The U.N.-sponsored Intergovernmental Panel on Climate Change (IPCC) report released today in Brussels has a familiar ring. As the climate disasters headlined recently--intense hurricanes, drought in the American West, Arctic thawing--become commonplace in a greenhouse world, plants, animals, and people will suffer. That has been the presumption, but the latest report from the IPCC projecting greenhouse impacts calculates mounting costs that will fall the heaviest on the world's poor.
February's IPCC report on the physical science of climate (ScienceNOW, 2 February) firmly links most of the recent warming of the world to human activity. Scientists authoring the second report had a tougher challenge: figuring out the likely consequences. To do that, they considered 29,000 datasets from 75 studies. Of those data series, 89% showed changes--receding glaciers or earlier blooming, for example--consistent with a response to warming. Because those responses usually occurred where the warming has been greatest, the scientists concluded that it's "very unlikely" the changes were due to natural variability of climate or of the system involved. "For the first time, we concluded anthropogenic warming has had an influence on many physical and biological systems," says Cynthia Rosenzweig of NASA's Goddard Institute for Space Studies in New York City, a coordinating lead author on the report.
The IPCC scientists also projected the effects of future warming. Assuming that nothing's done to slow greenhouse emissions, the February report predicted a temperature increase of roughly 3°C toward the end of the century, drying at lower latitudes, more precipitation at higher latitudes, and rising sea levels. This report finds that such a warming will bleach most coral reefs by mid-century, drying will begin decreasing crop yields at lower latitudes within a few decades, and sea level rise and tropical cyclone intensification will increase the likelihood of millions of people being flooded out each year on river mega-deltas such as that of the Ganges-Brahmaputra in southern Asia.
Bottom line? "You don't want to be poor and living on a river delta or the Florida coast," says climate scientist Stephen Schneider of Stanford University, a coordinating lead author. The poor--especially subsistence farmers--tend to be more vulnerable to climate change, notes the report. And they are least able to adapt, say by building levees against storms or dams for irrigation. Schneider's other advice: "Try not to go over 2°C or 3°C because that triggers the really nasty stuff." With that much warming, the bad effects of this century only get worse, and the rare benefits, such as higher crop yields in wetter areas, fade. To avoid that disaster, see next month's IPCC report on how to reduce greenhouse gas emissions.