{{Short description|Average temperature of the Earth's surface}} {{Merge from |1=Temperature record of the last 2,000 years |target=Global surface temperature |afd=Temperature record of the last 2,000 years |date =May 2026 }}{{Use dmy dates|date=August 2024}} {{about|the global average temperature at the Earth's surface |records of extreme weather|List of weather records}} [[File:Common_Era_Temperature.svg|thumb|The blue line represents global surface temperature reconstructed over the last 2,000 years using proxy data from tree rings, corals, and ice cores.<ref name=":0" /> The red line shows direct surface temperature measurements since 1880.<ref name="nasa temperatures2">{{cite web |title=Global Annual Mean Surface Air Temperature Change |url=https://data.giss.nasa.gov/gistemp/graphs_v4/ |access-date=23 February 2020 |publisher=NASA}}</ref>]] '''Global surface temperature''' ('''GST''') is the average temperature of Earth's surface at a given time. It is a combination of sea surface temperature and the near-surface air temperature over land, weighted by their respective areas. Temperature data comes mainly from weather stations and satellites. To estimate data in the distant past, proxy data can be used for example from tree rings, corals, and ice cores.<ref name=":0">{{Cite journal |last=((PAGES 2k Consortium)) |date=2019 |title=Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era |journal=Nature Geoscience |language=en |volume=12 |issue=8 |pages=643–649 |bibcode=2019NatGe..12..643P |doi=10.1038/s41561-019-0400-0 |issn=1752-0894 |pmc=6675609 |pmid=31372180}}</ref> Observing the rising GST over time is one of the many lines of evidence supporting the scientific consensus on climate change, which is that human activities are causing climate change. Alternative terms for the same concept are '''global mean surface temperature''' ('''GMST''') or '''global average surface temperature'''.
Series of reliable temperature measurements in some regions began in the 1850—1880 time frame (this is called the '''instrumental temperature record'''). 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.<ref name=":3">{{cite journal |last1=Brohan |first1=P. |last2=Kennedy |first2=J. J. |last3=Harris |first3=I. |last4=Tett |first4=S. F. B. |last5=Jones |first5=P. D. |year=2006 |title=Uncertainty estimates in regional and global observed temperature changes: a new dataset from 1850 |journal=J. Geophys. Res. |volume=111 |issue=D12 |pages=D12106 |bibcode=2006JGRD..11112106B |citeseerx=10.1.1.184.4382 |doi=10.1029/2005JD006548 |s2cid=250615}}</ref> For temperature measurements in the upper atmosphere a variety of methods can be used. This includes radiosondes launched using weather balloons, a variety of satellites, and aircraft.<ref>{{Cite web |title=Remote Sensing Systems |url=https://www.remss.com/measurements/upper-air-temperature/validation/#:~:text=The%20most%20widespread%20instruments%20for,results%20back%20to%20the%20surface. |access-date=2022-05-19 |website=www.remss.com |language=en}}</ref> Satellites can monitor temperatures in the upper atmosphere but are not commonly used to measure temperature change at the surface. Ocean temperatures at different depths are measured to add to global surface temperature datasets. This data is also used to calculate the ocean heat content.
GMST is often further aggregated by year or month. Through 1940, the average annual GMST 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.<ref>[https://earthobservatory.nasa.gov/world-of-change/decadaltemp.php World of change: Global Temperatures] {{Webarchive|url=https://web.archive.org/web/20190903121233/https://earthobservatory.nasa.gov/world-of-change/decadaltemp.php|date=2019-09-03}} The global mean surface air temperature for the period 1951–1980 was estimated to be {{convert|14|°C|°F|abbr=on}}, with an uncertainty of several tenths of a degree.</ref> The current annual GMST is about {{convert|15|C|F}},<ref name="NASAtemp_20230904">{{cite web |date=4 September 2023 |title=Solar System Temperatures |url=https://science.nasa.gov/resource/solar-system-temperatures/ |url-status=live |archive-url=https://archive.today/20231001035325/https://science.nasa.gov/resource/solar-system-temperatures/ |archive-date=1 October 2023 |publisher=National Aeronautics and Space Administration (NASA)}} ([https://web.archive.org/web/20231001035210/https://smd-cms.nasa.gov/wp-content/uploads/2023/09/Solar_System_Thermometer-02152022.jpg link to NASA graphic])</ref> though monthly temperatures can vary almost {{convert|2|C-change|0}} above or below this figure.<ref name="Copernicus_20230615">{{cite web |date=15 June 2023 |title=Tracking breaches of the 1.5 °C global warming threshold |url=https://climate.copernicus.eu/sites/default/files/custom-uploads/Page%20Uploads/daily%20GAT.png |url-status=live |archive-url=https://web.archive.org/web/20230914161957/https://climate.copernicus.eu/sites/default/files/custom-uploads/Page%20Uploads/daily%20GAT.png |archive-date=14 September 2023 |publisher=Copernicus Programme}}</ref>
The global average and combined land and ocean surface temperature show a warming of 1.09 °C (range: 0.95 to 1.20 °C) from 1850–1900 to 2011–2020, based on multiple independently produced datasets.<ref name=":03">{{Cite book |author=IPCC |author-link=IPCC |url=https://www.ipcc.ch/report/ar6/wg1/ |title=The Physical Science Basis |year=2021 |isbn=978-92-9169-158-6 |series=Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |pages= |chapter=Summary for Policymakers |ref={{harvid|IPCC AR6 WG1 Summary for Policymakers|2021}} |chapter-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM_final.pdf}}</ref>{{rp|5}} The trend is faster since the 1970s than in any other 50-year period over at least the last 2000 years.<ref name=":03" />{{rp|8}} Within that upward trend, some variability in temperatures happens because of natural internal variability (for example due to El Niño–Southern Oscillation).
The global temperature record shows the changes of the temperature of the atmosphere and the oceans through various spans of time. There are numerous estimates of temperatures since the end of the Pleistocene glaciation, particularly during the current Holocene epoch. Some temperature information is available through geologic evidence, going back millions of years. More recently, information from ice cores covers the period from 800,000 years ago until now. Tree rings and measurements from ice cores can give evidence about the global temperature from 1,000–2,000 years before the present until now.<ref name=":1" />
== Definition == [[File:Projected_Change_in_Temperatures_by_2090.svg|thumb|Projected surface temperature changes relative to 1850–1900, based on CMIP6 multi-model mean changes]]
The IPCC Sixth Assessment Report defines ''global mean surface temperature'' (GMST) as 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".<ref name="IPCC glossary">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf 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 [https://www.ipcc.ch/report/ar6/wg1/ 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.</ref>{{rp|2231}}
Put simply, the global surface temperature (GST) is calculated by averaging the temperature at the surface layer of the ocean (sea surface temperature) and over land (surface air temperature).
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."<ref name="IPCC glossary" />{{rp|2231}}
''Global temperature'' can have different definitions. There is a small difference between air and surface temperatures.<ref name="IPCC SR15 SPM">{{cite book |author=IPCC |author-link=IPCC |title=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 |year=2018 |pages=3–24 |chapter=Summary for Policymakers |ref={{harvid|IPCC SR15 Summary for Policymakers|2018}} <!-- ipcc:20200312 --> |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/2/2019/05/SR15_SPM_version_report_HR.pdf}}</ref>{{rp|12}}
== Temperature data from 1850 to the present time == === Total warming and trends === {{See also|Climate change#Global temperature rise}} thumb|NASA animation portraying global surface temperature changes since 1880. The colour blue denotes cooler temperatures and red denotes warmer temperatures. As reference value the mean temperature from 1951 to 1980 is used.Changes in global temperatures over the past century provide evidence for the effects of increasing greenhouse gases. When the climate system reacts to such changes, climate change follows. Measurement of the GST 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.
