paleotemperature

Paleotemperature refers to the estimation of Earth's past temperatures, including surface air temperatures, sea surface temperatures, and near-surface land temperatures, inferred from indirect evidence preserved in geological and archival records. It covers timescales from millions of years ago to recent centuries and is key to understanding climate dynamics.

Researchers obtain paleotemperature through climate proxies that respond to temperature changes. Common marine proxies include oxygen isotope ratios (O-18/O-16) in carbonate shells and Mg/Ca ratios in foraminifera and other shells, as well as alkenone unsaturation indices. Terrestrial proxies include leaf stomatal density and index, cellulose and wood isotopes, and soil and borehole temperature profiles; stalagmites give speleothem isotopic records. Ice cores yield direct quantitative temperature estimates in higher latitudes, while sedimentary facies and fossil assemblages help interpret warmth and cooling in other regions.

Reconstructions combine multiple proxies with calibration against modern observations and climate models. Notable periods include the Paleocene–Eocene Thermal Maximum around 56 million years ago, the Cretaceous greenhouse phases, the Neogene cooling trend, and Pleistocene glacial–interglacial cycles, including rapid transitions at terminations. The most recent interval shows reconstructed temperature changes during the last glacial maximum and the Holocene.

Uncertainties arise from diagenesis, proxy nonlinearity, regional biases, dating uncertainties, and the challenge of correlating proxies with exact temperatures. Regional warmth can coexist with global anomalies, and different proxies may trace different seasons or depths.

Paleotemperature data constrain models of climate sensitivity, help interpret carbon cycle dynamics, and contextualize current warming. They inform estimates of future change, while highlighting long-term variability and the potential for abrupt climate shifts.