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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 [1] and enable scientists to reconstruct the climatic conditions over a longer fraction of the Earth's history.
Smith et al. 2006 "Reconstructing hemispheric-scale climates from multiple stalagmite records". Lee, Zwiers & Tsao 2008 "Evaluation of proxy-based millennial reconstruction methods". Huang, Pollack & Shen 2008 "A late Quaternary climate reconstruction based on borehole heat flux data, borehole temperature data, and the instrumental record"
Paleoclimatology uses a variety of proxy methods from Earth and life sciences to obtain data previously preserved within rocks, sediments, boreholes, ice sheets, tree rings, corals, shells, and microfossils. Combined with techniques to date the proxies, the paleoclimate records are used to determine the past states of Earth's atmosphere.
An important distinction is between so-called 'multi-proxy' reconstructions, which attempt to obtain a global temperature reconstruction by using multiple proxy records distributed over the globe and more regional reconstructions. Usually, the various proxy records are combined arithmetically, in some weighted average.
Global paleoclimate indicators are the proxies sensitive to global paleoclimatic environment changes. They are mostly derived from marine sediments . Paleoclimate indicators derived from terrestrial sediments, on the other hand, are commonly influenced by local tectonic movements and paleogeographic variations.
Projected global 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 ...
Hockey stick graphs present the global or hemispherical mean temperature record of the past 500 to 2000 years as shown by quantitative climate reconstructions based on climate proxy records. These reconstructions have consistently shown a slow long term cooling trend changing into relatively rapid warming in the 20th century, with the ...
Their research used paleoclimate proxy data from Bradley's previous work and methods Mann had developed with Park, to find oscillations in the longer proxy records. "Global Interdecadal and Century-Scale Climate Oscillations During the Past Five Centuries" was published by Nature in November 1995. [16]