Another is the loss of sea ice. Mean summer temperatures in the Arctic have risen about three degrees Fahrenheit since 1960, and summer sea ice is shrinking more than 11% per decade. This year ranks third for the minimum Arctic summer sea ice extent since satellite record-keeping began in 1979. 2007 and 2008 hold the records, and 2009 is in fourth place. Continue reading →
Jeff Dozier approaches an instrument tower on Mammoth Mountain. Photo: Molly Samuel
When Jeff Dozier, a hydrologist at UC Santa Barbara, goes to work, he gets to enjoy quite a view. His snow lab is perched halfway up Mammoth Mountain in the central Sierra. We took a gondola to get up there; the other passengers were skiers and snowboarders itching to get out on the freshly fallen snow.
But the instrument platform from which we enjoyed views of the White Mountains is really only half the story. Dozier’s computer lab has much less of a view. In fact, it has no view. It’s buried under the snow, accessible only through what he calls a “Santa Claus entrance” (in the picture above, you can see the entrance–it’s the white tubular “chimney” extending down into the snow from the center of the platform).
Radiation is an important one. Instruments called radiometers are mounted on the tower. Some point up, measuring the radiation coming from the sun; others point down, measuring how much is reflected back to the sky by the snow.
“Albedo” is the measurement of how reflective the snow is. Something completely white that reflects all of the sun’s energy has an albedo of one; something black, that absorbs all the energy, is zero. Bright, freshly fallen snow has a high albedo, typically above 0.8.
Even if the term is new to you, albedo is probably a familiar concept. As I reported for KQED’s The California Report this morning, Hans Moosmuller of the University of Nevada’s Desert Research Institute explains it in terms of outfits: on a sunny day, if you wear a black sweater you’ll be warmer than if wear a white one. You may notice it with roofs, too. I grew up in Atlanta, in a house with a black roof. Before my parents got an air conditioner, the upstairs bedrooms were unbearable in the summer. If we’d had a white
These radiometers measure radiation coming from the sun. Photo: Molly Samuel
roof, it would have been a little more bearable (though I can’t say it would have helped with Atlanta’s other charming summer attributes, humidity and mosquitoes).
The color sweater you wear has no bearing on the earth’s climate. Roof color could have an effect on a large enough scale. What really matters are the huge swaths of dark and light that cover the globe: ocean and snow.
When warming causes sea ice near the poles to melt faster, areas that had a high albedo (ice is very reflective) become areas with a very low albedo (the blue ocean absorbs more radiation than forests or plain dirt). Moosmuller says it creates a feedback loop. The more dark spots there are, the more radiation is absorbed. So melting speeds up, and warming increases, exposing even more dark areas, and so on.
Pollution plays an important role that’s coming under increasing scrutiny. Deposits of soot or dust make the snow darker, so it melts faster, exposes more dark ground, and there’s that feedback loop again. In the Himalayas soot, also known as black carbon, from stoves, tailpipes, factories, and fires is having a measurable impact.
In the Rockies, there’s a similar problem caused by dust kicked up from ranches. Tom Painter of the University of Utah says the snow in the Colorado River Basin melts a full month earlier than normal. The difference the dust makes is so drastic, Painter says, that “We’re in an entirely new regime for snow melt…it would be like if we started measuring climate impacts fifty years from now.”
No one has yet done a long-term study on the effects of dust and soot on the Sierra Nevada snow pack. Moosmuller says he’s beginning to look into it now. In the summer, black carbon drifts into the mountains from California’s cities, ports, highways and farms in the Central Valley. Tony Van Curen, in a research project at UC Davis, has found that soot blows over from Asia, too.
There is good news in all of this: Black carbon, unlike most greenhouse gases, lingers in the atmosphere only for a couple of weeks. So reducing emissions could have a relatively quick impact.