Arctic temperatures near a prehistoric level when seas were 16 to 20 feet higher, studies say.So, within five years we've jumped 100 years ahead of schedule? I predict that in five more years, 2011 we'll be told, again, that we are 100 years ahead of schedule. We'll be told that it is now... right now.
Global warming appears to be pushing vast reservoirs of ice on Greenland and Antarctica toward a significant, long-term meltdown. The world may have as little as a decade to take the steps to avoid this scenario.
Those are the implications of new studies that looked to climate history for clues about how the planet's major ice sheets might respond to human-triggered climate change.
Already, temperatures in the Arctic are close to those that thawed much of Greenland's ice cap some 130,000 years ago, when the planet last enjoyed a balmy respite from continent-covering glaciers, say the studies' authors.
By 2100, spring and summer temperatures in the Arctic could reach levels that trigger an unstoppable repeat performance, they say. Over several centuries, the melt could raise sea levels by as much as 20 feet, submerging major cities worldwide as well as chains of islands, such as the present-day Bahamas.
The US would lose the lower quarter of Florida, southern Louisiana up to Baton Rouge, and North Carolina's Outer Banks. The ocean would even flood a significant patch of California's Central Valley, lapping at the front porches of Sacramento.
These estimates may understate the potential rise. The teams say their studies provide the first hints that during the last interglacial period, ice sheets in both hemispheres worked together to raise sea levels, rather than the Northern Hemisphere's ice alone. This raises concerns that Antarctic melting might be more severe this time, because additional melt mechanisms may be at work.
"It sounds bad," acknowledges Jonathan Overpeck, a University of Arizona researcher who led one of the two studies. He notes that rising temperatures are approaching a threshold. But "we know about it far enough in advance to avoid crossing it." The challenge, he and others say, is to take advantage of the remaining window by reducing emissions of greenhouse gases substantially.
The two studies were published in Friday's issue of the journal Science.
Ice on Greenland and Antarctica is already thinning faster than it's being replaced - and faster than scientists thought it would, notes Richard Alley, a paleoclimatologist at Penn State University and member of one of the research teams. Only five years ago, he notes, climate scientists expected the ice sheets to gain mass through 2100, then begin to melt. "We're now 100 years ahead of schedule," he says.
But the window for action is relatively short, Dr. Overpeck says. CO2 remains in the atmosphere for more than a century after it's first emitted. And it takes time to implement policies and adopt technologies. Thus for all practical purposes, the tipping point may come sooner than atmospheric chemistry would suggest.
Thanks to Dave Lucas for pointing me to this article.