re: climate change-globe is dimming
A Google search on"global dimming" reveals a lot of articles like the following one'
http://166.70.44.66/2004/May/05092004/nation_w/164867.asp SUNDAY May 09, 2004 Scientists say less sunlight reaching Earth By Robert Boyd Knight Ridder News Service
WASHINGTON -- Scientists call it "global dimming," a little-known trend that may be making the world darker than it used to be. Thanks to thicker clouds and growing air pollution, much of the Earth's surface is receiving about 15 percent less sunlight than it did 50 years ago, according to Michael Roderick, a climate researcher at Australian National University in Canberra. "Global dimming means that the transmission of sunlight through the atmosphere is decreasing," Roderick said. "Just look out the window when you fly into New York or to California -- it's dimmer," said Beate Liepert, a climatologist at the Lamont-Doherty Earth Observatory of Columbia University in New York. Researchers say global dimming, also known as solar dimming, partially offsets the global warming that most scientists agree is produced by "greenhouse gases" such as auto exhaust and emissions from coal-burning power plants. The solar dimming effect is "about half as large as the greenhouse gas warming," said James Hansen, the director of NASA's Goddard Institute for Space Studies in New York. In global warming, gases in the atmosphere, such as carbon dioxide, trap some of the sun's heat and keep it from radiating back out to space, thereby raising the Earth's temperature. Clouds and air pollution, on the other hand, block a portion of the heat energy that's coming from the sun, just as it's cooler sitting under a beach umbrella than under a bright sky. Although global warming has been widely accepted, global dimming remains controversial. The theory has been advanced in recent years by a handful of researchers who measure the decline of solar radiation at hundreds of sites around the globe. "Initially, people were very skeptical, but now there's other pieces of evidence that all fit together," Roderick told a radio interviewer last December. Reductions in sunlight of 10 percent to 20 percent have been observed in many places over the past 50 years, he said. "We still face a lot of controversy, but it's [solar dimming] getting accepted," Liepert said. "The conclusion that, on average, there has been a reduction in surface solar irradiance over the past half-century is pretty clear," NASA's Hansen said. Support for the theory comes from two types of data collected in recent decades: * Radiation meters -- black metal plates that absorb the sun's rays -- aren't heating up as rapidly as they previously did. * The rate at which water evaporates from special measuring pans placed in the sunlight has slowed over the years. Roderick, for example, measures the height of the water in his pans at 9 a.m. each day, subtracts any rain that may have fallen and calculates how much has evaporated from the day before. "There's less evaporation out of pans of water all around the world, and that's consistent with global dimming," he said The measurements indicate that the amount of energy from the sun -- solar radiation -- is shrinking by about 3 percent per decade, according to Gerald Stanhill, a biologist at Israel's Agricultural Research Organization.
