New perils seen to even modest warming

Douglas Fischer in the Daily Climate: Amounts of warming previously thought to be safe may instead trigger widespread melting of the world's ice sheets and other catastrophic impacts, scientists said Tuesday. Accelerating melting on the world's ice sheets and other new observations have scientists concluding that even a two-degree Celsius rise in temperatures – a benchmark long seen as safe in global climate talks and other emissions reductions scenarios – could lead to an 80-foot rise in sea levels.

"The dangerous level of global warming is less than what we thought a few years ago," said James Hansen, director of NASA Goddard Institute for Space Studies. "It was natural to think that a few degrees wasn't so bad.... (But) a target of two degrees is actually a prescription for long-term disaster." Antarctica and Greenland are losing ice at a surprising clip, Hansen said, and methane hydrates – a potent source of greenhouse gas frozen beneath the seas – are starting to bubble up.

The key question for climatologists: How sensitive is the climate to increasing amounts of fossil fuel emissions. Last year humanity pumped almost 10 billion tons of carbon dioxide into the atmosphere, a half-billion tons more than 2009 and the largest jump in any year since the Industrial Revolution, according to the Global Carbon Project.

"There's evidence that climate sensitivity may be quite a bit higher than what the models are suggesting," said Ken Caldiera, a senior scientist at Stanford University's Carnegie Institution for Science. Caldiera and Hansen spoke at the American Geophysical Union meeting in San Francisco, one of the world's largest gatherings of geophysical researchers.

The problem, those researchers said, is the "hang time" for carbon dioxide in the atmosphere. Even if greenhouse gas emissions stopped tomorrow, "climatically important" amounts of carbon dioxide and other compounds emitted today would continue to influence the atmosphere for thousands of years, Caldiera said. That kind of pressure, or "forcing," on the atmosphere could be devastating, he cautioned....

Iceland's Skaftafellsjökull glacier is melting, shot by Someone35, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license