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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.
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.
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.
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"
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.
The report provided a summary and an overview, followed by 11 technical chapters covering the instrumental and proxy records, statistical procedures, paleoclimate models, and the synthesis of large scale temperature reconstructions with an assessment of the "strengths, limitations, and prospects for improvement" in techniques used. [27]
Paleoclimatology (the study of past climates) uses proxy data in order to relate elements collected in modern-day samples to climatic conditions of the past. In paleolimnology, proxy data refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological measurements.
CLIMAP has been a cornerstone of paleoclimate research and remains the most used sea surface temperature reconstruction of the global ocean during the last glacial maximum (Yin and Battisti 2001), but it has also been persistently controversial. CLIMAP resulted in estimates of global cooling of only 3.0 ± 0.6 °C relative to the modern day ...