Last week I briefly mentioned some stark estimates about the potential extinctions that could be triggered by global warming. Since then, some global warming skeptics have tried to pour cold water on these results by making some dubious claims about natural selection and extinctions. While I have reported about global warming from time to time, I leave blogging on the subject to others (particularly David Appell over at Quark Soup). But in this case, evolution is drawn into the mix.
Here, in a nutshell, is what the scientists wrote last week in their Nature paper (which the editors have made available for free). They studied over 1,000 species in all sorts of terrestrial habitats, from Mexican deserts to Australian rainforests. Using information on their ranges, the scientists estimated the range of temperature, moisture, and other climate conditions in which the species currently persist (what they call a "climate envelope"). As the climate changes in the coming century, these climate envelopes will change shape. Some may expand towards the pole, while others will slide, and others will shrink. To estimate the shape and position of these new climate envelopes, the scientists looked at the shift in these ranges in three different scenarios for life in 2050--a "small" change of .8-1.7 degrees C, a medium change of 1.8-2.0 degrees, and a big change of over 2 degrees. (These ranges come from IPCC projections, which in turn are based on a range of potential future emissions of carbon dioxide. For comparison, the planet has warmed an estimated .6 degrees C in the past century.)
Some species that can spread quickly may be able to move into their new climate envelope. Others that disperse slowly--animals that only live in isolated patches of heath, for example--may only be able to survive in the overlap between today's climate envelope and the envelope of 2050. Others still may simply have nowhere to go--Australia's rainforest, for example, are on the northern coast of the country. Global warming is predicted to chew away at their habitat at the south, but they can hardly find new territory in the ocean to the north.
