The Oxygen Planet Struts Its Stuff

For some time, climatologists have been warning us that much of the West is on the verge of downshifting to a new, perilous level of aridity. Droughts like those that shaped the Dust Bowl in the 1930s and the even drier 1950s will soon be “the new climatology” of the region -- not passing phenomena but terrifying business-as-usual weather. Western forests already show the effects of this transformation.

In 2007, the Intergovernmental Panel on Climate Change forecast a temperature increase of 4ºC for the Southwest over the present century. Given a faster than expected build-up of greenhouse gases (and no effective mitigation), that number looks optimistic today. Estimates vary, but let’s say our progress into the sweltering future is an increase of slightly less than 1ºC so far. That means we still have an awful long way to go. If the fires we’re seeing now are a taste of what the century will bring, imagine what the heat stress of a 4ºC increase will produce. And these numbers reflect mean temperatures. The ones to worry about are the extremes, the record highs of future heat waves. In the amped-up climate of the future, it is fair to think that the extremes will increase faster than the means.

More than scenery is at stake, more even than the stability of soils, ecosystems, and watersheds: the forests of the western United States account for 20% to 40% of total U.S. carbon sequestration. At some point, as western forests succumb to the ills of climate change, they will become a net releaser of atmospheric carbon, rather than one of the planet’s principle means of storing it.

No such equivocation attends a Goddard Institute for Space Studies appraisal of the heat wave that assaulted Texas, Oklahoma, and northeastern Mexico last summer. Their report represents a sea change in high-level climate studies in that they boldly assert a causal link between specific weather events and global warming. The Texas heat wave, like a similar one in Russia the previous year, was so hot that its probability of occurring under “normal” conditions (defined as those prevailing from 1951 to 1980) was approximately 0.13%. It wasn’t a 100-year heat wave or even a 500-year one; it was so colossally improbable that only changes in the underlying climate could explain it.