"There is finally a greater flow of climate science from the administration," Moss said, noting that the report was originally scheduled to come out in 2007. "It really is showing the potential for abrupt climate change is real."
The report is reassuring, however, on the prospects for some potentially drastic effects, such as a huge release of methane, a potent heat-trapping gas, that is now locked deep in the seabed and underneath the Arctic permafrost. That is unlikely to occur in the near future, the scientists said.
"It's unlikely that we're going to see an abrupt change in methane over the next hundred years, but we should worry about it over a longer time frame," said Ed Brook, the lead author of the methane chapter and a geosciences professor at Oregon State University. "All of these places where methane is stored are vulnerable to leaking."
By the end the century, Brook said, the amount of methane escaping from natural sources such as the Arctic tundra and waterlogged soils in warmer regions "could possibly double," but that would still be less than the current level of human-generated methane emissions. Over the course of the next thousand years, he added, methane hydrates stored deep in the seabed could be released.
"Once you start melting there, you can't really take it back," he said.
