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What evidence do scientists use to reconstruct climates before instrumental records began?

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World map with continents shaded in colors representing climate zones, from warm reds and yellows near the equator to cool blues and whites at the poles. — Climate Even in our warming world, there will be some chilly evenings.

To reconstruct climates before the existence of instrumental records, scientists rely on "proxy" evidence—natural archives that indirectly record past climatic conditions. Because these records are often fragmentary, researchers frequently use multiple lines of evidence to cross-check their findings.12

Natural Archives

Scientists analyze various biological and geological processes that respond to climate:
* Dendrochronology: By analyzing tree ring patterns, researchers can infer past temperatures and precipitation levels, sometimes extending back thousands of years.13
* Ice Cores: Drilled from glaciers and ice sheets, these cores contain trapped air bubbles and isotopic ratios (such as oxygen and hydrogen) that reveal ancient atmospheric composition and temperature fluctuations.14
* Sediment and Geochemical Indicators: Cores taken from lakes, bogs, and oceans provide long-term data on past environmental conditions.12
* Biological Remains: Fossil records of plant and animal distributions, as well as pollen data, help map historical climate shifts.12
* Geological Features: Researchers examine stalagmites, glacial moraines, and geological strata to interpret past climates.12

Historical Documents

For the last few hundred years, scientists also utilize written records, such as ship logs, diaries, church and court records, and tax rolls, which can document specific events like droughts, floods, and monsoons.1