Late Glacial Interstadial

The Late Glacial Interstadial (LGI) c. 14,670 to c. 12,890 BP, also called the Bølling–Allerød interstadial, represents the first pronounced warming since the end of the Last Glacial Maximum (LGM). Human populations, which had previously been forced into refuge areas, gradually begin to repopulate the Northern Hemisphere's Eurasian landmass.

Evidence for its occurrence stems from two main types of analysis. The first is the use of oxygen isotope stages (OIS) gathered from stratified deep-sea sediment cores. Samples are gathered and measured for change in isotope levels to determine temperature fluctuation for given periods of time. The second is a proxy measurement, the observation of certain reappearing fauna and flora fossils that can survive only in temperate climates, thus indicating warming trends for a given geographic area.

Archaeological evidence of settlement and resettlement in certain areas by humans also serves as proxy measurements. Towards the end of OIS 2 in which the Last Glacial Maximum occurs, the deep-sea sediment cores indicate a gradually warming climate, and the reappearance of certain warm-weather flora and fauna remains throughout the Northern Hemisphere correlate with that trend. The Late Glacial Interstadial was followed by a severe decline in temperatures during the Younger Dryas from c. 12,890 to c. 11,650 BP.