Oh, those hysteria-prone environmentalists, always exaggerating how bad things are going to get as a result of global warming. Or so the deniers would have you believe. They may want to rethink that attack in light of the most recent evidence that models of future climate are underplaying the extent of the coming crisis: projections by the Intergovernmental Panel on Climate Change (IPCC), composed of hundreds of scientists from around the world, have been falling short of reality when it comes to how quickly Arctic sea ice is melting.

According to the IPCC, the Arctic might have no summer sea ice as early as 2050, something that has not happened for about a million years. While that's bad news for the polar bears that use the ice as a hunting platform, and who are going to be in big trouble as sea ice keeps shrinking, it also has dire implications for those of us living thousands of miles to the south: when sea ice is replaced with open water for even a few weeks in September (usually the month with the least sea ice), it changes atmospheric wind patterns in a way that could throw a huge wrench in our weather. Sea ice has been shrinking since the middle of the 20^th century "at a rate, new research finds, some three times faster than predicted by the 18 climate models the IPCC uses. That means Arctic sea ice could vanish by 2020, not 2050.

The difference between models and reality seems to lie in the fact that models capture large-scale changes--but the melting of sea ice is also driven by small fluctuations in the temperature of the ocean and the thickness of ice, for example. When climatologists led by Julienne Stroeve of the National Snow and Ice Data Center at the University of Colorado, Boulder, compared IPCC projections to observations of melting sea ice made by satellites, ships and aircraft, they found a significant gap. The models forecast ice losses of 2.5 percent per decade from 1953 to 2006, but real-world observations documented a loss of 7.8 percent per decade, on average, they report in the online edition of the journal Geophysical Research Letters. The discrepancy seems to come about because the models understate how much warmth from temperate regions of the Atlantic Ocean and Bering Sea is carried into the Arctic. Whatever the explanation for the gap, those models constantly being criticized by climate deniers as Cassandra-ish are, in other words, too conservative.

What other predictions "of rising sea levels, displaced agriculture zones, more extreme storms, more frequent deluges "are also going to be worse than forecast?