Climate Change: Global Temperature

Photo by Pixabay on Pexels.com

 BY REBECCA LINDSEY AND LUANN DAHLMAN  REVIEWED BY JESSICA BLUNDEN

Given the tremendous size and heat capacity of the global oceans, it takes a massive amount of heat energy to raise Earth’s average yearly surface temperature even a small amount. The roughly 2-degree Fahrenheit (1 degrees Celsius) increase in global average surface temperature that has occurred since the pre-industrial era (1880-1900) might seem small, but it means a significant increase in accumulated heat.

That extra heat is driving regional and seasonal temperature extremes, reducing snow cover and sea ice, intensifying heavy rainfall, and changing habitat ranges for plants and animals—expanding some and shrinking others.  As the map below shows, most land areas have warmed faster than most ocean areas, and the Arctic is warming faster than most other regions.

Global map of temeperature trends 1990-2021

About surface temperature

The concept of an average temperature for the entire globe may seem odd. After all, at this very moment, the highest and lowest temperatures on Earth are likely more than 100°F (55°C) apart. Temperatures vary from night to day and between seasonal extremes in the Northern and Southern Hemispheres. This means that some parts of Earth are quite cold while other parts are downright hot. To speak of the “average” temperature, then, may seem like nonsense. However, the concept of a global average temperature is convenient for detecting and tracking changes in Earth’s energy budget—how much sunlight Earth absorbs minus how much it radiates to space as heat—over time.

To calculate a global average temperature, scientists begin with temperature measurements taken at locations around the globe. Because their goal is to track changes in temperature, measurements are converted from absolute temperature readings to temperature anomalies—the difference between the observed temperature and the long-term average temperature for each location and date. Multiple independent research groups across the world perform their own analysis of the surface temperature data, and they all show a similar upward trend. 

Blue marble globe with temperature graph overlay

Across inaccessible areas that have few measurements, scientists use surrounding temperatures and other information to estimate the missing values. Each value is then used to calculate a global temperature average. This process provides a consistent, reliable method for monitoring changes in Earth’s surface temperature over time. Read more about how the global surface temperature record is built in our Climate Data Primer.

Global temperature in 2021

According to the 2021 Global Climate Report from NOAA National Centers for Environmental Information, every month of 2021 was warmer than average, despite the cooling influence from the La Niña climate pattern in the tropical Pacific. The “coolest” month was February, which was 1.15 ˚F warmer than average; the rest of the year temperatures were more than 1.4 ˚F warmer than average.

Animated gif of bar graph of annual temperatures from 1976 to 2021

According to NCEI,

The year culminated as the sixth warmest year on record for the globe with a temperature that was 0.84°C (1.51°F) above the 20th century average. The years 2013–2021 all rank among the ten warmest years on record. The year 2021 was also the 45th consecutive year (since 1977) with global temperatures, at least nominally, above the 20th century average. Of note, the year 2005, which was the first year to set a new global temperature record in the 21st century, currently ties with 2013 as the 10th warmest year on record and 2010 ranks as the ninth warmest on record.

For more regional details and 2021 climate statistics, see the 2021 Annual Climate Report from NOAA’s National Centers for Environmental Information. 

Past and future change in global temperature

Though warming has not been uniform across the planet, the upward trend in the globally averaged temperature shows that more areas are warming than cooling. According to NOAA’s 2021 Annual Climate Report the combined land and ocean temperature has increased at an average rate of 0.14 degrees Fahrenheit ( 0.08 degrees Celsius) per decade since 1880; however, the average rate of increase since 1981 (0.18°C / 0.32°F) has been more than twice that rate.

The amount of future warming Earth will experience depends on how much carbon dioxide and other greenhouse gases we emit in coming decades. Today, our activities—burning fossil fuels and clearing forests—add about 11 billion metric tons of carbon (equivalent to a little over 40 billion metric tons of carbon dioxide) to the atmosphere each year. Because that is more carbon than natural processes can remove, atmospheric carbon dioxide increases each year.

side by side graphs showing future carbon emissions (left) and projected temperatures that would result (right)

According to the 2017 U.S. Climate Science Special Report, if yearly emissions continue to increase rapidly, as they have since 2000, models project that by the end of this century, global temperature will be at least 5 degrees Fahrenheit warmer than the 1901-1960 average, and possibly as much as 10.2 degrees warmer. If annual emissions increase more slowly and begin to decline significantly by 2050,  models project temperatures would still be at least 2.4 degrees warmer than the first half of the 20th century, and possibly up to 5.9 degrees warmer.

References

NOAA National Centers for Environmental Information, State of the Climate: Global Climate Report for 2021, online January 2021, retrieved on June 28, 2022, from https://www.ncdc.noaa.gov/sotc/global/202113.

IPCC, 2013: Summary for Policymakers.  In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group 1 to the 5th 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.

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., doi: 10.7930/J0J964J6.

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