thumb|A chronology of climatic events of importance for the Last Glacial Period, about the last 120,000 years|upright=1.3
thumb|The Last Glacial Period caused a much lower global sea level.|upright=1.3
The Last Glacial Period (LGP), also known as the last glacial cycle, occurred from the end of the Last Interglacial to the beginning of the Holocene, years ago, and thus corresponds to most of the timespan of the Late Pleistocene. It thus formed the most recent period of what is colloquially known as the "Ice Age".
The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing. The glaciation and the current Quaternary Period both began with the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Mya (million years ago), in the mid-Cenozoic (Eocene–Oligocene extinction event), and the term Late Cenozoic Ice Age is used to include this early phase with the current glaciation. The previous ice age within the Quaternary is the Penultimate Glacial Period, which ended about 128,000 years ago, was more severe than the Last Glacial Period in some areas such as Britain, but less severe in others.
The last glacial period saw alternating episodes of glacier advance and retreat with the Last Glacial Maximum occurring between 26,000 and 20,000 years ago. While the general pattern of cooling and glacier advance around the globe was similar, local differences make it difficult to compare the details from continent to continent (see picture of ice core data below for differences). The most recent cooling, the Younger Dryas, began around 12,800 years ago and ended around 11,700 years ago, also marking the end of the LGP and the Pleistocene epoch. It was followed by the Holocene, the current geological epoch.
Origin and definition
thumb|upright=1.15|An artist's impression of the last glacial period at glacial maximum
The LGP is often colloquially referred to as the "last ice age", though the term ice age is not strictly defined, and on a longer geological perspective, the last few million years could be termed a single ice age given the continual presence of ice sheets near both poles. Glacials are somewhat better defined, as colder phases during which glaciers advance, separated by relatively warm interglacials. The end of the last glacial period, which was about 10,000 years ago, is often called the end of the ice age, although extensive year-round ice persists in Antarctica and Greenland. Over the past few million years, the glacial-interglacial cycles have been "paced" by periodic variations in the Earth's orbit via Milankovitch cycles.
The LGP has been intensively studied in North America, northern Eurasia, the Himalayas, and other formerly glaciated regions around the world. The glaciations that occurred during this glacial period covered many areas, mainly in the Northern Hemisphere and to a lesser extent in the Southern Hemisphere. They have different names, historically developed and depending on their geographic distributions: Fraser (in the Pacific Cordillera of North America), Pinedale (in the Central Rocky Mountains), Wisconsinan or Wisconsin (in central North America), Devensian (in the British Isles), Midlandian (in Ireland), Würm (in the Alps), Mérida (in Venezuela), Weichselian or Vistulian (in Northern Europe and northern Central Europe), Valdai in Russia and Zyryanka in Siberia, Llanquihue in Chile, and Otira in New Zealand. The geochronological Late Pleistocene includes the late glacial (Weichselian) and the immediately preceding penultimate interglacial (Eemian) period.
Overview
thumb|Vegetation types at the time of the [[Last Glacial Maximum|upright=1.3]]
thumb|Last glacial period, as seen in [[ice core data from Antarctica and Greenland|upright=1.3]]
Northern Hemisphere
Canada was almost completely covered by ice, as was the northern part of the United States, both blanketed by the huge Laurentide Ice Sheet. Alaska remained mostly ice free due to arid climate conditions. Local glaciations existed in the Rocky Mountains and the Cordilleran ice sheet and as ice fields and ice caps in the Sierra Nevada in northern California. In northern Eurasia, the Scandinavian ice sheet once again reached the northern parts of the British Isles, Germany, Poland, and Russia, extending as far east as the Taymyr Peninsula in western Siberia.
The maximum extent of western Siberian glaciation was reached by about 18,000 to 17,000 BP, later than in Europe (22,000–18,000 BP). Northeastern Siberia was not covered by a continental-scale ice sheet. Instead, large, but restricted, icefield complexes covered mountain ranges within northeast Siberia, including the Kamchatka-Koryak Mountains.
The Arctic Ocean between the huge ice sheets of America and Eurasia was not frozen throughout, but like today, probably was covered only by relatively shallow ice, subject to seasonal changes and riddled with icebergs calving from the surrounding ice sheets. According to the sediment composition retrieved from deep-sea cores, even times of seasonally open waters must have occurred.
Outside the main ice sheets, widespread glaciation occurred on the highest mountains of the Alpide belt. In contrast to the earlier glacial stages, the Würm glaciation was composed of smaller ice caps and mostly confined to valley glaciers, sending glacial lobes into the Alpine foreland. Local ice fields or small ice sheets could be found capping the highest massifs of the Pyrenees, the Carpathian Mountains, the Balkan Mountains, the Caucasus, and the mountains of Turkey and Iran.
In the Himalayas and the Tibetan Plateau, there is evidence that glaciers advanced considerably, particularly between 47,000 and 27,000 BP, but the exact ages, as well as the formation of a single contiguous ice sheet on the Tibetan Plateau, is controversial.
thumb|upright=1.3|The [[Late Pleistocene saw extinctions of numerous predominantly megafaunal species, coinciding in time with the early human migrations across continents.]]
Other areas of the Northern Hemisphere did not bear extensive ice sheets, but local glaciers were widespread at high altitudes. Parts of Taiwan, for example, were repeatedly glaciated between 44,250 and 10,680 BP as well as the Japanese Alps. In both areas, maximum glacier advance occurred between 60,000 and 30,000 BP. To a still lesser extent, glaciers existed in Africa, for example in the High Atlas, the mountains of Morocco, the Mount Atakor massif in southern Algeria, and several mountains in Ethiopia. Just south of the equator, an ice cap of several hundred square kilometers was present on the east African mountains in the Kilimanjaro massif, Mount Kenya, and the Rwenzori Mountains, which still bear relic glaciers today.
Southern Hemisphere
Glaciation of the Southern Hemisphere was less extensive. Ice sheets existed in the Andes (Patagonian Ice Sheet), where six glacier advances between 33,500 and 13,900 BP in the Chilean Andes have been reported. Antarctica was entirely glaciated, much like today, but unlike today the ice sheet left no uncovered area. In mainland Australia only a very small area in the vicinity of Mount Kosciuszko was glaciated, whereas in Tasmania glaciation was more widespread. An ice sheet formed in New Zealand, covering all of the Southern Alps, where at least three glacial advances can be distinguished.
Local ice caps existed in the highest mountains of the island of New Guinea, where temperatures were 5 to 6 °C colder than at present.
Small glaciers developed in a few favorable places in Southern Africa during the last glacial period.