Monday, July 27, 2009

Climate Change News: Sea Ice and Feedbacks

Over the weekend, several articles appeared with disturbing information about how far climate change has come and what we might be facing. Last week the Obama administrations declassified over 1,000 photos from military satellites that depict the extent of ice cover in the Arctic over the past several years. The image above juxtaposes photos of the Chukchi Sea near Barrow, Alaska, in consecutive years. (The sea ice has had a similar extent to July 2007 in subsequent summers.) While the disappearance of sea ice in many areas might seem a boon to navigators, it has severe consequences for wildlife and for our climate.

Disappearing summer sea ice poses considerable dangers, scientists have warned. Ice shelves are used by animals such as polar bears as platforms for hunting seals and other sea creatures. Without them, they could starve. In addition, ice reflects solar radiation. Without that process, the Arctic sea could warm up even more. The phenomenon threatens to set off runaway heating of the planet, say climatologists.
Images from military satellites are especially valuable since many environmental satellites are nearing the end of their useful lifespan. Many replacement satellites have been cut, and one planned climate satellite failed to reach orbit.
In February, a Nasa satellite carrying instruments to produce the first map of the Earth's carbon emissions crashed near Antarctica only three minutes after lift-off.

The satellite would have measured carbon emissions at 100,000 points around the planet every day, providing a wealth of data compared to the 100 or so fixed towers currently in operation in a land-based network.
Year-to-year changes, as in the image above, are not all that significant, but they form part of a larger trend of rapidly receding sea ice. A second article points out places where climate scientists might be wrong – not because anthropogenic global warming is not real, but because it is actually worse than predicted. One such area is the loss of Arctic sea ice, which has outpaced the IPCC report. A second area is sea-level rise.
The IPCC may also have been too cautious on Greenland, assuming that the melting of its glaciers would contribute little to sea-level rise. Some studies found that Greenland's glacial streams were surging and surface ice was morphing into liquid lakes, but others made a strong case that those surges and melts were aberrations, not long-term trends. It seemed to be a standoff. More reliable data, however, such as satellite measurements of Greenland's mass, show that it is losing about 52 cubic miles per year and that the melting is accelerating. So while the IPCC projected that sea level would rise 16 inches this century, "now a more likely figure is one meter [39 inches] at the least," says Carlson. "Chest high instead of knee high, with half to two thirds of that due to Greenland." Hence the "no idea how bad it was."
Another recently published study claims to find confirmation for the IPCC estimates of sea-level rise, so I am not ready to rely on the higher numbers just yet. However, the IPCC report is a consensus of climate scientists, which means that it is likely to represent a more conservative view than the latest research. The potential for a faster and higher sea-level rise has always been there and will remain as long as we continue pumping excess greenhouse gases into the atmosphere.

Speaking of gases, one potential source of climate change feedback is the vast reserve of frozen methane in the tundra's permafrost. If the permafrost starts to melt, it will release its methane, a greenhouse gas far more potent than carbon dioxide.
The frozen north had another surprise in store. Scientists have long known that permafrost, if it melted, would release carbon, exacerbating global warming, which would melt more permafrost, which would add more to global warming, on and on in a feedback loop. But estimates of how much carbon is locked into Arctic permafrost were, it turns out, woefully off. "It's about three times as much as was thought, about 1.6 trillion metric tons, which has surprised a lot of people," says Edward Schuur of the University of Florida. "It means the potential for positive feedbacks is greatly increased." That 1.6 trillion tons is about twice the amount now in the atmosphere. And Schuur's measurements of how quickly CO2 can come out of permafrost, reported in May, were also a surprise: 1 billion to 2 billion tons per year. Cars and light trucks in the U.S. emit about 300 million tons per year.
All of this makes makes it all the more important to start reducing greenhouse gas output and reduce it rapidly in future years. The longer we wait, the worse the consequences will be.