One of the many troubling aspects of global warming is the possibility of feedback effects, where changes resulting from a warming atmosphere serve to further exacerbate the warming. An example of how this could work is the interaction between warming and snow cover. According to Stephan Vavrus at the Unversity of Wisconsin-Madison's Center for Climate Research, if global warming manages to melt off the current snow cover in the far north -- a distinct possibility -- the result would be a further increase in temperature of close to another degree (which would, in turn, further accelerate other effects of temperature increases).
The snow itself does more than reflect the sun's heat; it also serves as insulation for the ground, so that snow-covered soil is warmer than it would be otherwise. As a result, regions now covered in snow would instead see an expansion of permafrost, with resulting damage to structures and roadways in places like Alaska. Of course, as temperatures continue to climb, even that permafrost won't be so permanent...
