Agencies' report warns of faster climate change

The study, which was commissioned by the U.S. Climate Change Science Program and issued this month, expands on the 2007 findings of the United Nations Intergovernment Panel on Climate Change. Looking at factors such as rapid sea ice loss in the Arctic and prolonged drought in the Southwest, the new assessment suggests that earlier projections may have underestimated the climatic shifts that could take place by 2100.

However, the assessment also suggests that some other feared effects of global warming are not likely to occur by the end of the century, such as an abrupt release of methane from the seabed and permafrost or a shutdown of the Atlantic Ocean circulation system that brings warm water north and colder water south. But the report projects an amount of potential sea level rise during that period that may be greater than what other researchers have anticipated, as well as a shift to a more arid climate pattern in the Southwest by midcentury.

Thirty-two scientists from federal and nonfederal institutions contributed to the report, which took nearly two years to complete. The Climate Change Science Program, which was established in 1990, coordinates the climate research of 13 federal agencies.

Tom Armstrong, senior advisor for global change programs at the U.S. Geological Survey, said the report "shows how quickly the information is advancing" on potential climate shifts. The prospect of abrupt climate change, he said, "is one of those things that keeps people up at night, because it's a low-probability but high-risk scenario. It's unlikely to happen in our lifetimes, but if it were to occur, it would be life-changing."

In one of the report's most worrisome findings, the agency estimates that in light of recent ice sheet melting, global sea levels could rise as much as 4 feet by 2100. The intergovernment panel had projected a rise of no more than 1.5 feet by that time, but satellite data over the last two years show the world's major ice sheets are melting much more rapidly than previously thought. The Antarctic and Greenland ice sheets are losing an average of 48 cubic miles of ice a year, equivalent to twice the amount of ice in the Alps.