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.
Western Europe and the North European Plain
The climate began to improve rapidly throughout Western Europe and the North European Plain c. 16,000-15,000 years ago. The environmental landscape became increasingly boreal, except in the far north, where conditions remained arctic. Sites of human occupation reappeared in northern France, Belgium, northwest Germany, and southern Britain between 15,500 and 14,000 years ago. Many of these sites are classified as Magdalenian, though other industries containing distinctive curved back and tanged points appeared as well. As the Fennoscandian ice sheet continued to shrink, plants and people began to repopulate the freshly deglaciated areas of southern Scandinavia.
Between 12,000 and 10,000 years ago, the western coast of Norway and southern Sweden to latitude 65° north became occupied by sites belonging to the Fosna-Hensbacka complex. They are defined by the appearance of tanged points and other artifacts similar to those found earlier in Northwest Germany. Komsa sites, dated to about 7,000 years ago, are found along Norway's Finnmark county above 70° north and further east on the Kola Peninsula. They are defined by surface finds of tanged points, burins, scrapers, and adzes. The primary game of Magdalenian hunters appears to have been reindeer, though evidence of bird and shellfish consumption persist, as well.
East European Plain
Periglacial loess-steppe environments prevailed across the East European Plain, but climates improved slightly during several brief interstadials and began to warm significantly after the beginning of the Late Glacial Maximum. Pollen profiles for this time indicate a pine-birch woodland interspersed with the steppe in the deglaciated northern plain, birch-pine forest with some broadleaf trees in the central region, and steppe in the south. The pattern reflects the reemergence of a marked zonation of biomes with the decline of glacial conditions. Human site occupation density was most prevalent in the Crimea region and increased as early as around 16,000 years ago.
Reoccupation of northern territories of the East European Plain did not occur until 13,000 years ago. Settlement of the central portion of the East European Plain had significantly reduced during a period of maximum cold around 21,000 to 17,000 years ago.
Overall, little archaeological evidence suggests major shifting settlement pattern during this time on the East European plain. That is unlike what was occurring in Western Europe, where Magdalenian industry producers were rapidly repopulating much of Europe. Evidence of this can be found as far east at Kunda sites (about 10,000 years ago, throughout the Baltics, where tanged point and other tool making traditions reminiscent of the northwestern European Magdalenian persist).