Editing Sea surface temperature (section)

==Variations and changes==
[[File:ECCO2 Sea Surface Temperature and Flows.ogv|thumb|Sea surface temperature and flows]]
===Local variations===
{{See also|Upwelling}}
The sea surface temperature (SST) has a [[Diurnal cycle|diurnal range]], just like the Earth's atmosphere above, though to a lesser degree due to its greater [[thermal inertia]].<ref>{{cite book|url=https://books.google.com/books?id=WdPg_1aTtr8C&pg=PA84|page=84|author=John Siegenthaler|title=Modern hydronic heating for residential and light commercial buildings|year=2003|publisher=Cengage Learning|isbn=978-0-7668-1637-4}}</ref> On calm days, the temperature can vary by {{convert|6|C-change|F-change|sigfig=1}}.<ref name="space"/> The temperature of the ocean at depth lags the Earth's atmosphere temperature by 15 days per {{convert|10|m|ft}}, which means for locations like the [[Aral Sea]], temperatures near its bottom reach a maximum in December and a minimum in May and June.<ref>{{cite book|url=https://books.google.com/books?id=Z-LxfJVFclgC&pg=PA27|title=Physical oceanography of the dying Aral Sea|author=Peter O. Zavialov|page=27|year=2005|isbn=978-3-540-22891-2|publisher=シュプリンガー・ジャパン株式会社}}</ref> Near the coastline, some offshore and longshore winds move the warm waters near the surface offshore, and replace them with cooler water from below in the process known as [[Ekman transport]]. This pattern generally increases nutrients for marine life in the region, and can have a profound effect in some regions where the bottom waters are particularly nutrient-rich.<ref>{{cite web | title =Envisat watches for La Niña | publisher =BNSC via the Internet Wayback Machine | date =2008-04-24 | url =http://www.bnsc.gov.uk/content.aspx?nid=5989 | access-date =2011-01-09 |archive-url = https://web.archive.org/web/20080424113710/http://www.bnsc.gov.uk/content.aspx?nid=5989 |archive-date = 2008-04-24}}</ref> Offshore of [[river delta]]s, freshwater flows over the top of the denser seawater, which allows it to heat faster due to limited vertical mixing.<ref>{{cite book|url=https://books.google.com/books?id=OeZ4e5MwRigC&pg=PA258|page=258|title=State and evolution of the Baltic Sea, 1952–2005: a detailed 50-year survey of meteorology and climate, physics, chemistry, biology, and marine environment|year=2008|publisher=John Wiley and Sons|isbn=978-0-471-97968-5|author1=Rainer Feistel |author2=Günther Nausch |author3=Norbert Wasmund}}</ref>  Remotely sensed SST can be used to detect the surface temperature signature due to [[tropical cyclone]]s. In general, an SST cooling is observed after the passing of a hurricane, primarily as the result of mixed layer deepening and surface heat losses.<ref name="NASA Cooling">{{cite web|author=Earth Observatory |url=http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17164 |title=Passing of Hurricanes Cools Entire Gulf |year=2005 |access-date=2006-04-26 |publisher=[[NASA|National Aeronautics and Space Administration]] |url-status=dead |archive-url=https://web.archive.org/web/20060930235454/http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17164 |archive-date=2006-09-30}}</ref> In the wake of several day long [[Mineral dust#Saharan dust|Saharan dust]] outbreaks across the adjacent northern Atlantic Ocean, sea surface temperatures are reduced 0.2 C to 0.4&nbsp;C (0.3 to 0.7&nbsp;F).<ref>{{cite book|url=https://books.google.com/books?id=b09YTtIW3f4C&pg=PA72|title=The Impact of Saharan Dust on the North Atlantic Circulation|author=Nidia Martínez Avellaneda|page=72|year=2010|publisher=GRIN Verlag|isbn=978-3-640-55639-7}}</ref> Other sources of short-term SST fluctuation include [[extratropical cyclone]]s, rapid influxes of [[glacier|glacial]] fresh water<ref>{{cite journal|last=Boyle|first=Edward A.|author2=Lloyd Keigwin |title=North Atlantic thermohaline circulation during the past 20,000 years linked to high-latitude surface temperature|journal=Nature|date=5 November 1987|volume=330|issue=6143|pages=35–40|url=http://www.whoi.edu/cms/files/Boyle(1987)Nature330_35_52423.pdf|access-date=10 February 2011|doi=10.1038/330035a0|bibcode = 1987Natur.330...35B |s2cid=4359752}}</ref> and concentrated [[phytoplankton]] blooms<ref>{{cite journal|last=Beaugrand|first=Grégory|author2=Keith M. Brander |author3=J. Alistair Lindley |author4=Sami Souissi |author5=Philip C. Reid |title=Plankton effect on cod recruitment in the North Sea|journal=Nature|date=11 December 2003|volume=426|pages=661–664|doi=10.1038/nature02164|issue=6967|pmid=14668864|bibcode = 2003Natur.426..661B |s2cid=4420759}}</ref> due to seasonal cycles or agricultural run-off.<ref>{{cite journal|last=Beman|first=J. Michael |author2=Kevin R. Arrigo |author3=Pamela A. Matson|title=Agricultural runoff fuels large phytoplankton blooms in vulnerable areas of the ocean|journal=Nature|date=10 March 2005|volume=434|pages=211–214|doi=10.1038/nature03370|issue=7030|pmid=15758999|bibcode = 2005Natur.434..211M |s2cid=2299664}}</ref>{{clarify|What effects do algal blooms have on SST?|date=January 2022}}

