Editing Climate (section)

==Definition==
Climate ({{etymology|grc|κλίμα|inclination}}) is commonly defined as the weather averaged over a long period.<ref>{{cite encyclopedia|title = Climate|encyclopedia = Glossary of Meteorology|publisher = [[American Meteorological Society]]|url = http://amsglossary.allenpress.com/glossary/search?id=climate1|access-date = 2008-05-14|archive-date = 2011-07-07|archive-url = https://web.archive.org/web/20110707113544/http://amsglossary.allenpress.com/glossary/search?id=climate1|url-status = live}}</ref> The standard averaging period is 30&nbsp;years,<ref>{{cite web|url=http://www.metoffice.gov.uk/climate/uk/averages |title=Climate averages |access-date=2008-05-17 |publisher=Met Office |url-status=dead |archive-url=https://web.archive.org/web/20080706025040/http://www.metoffice.gov.uk/climate/uk/averages/ |archive-date=2008-07-06 }}</ref> but other periods may be used depending on the purpose. Climate also includes statistics other than the average, such as the magnitudes of day-to-day or year-to-year variations. The [[Intergovernmental Panel on Climate Change]] (IPCC) [[IPCC Third Assessment Report|2001]] glossary definition is as follows:

{{blockquote|"Climate in a narrow sense is usually defined as the "average weather", or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period ranging from months to thousands or millions of years. The classical period is 30&nbsp;years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system."<ref>[[Intergovernmental Panel on Climate Change]]. [http://www.grida.no/climate/ipcc_tar/wg1/518.htm Appendix I: Glossary.] {{webarchive|url=https://web.archive.org/web/20170126132100/http://www.grida.no/climate/ipcc_tar/wg1/518.htm |date=2017-01-26 }} Retrieved on 2007-06-01.</ref>}}

The [[World Meteorological Organization]] (WMO) describes "[[climate normal]]s" as "reference points used by [[Climatology|climatologists]] to compare current climatological trends to that of the past or what is considered typical. A climate normal is defined as the arithmetic average of a climate element (e.g. temperature) over a 30-year period. A 30-year period is used as it is long enough to filter out any interannual variation or anomalies such as [[El Niño–Southern Oscillation]], but also short enough to be able to show longer climatic trends."<ref name="WMO data">{{cite web|title=Climate Data and Data Related Products |website=[[World Meteorological Organization]] |url=https://www.wmo.int/pages/themes/climate/climate_data_and_products.php |archive-url=http://webarchive.loc.gov/all/20141001233620/https%3A//www.wmo.int/pages/themes/climate/climate_data_and_products.php |url-status=dead |archive-date=1 October 2014 |access-date=1 September 2015 }}</ref>

The WMO originated from the [[International Meteorological Organization]] which set up a technical commission for climatology in 1929. At its 1934 [[Wiesbaden]] meeting, the technical commission designated the thirty-year period from 1901 to 1930 as the reference time frame for climatological standard normals. In 1982, the WMO agreed to update climate normals, and these were subsequently completed on the basis of climate data from 1 January 1961 to 31 December 1990.<ref name="WMO history">{{cite web | title=Commission For Climatology: Over Eighty Years of Service |year=2011 | publisher=World Meteorological Organization | url=http://www.wmo.int/pages/prog/wcp/ccl/documents/WMO1079_web.pdf |pages=6, 8, 10, 21, 26 | access-date=1 September 2015|archive-url=https://web.archive.org/web/20150913033109/http://www.wmo.int/pages/prog/wcp/ccl/documents/WMO1079_web.pdf|archive-date=13 September 2015}}</ref> The 1961–1990 climate normals serve as the baseline reference period. The next set of climate normals to be published by WMO is from 1991 to 2010.<ref>{{Cite web |title=WMO Climatological Normals |publisher=[[World Meteorological Organization]] |url=https://community.wmo.int/wmo-climatological-normals |access-date=2022-08-21 |archive-date=2022-08-21 |archive-url=https://web.archive.org/web/20220821010013/https://community.wmo.int/wmo-climatological-normals |url-status=live }}</ref> Aside from collecting from the most common atmospheric variables (air temperature, pressure, precipitation and wind), other variables such as humidity, visibility, cloud amount, solar radiation, soil temperature, pan evaporation rate, days with thunder and days with hail are also collected to measure change in climate conditions.<ref>{{Cite book |date=2017 |title=WMO Guidelines on the Calculation of Climate Normals |url=https://library.wmo.int/doc_num.php?explnum_id=4166 |access-date=2022-08-20 |publisher=World Meteorological Organization |format=PDF |isbn=978-92-63-11203-3 |archive-date=2022-08-08 |archive-url=https://web.archive.org/web/20220808132316/https://library.wmo.int/doc_num.php?explnum_id=4166 |url-status=live }}</ref>

