18,000 years ago ice sheets covered large areas of land

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The growth of the ice sheets began about 120,000 years ago as ice built up on the continents in the Northern Hemisphere, especially in Canada and Europe. The largest extent of these ice sheets occurred 18,000 years ago. At that time the largest ice sheets were between 3.5 and 4 km thick. In North America the largest ice sheet was the Laurentide Ice Sheet centered on Hudson Bay with other sheets centered on Greenland and in the Canadian Rocky Mountains. As these ice sheets expanded they grew together, covering Baffin Bay and eventually the Great Lakes and New England. In northwestern Europe the Fennoscandian Ice Sheet began to grow and expand south to cover what is now Norway and Sweden and north to cover the exposed continental shelf. Over time the ice sheet grew to cover Finland and the United Kingdom. This ice sheet extended east to the Ural Mountains where it met the Siberian Ice Sheet. Before the last ice age ice sheets already existed on Antarctica and on Greenland.

Credit: Museums Teaching Planet Earth; data from Peltier, W., 1993, Time Dependent Topography Through Glacial Cycle. IGBP PAGES/World Data Center-A for Paleoclimatology Data Contribution Series #93-015. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA.; J. Kutzbach, R. Gallimore, S. Harrison, P. Behling, R. Selin, and F. Laarif (1998) Climate and Biome Simulations for the Past 21,000 Years. Quaternary Science Reviews, 17, 473-506.

For more info: http://vathena.arc.nasa.gov/curric/land/global/climchng.html