This article is about the average temperature at the Earth's surface, in general. For more specific temperature information recorded since the advent of modern scientific monitoring (since about 1850), see
Instrumental temperature record.
Alternative terms for the same thing are global mean surface temperature (GMST) or global average surface 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
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
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
The ecosystems most immediately threatened by climate change are in the
mountains,
coral reefs, and
the Arctic. Excess heat is causing environmental changes in those locations that exceed the ability of animals to adapt.[30] Species are escaping heat by migrating towards the poles and to higher ground when they can.[31] Sea level rise threatens coastal
wetlands with
flooding. Decreases in
soil moisture in certain locations can cause
desertification and damage ecosystems like the
Amazon Rainforest.[32]: 9 At 2 °C (3.6 °F) of warming, around 10% of species on land would become critically endangered.[33]: 259
^"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.
^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.
^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.
ISBN978-92-63-11233-0.
Archived from the original on 12 November 2019. Retrieved 24 November 2019.
^
abLindsey, 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.
^
abIntergovernmental Panel on Climate Change (IPCC), ed. (2022),
"Summary for Policymakers", The Ocean and Cryosphere in a Changing Climate: Special Report of the Intergovernmental Panel on Climate Change, Cambridge: Cambridge University Press, pp. 3–36,
doi:10.1017/9781009157964.001,
ISBN978-1-009-15796-4, retrieved 2023-04-24
^EPA (19 January 2017).
"Climate Impacts on Ecosystems".
Archived from the original on 27 January 2018. Retrieved 5 February 2019. Mountain and arctic ecosystems and species are particularly sensitive to climate change... As ocean temperatures warm and the acidity of the ocean increases, bleaching and coral die-offs are likely to become more frequent.
^Pecl, Gretta T.; Araújo, Miguel B.; Bell, Johann D.; Blanchard, Julia; Bonebrake, Timothy C.; Chen, I-Ching; Clark, Timothy D.; Colwell, Robert K.; Danielsen, Finn; Evengård, Birgitta; Falconi, Lorena; Ferrier, Simon; Frusher, Stewart; Garcia, Raquel A.; Griffis, Roger B.; Hobday, Alistair J.; Janion-Scheepers, Charlene; Jarzyna, Marta A.; Jennings, Sarah; Lenoir, Jonathan; Linnetved, Hlif I.; Martin, Victoria Y.; McCormack, Phillipa C.; McDonald, Jan; Mitchell, Nicola J.; Mustonen, Tero; Pandolfi, John M.; Pettorelli, Nathalie; Popova, Ekaterina; Robinson, Sharon A.; Scheffers, Brett R.; Shaw, Justine D.; Sorte, Cascade J. B.; Strugnell, Jan M.; Sunday, Jennifer M.; Tuanmu, Mao-Ning; Vergés, Adriana; Villanueva, Cecilia; Wernberg, Thomas; Wapstra, Erik; Williams, Stephen E. (31 March 2017).
"Biodiversity redistribution under climate change: Impacts on ecosystems and human well-being". Science. 355 (6332): eaai9214.
doi:
10.1126/science.aai9214.
hdl:10019.1/120851.
PMID28360268.
S2CID206653576.