Paleoclimate

Paleoclimate refers to the climate of the Earth in the geological past before reliable instrumental records. It covers timescales from millions of years to thousands of years ago and is reconstructed from natural archives known as proxies.

Proxies include ice cores (which preserve ancient air and isotopic information), marine and lake sediments, fossil corals, pollen and plant remains, tree rings, speleothems in caves, loess deposits, and fossilized organisms. Dating and correlation rely on radiometric methods, biostratigraphy, magnetostratigraphy, varve counting, and other techniques. Isotope ratios, especially oxygen-18 to oxygen-16 in calcite or water, yield estimates of past temperatures and ice volume; carbon isotopes and trace elements inform on the carbon cycle and past productivity.

Paleoclimate is driven by multiple factors and feedbacks. Orbital variations of Earth’s tilt, eccentricity, and precession (Milankovitch cycles) modulate insolation and influence glacial cycles. Greenhouse gas concentrations, volcanic activity, and tectonic movements shift baseline climates over longer timescales. Feedbacks such as changes in ice reflectivity (albedo), vegetation, and atmospheric chemistry amplify or dampen responses.

Major intervals include warm, low-ice periods such as the Cretaceous and Eocene; cooling and the growth of continental ice sheets during the Oligocene to Pleistocene; pronounced glacial–interglacial cycles in the Pleistocene; and the relatively warm and stable Holocene, punctuated by events like the Medieval Climate Anomaly and the Little Ice Age. The end of the last Ice Age, about 11,700 years ago, marks the start of the current interglacial.

Paleoclimate research helps quantify natural climate variability, calibrate models, constrain climate sensitivity, and provide context for modern anthropogenic change.