The tropical ocean has been warming faster than other regions since 1950, with the greatest rates of warming in the tropical Indian Ocean, western Pacific Ocean, and western boundary currents of the [[Subtropical gyre|subtropical gyres]].<ref name="AR6_WG1_Chapter9" /> However, the eastern Pacific Ocean, subtropical North Atlantic Ocean, and Southern Ocean have warmed more slowly than the global average or have experienced cooling since the 1950s.<ref name="AR6_WG1_Chapter9" />

====Atlantic Multidecadal Oscillation====
[[Ocean current]]s, such as the [[Atlantic multidecadal oscillation|Atlantic Multidecadal Oscillation]], can affect sea surface temperatures over several decades.<ref>{{Cite journal |last1=McCarthy |first1=Gerard D. |last2=Haigh |first2=Ivan D. |last3=Hirschi |first3=Joël J.-M. |last4=Grist |first4=Jeremy P. |last5=Smeed |first5=David A. |date=2015-05-28 |title=Ocean impact on decadal Atlantic climate variability revealed by sea-level observations |url=http://mural.maynoothuniversity.ie/12187/1/McCarthy_Ocean_2015.pdf |journal=Nature |volume=521 |issue=7553 |pages=508–510 |bibcode=2015Natur.521..508M |doi=10.1038/nature14491 |issn=1476-4687 |pmid=26017453 |s2cid=4399436}}</ref> The Atlantic Multidecadal Oscillation (AMO) is an important driver of North Atlantic SST and Northern Hemisphere climate, but the mechanisms controlling AMO variability remain poorly understood.<ref>{{Cite journal |last1=Knudsen |first1=Mads Faurschou |last2=Jacobsen |first2=Bo Holm |last3=Seidenkrantz |first3=Marit-Solveig |last4=Olsen |first4=Jesper |date=2014-02-25 |title=Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age |journal=Nature Communications |volume=5 |pages=3323 |bibcode=2014NatCo...5.3323K |doi=10.1038/ncomms4323 |issn=2041-1723 |pmc=3948066 |pmid=24567051}}</ref> Atmospheric internal variability, changes in ocean circulation, or anthropogenic drivers may control the multidecadal temperature variability associated with AMO.<ref>{{Cite journal |last1=Wills |first1=R.C. |last2=Armour |first2=K.C. |last3=Battisti |first3=D.S. |last4=Hartmann |first4=D.L. |date=2019 |title=Ocean–atmosphere dynamical coupling fundamental to the Atlantic multidecadal oscillation |journal=Journal of Climate |volume=32 |issue=1 |pages=251–272|doi=10.1175/JCLI-D-18-0269.1 |bibcode=2019JCli...32..251W |s2cid=85450306 |doi-access=free}}</ref> These changes in North Atlantic SST may influence winds in the subtropical North Pacific and produce warmer SSTs in the western Pacific Ocean.<ref>{{Cite journal |last1=Wu |first1=Baolan |last2=Lin |first2=Xiaopei |last3=Yu |first3=Lisan |date=17 February 2020 |title=North Pacific subtropical mode water is controlled by the Atlantic Multidecadal Variability |url=https://www.nature.com/articles/s41558-020-0692-5 |journal=Nature Climate Change |language=en |volume=10 |issue=3 |pages=238–243 |doi=10.1038/s41558-020-0692-5 |bibcode=2020NatCC..10..238W |s2cid=211138572 |issn=1758-6798}}</ref>[[File:Weeklysst.gif|thumb|right|Weekly average sea surface temperature in the ocean during the first week of February 2011, during a period of [[El Niño-Southern Oscillation#Effects of ENSO's cool phase (La Niña)|La Niña]].]]

