A BIG THAW The warming of many parts of the Arctic is already reducing the amount of perpetually frozen ground, or permafrost, and that trend will almost certainly continue, creating problems for oil companies, road networks and structures built on a thawing landscape. The frozen season has also been shrinking. The number of days in which oil companies can explore for oil on Alaska's North Slope has been cut in half in 30 years. The ecological impact of the trend is harder to predict. For example, while water may drain from existing tundra lakes through thawed ground, other ponds and lakes may form in thawed spots where the surface sinks, creating more aquatic habitat.
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