The global average and combined land and ocean surface temperature, show a warming of 1.09 °C (range: 0.95 to 1.20 °C) from 1850–1900 to 2011–2020, based on multiple independently produced datasets.<ref name=":03" />{{rp|5}} The trend is faster since the 1970s than in any other 50-year period over at least the last 2000 years.<ref name=":03" />{{rp|8}}
Most of the observed warming occurred in two periods: around 1900 to around 1940 and around 1970 onwards;<ref>{{Cite web |title=IPCC AR5 Chapter 2 page 193 |url=https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter02_FINAL.pdf |url-status=live |archive-url=https://web.archive.org/web/20161121185228/http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter02_FINAL.pdf |archive-date=21 November 2016 |access-date=28 January 2016}}</ref> the cooling/plateau from 1940 to 1970 has been mostly attributed to sulfate aerosol.<ref>{{cite web |display-authors=etal |year=2001 |editor=Houghton |title=Climate Change 2001: Working Group I: The Scientific Basis – Chapter 12: Detection of Climate Change and Attribution of Causes |url=http://www.grida.no/climate/ipcc_tar/wg1/462.htm |url-status=dead |archive-url=https://web.archive.org/web/20070711023544/http://www.grida.no/climate/ipcc_tar/wg1/462.htm |archive-date=11 July 2007 |access-date=13 July 2007 |publisher=IPCC}}</ref><ref>{{Cite book |author1=National Research Council |title=Advancing the Science of Climate Change |year=2010 |isbn=978-0-309-14588-6 |chapter=Ch 6. Changes in the Climate System |doi=10.17226/12782 |bibcode=2010nap..book12782N |chapter-url=http://www.nap.edu/openbook.php?record_id=12782&page=207}}</ref>{{rp|207}} Some of the temperature variations over this time period may also be due to ocean circulation patterns.<ref>{{Cite journal |last1=Swanson |first1=K.L. |last2=Sugihara |first2=G. |last3=Tsonis |first3=A.A. |date=22 September 2009 |title=Long-term natural variability and 20th century climate change |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=106 |issue=38 |pages=16120–3 |bibcode=2009PNAS..10616120S |doi=10.1073/pnas.0908699106 |pmc=2752544 |pmid=19805268 |doi-access=free}}</ref>
Land air temperatures are rising faster than sea surface temperatures. Land temperatures have warmed by 1.59 °C (range: 1.34 to 1.83 °C) from 1850–1900 to 2011–2020, while sea surface temperatures have warmed by 0.88 °C (range: 0.68 to 1.01 °C) over the same period.<ref name=":03" />{{rp|5}}
For 1980 to 2020, the linear warming trend for combined land and sea temperatures has been 0.18 °C to 0.20 °C per decade, depending on the data set used.<ref name=":13">Gulev, S. K., P. W. Thorne, J. Ahn, F. J. Dentener, C. M. Domingues, S. Gerland, D. Gong, D. S. Kaufman, H. C. Nnamchi, J. Quaas, J. A. Rivera, S. Sathyendranath, S. L. Smith, B. Trewin, K. von Shuckmann, R. S. Vose, 2021, [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_02.pdf Changing State of the Climate System (Chapter 2)] {{Webarchive|url=https://web.archive.org/web/20220302154841/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_02.pdf|date=2 March 2022}}. 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.</ref>{{rp|Table 2.4}}
It is unlikely that any uncorrected effects from urbanisation, or changes in land use or land cover, have raised global land temperature changes by more than 10%.<ref>IPCC, 2013: [https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_all_final.pdf Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change] {{Webarchive|url=https://web.archive.org/web/20190302025020/https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_all_final.pdf|date=2 March 2019}} [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, 1535 pp.</ref>{{rp|189}} However, larger urbanisation signals have been found locally in some rapidly urbanising regions, such as eastern China.<ref name=":13" />{{rp|Section 2.3.1.1.3}}{{excerpt|Effects of climate change#Changes in temperature|paragraphs=1-2}} [[File:20200324 Global average temperature - NASA-GISS HadCrut NOAA Japan BerkeleyE.svg|thumb |Global average temperature datasets from various scientific organizations show substantial agreement concerning the progress and extent of global warming: 1880– pairwise correlations of the four longer-term datasets are at least 99.29%.]] [[File:GISTEMP Spiral 2022-03-06 2257.webm|thumb|A climate spiral depicting monthly anomalies in global temperature from 1880 till 2021.]]
=== Methods === The instrumental temperature record is a record of temperatures within Earth's climate based on direct measurement of air temperature and ocean temperature. Instrumental temperature records do not use indirect reconstructions using climate proxy data such as from tree rings and marine sediments.<ref name="NCDC_proxy">{{cite web |date=2014 |title=What Are "Proxy" Data? |url=https://www.ncdc.noaa.gov/news/what-are-proxy-data |url-status=live |archive-url=https://web.archive.org/web/20141010184434/https://www.ncdc.noaa.gov/news/what-are-proxy-data |archive-date=10 October 2014 |website=NCDC.NOAA.gov |publisher=National Climatic Data Center, later called the National Centers for Environmental Information, part of the National Oceanic and Atmospheric Administration}}</ref>
==== Early temperature records ==== [[File:Stevenson_screen_exterior.JPG|thumb|Exterior of a Stevenson screen used for temperature measurements on land stations.]] thumb|Interior of a Stevenson screen The longest-running temperature record is the Central England temperature data series, a single-location data set that starts in 1659.<ref name=MetOfficeCET_20190731>Data source: {{cite web |author1=Met Office U.K. |title=mean CET ranked coldest to warmest from 1659 to 2019 |url=https://www.metoffice.gov.uk/hadobs/hadcet/mly_cet_mean_sort.txt |publisher=Met Office, Hadley Centre for Climate Prediction and Research |access-date=31 July 2019 |archive-url=https://web.archive.org/web/20190521172358/https://www.metoffice.gov.uk/hadobs/hadcet/mly_cet_mean_sort.txt |archive-date=21 May 2019 |date=31 July 2019 |url-status=live }}</ref>
On 15 December 2025, the Copernicus Programme's Earth System Science Data released the GloSAT reference analysis, a gridded data set of air temperature change across global land and ocean extending back to the 1780s, using marine air temperature observations rather than the sea surface temperature measurements.<ref name=ESSD_20251215>{{cite journal |last1=Morice |first1=Colin P. |last2=Berry |first2=David I. |display-authors=1 |title=An observational record of global gridded near-surface air temperature change over land and ocean from 1781 |journal=Earth System Science Data |date=15 December 2025 |volume=17 |issue=12 |pages=7079–7100 |doi=10.5194/essd-17-7079-2025 |doi-access=free |bibcode=2025ESSD...17.7079M }}</ref>
Before GloSAT's release, the period for which reasonably reliable instrumental records of near-surface land temperature exist with quasi-global coverage was generally considered to begin around 1850.<ref name=":3" /> Earlier records exist, but with sparser coverage, largely confined to the Northern Hemisphere, and less standardized instrumentation.
The temperature data for the record come from measurements from land stations, ships, and buoys. On land, temperatures are measured either using electronics sensors, or mercury or alcohol thermometers which are read manually, with the instruments being sheltered from direct sunlight using a shelter such as a Stevenson screen. The sea record consists of ships taking sea temperature measurements, mostly from hull-mounted sensors, engine inlets or buckets, and more recently includes measurements from moored and drifting buoys. The land and marine records can be compared.
Areas that are densely populated tend to have a high density of measurement points. In contrast, temperature observations are more spread out in sparsely populated areas such as polar regions and deserts, as well as in many regions of Africa and South America.<ref>{{Cite web |title=GCOS – Deutscher Wetterdienst – CLIMAT Availability |url=https://gcos.dwd.de/DWD-GCOS/EN/nationalcontributions/servicesforgcos/centresforqualityassurance/gsmnc/gsnmc_monitoring_produkte/gsnmc/climat_avail_new/climat_avail_node.html |access-date=2022-05-12 |website=gcos.dwd.de |language=en}}</ref> In the past, thermometers were read manually to record temperatures. Nowadays, measurements are usually connected with electronic sensors which transmit data automatically. Surface temperature data is usually presented as anomalies rather than as absolute values.
Land and sea measurement and instrument calibration is the responsibility of national meteorological services. Standardization of methods is organized through the World Meteorological Organization (and formerly through its predecessor, the International Meteorological Organization).<ref name="GOSGuide">{{cite book |url=http://www.wmo.ch/pages/prog/www/OSY/Manual/488_Guide_2007.pdf |title=Guide to the Global Observing System |publisher=WMO |year=2007 |isbn=978-9263134882}}</ref>
Most meteorological observations are taken for use in weather forecasts. Centers such as European Centre for Medium-Range Weather Forecasts show instantaneous map of their coverage; or the Hadley Centre show the coverage for the average of the year 2000. Coverage for earlier in the 20th and 19th centuries would be significantly less. While temperature changes vary both in size and direction from one location to another, the numbers from different locations are combined to produce an estimate of a global average change.
==== Satellite and balloon temperature records (1950s–present) ==== {{main article|Satellite temperature measurement}}
Weather balloon radiosonde measurements of atmospheric temperature at various altitudes begin to show an approximation of global coverage in the 1950s. Since December 1978, microwave sounding units on satellites have produced data which can be used to infer temperatures in the troposphere.
Several groups have analyzed the satellite data to calculate temperature trends in the troposphere. Both the University of Alabama in Huntsville (UAH) and the private, NASA funded, corporation Remote Sensing Systems (RSS) find an upward trend. For the lower troposphere, UAH found a global average trend between 1978 and 2019 of 0.130 degrees Celsius per decade.<ref>{{cite web |title=Global Temperature Report: January 2019 |url=https://www.nsstc.uah.edu/climate/2019/GTR_201901Jan_1.pdf |work=UAH}}</ref> RSS found a trend of 0.148 degrees Celsius per decade, to January 2011.<ref>{{cite web |title=RSS / MSU and AMSU Data / Description |url=http://www.ssmi.com/msu/msu_data_description.html |url-status=dead |archive-url=https://web.archive.org/web/20121123040542/http://www.ssmi.com/msu/msu_data_description.html |archive-date=23 November 2012 |access-date=26 February 2011}}</ref>
In 2004 scientists found trends of +0.19 degrees Celsius per decade when applied to the RSS dataset.<ref>{{Cite web |title=letters to nature |url=http://www.ncdc.noaa.gov/temp-and-precip/msu/nature02524-UW-MSU.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110314175253/http://www.ncdc.noaa.gov/temp-and-precip/msu/nature02524-UW-MSU.pdf |archive-date=2011-03-14 |access-date=2011-03-04}}</ref> Others found 0.20 degrees Celsius per decade up between 1978 and 2005, since which the dataset has not been updated.<ref>{{Cite web|url=https://www2.atmos.umd.edu/~kostya/CCSP/|title=index of CCSP|website=www2.atmos.umd.edu}}</ref>
The most recent climate model simulations give a range of results for changes in global-average temperature. Some models show more warming in the troposphere than at the surface, while a slightly smaller number of simulations show the opposite behaviour. There is no fundamental inconsistency among these model results and observations at the global scale.<ref>{{Cite web |title=Temperature Trends in the Lower Atmosphere – Understanding and Reconciling Differences |url=http://www.gfdl.noaa.gov/bibliography/related_files/tmlw0602.pdf |url-status=live |archive-url=https://web.archive.org/web/20160304050727/http://www.gfdl.noaa.gov/bibliography/related_files/tmlw0602.pdf |archive-date=4 March 2016 |access-date=29 January 2016}}</ref>
The satellite records used to show much smaller warming trends for the troposphere which were considered to disagree with model prediction; however, following revisions to the satellite records, the trends are now similar.
