Paleoclimatology

Paleoclimatology reconstructs Earth’s climates before instrumental records by interpreting natural archives such as ice cores, sediments, and tree rings.

Climate proxy: A measurable feature of a natural archive that indirectly records past environmental conditions. Proxy records provide paleoclimatology’s evidence when direct measurements do not exist.
Ice core: A cylindrical sample of ice containing layered snowfall, trapped gases, and particles accumulated over time. Ice layers and trapped air preserve temperature clues and samples of ancient atmospheres.
Last Glacial Maximum: The interval when global ice sheets reached their greatest extent during the last glacial period, about 26,000 to 19,000 years ago. Its global temperature and ice extent are reconstructed from many independent archives.
Cesare Emiliani: An Italian-American geologist who pioneered the use of oxygen isotopes in foraminifera to study past ocean temperatures. His isotope records helped establish marine sediments as a source of climate history.
Proxy calibration: The process of relating a climate proxy to measured environmental conditions over a period of overlap. Calibration tests whether an archive’s signal reliably tracks the climate variable being reconstructed.
Stable isotope analysis: A method that uses variations in stable-isotope ratios to infer environmental conditions or processes. Isotope ratios in archives can reveal past temperatures and shifts in water sources.
Marine sediment core: A cylindrical sample of seafloor sediment that preserves successive layers of deposited material. Marine microfossils and sediment chemistry record changes in ocean and climate conditions.
Younger Dryas: A roughly 1,200-year return to near-glacial conditions in the North Atlantic region near the end of the last ice age. Its abrupt cooling is a classic test of how quickly climate can shift.
Willie Dansgaard: A Danish paleoclimatologist who used stable isotopes in ice to investigate past climate and atmospheric circulation. His Greenland ice-core work identified abrupt climate shifts later named for him.
Proxy seasonality: The tendency of a proxy to record climate conditions from particular seasons rather than the whole year. Seasonal bias can make a proxy’s apparent annual climate signal misleading.

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