===Regional variations===
[[File:1997 El Nino TOPEX.jpg|thumb|200px|right|The 1997 El Niño observed by [[TOPEX/Poseidon]]. The white areas off the tropical coasts of South and North America indicate the pool of warm water.<ref>{{cite web | url = http://www.jpl.nasa.gov/news/releases/97/elninoup.html | title =Independent NASA Satellite Measurements Confirm El Niño is Back and Strong | publisher = NASA/JPL}}</ref>]]
{{Main|El Niño-Southern Oscillation}}
El Niño is defined by prolonged differences in Pacific Ocean surface temperatures when compared with the average value. The accepted definition is a warming or cooling of at least 0.5&nbsp;°C (0.9&nbsp;°F) averaged over the east-central tropical Pacific Ocean. Typically, this anomaly happens at irregular intervals of 2–7 years and lasts nine months to two years.<ref>{{cite web|url=http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HOWOFTEN|title=ENSO FAQ: How often do El Niño and La Niña typically occur?|access-date=2009-07-26|date=2005-12-19|author=Climate Prediction Center|publisher=[[National Centers for Environmental Prediction]]|author-link=Climate Prediction Center|archive-url=https://web.archive.org/web/20090827143632/http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HOWOFTEN|archive-date=2009-08-27|url-status=dead}}</ref> The average period length is 5 years. When this warming or cooling occurs for only seven to nine months, it is classified as El Niño/La Niña "conditions"; when it occurs for more than that period, it is classified as El Niño/La Niña "episodes".<ref>{{cite web|url=http://www.ncdc.noaa.gov/oa/climate/research/enso/?year=2009&month=6&submitted=true|title=El Niño / Southern Oscillation (ENSO) June 2009|author=National Climatic Data Center|publisher=National Oceanic and Atmospheric Administration|date=June 2009|access-date=2009-07-26|author-link=National Climatic Data Center}}</ref>

The sign of an El Niño in the sea surface temperature pattern is when warm water spreads from the west Pacific and the [[Indian Ocean]] to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific. El Niño's warm rush of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the [[Humboldt Current]]. When El Niño conditions last for many months, extensive [[ocean warming]] and the reduction in Easterly Trade winds limits upwelling of cold nutrient-rich deep water and its economic impact to local fishing for an international market can be serious.<ref name="deadfish">{{cite web|url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/eln/home.rxml|title=El Niño|date=1998-04-28|access-date=2009-07-17|author=WW2010|publisher=University of Illinois at Urbana-Champaign}}</ref>

Among scientists, there is medium confidence that the tropical Pacific will transition to a mean pattern resembling that of El Niño on centennial time scale, but there is still high uncertainty in tropical Pacific SST projections because it is difficult to capture El Niño variability in climate models.<ref name="AR6_WG1_Chapter9" />[[File:Land vs Ocean Temperature.svg|thumb|upright=1.35|right|Surface air temperatures over land masses have been increasing faster than the sea surface temperature.<ref>Data from [https://web.archive.org/web/20200416074510/https://data.giss.nasa.gov/gistemp/graphs_v4/ NASA GISS].</ref>]]

=== Recent increase due to climate change ===
[[File:1880- Global average sea surface temperature - global warming.svg|thumb|upright=1.2|The global average sea surface temperature has been increasing since around 1900 (graph showing annual average and 5-year smoothed average, relative to the average value for the years 1951-1980).]]
{{Further|Effects of climate change on oceans#Rising ocean temperature}}
Overall, scientists project that all regions of the oceans will warm by 2050, but models disagree for SST changes expected in the subpolar North Atlantic, the equatorial Pacific, and the Southern Ocean.<ref name="AR6_WG1_Chapter9" /> The future global mean SST increase for the period 1995-2014 to 2081-2100 is 0.86&nbsp;°C under the most modest greenhouse gas emissions scenarios, and up to 2.89&nbsp;°C under the most severe emissions scenarios.<ref name="AR6_WG1_Chapter9" />

A study published in 2025 in ''[[Environmental Research Letters]]'' reported that global mean sea surface temperature increases had more than quadrupled, from 0.06{{nbsp}}K per decade during 1985–89 to 0.27{{nbsp}}K per decade for 2019–23.<ref name=EnvRschLtrs_20250128/> The researchers projected that the increase inferred over the past 40 years would likely be exceeded within the next 20 years.<ref name=EnvRschLtrs_20250128>{{cite journal |last1=Merchant |first1=Christopher J. |last2=Allan |first2=Richard P. |last3=Embury |first3=Owen |title=Quantifying the acceleration of multidecadal global sea surface warming driven by Earth's energy imbalance |journal=Environmental Research Letters |date=28 January 2025 |volume=20 |issue=2 |page=024037 |doi=10.1088/1748-9326/adaa8a|doi-access=free |bibcode=2025ERL....20b4037M }}</ref>