==== Global surface and ocean datasets ==== {{See also|Temperature measurement}}
The methods used to derive the principal estimates of global surface temperature trends are largely independent from each other and include:
* The National Oceanic and Atmospheric Administration (NOAA) maintains the Global Historical Climatology Network (GHCN-Monthly) data base containing historical temperature, precipitation, and pressure data for thousands of land stations worldwide.<ref name="GHCN">{{cite web |title=GHCN-Monthly Version 2 |url=https://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/global-historical-climatology-network-ghcn |access-date=13 July 2007 |publisher=NOAA}}</ref> Also, NOAA's National Climatic Data Center (NCDC)<ref>{{Cite web |title=NCDC State of the Climate Global Analysis, April 2010 |url=http://www.ncdc.noaa.gov/sotc/?report=global&year=2010&month=4 |url-status=live |archive-url=https://web.archive.org/web/20100616044900/http://www.ncdc.noaa.gov/sotc/?report=global&year=2010&month=4 |archive-date=16 June 2010 |access-date=15 June 2010}}</ref> of surface temperature measurements maintains a global temperature database since 1880.<ref name="NCDC">{{cite web |title=Global Surface Temperature Anomalies |url=http://www.ncdc.noaa.gov/cmb-faq/anomalies.html |access-date=16 June 2010 |publisher=National Climatic Data Center}}</ref> * HadCRUT is a collaboration between the University of East Anglia's Climatic Research Unit and the Hadley Centre for Climate Prediction and Research. * NASA's Goddard Institute for Space Studies maintains GISTEMP. * More recently the Berkeley Earth Surface Temperature dataset was started. It is now one of the datasets used by IPCC and WMO in their assessments.
These datasets are updated frequently, and are generally in close agreement with each other.
==== Absolute temperatures v. anomalies ==== {{Main|Temperature anomaly}}
Records of global average surface temperature are usually presented as anomalies rather than as absolute temperatures. A temperature anomaly is measured against a ''reference value'' (also called ''baseline period'' or ''long-term average'').<ref>{{Cite web |author=CMB and Crouch, J. |date=17 September 2012 |title=Global Surface Temperature Anomalies: Background Information – FAQ 1 |url=http://www.ncdc.noaa.gov/cmb-faq/anomalies.php |publisher=NOAA NCDC}}</ref> Usually it is a period of 30 years. For example, a commonly used baseline period is 1951–1980. Therefore, if the average temperature for that time period was 15 °C, and the currently measured temperature is 17 °C, then the temperature anomaly is +2 °C.
Temperature anomalies are useful for deriving average surface temperatures because they tend to be highly correlated over large distances (of the order of 1000 km).<ref>{{Cite web |author=Hansen, J.E. |date=20 November 2012 |title=Data.GISS: GISS Surface Temperature Analysis (GISTEMP) |url=http://data.giss.nasa.gov/gistemp/ |publisher=NASA GISS |location=New York, NY, USA}}. Website curator: Schmunk, R.B.</ref> In other words, anomalies are representative of temperature changes over large areas and distances. By comparison, absolute temperatures vary markedly over even short distances. A dataset based on anomalies will also be less sensitive to changes in the observing network (such as a new station opening in a particularly hot or cold location) than one based on absolute values will be.
The Earth's average surface absolute temperature for the 1961–1990 period has been derived by spatial interpolation of average observed near-surface air temperatures from over the land, oceans and sea ice regions, with a best estimate of 14 °C (57.2 °F).<ref name="jonesreview">{{cite journal |vauthors=Jones PD, New M, Parker DE, Martin S, Rigor IG |date=1999 |title=Surface air temperature and its changes over the past 150 years |journal=Reviews of Geophysics |volume=37 |issue=2 |pages=173–199 |bibcode=1999RvGeo..37..173J |doi=10.1029/1999RG900002 |doi-access=free}}</ref> The estimate is uncertain, but probably lies within 0.5 °C of the true value.<ref name="jonesreview" /> Given the difference in uncertainties between this absolute value and any annual anomaly, it's not valid to add them together to imply a precise absolute value for a specific year.<ref>{{Cite web |title=Data.GISS: GISTEMP — the Elusive Absolute Surface Air Temperature |url=http://data.giss.nasa.gov/gistemp/abs_temp.html}}</ref>
==== Siting of temperature measurement stations ==== The U.S. National Weather Service Cooperative Observer Program has established minimum standards regarding the instrumentation, siting, and reporting of surface temperature stations.<ref>{{Cite web |title=NOAA National Weather Service Cooperative Observer Program: Proper Siting |url=http://www.nws.noaa.gov/om/coop/standard.htm |url-status=live |archive-url=https://web.archive.org/web/20070705194343/http://www.nws.noaa.gov/om/coop/standard.htm |archive-date=5 July 2007 |access-date=12 July 2007}}</ref> The observing systems available are able to detect year-to-year temperature variations such as those caused by El Niño or volcanic eruptions.<ref name="CCSP">[http://templatelab.com/climatescience-sap1-final-report/ Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences.] {{webarchive|url=https://web.archive.org/web/20070203081058/http://www.climatescience.gov/Library/sap/sap1-1/finalreport/default.htm|date=3 February 2007}} Thomas R. Karl, Susan J. Hassol, Christopher D. Miller, and William L. Murray, editors, 2006. A Report by the Climate Change Science Program and the Subcommittee on Global Change Research, Washington, DC.</ref>
Another study concluded in 2006, that existing empirical techniques for validating the local and regional consistency of temperature data are adequate to identify and remove biases from station records, and that such corrections allow information about long-term trends to be preserved.<ref>{{cite journal |last=Peterson |first=Thomas C. |date=August 2006 |title=Examination of potential biases in air temperature caused by poor station locations |journal=Bull. Amer. Meteor. Soc. |volume=87 |issue=8 |pages=1073–89 |bibcode=2006BAMS...87.1073P |doi=10.1175/BAMS-87-8-1073 |s2cid=122809790 |doi-access=free}}</ref> A study in 2013 also found that urban bias can be accounted for, and when all available station data is divided into rural and urban, that both temperature sets are broadly consistent.<ref>{{cite journal |last1=Hausfather |first1=Zeke |last2=Menne |first2=Matthew J. |last3=Williams |first3=Claude N. |last4=Masters |first4=Troy |last5=Broberg |first5=Ronald |last6=Jones |first6=David |date=30 January 2013 |title=Quantifying the effect of urbanization on U.S. Historical Climatology Network temperature records |journal=Journal of Geophysical Research |volume=118 |issue=2 |pages=481–494 |bibcode=2013JGRD..118..481H |doi=10.1029/2012JD018509 |doi-access=free}}</ref>
=== Warmest periods === ==== Warmest years ==== {{Anchor|Warmest year|Hottest year}} thumb|In recent decades, new high temperature records have substantially outpaced new low temperature records on a growing portion of Earth's surface.<ref name="NOAA_October2">{{cite web |date=November 2023 |title=Mean Monthly Temperature Records Across the Globe / Timeseries of Global Land and Ocean Areas at Record Levels for October from 1951–2023 |url=https://www.ncei.noaa.gov/access/monitoring/monthly-report/global/202310/supplemental/page-3 |url-status=live |archive-url=https://web.archive.org/web/20231116185412/https://www.ncei.noaa.gov/access/monitoring/monthly-report/global/202310/supplemental/page-3 |archive-date=16 November 2023 |website=NCEI.NOAA.gov |publisher=National Centers for Environmental Information (NCEI) of the National Oceanic and Atmospheric Administration (NOAA)}} (change "202310" in URL to see years other than 2023, and months other than 10=October)</ref> Comparison shows seasonal variability for record increases.
The period from 2015 through 2025 included all of the 11 warmest years on record since 1850.<ref name=EarthCom_20251209>{{cite web |last1=Igini |first1=Martina |title=2025 on Track to Be Joint-Second Warmest Year on Record |url=https://earth.org/2025-on-track-to-be-joint-second-warmest-years-on-record/ |publisher=Earth.org |archive-url=https://web.archive.org/web/20251216214859/https://earth.org/2025-on-track-to-be-joint-second-warmest-years-on-record/ |archive-date=16 December 2025 |date=9 December 2025 |url-status=live}}</ref>
The year 2023 was 1.48 °C hotter than the average in the years 1850–1900 according to the Copernicus Climate Change Service. It was declared as the warmest on record almost immediately after it ended and broke many climate records.<ref>{{cite news |last1=Poynting |first1=Mark |last2=Rivault |first2=Erwan |date=9 January 2023 |title=2023 confirmed as world's hottest year on record |url=https://www.bbc.com/news/science-environment-67861954 |access-date=17 January 2024 |agency=BBC}}</ref><ref>{{cite news |date=10 January 2024 |title=Scientists confirm 2023 was hottest year on record, 1.48 °C warmer than pre-industrial level |url=https://asianews.network/scientists-confirm-2023-was-hottest-year-on-record-1-48-c-warmer-than-pre-industrial-level/ |access-date=17 January 2024 |agency=Asia News Network}}</ref>
There is a long-term warming trend, and there is variability about this trend because of natural sources of variability (e.g. ENSO such as 2014–2016 El Niño event, volcanic eruption).<ref name="MetOfficePR">{{cite press release |title=2016: one of the warmest two years on record |date=18 January 2017 |publisher=Met Office of the United Kingodom |url=http://www.metoffice.gov.uk/news/releases/2017/2016-record-breaking-year-for-global-temperature |access-date=20 January 2017}}</ref> Not every year will set a record but record highs are occurring regularly.
While record-breaking years can attract considerable public interest,<ref name="bbc 2017">{{cite news |date=18 January 2017 |title=Climate change: Data shows 2016 likely to be warmest year yet |url=https://www.bbc.com/news/science-environment-38652746 |access-date=19 January 2017 |work=BBC News Online}}</ref> individual years are less significant than the overall trend.<ref name="NASA-NOAA2016">{{cite press release |title=NASA, NOAA Data Show 2016 Warmest Year on Record Globally |date=19 January 2017 |publisher=NASA |url=https://www.nasa.gov/press-release/nasa-noaa-data-show-2016-warmest-year-on-record-globally |last1=Potter |first1=Sean |last2=Cabbage |first2=Michael |last3=McCarthy |first3=Leslie |access-date=20 January 2017}}</ref><ref>{{cite news |last=Brumfiel |first=Geoff |date=18 January 2017 |title=U.S. Report Confirms 2016 Was The Hottest Year On Record |url=https://www.npr.org/2017/01/18/510472493/u-s-report-confirms-2016-was-the-hottest-year-on-record |access-date=20 January 2017 |newspaper=NPR}}</ref> Some climatologists have criticized the attention that the popular press gives to ''warmest year'' statistics.<ref name="Gavin Schmidt 201501">{{cite web |last=Schmidt |first=Gavin |author-link=Gavin Schmidt |date=22 January 2015 |title=Thoughts on 2014 and ongoing temperature trends |url=http://www.realclimate.org/index.php/archives/2015/01/thoughts-on-2014-and-ongoing-temperature-trends/ |access-date=4 September 2015 |website=RealClimate}}</ref><ref name="NASA-NOAA2016" />
Based on the NOAA dataset (note that other datasets produce different rankings<ref>{{Cite news |date=4 January 2018 |title=2017 was second hottest year on record, after sizzling 2016 – report |url=https://uk.reuters.com/article/uk-climatechange-temperatures/2017-was-second-hottest-year-on-record-after-sizzling-2016-report-idUKKBN1ET1L3 |archive-url=https://web.archive.org/web/20180104171150/https://uk.reuters.com/article/uk-climatechange-temperatures/2017-was-second-hottest-year-on-record-after-sizzling-2016-report-idUKKBN1ET1L3 |url-status=dead |archive-date=4 January 2018 |newspaper=Reuters}}</ref>), the following table lists the global combined land and ocean annually averaged temperature rank and anomaly for each of the 10 warmest years on record.<ref name="NOAA2015">{{cite news |title=Global Climate Report – Annual 2020 |url=https://www.ncdc.noaa.gov/sotc/global/202013 |access-date=14 January 2021 |publisher=NOAA}}</ref> For comparison: IPCC uses the mean of four different datasets and expresses the data relative to 1850–1900.{{citation needed|date=March 2022}} Although global instrumental temperature records begin only in 1850, reconstructions of earlier temperatures based on climate proxies, suggest these recent years may be the warmest for several centuries to millennia, or longer.<ref name=":13" />{{rp|2–6}} {| class="wikitable sortable" style="margin:auto;" |+'''Top 10 warmest years (data from NOAA)''' |+(1880–2025) !Rank !Year !Anomaly °C !Anomaly °F |- align="left" |1 |2024 |1.29 |2.23 |- align="left" |2 |2023 |1.19 |2.14 |- align="left" |3 |2025 |1.17 |2.11 |- align="left" |4 |2016 |1.03 |1.85 |- align="left" |5 |2020 |1.02 |1.83 |- align="left" |6 |2019 |0.99 |1.78 |- align="left" |7 |2017 |0.94 |1.69 |- align="left" |8 |2015 |0.92 |1.65 |- align="left" |9 |2022 |0.86 |1.55 |- align="left" |10 |2021 |0.84 |1.51 |}
==== Warmest decades ==== [[File:20211115_Progression_of_global_warming_-_decadal_analysis_-_bar_chart.svg|thumb|Global warming by decade: In the last four decades, global average surface temperatures during a given decade have almost always been higher than the average temperature in the preceding decade (data for 1850 to 2020 based on HadCRUT datasets).]] Numerous drivers have been found to influence annual global mean temperatures. An examination of the average global temperature changes by decades reveals continuing climate change: each of the last four decades has been successively warmer at the Earth's surface than any preceding decade since 1850. The most recent decade (2011–2020) was warmer than any multi-centennial period in the past 11,700 years.<ref name=":13" />{{rp|2–6}}
The following chart is from NASA data of combined land-surface air and sea-surface water temperature anomalies.<ref>{{Cite web |title=Data.GISS: GISS Surface Temperature Analysis (GISTEMP v4) |url=https://data.giss.nasa.gov/gistemp/ |access-date=2022-03-17 |website=data.giss.nasa.gov |language=en}}</ref> {| class="wikitable sortable" style="margin:auto;" |+'''Combined land-surface air and sea-surface water temperature anomalies (data from NASA)''' !Years !Temperature anomaly, °C (°F) from 1951 to 1980 mean !Change from previous decade, °C (°F) |- |1880–1889 |{{convert|-0.274|C-change|3|sortable=on}} |N/A |- |1890–1899 |{{convert|-0.254|C-change|3|sortable=on}} |{{convert|+0.020|C-change|3|sortable=on}} |- |1900–1909 |{{convert|-0.259|C-change|3|sortable=on}} |{{convert|-0.005|C-change|3|sortable=on}} |- |1910–1919 |{{convert|-0.276|C-change|3|sortable=on}} |{{convert|-0.017|C-change|3|sortable=on}} |- |1920–1929 |{{convert|-0.175|C-change|3|sortable=on}} |{{convert|+0.101|C-change|3|sortable=on}} |- |1930–1939 |{{convert|-0.043|C-change|3|sortable=on}} |{{convert|+0.132|C-change|3|sortable=on}} |- |1940–1949 |{{convert|0.035|C-change|3|sortable=on}} |{{convert|+0.078|C-change|3|sortable=on}} |- |1950–1959 |{{convert|-0.02|C-change|3|sortable=on}} |{{convert|-0.055|C-change|3|sortable=on}} |- |1960–1969 |{{convert|-0.014|C-change|3|sortable=on}} |{{convert|+0.006|C-change|3|sortable=on}} |- |1970–1979 |{{convert|-0.001|C-change|3|sortable=on}} |{{convert|+0.013|C-change|3|sortable=on}} |- |1980–1989 |{{convert|0.176|C-change|3|sortable=on}} |{{convert|+0.177|C-change|3|sortable=on}} |- |1990–1999 |{{convert|0.313|C-change|3|sortable=on}} |{{convert|+0.137|C-change|3|sortable=on}} |- |2000–2009 |{{convert|0.513|C-change|3|sortable=on}} |{{convert|+0.200|C-change|3|sortable=on}} |- |2010–2019 |{{convert|0.753|C-change|3|sortable=on}} |{{convert|+0.240|C-change|3|sortable=on}} |- |2020–2029 (incomplete) |{{convert|1.062|C-change|2|sortable=on}} |{{convert|+0.309|C-change|2|sortable=on}} |}
== Factors influencing global temperature == {{Further|Causes of climate change|Climate variability and change}} [[File:20210827_Global_surface_temperature_bar_chart_-_bars_color-coded_by_El_Niño_and_La_Niña_intensity.svg|thumb|Colored bars show how El Niño years (red, regional warming) and La Niña years (blue, regional cooling) relate to overall global warming. The El Niño–Southern Oscillation has been linked to variability in longer-term global average temperature increase, with El Niño years usually corresponding to annual global temperature increases.]] Factors that influence global temperature include:
* Greenhouse gases trap outgoing radiation warming the atmosphere which in turn warms the land (greenhouse effect). * El Niño–Southern Oscillation (ENSO): El Niño generally tends to increase global temperatures. La Niña, on the other hand, usually causes years which are cooler than the short-term average.<ref name="NOAA">{{cite web |title=NOAA National Climatic Data Center, State of the Climate: Global Analysis for Annual 2014 |url=http://www.ncdc.noaa.gov/sotc/global/2014/13 |access-date=21 January 2015 |publisher=NOAA}}</ref> El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO) and La Niña the cold phase. In the absence of other short-term influences such as volcanic eruptions, strong El Niño years are typically 0.1 °C to 0.2 °C warmer than the years immediately preceding and following them, and strong La Niña years 0.1 °C to 0.2 °C cooler. The signal is most prominent in the year in which the El Niño or La Niña phase ends, with global average temperatures typically rising by 0.1 °C to 0.2 °C during strong El Niño years, and falling by a similar margin during strong La Niña events, in the absence of other short-term influences such as volcanic eruptions.<ref>{{cite web |title=Global Temperature Report for 2024 |url=https://berkeleyearth.org/global-temperature-report-for-2024/ |website=Berkeley Earth |date=15 February 2025 |access-date=8 May 2025}}</ref> * Aerosols and volcanic eruptions: Aerosols diffuse incoming radiation generally cooling the planet. On a long-term basis, aerosols are primarily of anthropogenic origin, but major volcanic eruptions can produce quantities of aerosols which exceed those from anthropogenic sources over periods of time up to a few years. Volcanic eruptions which are sufficiently large to inject significant quantities of sulfur dioxide into the stratosphere can have a significant global cooling effect for one to three years after the eruption. This effect is most prominent for tropical volcanoes as the resultant aerosols can spread over both hemispheres. The largest eruptions of the last 100 years, such as the Mount Pinatubo eruption in 1991 and Mount Agung eruption in 1963–1964, have been followed by years with global mean temperatures 0.1 °C to 0.2 °C below long-term trends at the time.{{citation needed|date=March 2022}} * Land use change like deforestation can increase greenhouse gases through burning biomass. Albedo can also be changed. * Incoming solar radiation varies very slightly, with the main variation controlled by the approximately 11-year solar magnetic activity cycle.
