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Climate - June 12

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Impure as the Driven Snow

David Biello, Scientific American
Belching from smokestacks, tailpipes and even forest fires, soot—or black carbon—can quickly sully any snow on which it happens to land. In the atmosphere, such aerosols can significantly cool the planet by scattering incoming radiation or helping form clouds that deflect incoming light. But on snow—even at concentrations below five parts per billion—such dark carbon triggers melting, and may be responsible for as much as 94 percent of Arctic warming.

"Impurities cause the snow to darken and absorb more sunlight," says Charlie Zender, a climate physicist at the University of California, Irvine. "A surprisingly large temperature response is caused by a surprisingly small amount of impurities in snow in polar regions." ..

Whereas forest fires contribute to the problem—the effect noticeably worsens in years with widespread boreal wildfires—roughly 80 percent of polar soot can be traced to human burning, adding as much as 0.054 watt of energy per square meter of Arctic land, according to the research published this week in the Journal of Geophysical Research. When the snow melts, it exposes dark land below it, further accelerating regional warming. "Black carbon in snow causes about three times the temperature change as carbon dioxide in the atmosphere," Zender says. "The climate is more responsive to this than [to] anything else we know." ..

He argues that simple steps, such as fully burning fossil fuels in more efficient engines and using cleaner-burning cooking stoves, could help preserve the dwindling Arctic snow cover and ice (see video here). Even changing the timing of such soot emissions could play a role. "If you have to burn dirty fuel, you can do it in the fall or winter" when it will be buried under subsequent snowfall, Zender says. "If you can time your emissions so they have the least impact then you will not trigger these very sensitive regions to start warming by this ice albedo feedback process."

Unfortunately, the soot problem extends beyond snow, he says, noting that similar studies are needed to assess how the smut affects the melting of sea ice. That meltdown may be the impetus for an accelerating doom as it opens up shipping lanes previously blocked by ice in the Arctic Sea. "Those ships are great emitters of soot," Zender points out, adding that, "putting a locally heavy source in the Arctic in the early spring," is virtually guaranteed "to polish off the summer sea ice." ..
(8 June 2007)


The wrath of 2007: America's great drought

Andrew Gumbel, Independent
America is facing its worst summer drought since the Dust Bowl years of the Great Depression. Or perhaps worse still.

From the mountains and desert of the West, now into an eighth consecutive dry year, to the wheat farms of Alabama, where crops are failing because of rainfall levels 12 inches lower than usual, to the vast soupy expanse of Lake Okeechobee in southern Florida, which has become so dry it actually caught fire a couple of weeks ago, a continent is crying out for water.

In the south-east, usually a lush, humid region, it is the driest few months since records began in 1895. California and Nevada, where burgeoning population centres co-exist with an often harsh, barren landscape, have seen less rain over the past year than at any time since 1924. The Sierra Nevada range, which straddles the two states, received only 27 per cent of its usual snowfall in winter, with immediate knock-on effects on water supplies for the populations of Las Vegas and Los Angeles.

The human impact, for the moment, has been limited, certainly nothing compared to the great westward migration of Okies in the 1930 - the desperate march described by John Steinbeck in The Grapes of Wrath.

Big farmers are now well protected by government subsidies and emergency funds, and small farmers, some of whom are indeed struggling, have been slowly moving off the land for decades anyway. The most common inconvenience, for the moment, are restrictions on hosepipes and garden sprinklers in eastern cities.

But the long-term implications are escaping nobody. Climatologists see a growing volatility in the south-east's weather - today's drought coming close on the heels of devastating hurricanes two to three years ago. In the West, meanwhile, a growing body of scientific evidence suggests a movement towards a state of perpetual drought by the middle of this century.
(11 June 2007)


Kilimanjaro not a victim of climate change, UW scientist says

The shrinking snowcap atop Mount Kilimanjaro has become an icon of global warming.

Pictures of the African peak, which has lost 90 percent of its ice cover, were featured in Al Gore's documentary, "An Inconvenient Truth." Greenpeace activists once held a satellite news conference on the summit to sway participants in an international climate conference.

But most scientists who study Kilimanjaro's glaciers have long been uneasy with the volcano's poster-child status.

Yes, ice cover has shrunk by 90 percent, they say.

But no, the buildup of greenhouse gases from cars, power plants and factories is not to blame.

"Kilimanjaro is a grossly overused mis-example of the effects of climate change," said University of Washington climate scientist Philip Mote, co-author of an article in the July/August issue of American Scientist magazine.

Mote is concerned that critics will try to use the article to debunk broader climate-change trends.

He hastens to add that global warming is, indeed, responsible for the fact that nearly every other glacier around the globe is melting away. Kilimanjaro just happens to be the worst possible case study.

Rising nearly four miles from the plains of eastern Tanzania, Kilimanjaro has seen its glaciers decline steadily for well over a century - since long before humans began pumping large amounts of carbon dioxide into the atmosphere, Mote points out.
(12 June 2007)

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