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The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. 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.[1] According to Clark et al., growth of ice sheets commenced 33,000 years ago and maximum coverage was between 26,500 years and 19–20,000 years ago, when 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.[2][3]

The LGM is referred to in Britain as the Dimlington Stadial, dated by Nick Ashton to between 31,000 and 16,000 years.[4][5] In the archaeology of Paleolithic Europe, the LGM spans the Aurignacian, Gravettian, Solutrean, Magdalenian and Périgordian cultures.

The LGM was followed by the Late Glacial Interstadial.

Glacial climate

Evolution of temperatures in the Post-Glacial period according to Greenland ice cores.[6]
Temperature proxies for the last 40,000 years.

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 °C (48 °F).[7] This is about 6°C (11°F) colder than the 2013–2017 average. This was confirmed in study published in 2020 which found that the Last Glacial Maximum was ~6.1 °C colder than today. The study also found that the equilibrium climate sensitivity was 3.4 °C, consistent with the established consensus range of 2–4.5 °C.[8][9]

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.[10] The USGS also states that sea level was about 125 meters (410 feet) lower than in present times (2012).[10]

When comparing to the present, the average global temperature was 15 °C (59 °F) for the 2013–2017 period.[11] Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice.[10]

The formation of an ice sheet or Stadial, dated by Nick Ashton to between 31,000 and 16,000 years.[4][5] In the archaeology of Paleolithic Europe, the LGM spans the Aurignacian, Gravettian, Solutrean, Magdalenian and Périgordian cultures.

The LGM was followed by the Late Glacial Interstadial.

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 °C (48 °F).[7] This is about 6°C (11°F) colder than the 2013–2017 average. This was confirmed in study published in 2020 which found that the Last Glacial Maximum was ~6.1 °C colder than today. The study also found that the equilibrium climate sensitivity was 3.4 °C, consistent with the established consensus range of 2–4.5 °C.[8][9]

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.[10] The USGS also states that sea level was about 125 meters (410 feet) lower than in present times (2012).[10]

When comparing to the present, the average global temperature was 15 °C (59 °F) for the 2013–2017 period.[11] Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice.[10]

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 have been diminished by up to 90% compared to the present, with flora 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.

The Amazon rainforest was split into two large blocks by extensive savanna, and the tropical rainforests of Southeast Asia probably were similarly affected, with deciduous forests expanding in their place except on the east and west extremities of the Sundaland shelf. Only in Central America and the Chocó region of Colombia did tropical rainforests remain substantially intact – probably due to the extraordinarily heavy rainfall of these regions.

[10] The USGS also states that sea level was about 125 meters (410 feet) lower than in present times (2012).[10]

When comparing to the present, the average global temperature was 15 °C (59 °F) for the 2013–2017 period.[11] Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice.[10]

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 have been diminished by up to 90% compared to the present, with flora 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.

The Amazon rainforest was split into two large blocks by extensive savanna, and the tropical rainforests of Southeast Asia probably were similarly affected, with deciduous forests expanding in their place except on the east and west extremities of the Sundaland shelf. Only in Central America and the Chocó region of Colombia did tropical rainforests remain substantially intact – probably due to the extraordinarily heavy rainfall of these regions.

Most of the world's deserts expanded. Exceptions were in what is now the western United States, where changes in the jet stream brought heavy rain to areas that are now desert and large pluvial lakes formed, the best known being Lake Bonneville in Utah. This also occurred in Afghanistan and Iran, where a major lake formed in the Dasht-e Kavir.

In Australia, shifting sand dunes covered half the continent, while the Chaco and Pampas in South America became similarly dry. Present-day subtropical regions also lost most of their forest cover, notably in eastern Australia, the Atlantic Forest of Brazil, and southern China, where open woodland became dominant due to drier conditions. In northern China – unglaciated despite its cold climate – a mixture of grassland and tundra p

In Australia, shifting sand dunes covered half the continent, while the Chaco and Pampas in South America became similarly dry. Present-day subtropical regions also lost most of their forest cover, notably in eastern Australia, the Atlantic Forest of Brazil, and southern China, where open woodland became dominant due to drier conditions. In northern China – unglaciated despite its cold climate – a mixture of grassland and tundra prevailed, and even here, the northern limit of tree growth was at least 20° farther south than today.

In the period before the Last Glacial Maximum, many areas that became completely barren desert were wetter than they are today, notably in southern Australia, where Aboriginal occupation is believed to coincide with a wet period between 40,000 and 60,000 years Before Present (BP, a formal measurement of uncalibrated radiocarbon years, counted from 1950 CE).

During the Last Glacial Maximum, much of the world was cold, dry, and inhospitable, with frequent storms and a dust-laden atmosphere. The dustiness of the atmosphere is a prominent feature in ice cores; dust levels were as much as 20 to 25 times greater than now.[12] This was probably due to a number of factors: reduced vegetation, stronger global winds, and less precipitation to clear dust from the atmosphere.[12] The massive sheets of ice locked away water, lowering the sea level, exposing continental shelves, joining land masses together, and creating extensive coastal plains.[13] During the last glacial maximum, 21,000 years ago, the sea level was about 125 meters (about 410 feet) lower than it is today.[14]

Africa and the Middle East