== Robustness of evidence == There is a scientific consensus that climate is changing and that greenhouse gases emitted by human activities are the primary driver.<ref name="joint statement on climate change">{{Cite web |date=21 October 2009 |title=Joint-statement on climate change by leaders of 18 scientific organizations |url=http://www.ucsusa.org/assets/documents/ssi/climate-change-statement-from.pdf |url-status=dead |archive-url=https://web.archive.org/web/20130806073923/http://www.ucsusa.org/assets/documents/ssi/climate-change-statement-from.pdf |archive-date=6 August 2013 |publisher=American Association for the Advancement of Science |location=Washington DC, USA}} Joint-statement by leaders of 18 scientific organizations: American Association for the Advancement of Science, American Chemical Society, American Geophysical Union, American Institute of Biological Sciences, American Meteorological Society, American Society of Agronomy, American Society of Plant Biologists, American Statistical Association, Association of Ecosystem Research Centers, Botanical Society of America, Crop Science Society of America, Ecological Society of America, Natural Science Collections, Alliance Organization of Biological Field Stations, Society for Industrial and Applied Mathematics, Society of Systematic Biologists, Soil Science Society of America, University Corporation for Atmospheric Research</ref> The scientific consensus is reflected, for example, by the Intergovernmental Panel on Climate Change (IPCC), an international body which summarizes existing science, and the U.S. Global Change Research Program.<ref name="joint statement on climate change" />
=== Other reports and assessments === [[File:Global_warming._Short-term_variations_versus_a_long-term_trend_(NCADAC).png|alt=Refer to caption|thumb|This graph shows how short-term variations occur in the measured temperature. The graph also shows a long-term trend of global warming.<ref>{{citation |author=Walsh, J. |title=Figure 6: Short-term Variations Versus Long-term Trend, in: D. Is the global temperature still increasing? Isn't there recent evidence that it is actually 1 cooling?, in: Appendix I: NCA Climate Science – Addressing Commonly Asked Questions from A to Z |url=http://ncadac.globalchange.gov/download/NCAJan11-2013-publicreviewdraft-appendix1-CAQ.pdf |archive-url=https://web.archive.org/web/20130112205257/http://ncadac.globalchange.gov/download/NCAJan11-2013-publicreviewdraft-appendix1-CAQ.pdf |url-status=dead |archive-date=12 January 2013 |display-authors=etal}}, in [http://downloads.globalchange.gov/nca/nca3-drafts/NCAJan11-2013-publicreviewdraft-fulldraft.pdf NCADAC 2013 p. 1065] {{Webarchive|url=https://web.archive.org/web/20220119004317/https://downloads.globalchange.gov/nca/nca3-drafts/NCAJan11-2013-publicreviewdraft-fulldraft.pdf|date=19 January 2022}}</ref>]] The U.S. National Academy of Sciences, both in its 2002 report to President George W. Bush, and in later publications, has strongly endorsed evidence of an average global temperature increase in the 20th century.<ref name="NA_brief">{{cite web |year=2005 |title=Understanding and Responding to Climate Change – Highlights of National Academies Reports |url=http://dels.nas.edu/dels/rpt_briefs/climate-change-final.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070611231645/http://dels.nas.edu/dels/rpt_briefs/climate-change-final.pdf |archive-date=11 June 2007 |access-date=13 July 2007 |publisher=United States National Academies}}</ref>
The preliminary results of an assessment carried out by the Berkeley Earth Surface Temperature group and made public in October 2011, found that over the past 50 years the land surface warmed by 0.911 °C, and their results mirrors those obtained from earlier studies carried out by the NOAA, the Hadley Centre and NASA's GISS. The study addressed concerns raised by ''skeptics'' (more often: climate change deniers).<ref name="SciDaily1011">{{cite web |date=21 October 2011 |title=Cooling the Warming Debate: Major New Analysis Confirms That Global Warming Is Real |url=https://www.sciencedaily.com/releases/2011/10/111021144716.htm |access-date=22 October 2011 |work=Science Daily}}</ref><ref>see also: {{Cite web |author=PBS |date=10 January 2007 |title=Interviews – James Hansen: Hot Politics: FRONTLINE: PBS |url=https://www.pbs.org/wgbh/pages/frontline/hotpolitics/interviews/hansen.html |publisher=PBS}}. "''(...) The 1990s is the real appearance of the science skeptics. How much did they come after you?'' I actually don't like the word "skeptics" for them; I think it's better to call them "contrarians", because skepticism is part of science; all scientists are skeptics (...)"</ref> Those concerns included urban heat island effects and apparently poor station quality,<ref name="SciDaily1011" /> and the "issue of data selection bias"<ref name="SciDaily1011" /> and found that these effects did not bias the results obtained from these earlier studies.<ref name="SciDaily1011" /><ref name="Guardian1011">{{cite news |author=Ian Sample |date=20 October 2011 |title=Global warming study finds no grounds for climate sceptics' concerns |url=https://www.theguardian.com/environment/2011/oct/20/global-warming-study-climate-sceptics |access-date=22 October 2011 |work=The Guardian}}</ref><ref name="bbcBlack">{{cite news |author=Richard Black |date=21 October 2011 |title=Global warming 'confirmed' by independent study |url=https://www.bbc.co.uk/news/science-environment-15373071 |access-date=21 October 2011 |work=BBC News}}</ref><ref name="Econ1011">{{cite news |date=22 October 2011 |title=Climate change: The heat is on |url=https://www.economist.com/science-and-technology/2011/10/22/the-heat-is-on |access-date=22 October 2011 |newspaper=The Economist}}</ref>[[File:GHCN_Temperature_Stations.png|thumb|Map of the land-based long-term monitoring stations included in the Global Historical Climatology Network. Colors indicate the length of the temperature record available at each site.]]
=== Internal climate variability and global warming === {{Further|Causes of climate change|Climate variability and change}}
One of the issues that has been raised in the media is the view that global warming "stopped in 1998".<ref>e.g., see {{Cite news |author=Carter, B. |date=9 April 2006 |title=There IS a problem with global warming... it stopped in 1998 |url=https://www.telegraph.co.uk/comment/personal-view/3624242/There-IS-a-problem-with-global-warming...-it-stopped-in-1998.html |newspaper=The Daily Telegraph}}</ref><ref name="scott variability p1">Edited quote from public-domain source: {{Cite journal |author=Scott, M. |date=31 December 2009 |title=Short-term Cooling on a Warming Planet, p.1 |url=http://www.climatewatch.noaa.gov/article/2009/short-term-cooling-on-a-warming-planet |url-status=dead |journal=ClimateWatch Magazine |publisher=NOAA |at=Introduction |archive-url=https://web.archive.org/web/20130219015155/http://www.climatewatch.noaa.gov/article/2009/short-term-cooling-on-a-warming-planet |archive-date=19 February 2013 |access-date=22 September 2012}}</ref> This view ignores the presence of internal climate variability.<ref name="scott variability p1" /><ref name="met office internal variability">{{Cite web |last1=Met Office |first1=Fitzroy Road |date=14 September 2009 |title=Global warming set to continue |url=http://www.metoffice.gov.uk/news/releases/archive/2009/global-warming |url-status=dead |archive-url=https://web.archive.org/web/20121027110118/http://www.metoffice.gov.uk/news/releases/archive/2009/global-warming |archive-date=27 October 2012 |publisher=UK Met Office}}</ref> Internal climate variability is a result of complex interactions between components of the climate system, such as the coupling between the atmosphere and ocean.<ref>{{Cite book |author=Albritton, D.L. |url=http://www.grida.no/climate/ipcc_tar/wg1/011.htm#box1 |title=Box 1: What drives changes in climate? in: Technical Summary, in: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press |year=2001 |editor=Houghton, J.T. |display-authors=etal |display-editors=etal}}</ref> An example of internal climate variability is the El Niño–Southern Oscillation (ENSO).<ref name="scott variability p1" /><ref name="met office internal variability" /> The El Niño in 1998 was particularly strong, possibly one of the strongest of the 20th century, and 1998 was at the time the world's warmest year on record by a substantial margin.
