Editing Sea surface temperature (section)

===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>]]