Several myths create confusion about past global temperatures, says Michael E. Mann, assistant professor of environmental sciences at the University of Virginia. Climate change skeptics use these misconceptions to try to show that there were periods during the past millennium when global temperatures were higher than they have been in recent times.

One myth is that Greenland was much warmer during the so-called medieval warm period than it is today, and that the warmth enabled the Norse to settle there. The truth is that a few hundred Norse settled in the fjord region of southwest Greenland beginning in 986 because it was the warmest part of the island, as it is today, Mann says.

The settlements collapsed totally by 1500, not primarily because of climate change, but because of social factors, Mann argues. Shipping routes changed, and the inhabitants had no way to get supplies or sell their products. The regional cooling in Greenland that set in between 1000 and 1400 was of the order of 1 °C or less--"not the kind of cooling that's going to cause massive upheaval," he explains.

Another myth is that grapes could be grown in England during medieval times but have not been cultivated there recently. "However, there are roughly 10 times as many vineyards in England today than at the height of the so-called medieval warm period," Mann explains. England has never been a major wine-producing region, not in medieval times and not today, he notes. However, "it has been suitable for grape growing for most of the past 1,000 years," he says.

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