Cooling over the 2007 to 2012 period, for instance, was likely driven by internal modes of climate variability such as La Niña.<ref name="scott variability p3">Edited quote from public-domain source: {{Cite journal |author=Scott, M. |date=31 December 2009 |title=Short-term Cooling on a Warming Planet, p.3 |url=http://www.climatewatch.noaa.gov/article/2009/short-term-cooling-on-a-warming-planet/3 |journal=ClimateWatch Magazine |publisher=NOAA |at=Deciphering Natural Variability |archive-date=20 June 2013 |access-date=23 August 2024 |archive-url=https://web.archive.org/web/20130620150744/http://www.climatewatch.noaa.gov/article/2009/short-term-cooling-on-a-warming-planet/3 |url-status=dead }}</ref> The area of cooler-than-average sea surface temperatures that defines La Niña conditions can push global temperatures downward, if the phenomenon is strong enough.<ref name="scott variability p3" /> The slowdown in global warming rates over the 1998 to 2012 period is also less pronounced in current generations of observational datasets than in those available at the time in 2012. The temporary slowing of warming rates ended after 2012, with every year from 2015 onwards warmer than any year prior to 2015, but it is expected that warming rates will continue to fluctuate on decadal timescales through the 21st century.<ref>Eyring, V., N. P. Gillett, K. M. Achuta Rao, R. Barimalala, M. Barreiro Parrillo, N. Bellouin, C. Cassou, P. J. Durack, Y. Kosaka, S. McGregor, S. Min, O. Morgenstern, Y. Sun, 2021, [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_03.pdf Human Influence on the Climate System (chapter 3). 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] {{Webarchive|url=https://web.archive.org/web/20220410134155/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_03.pdf|date=10 April 2022}} [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.</ref>{{rp|Box 3.1}}
== Related research == [[File:20190909_STACKED_country_warming_stripes_AND_global_average_(1901-_).png|thumb|Top graphic (comprehensive): 196 rows represent 196 countries, grouped by continent. Each row has 118 color-coded annual temperatures, showing {{blue|1901}}—{{red|2018}} warming patterns in each region and country.<ref name="ClimateLabBookSTACKED_20190721">{{cite web |last1=Hawkins |first1=Ed |date=21 July 2019 |title=#ShowYourStripes / Temperature changes around the world (1901–2018) |url=http://www.climate-lab-book.ac.uk/2019/showyourstripes/#more-5629 |url-status=live |archive-url=https://web.archive.org/web/20190802205935/http://www.climate-lab-book.ac.uk/2019/showyourstripes/ |archive-date=2 August 2019 |website=Climate Lab Book}} ([https://web.archive.org/web/20190802210355/http://www.climate-lab-book.ac.uk/files/2019/06/all_countries_BBC-e1563724721978.png Direct link to image]).</ref><ref name="BBC_20190621">{{cite news |last1=Amos |first1=Jonathan |date=21 June 2019 |title=The chart that defines our warming world / Is this the simplest way to show what is meant by global warming? The chart below organises all the countries of the world by region, time and temperature. The trend is unmistakeable. |url=https://www.bbc.com/news/science-environment-48678196 |url-status=live |archive-url=https://web.archive.org/web/20190629140556/https://www.bbc.com/news/science-environment-48678196 |archive-date=29 June 2019 |work=BBC}} ([https://web.archive.org/web/20190626084354/https://ichef.bbci.co.uk/news/660/cpsprodpb/133A5/production/_107475787_climate_stripes_976-nc.png Link to png image])</ref> Bottom graphic (summary): global average {{blue|1901}}—{{red|2018}}.<ref name="Hawkins_20181204">{{cite web |last1=Hawkins |first1=Ed |date=4 December 2018 |title=2018 visualisation update / Warming stripes for 1850–2018 using the WMO annual global temperature dataset. |url=http://www.climate-lab-book.ac.uk/2018/2018-visualisation-update/ |url-status=live |archive-url=https://web.archive.org/web/20190417024828/http://www.climate-lab-book.ac.uk/2018/2018-visualisation-update/ |archive-date=17 April 2019 |website=Climate Lab Book |quote=LICENSE / Creative Commons License / These blog pages & images are licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.}} ([https://web.archive.org/web/20190403013148/http://www.climate-lab-book.ac.uk/files/2018/12/wmo_stripes.png Direct link to image]).</ref> Data visualization: warming stripes.]]
=== Trends and predictions === {{Further|Climate change#Future warming and the carbon budget|Climate change scenario}}
Each of the seven years in 2015–2021 was clearly warmer than any pre-2014 year, and this trend is expected to be true for some time to come (that is, the 2016 record will be broken before 2026 etc.).<ref>{{cite web |title=2021 one of the seven warmest years on record, WMO consolidated data shows |url=https://wmo.int/media/news/2021-one-of-seven-warmest-years-record-wmo-consolidated-data-shows |website=World Meteorological Organization |date=17 January 2022 }}</ref><ref>{{cite web |title=WMO update: 50:50 chance of global temperature temporarily reaching 1.5°C threshold in next five years |url=https://wmo.int/news/media-centre/wmo-update-5050-chance-of-global-temperature-temporarily-reaching-15degc-threshold-next-five-years |website=World Meteorological Organization |date=9 May 2022 }}</ref> A decadal forecast by the World Meteorological Organisation issued in 2021 stated a probability of 40% of having a year above 1.5 C in the 2021–2025 period.<ref>{{cite web |last1=World Meteorological Organization |title=WMO Global Annual to Decadal Climate Update Target years: 2021 and 2021–2025 |url=https://library.wmo.int/records/item/56312-wmo-global-annual-to-decadal-climate-update |website=World Meteorological Organization e-Library |publisher=World Meteorological Organization |access-date=18 February 2025}}</ref>
Global warming is very likely to reach 1.0 °C to 1.8 °C by the late 21st century under the very low GHG emissions scenario. In an intermediate scenario global warming would reach 2.1 °C to 3.5 °C, and 3.3 °C to 5.7 °C under the very high GHG emissions scenario.<ref name=":03" />{{rp|SPM-17}} These projections are based on climate models in combination with observations.<ref>Arias, P.A., N. Bellouin, E. Coppola, R.G. Jones, G. Krinner, J. Marotzke, V. Naik, M.D. Palmer, G.-K. Plattner, J. Rogelj, M. Rojas, J. Sillmann, T. Storelvmo, P.W. Thorne, B. Trewin, K. Achuta Rao, B. Adhikary, R.P. Allan, K. Armour, G. Bala, R. Barimalala, S. Berger, J.G. Canadell, C. Cassou, A. Cherchi, W. Collins, W.D. Collins, S.L. Connors, S. Corti, F. Cruz, F.J. Dentener, C. Dereczynski, A. Di Luca, A. Diongue Niang, F.J. Doblas-Reyes, A. Dosio, H. Douville, F. Engelbrecht, et al., 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf Technical Summary. 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] {{Webarchive|url=https://web.archive.org/web/20220721021347/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf|date=21 July 2022}} [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.</ref>{{rp|TS-30}}
=== Regional temperature changes === {{see also|Effects of climate change|Climate variability and change#Variability between regions}}
The changes in climate are not expected to be uniform across the Earth. In particular, land areas change more quickly than oceans, and northern high latitudes change more quickly than the tropics. There are three major ways in which global warming will make changes to regional climate: melting ice, changing the hydrological cycle (of evaporation and precipitation) and changing currents in the oceans.
