South America became linked to North America through the Isthmus of Panama, bringing a nearly complete end to South America's distinctive marsupial fauna.
The formation of the isthmus had major consequences on global temperatures, because warm equatorial ocean currents were cut off, and the cold Arctic and Antarctic waters lowered temperatures in the now-isolated Atlantic Ocean.
In the northern hemisphere, many glaciers fused into one.
The Cordilleran ice sheet covered the North American northwest; the Laurentide covered the east.
The climate during the Paleolithic consisted of a set of glacial and interglacial periods in which the climate periodically fluctuated between warm and cool temperatures.
Archaeological and genetic data suggest that the source populations of Paleolithic humans survived in sparsely wooded areas and dispersed through areas of high primary productivity while avoiding dense forest cover.
This epoch experienced important geographic and climatic changes that affected human societies.
During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions. Antarctica was ice-bound throughout the Pleistocene and the preceding Pliocene.The Pleistocene climate was characterized by repeated glacial cycles during which continental glaciers pushed to the 40th parallel in some places.Four major glacial events have been identified, as well as many minor intervening events.According to Mark Lynas (through collected data), the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, and other El Niño markers.The Paleolithic is often held to finish at the end of the ice age (the end of the Pleistocene epoch), and Earth's climate became warmer.The Fenno-Scandian ice sheet covered northern Europe, including Great Britain; the Alpine ice sheet covered the Alps.Scattered domes stretched across Siberia and the Arctic shelf. During the late Upper Paleolithic (Latest Pleistocene) which may have prevented early Paleo-Indians such as the Clovis culture from directly crossing Beringia to reach the Americas.A major event is a general glacial excursion, termed a "glacial". During a glacial, the glacier experiences minor advances and retreats.The minor excursion is a "stadial"; times between stadials are "interstadials".This may have caused or contributed to the extinction of the Pleistocene megafauna, although it is also possible that the late Pleistocene extinctions were (at least in part) caused by other factors such as disease and overhunting by humans.Scientists suggest that climate change during the end of the Pleistocene caused the mammoths' habitat to shrink in size, resulting in a drop in population.