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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.
In geochemistry, paleoclimatology and paleoceanography δ 18 O or delta-O-18 is a measure of the deviation in ratio of stable isotopes oxygen-18 (18 O) and oxygen-16 (16 O). It is commonly used as a measure of the temperature of precipitation, as a measure of groundwater/mineral interactions, and as an indicator of processes that show isotopic fractionation, like methanogenesis.
The temperature on land rose by 1.59 °C while over the ocean it rose by 0.88 °C. [3] In 2020 the temperature was 1.2 °C above the pre-industrial era. [4] In September 2023 the temperature was 1.75 °C above pre-industrial level and during the entire year of 2023 is expected to be 1.4 °C above it. [5]
Changes in the layering thickness can be used to determine changes in precipitation or temperature. Oxygen-18 quantity changes (δ 18 O) in ice layers represent changes in average ocean surface temperature. Water molecules containing the heavier O-18 evaporate at a higher temperature than water molecules containing the normal Oxygen-16 isotope ...
To balance dense networks of tree-ring proxies against sparse proxy temperature records such as lake sediments, ice cores or corals, MBH 1998 (and 1999) used principal component analysis (PCA) to find the leading patterns of variation (PC1, PC2, PC3 etc.), with an objective method establish how many significant principal components should be ...
The instrumental temperature record is a record of temperatures within Earth's climate based on direct measurement of air temperature and ocean temperature. Instrumental temperature records do not use indirect reconstructions using climate proxy data such as from tree rings and marine sediments .
Equilibrium isotope fractionation is the partial separation of isotopes between two or more substances in chemical equilibrium. Equilibrium fractionation is strongest at low temperatures, and (along with kinetic isotope effects) forms the basis of the most widely used isotopic paleothermometers (or climate proxies): D/H and 18 O/ 16 O records from ice cores, and 18 O/ 16 O records from calcium ...
The oldest TEX 86 record is from the middle Jurassic (~160Ma) and indicates relatively warm sea surface temperatures. [15] TEX 86 has been used to reconstruct temperature throughout the Cenozoic era (65–0 Ma) [16] [17] and is useful when other SST proxies are diagenetically altered (e.g. planktonic foraminifera [18]) or absent (e.g. alkenones ...