The difference between climate and weather is usefully summarized by the popular phrase "Climate is what you expect, weather is what you get."<ref>National Weather Service Office Tucson, Arizona. [http://www.wrh.noaa.gov/twc/ Main page.] {{Webarchive|url=https://web.archive.org/web/20170312090813/http://www.wrh.noaa.gov/twc/ |date=2017-03-12 }} Retrieved on 2007-06-01.</ref> Over [[history|historical]] time spans, there are a number of nearly constant variables that determine climate, including [[latitude]], altitude, proportion of land to water, and proximity to oceans and mountains. All of these variables change only over periods of millions of years due to processes such as [[plate tectonics]]. Other climate determinants are more dynamic: the [[thermohaline circulation]] of the ocean leads to a 5&nbsp;°C (9&nbsp;°F) warming of the northern Atlantic Ocean compared to other ocean basins.<ref>{{cite web |first=Stefan |last=Rahmstorf |url=http://www.pik-potsdam.de/~stefan/thc_fact_sheet.html |title=The Thermohaline Ocean Circulation: A Brief Fact Sheet |publisher=Potsdam Institute for Climate Impact Research |archive-url=https://web.archive.org/web/20130327151821/http://www.pik-potsdam.de/~stefan/thc_fact_sheet.html |archive-date=2013-03-27 |url-status=live |access-date=2008-05-02}}</ref> Other [[ocean current]]s redistribute heat between land and water on a more regional scale. The density and type of vegetation coverage affects solar heat absorption,<ref>{{cite web |first1=Gertjan |last1=de Werk |first2=Karel |last2=Mulder |url=http://www.enhr2007rotterdam.nl/documents/W15_paper_DeWerk_Mulder.pdf |url-status=dead |title=Heat Absorption Cooling For Sustainable Air Conditioning of Households |series=Sustainable Urban Areas Rotterdam |date=2007 |archive-url=https://web.archive.org/web/20080527223539/http://www.enhr2007rotterdam.nl/documents/W15_paper_DeWerk_Mulder.pdf |archive-date=2008-05-27 |access-date=2008-05-02}}</ref> water retention, and rainfall on a regional level. Alterations in the quantity of atmospheric [[greenhouse gas]]es (particularly [[carbon dioxide]] and [[methane]]) determines the amount of solar energy retained by the planet, leading to [[global warming]] or [[global cooling]]. The variables which determine climate are numerous and the interactions complex, but there is general agreement that the broad outlines are understood, at least insofar as the determinants of historical climate change are concerned.<ref>[https://www.un.org/en/climatechange/what-is-climate-change What Is Climate Change?]</ref><ref name=Ledley1999>{{cite journal|author = Ledley, T.S.|year = 1999|title = Climate change and greenhouse gases|journal = [[Eos (journal)|EOS]]|volume = 80|issue = 39|page = 453|doi = 10.1029/99EO00325|last2 = Sundquist|first2 = E. T.|last3 = Schwartz|first3 = S. E.|last4 = Hall|first4 = D. K.|last5 = Fellows|first5 = J. D.|last6 = Killeen|first6 = T. L.|bibcode = 1999EOSTr..80Q.453L|hdl = 2060/19990109667|doi-access = free|hdl-access = free}}</ref>