Environmental Change

Wisconsin Glaciation and the Little Ice Age

Wisconsin Glaciation e Last Glacial Maximum (LGM) refers to a period in our planet's climate history when ice sheets were at their maximum extension during the last glacial period, between 26,500 and 19,000–20,000 years ago. During this time, vast ice sheets covered much of North America, northern Europe and Asia. These ice sheets profoundly impacted Earth's climate, causing drought, desertification, and a dramatic drop in sea levels.

In 960, Thorvald Asvaldsson of Jaederen in Norway killed a man. He was forced to leave the country so he moved to northern Iceland. He had a ten year old son named Eric, later to be called Eric Röde, or Eric the Red. Eric too had a violent streak and in 982 he killed two men. Eric the Red was banished from Iceland for three years so he sailed west to find a land that Icelanders had discovered years before but knew little about. Eric searched the coast of this land and found the most hospitable area, a deep fiord on the southwestern coast. Warmer Atlantic currents met the island there and conditions were not much different than those in Iceland (trees and grasses.) He called this new land "Greenland" because he "believed more people would go thither if the country had a beautiful name," according to one of the Icelandic chronicles (Hermann, 1954) although Greenland, as a whole, could not be considered "green." Additionally, the land was not very good for farming. Nevertheless, Eric was able to draw thousands to the three areas shown in Fig. 15.

By the year 1300 more than 3,000 colonists lived on 300 farms scattered along the west coast of Greenland (Schaefer, 1997.) However, even as early as 1197, the climate had turned much less favorable and drift ice was beginning to appear along the vital trade routes (Lamb, 1995.) Cool weather caused poor harvests in an already fragile climate. Because of the poor harvests there was less food for the livestock which resulted in a decreased meat supply. These conditions made it even more vital that trade continued with Iceland and the rest of Europe. The Vikings in Iceland did not escape the negative impact of a rapidly cooling climate either. Although not completely wiped out like the Greenlanders, Icelandic Vikings were hit hard by the climate change. Olafur Einarsson ( ), a pastor in eastern Iceland, wrote the following poem (Bryson, 1977) which illustrates the troubles Icelanders faced: Formerly the earth produced all sorts of fruit, plants and roots. But now almost nothing grows.... Then the floods, the lakes and the blue waves Brought abundant fish. But now hardly one can be seen. The misery increases more. The same applies to other goods.... Frost and cold torment people The good years are rare. If everything should be put in a verse Only a few take care of the miserables....

Historical data examined by Levitus et al (Science, 1999) shows changes in the ocean heat content (to depths of 3000 meters) to be slowly increasing with substantial decadal time scale variations related to climate variability. The sequestering of heat deep into the ocean, mitigates global warming of the atmosphere. Deep heat increases reflect changes in properties of deep water formed at high latitude in winter. -from Woods Hole Oceanographic Institute

A summary of the path of the thermohaline circulation/ Great Ocean Conveyor. Blue paths represent deep-water currents, while red paths represent surface currents

Loss of Biodiversity