== Temperature estimates from prior to 1850 == [[File:1781- GloSAT surface air temperature.svg |thumb |A December 2025 article published in the Copernicus Programme's ''Earth System Science Data'' presented a GloSAT global surface air temperature dataset based on marine air temperature observations rather than the sea surface temperature measurements typically used. GloSAT extended back to the 1780s, earlier than 1850 covered by previous datasets.<ref name=ESSD_Copernicus_20251215>GloSAT date from {{cite journal |author1=Morice, C. P., Berry, D. I., Cornes, R. C., Cowtan, K., Cropper, T., Hawkins, E., Kennedy, J. J., Osborn, T. J., Rayner, N. A., Recinos Rivas, B., Schurer, A. P., Taylor, M., Teleti, P. R., Wallis, E. J., Winn, J., and Kent, E. C. |title=An observational record of global gridded near-surface air temperature change over land and ocean from 1781 |journal=Earth System Science Data |date=15 December 2025 |volume=17 |issue=12 |pages=7079–7100 |doi=10.5194/essd-17-7079-2025 |doi-access=free |bibcode=2025ESSD...17.7079M }} ● HadCRUT data from {{cite web |title=Global temperature / Get the data / HadCRUT5 |url=https://climate.metoffice.cloud/temperature.html |publisher=Met Office (UK) |archive-url=https://web.archive.org/web/20250125193418/https://climate.metoffice.cloud/temperature.html |archive-date=25 January 2025 |date=2025 |url-status=live}}</ref>]] The global temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. There are numerous estimates of temperatures since the end of the Pleistocene glaciation, particularly during the current Holocene epoch. Some temperature information is available through geologic evidence, going back millions of years. More recently, information from ice cores covers the period from 800,000 years ago until now. A study of the paleoclimate covers the time period from 12,000 years ago. Tree rings and measurements from ice cores can give evidence about the global temperature from 1,000–2,000 years ago. The most detailed information exists since 1850, when methodical thermometer-based records began. Modifications on the Stevenson-type screen were made for uniform instrument measurements around 1880.<ref name=":1">NOAA National Centers for Environmental Information, Monthly Global Climate Report for Annual 2022, published online January 2023, Retrieved on July 25, 2023 from https://www.ncei.noaa.gov/access/monitoring/monthly-report/global/202213. </ref>
=== Tree rings and ice cores (from 1,000–2,000 years before present) === {{Further|Temperature record of the last 2,000 years}} Proxy measurements can be used to reconstruct the temperature record before the historical period. Quantities such as tree ring widths, coral growth, isotope variations in ice cores, ocean and lake sediments, cave deposits, fossils, ice cores, borehole temperatures, and glacier length records are correlated with climatic fluctuations. From these, proxy temperature reconstructions of the last 2000 years have been performed for the northern hemisphere, and over shorter time scales for the southern hemisphere and tropics.<ref>{{cite book |url=http://www.grida.no/publications/other/ipcc%5Ftar/?src=/climate/ipcc_tar/wg1/figspm-1.htm |title=Summary for policy makers |publisher=Intergovernmental Panel on Climate Change |year=2001 |editor=J.T. Houghton |series=IPCC Third Assessment Report – Climate Change 2001 Contribution of Working Group I |contribution=Figure 1: Variations of the Earth's surface temperature over the last 140 years and the last millennium. |access-date=May 12, 2011 |display-editors=etal |archive-url=https://web.archive.org/web/20161113140602/http://www.grida.no/publications/other/ipcc_tar/?src=%2Fclimate%2Fipcc_tar%2Fwg1%2Ffigspm-1.htm |archive-date=November 13, 2016 |url-status=dead}}</ref><ref>{{cite book |url=http://www.grida.no/publications/other/ipcc%5Ftar/?src=/climate/ipcc_tar/wg1/069.htm#fig220 |title=Chapter 2. Observed climate variability and change |publisher=Intergovernmental Panel on Climate Change |year=2001 |editor=J.T. Houghton |series=Climate Change 2001: Working Group I The Scientific Basis |access-date=May 12, 2011 |display-editors=etal |archive-url=https://web.archive.org/web/20160309180529/http://www.grida.no/publications/other/ipcc_tar/?src=%2Fclimate%2Fipcc_tar%2Fwg1%2F069.htm#fig220 |archive-date=March 9, 2016 |url-status=dead}}</ref><ref name="National Research Council 2006">National Research Council (U.S.). Committee on Surface Temperature Reconstructions for the Last 2,000 Years ''Surface temperature reconstructions for the last 2,000 years'' (2006), National Academies Press {{ISBN|978-0-309-10225-4}}</ref>
Geographic coverage by these proxies is necessarily sparse, and various proxies are more sensitive to faster fluctuations. For example, tree rings, ice cores, and corals generally show variation on an annual time scale, but borehole reconstructions rely on rates of thermal diffusion, and small scale fluctuations are washed out. Even the best proxy records contain far fewer observations than the worst periods of the observational record, and the spatial and temporal resolution of the resulting reconstructions is correspondingly coarse. Connecting the measured proxies to the variable of interest, such as temperature or rainfall, is highly non-trivial. Data sets from multiple complementary proxies covering overlapping time periods and areas are reconciled to produce the final reconstructions.<ref name="National Research Council 2006" /><ref>{{cite journal |last1=Mann |first1=Michael E. |last2=Zhang |first2=Zhihua |last3=Hughes |first3=Malcolm K. |last4=Bradley |first4=Raymond S. |last5=Miller |first5=Sonya K. |last6=Rutherford |first6=Scott |last7=Ni |first7=Fenbiao |year=2008 |title=Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia |journal=Proceedings of the National Academy of Sciences |volume=105 |issue=36 |pages=13252–13257 |bibcode=2008PNAS..10513252M |doi=10.1073/pnas.0805721105 |pmc=2527990 |pmid=18765811 |doi-access=free}}</ref>[[File:2000+ year global temperature including Medieval Warm Period and Little Ice Age - Ed Hawkins.svg|thumb|upright=1.5|Temperature record of the last 2,000 years (the so-called Medieval Warm Period and Little Ice Age were not planet-wide phenomena)]]Proxy reconstructions extending back 2,000 years have been performed, but reconstructions for the last 1,000 years are supported by more and higher quality independent data sets. These reconstructions indicate:<ref name="National Research Council 2006" /> * global mean surface temperatures over the last 25 years have been higher than any comparable period since AD 1600, and probably since AD 900 * there was a Little Ice Age centered on AD 1700 * there was a Medieval Warm Period centered on AD 1000, but this was not a global phenomenon.<ref>{{Cite web |date=2019-07-24 |title=The Climate Epochs That Weren't |url=https://news.climate.columbia.edu/2019/07/24/climate-epochs-that-werent/ |access-date=2021-11-27 |website=State of the Planet |language=en}}</ref>
==== Indirect historical proxies ====
As well as natural, numerical proxies (tree-ring widths, for example) there exist records from the human historical period that can be used to infer climate variations, including: reports of frost fairs on the Thames; records of good and bad harvests; dates of spring blossom or lambing; extraordinary falls of rain and snow; and unusual floods or droughts.<ref>O.Muszkat, ''The outline of the problems and methods used for research of the history of the climate in the Middle Ages'', (in polish), Przemyśl 2014, {{ISSN|1232-7263}}</ref> Such records can be used to infer historical temperatures, but generally in a more qualitative manner than natural proxies.{{fact|date=August 2024}}
Recent evidence suggests that a sudden and short-lived climatic shift between 2200 and 2100 BCE occurred in the region between Tibet and Iceland, with some evidence suggesting a global change. The result was a cooling and reduction in precipitation. This is believed to be a primary cause of the collapse of the Old Kingdom of Egypt.<ref>[https://www.bbc.co.uk/history/ancient/egyptians/apocalypse_egypt_01.shtml The Fall of the Egyptian Old Kingdom] Hassan, Fekri BBC June 2001</ref>
=== Paleoclimate (from 12,000 years before present) ===
240px|thumb|Plot showing the variations, and relative stability, of climate during the last 12000 years. {{main|Paleoclimatology}}
Many estimates of past temperatures have been made over Earth's history. The field of paleoclimatology includes ancient temperature records. As the present article is oriented toward recent temperatures, there is a focus here on events since the retreat of the Pleistocene glaciers. The 10,000 years of the Holocene epoch covers most of this period, since the end of the Northern Hemisphere's Younger Dryas millennium-long cooling. The Holocene Climatic Optimum was generally warmer than the 20th century, but numerous regional variations have been noted since the start of the Younger Dryas.
=== Ice cores (from 800,000 years before present) === thumb|400px|Temperature estimates over 800,000 years of the EPICA ice cores in Antarctica. Temperatures are in Celsius relative to the average of the most recent 1,000 years; year 0 is 1950.{{Unreferenced section|date=August 2024}} Even longer term records exist for few sites: the recent Antarctic EPICA core reaches 800 kyr; many others reach more than 100,000 years. The EPICA core covers eight glacial/interglacial cycles. The NGRIP core from Greenland stretches back more than 100 kyr, with 5 kyr in the Eemian interglacial. Whilst the large-scale signals from the cores are clear, there are problems interpreting the detail, and connecting the isotopic variation to the temperature signal.{{fact|date=August 2024}}<ref>{{Cite web|url=http://www.climatedata.info/proxies/ice-cores/index.html|title=Ice Core Data for Antarctic and Arctic|website=Climate Data Information}}</ref>
==== Ice core locations ==== thumb|400px|Ice core data location<ref>{{Cite web |last=GIS |title=Paleoclimatology Data |url=https://www.ncei.noaa.gov/maps/ |access-date=2024-08-12 |website=National Centers for Environmental Information (NCEI) |date=14 December 2018 |language=en}}</ref> The World Paleoclimatology Data Center (WDC) maintains the ice core data files of glaciers and ice caps in polar and low latitude mountains all over the world.
