Last Glacial Maximum

The Last Glacial Maximum (LGM) was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Vast ice sheets covered much of North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing drought, desertification, and a large drop in sea levels. The ice sheets reached their maximum coverage about 26,500 years ago (26.5 ka BP). Deglaciation commenced in the Northern Hemisphere at approximately 19 ka and in Antarctica approximately at 14.5 ka, consistent with evidence for an abrupt rise in the sea level at about 14.5 ka. The Last Glacial Maximum (LGM) was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Vast ice sheets covered much of North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing drought, desertification, and a large drop in sea levels. The ice sheets reached their maximum coverage about 26,500 years ago (26.5 ka BP). Deglaciation commenced in the Northern Hemisphere at approximately 19 ka and in Antarctica approximately at 14.5 ka, consistent with evidence for an abrupt rise in the sea level at about 14.5 ka. The LGM is referred to in Britain as the Dimlington Stadial, dated by Nick Ashton to between 31 and 16 ka.In the archaeology of Paleolithic Europe, the LGM spans the Gravettian, Solutrean, Magdalenian and Périgordian. The LGM was followed by the Late Glacial. According to Blue Marble 3000 (a video by the Zurich University of Applied Sciences), the average global temperature around 19,000 BC (about 21,000 years ago) was 9.0 °C (48.2 °F). This is about 6.0 °C (10.8°F) colder than the 2013-2017 average. According to the United States Geological Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum. The USGS also states that sea level was about 125 meters (410 feet) lower than in present times (2012). When comparing to the present, the average global temperature was 15.0 °C (58.9 °F) for the 2013-2017 period. Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice. The formation of an ice sheet or ice cap requires both prolonged cold and precipitation (snow). Hence, despite having temperatures similar to those of glaciated areas in North America and Europe, East Asia remained unglaciated except at higher elevations. This difference was because the ice sheets in Europe produced extensive anticyclones above them. These anticyclones generated air masses that were so dry on reaching Siberia and Manchuria that precipitation sufficient for the formation of glaciers could never occur (except in Kamchatka where these westerly winds lifted moisture from the Sea of Japan). The relative warmth of the Pacific Ocean due to the shutting down of the Oyashio Current and the presence of large 'east-west' mountain ranges were secondary factors preventing continental glaciation in Asia. All over the world, climates at the Last Glacial Maximum were cooler and almost everywhere drier. In extreme cases, such as South Australia and the Sahel, rainfall could be diminished by up to 90% from present, with florae diminished to almost the same degree as in glaciated areas of Europe and North America. Even in less affected regions, rainforest cover was greatly diminished, especially in West Africa where a few refugia were surrounded by tropical grasslands.