be 14 °C (57 °F), with an uncertainty of several tenths of a degree.
  4. ↑ "Solar System Temperatures". National Aeronautics and Space Administration (NASA). 4 September 2023. Archived from the original on 1 October 2023. (link to NASA graphic)
  5. ↑ "Tracking breaches of the 1.5 °C global warming threshold". Copernicus Programme. 15 June 2023. Archived from the original on 14 September 2023.
  6. 1 2 IPCC, 2021: Annex VII: Glossary [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Semenov, A. Reisinger (eds.)]. 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. 2215–2256, doi:10.1017/9781009157896.022.
  7. ↑ "GISS Surface Temperature Analysis (v4)". NASA. Retrieved 12 January 2024.
  8. ↑ "What Are "Proxy" Data?". NCDC.NOAA.gov. National Climatic Data Center, later called the National Centers for Environmental Information, part of the National Oceanic and Atmospheric Administration. 2014. Archived from the original on 10 October 2014.
  9. ↑ Brohan, P.; Kennedy, J. J.; Harris, I.; Tett, S. F. B.; Jones, P. D. (2006). "Uncertainty estimates in regional and global observed temperature changes: a new dataset from 1850". J. Geophys. Res. 111 (D12): D12106. Bibcode:2006JGRD..11112106B. CiteSeerX 10.1.1.184.4382. doi:10.1029/2005JD006548. S2CID 250615.
  10. ↑ IPCC (2018). "Summary for Policymakers" (PDF). Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. pp. 3–24.
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  12. ↑ Kennedy, John; Ramasamy, Selvaraju; Andrew, Robbie; Arico, Salvatore; Bishop, Erin; Braathen, Geir (2019). WMO statement on the State of the Global Climate in 2018. Geneva: Chairperson, Publications Board, World Meteorological Organization. p. 6. ISBN 978-92-63-11233-0. Archived from the original on 12 November 2019. Retrieved 24 November 2019.
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  14. ↑ State of the Global Climate 2021 (Report). World Meteorological Organization. 2022. p. 2. Archived from the original on 18 May 2022. Retrieved 23 April 2023.
  15. 1 2 Lindsey, Rebecca; Dahlman, Luann (June 28, 2022). "Climate Change: Global Temperature". climate.gov. National Oceanic and Atmospheric Administration. Archived from the original on September 17, 2022.
  16. ↑ Davy, Richard; Esau, Igor; Chernokulsky, Alexander; Outten, Stephen; Zilitinkevich, Sergej (January 2017). "Diurnal asymmetry to the observed global warming". International Journal of Climatology. 37 (1): 79–93. Bibcode:2017IJCli..37...79D. doi:10.1002/joc.4688.
  17. ↑ Schneider, S.H., S. Semenov, A. Patwardhan, I. Burton, C.H.D. Magadza, M. Oppenheimer, A.B. Pittock, A. Rahman, J.B. Smith, A. Suarez and F. Yamin, 2007: Chapter 19: Assessing key vulnerabilities and the risk from climate change. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 779-810.
  18. ↑ Joyce, Christopher (30 August 2018). "To Predict Effects Of Global Warming, Scientists Looked Back 20,000 Years". NPR. Archived from the original on 29 December 2019. Retrieved 29 December 2019.
  19. ↑ Overpeck, J.T. (20 August 2008), NOAA Paleoclimatology Global Warming – The Story: Proxy Data, NOAA Paleoclimatology Program – NCDC Paleoclimatology Branch, archived from the original on 3 February 2017, retrieved 20 November 2012
  20. ↑ The 20th century was the hottest in nearly 2,000 years, studies show Archived 25 July 2019 at the Wayback Machine, 25 July 2019
  21. ↑ Nicholls, R.J., P.P. Wong, V.R. Burkett, J.O. Codignotto, J.E. Hay, R.F. McLean, S. Ragoonaden and C.D. Woodroffe, 2007: Chapter 6: Coastal systems and low-lying areas. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 315-356.
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  26. ↑ Doney, Scott C.; Busch, D. Shallin; Cooley, Sarah R.; Kroeker, Kristy J. (2020-10-17). "The Impacts of Ocean Acidification on Marine Ecosystems and Reliant Human Communities". Annual Review of Environment and Resources. 45 (1): 83–112. doi:10.1146/annurev-environ-012320-083019. ISSN 1543-5938. S2CID 225741986.
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  30. ↑ Parmesan, Camille; Morecroft, Mike; Trisurat, Yongyut; et al. "Chapter 2: Terrestrial and Freshwater Ecosystems and their Services" (PDF). Climate Change 2022: Impacts, Adaptation and Vulnerability. The Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.
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