News Stories

Global Dimming Finally Reversing

Newswise - Over a year ago, we posted a story explaining howglobaldimming is caused by a buildup of greenhouse gases in theatmosphere. Now climate scientists say that after 30years, this is finally reversing. Earth's surface hasbrightened by about 4% during the past decade, a reversal ofthe dimming trend that masks the full effect of greenhousewarming.

Reflectivity, or albedo, is largely controlled by clouds andatmospheric particles called aerosols. Scientists are tryingto understand how this affects global warming. Atmosphericscientist Robert J. Charlson says, "If we don't understandthe albedo-related effects, that is aerosols and clouds,then we can't understand the effects of greenhouse gases."

The Earth's albedo, or "Earthshine," was first measured inthe 1920s by astronomers who measured the Earth's reflectionon the dark side of the moon and made comparisons to thesunlit side of the moon.

Francisco P.J. Valero is the lead scientist on a projectcalled Deep Space Climate Observatory, designed to place asatellite in orbit around the sun, about 1 million milesfrom Earth, where it will orbit the sun in the same time asEarth does, and thus be able to aim albedo sensorsconstantly at the Earth's sunlit side. That satellite wasscheduled to be launched on the space shuttle in December,2000 but since shuttles have been temporarily halted eversince the Columbia explosion, the project is on hold.

But isn't a buildup of atmospheric aerosols that reflectheat away from Earth a good thing, that helps offsetgreenhouse warming? Charlson calls that idea "a redherring," and says, "The greenhouse gases work 24 hours aday. They are out there, all over the world, changing theenergy budget of the planet all day and all night, everyday. Albedo is only active during the day?There is nosimplistic balance between these two effects. It isn'theating versus cooling. It's scientific understanding versusnot understanding."

Climatologist Charles N. Long says, "The atmosphere isheated from the bottom up, and more solar energy at thesurface means we might finally see the increases intemperature that we expected to see with global greenhousewarming."

Let's hope theDay AfterTomorrow doesn't arrive as soon as itlooks like itwill!

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