Editing Proxy (climate) (section)

{{short description|Preserved physical characteristics allowing reconstruction of past climatic conditions}}
{{About|climatic patterns |other uses|Proxy (disambiguation){{!}}Proxy}}
[[File:Temperature reconstruction last two millennia.svg|thumb|280x280px|Reconstructions of global temperature of the past 2000 years, using composite of different proxy methods]]
In the study of past climates ("[[paleoclimatology]]"), '''climate proxies''' are preserved physical characteristics of the past that stand in for direct meteorological measurements<ref>{{Cite web|url=https://www.ncdc.noaa.gov/news/what-are-proxy-data|title=What Are "Proxy" Data? {{!}} National Centers for Environmental Information (NCEI) formerly known as National Climatic Data Center (NCDC)|website=www.ncdc.noaa.gov|access-date=2017-10-12|archive-date=2020-03-08|archive-url=https://web.archive.org/web/20200308170642/https://www.ncdc.noaa.gov/news/what-are-proxy-data}}</ref> and enable scientists to reconstruct the [[Climate|climatic conditions]] over a longer fraction of the Earth's history. Reliable [[global surface temperature|global records of climate]] only began in the 1880s, and proxies provide the only means for scientists to determine climatic patterns before record-keeping began.

A large number of climate proxies have been studied from a variety of geologic contexts. Examples of proxies include stable isotope measurements from [[ice core]]s, growth rates in [[tree rings]], [[species composition]] of [[palynology|sub-fossil pollen]] in lake sediment or [[foraminifera]] in ocean sediments, temperature profiles of [[borehole]]s, and stable isotopes and mineralogy of [[coral]]s and carbonate [[speleothems]]. In each case, the proxy indicator has been influenced by a particular seasonal climate parameter (e.g., summer temperature or monsoon intensity) at the time in which they were laid down or grew. Interpretation of climate proxies requires a range of ancillary studies, including calibration of the sensitivity of the proxy to climate and cross-verification among proxy indicators.<ref>[http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/wg1/068.htm "Climate Change 2001: 2.3.2.1 Palaeoclimate proxy indicators."] {{webarchive|url=https://web.archive.org/web/20091204100159/http://www.grida.no/publications/other/ipcc_tar/?src=%2Fclimate%2Fipcc_tar%2Fwg1%2F068.htm |date=2009-12-04 }}</ref>

Proxies can be combined to produce temperature reconstructions longer than the [[instrumental temperature record]] and can inform discussions of [[global warming]] and climate history. The geographic distribution of proxy records, just like the instrumental record, is not at all uniform, with more records in the northern hemisphere.<ref name="unisci.com">[http://unisci.com/stories/20011/0227012.htm "Borehole Temperatures Confirm Global Warming Pattern."]</ref>