The isotopic fingerprints of precipitation can be locked into stable historical archives, such as glaciers and polar ice, ocean and lake sediments, tree rings and ancient groundwater. These paleo-climatic archives can be used to reconstruct past climatic conditions and document environmental changes over centuries and millennia.
To age-date the paleo-climatic archives, several radioactive isotopes can be used, whereas stable isotopes of oxygen and hydrogen are the key tools to reconstruct past temperature and environmental conditions. Climate researchers and modelling experts have used water isotopes for decades to better understand atmospheric circulation patterns, present-day meteorological processes and past climatic conditions at various space and time scales. A key resource in paleo-climatic research is the Global Network of Isotopes in Precipitation, a database of isotopic information operated by the IAEA and the World Meteorological Organization since 1961.