==== Ice core records from Greenland ==== As a paleothermometry, the ice core in central Greenland showed consistent records on the surface-temperature changes.<ref name=":12">{{Cite journal |last=Alley |first=R. B. |date=2000-02-15 |title=Ice-core evidence of abrupt climate changes |journal=Proceedings of the National Academy of Sciences |volume=97 |issue=4 |pages=1331–1334 |bibcode=2000PNAS...97.1331A |doi=10.1073/pnas.97.4.1331 |issn=0027-8424 |pmc=34297 |pmid=10677460 |doi-access=free}}</ref> According to the records, changes in global climate are rapid and widespread. Warming phase only needs simple steps, however, the cooling process requires more prerequisites and bases.<ref>{{Cite journal |last1=Severinghaus |first1=Jeffrey P. |last2=Sowers |first2=Todd |last3=Brook |first3=Edward J. |last4=Alley |first4=Richard B. |last5=Bender |first5=Michael L. |date=January 1998 |title=Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice |url=http://dx.doi.org/10.1038/34346 |journal=Nature |volume=391 |issue=6663 |pages=141–146 |bibcode=1998Natur.391..141S |doi=10.1038/34346 |issn=0028-0836 |s2cid=4426618|url-access=subscription }}</ref> Also, Greenland has the clearest record of abrupt climate changes in the ice core, and there are no other records that can show the same time interval with equally high time resolution.<ref name=":12" />
When scientists explored the trapped gas in the ice core bubbles, they found that the methane concentration in Greenland ice core is significantly higher than that in Antarctic samples of similar age, the records of changes of concentration difference between Greenland and Antarctic reveal variation of latitudinal distribution of methane sources.<ref>{{Citation |last1=Webb |first1=Robert S. |title=Preface |date=1999 |url=http://dx.doi.org/10.1029/gm112p0vii |work=Mechanisms of Global Climate Change at Millennial Time Scales |volume=112 |pages=vii–viii |place=Washington, D. C. |publisher=American Geophysical Union |bibcode=1999GMS...112D...7W |doi=10.1029/gm112p0vii |isbn=0-87590-095-X |access-date=2021-04-18 |last2=Clark |first2=Peter U. |last3=Keigwin |first3=Lloyd D.|doi-broken-date=12 July 2025 |url-access=subscription }}</ref> Increase in methane concentration shown by Greenland ice core records implies that the global wetland area has changed greatly over past years.<ref>{{Cite journal |last1=Chappellaz |first1=Jérôme |last2=Brook |first2=Ed |last3=Blunier |first3=Thomas |last4=Malaizé |first4=Bruno |date=1997-11-30 |title=CH4and δ18O of O2records from Antarctic and Greenland ice: A clue for stratigraphic disturbance in the bottom part of the Greenland Ice Core Project and the Greenland Ice Sheet Project 2 ice cores |journal=Journal of Geophysical Research: Oceans |volume=102 |issue=C12 |pages=26547–26557 |bibcode=1997JGR...10226547C |doi=10.1029/97jc00164 |issn=0148-0227 |doi-access=free}}</ref> As a component of greenhouse gases, methane plays an important role in global warming. The variation of methane from Greenland records makes a unique contribution for global temperature records undoubtedly.{{Cn|date=August 2024}}
==== Ice core records from Antarctica ==== The Antarctic ice sheet originated in the late Eocene, the drilling has restored a record of 800,000 years in Dome Concordia, and it is the longest available ice core in Antarctica. In recent years, more and more new studies have provided older but discrete records.<ref>{{Cite journal |last1=Higgins |first1=John A. |last2=Kurbatov |first2=Andrei V. |last3=Spaulding |first3=Nicole E. |last4=Brook |first4=Ed |last5=Introne |first5=Douglas S. |last6=Chimiak |first6=Laura M. |last7=Yan |first7=Yuzhen |last8=Mayewski |first8=Paul A. |last9=Bender |first9=Michael L. |date=2015-05-11 |title=Atmospheric composition 1 million years ago from blue ice in the Allan Hills, Antarctica |journal=Proceedings of the National Academy of Sciences |volume=112 |issue=22 |pages=6887–6891 |bibcode=2015PNAS..112.6887H |doi=10.1073/pnas.1420232112 |issn=0027-8424 |pmc=4460481 |pmid=25964367 |doi-access=free}}</ref> Due to the uniqueness of the Antarctic ice sheet, the Antarctic ice core not only records the global temperature changes, but also contains huge quantities of information about the global biogeochemical cycles, climate dynamics and abrupt changes in global climate.<ref>{{Cite journal |last1=Brook |first1=Edward J. |last2=Buizert |first2=Christo |date=June 2018 |title=Antarctic and global climate history viewed from ice cores |url=http://dx.doi.org/10.1038/s41586-018-0172-5 |journal=Nature |volume=558 |issue=7709 |pages=200–208 |bibcode=2018Natur.558..200B |doi=10.1038/s41586-018-0172-5 |issn=0028-0836 |pmid=29899479 |s2cid=49191229|url-access=subscription }}</ref>
By comparing with current climate records, the ice core records in Antarctica further confirm that polar amplification.<ref>{{Cite journal |last1=Cuffey |first1=Kurt M. |last2=Clow |first2=Gary D. |last3=Steig |first3=Eric J. |last4=Buizert |first4=Christo |last5=Fudge |first5=T. J. |last6=Koutnik |first6=Michelle |last7=Waddington |first7=Edwin D. |last8=Alley |first8=Richard B. |last9=Severinghaus |first9=Jeffrey P. |date=2016-11-28 |title=Deglacial temperature history of West Antarctica |journal=Proceedings of the National Academy of Sciences |volume=113 |issue=50 |pages=14249–14254 |bibcode=2016PNAS..11314249C |doi=10.1073/pnas.1609132113 |issn=0027-8424 |pmc=5167188 |pmid=27911783 |doi-access=free}}</ref> Although Antarctica is covered by the ice core records, the density is rather low considering the area of Antarctica. Exploring more drilling stations is the primary goal for current research institutions.{{Cn|date=August 2024}}
==== Ice core records from low-latitude regions ==== The ice core records from low-latitude regions are not as common as records from polar regions, however, these records still provide much useful information for scientists. Ice cores in low-latitude regions are usually from high altitude areas. The Guliya record is the longest record from low-latitude, high altitude regions, which spans over 700,000 years.<ref name=":02">{{Citation |last=Thompson |first=L. G. |title=High Altitude, Mid- and Low-Latitude Ice Core Records: Implications for Our Future |work=Earth Paleoenvironments: Records Preserved in Mid- and Low-Latitude Glaciers |volume=9 |pages=3–15 |year=2004 |series=Developments in Paleoenvironmental Research |place=Dordrecht |publisher=Kluwer Academic Publishers |doi=10.1007/1-4020-2146-1_1 |isbn=1-4020-2145-3 |doi-access=free }}</ref> According to these records, scientists found the evidence which can prove the Last Glacial Maximum (LGM) was colder in the tropics and subtropics than previously believed.<ref>{{Cite journal |last1=Thompson |first1=L. G. |last2=Mosley-Thompson |first2=E. |last3=Davis |first3=M. E. |last4=Lin |first4=P. -N. |last5=Henderson |first5=K. A. |last6=Cole-Dai |first6=J. |last7=Bolzan |first7=J. F. |last8=Liu |first8=K. -b. |date=1995-07-07 |title=Late Glacial Stage and Holocene Tropical Ice Core Records from Huascaran, Peru |url=http://dx.doi.org/10.1126/science.269.5220.46 |journal=Science |volume=269 |issue=5220 |pages=46–50 |bibcode=1995Sci...269...46T |doi=10.1126/science.269.5220.46 |issn=0036-8075 |pmid=17787701 |s2cid=25940751|url-access=subscription }}</ref> Also, the records from low-latitude regions helped scientists confirm that the 20th century was the warmest period in the last 1000 years.<ref name=":02" />
=== Geologic evidence (millions of years) === [[File:Five Myr Climate Change.png|thumb|400px|Reconstruction of the past 5 million years of climate history, based on oxygen isotope fractionation in deep sea sediment cores (serving as a proxy for the total global mass of glacial ice sheets), fitted to a model of orbital forcing (Lisiecki and Raymo 2005)<ref>{{cite journal |last=Lisiecki |first=Lorraine E. |author2=Raymo, Maureen E. |date=January 2005 |title=A Pliocene-Pleistocene stack of 57 globally distributed benthic d<sup>18</sup>O records |url=http://lorraine-lisiecki.com/LisieckiRaymo2005.pdf |journal=Paleoceanography |volume=20 |issue=1 |pages=PA1003 |bibcode=2005PalOc..20.1003L |doi=10.1029/2004PA001071 |s2cid=12788441 |hdl=2027.42/149224}}
:* Supplement: {{cite journal |last=Lisiecki |first=L. E. |author2=Raymo, M. E. |year=2005 |title=Pliocene-Pleistocene stack of globally distributed benthic stable oxygen isotope records |journal=Pangaea |doi=10.1594/PANGAEA.704257}} </ref> and to the temperature scale derived from Vostok ice cores following Petit et al. (1999).<ref>{{cite journal |last=Petit |first=J. R. |author2=Jouzel, J. |author3=Raynaud, D. |author4=Barkov, N. I. |author5=Barnola, J. M. |author6=Basile, I. |author7=Bender, M. |author8=Chappellaz, J. |author9=Davis, J. |author10=Delaygue, G. |author11=Delmotte, M. |author12=Kotlyakov, V. M. |author13=Legrand, M. |author14=Lipenkov, V. |author15=Lorius, C. |year=1999 |title=Climate and Atmospheric History of the Past 420,000 years from the Vostok Ice Core, Antarctica |url=http://www.escholarship.org/uc/item/7rx4413n |journal=Nature |volume=399 |issue=6735 |pages=429–436 |bibcode=1999Natur.399..429P |doi=10.1038/20859 |s2cid=204993577 |author16=Pépin, L. |author17=Ritz, C. |author18=Saltzman, E. |author19=Stievenard, M.}}</ref> ]]
{{main|Geologic temperature record}}
On longer time scales, sediment cores show that the cycles of glacials and interglacials are part of a deepening phase within a prolonged ice age that began with the glaciation of Antarctica approximately 40 million years ago. This deepening phase, and the accompanying cycles, largely began approximately 3 million years ago with the growth of continental ice sheets in the Northern Hemisphere. Gradual changes in Earth's climate of this kind have been frequent during the existence of planet Earth. Some of them are attributed to changes in the configuration of continents and oceans due to continental drift.{{citation needed|date=May 2022}}
== See also == {{portal|border=no|Climate change|Environment|Ecology|World}} *{{annotated link|Atmospheric reanalysis}} * {{annotated link|Carbon dioxide in Earth's atmosphere}} * {{annotated link|Climate variability and change}} * {{annotated link|Heat wave}} * {{annotated link|Dendroclimatology}} * {{annotated link|Temperature anomaly}} *{{annotated link|Temperature record of the last 2,000 years}} * {{annotated link|Warming stripes}} * {{annotated link|Ocean heat content}}
== References == {{reflist}}
==External links==
* [https://web.archive.org/web/20051104005338/http://www.met-office.gov.uk/research/hadleycentre/obsdata/globaltemperature.html Hadley Centre: Global temperature data] * [http://data.giss.nasa.gov/gistemp/ NASA's Goddard Institute for Space Studies] (GISS) — Global Temperature Trends. * [http://data.giss.nasa.gov/gistemp/ GISS Surface Temperature Analysis (GISTEMP)] * [http://www.cru.uea.ac.uk/cru/data/crutem/ge/ Google Earth interface for CRUTEM4 land temperature data] {{climate change}} * [https://www.theworldcounts.com/embeds/counters/21?background_color=white&color=black&font_family=%22Helvetica+Neue%22%2C+Arial%2C+sans-serif&font_size=14]
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