Last Glacial Maximum

The Last Glacial Maximum (LGM), also referred to as the Last Glacial Coldest Period, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent 26 ka - 20 ka ago. Ice sheets covered much of Northern North America, Northern Europe, and Asia and profoundly affected Earth's climate by causing a major expansion of deserts, along with a large drop in sea levels. Based on changes in position of ice sheet margins dated via terrestrial cosmogenic nuclides and radiocarbon dating, growth of ice sheets commenced 33,000 years ago and maximum coverage has been estimated to have occurred sometime between 26,500 years ago and 20,000 years ago. After this, deglaciation commenced in the Northern Hemisphere, causing an abrupt rise in sea level. Decline of the West Antarctica ice sheet occurred between 14,000 and 15,000 years ago, consistent with evidence for another abrupt rise in the sea level about 14,500 years ago. Glacier fluctuations around the Strait of Magellan suggest the peak in glacial surface area was constrained to between 25,200 and 23,100 years ago. Continental ice sheets never reached their isostatic equilibrium during the LGM, as evidenced by high variability in ice volume over short spans of time. The LGM is referred to in Britain as the Dimlington Stadial, dated to between 31,000 and 16,000 years. In the archaeology of Paleolithic Europe, the LGM spans the Aurignacian, Gravettian, Solutrean, Magdalenian and Périgordian cultures. The average global temperature around 19,000 BC (about 21,000 years ago) was about 6 °C (11 °F) colder than today. 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 lower than in present times (2012). When comparing to the present, the average global temperature was for the 2013–2017 period. As of 2012 about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice.