Per the NYT, the amount of sunlight reaching the ground has been\nincreasing over the past 10 year or so reversing a dimming trend.\n(Local dimness in Hong Kong/India remain).\n\n[URL]http://www.nytimes.com/2005/05/06/science/06bright.html[/URL]\n\nMay 6, 2005\nEarth Has Become Brighter, but No One Is Sure Why\nBy KENNETH CHANG\n\nReversing a decades-long trend toward "global dimming," Earth's surface\nhas become brighter since 1990, scientists are reporting today.\n\nThe brightening means that more sunlight - and thus more heat - is\nreaching the ground. That could partly explain the record-high global\ntemperatures reported in the late 1990's, and it could accelerate the\nplanet's warming trend.\n\n"We see the dimming is no longer there," said Dr. Martin Wild, a\nclimatologist at the Swiss Federal Institute of Technology in Zurich and\nthe lead author of one of three papers analyzing sunlight that appear in\ntoday's issue of the journal Science. "If anything, there is a brightening."\n\nSome scientists have reported that from 1960 to 1990, the amount of\nsunshine reaching the ground decreased at a rate of 2 percent to 3\npercent per decade.\n\nIn some places, the brightening of the 1990's has more than offset the\ndimming, Dr. Wild said. In other places, like Hong Kong, which lost more\nthan a third of its sunlight, the dimming has leveled off, but skies\nremain darker than in the past. In a few places, like India, the dimming\ntrend continues, he said.\n\nThe new papers also call attention to a major gap in the understanding\nof climate. Scientists do not exactly know what caused the dimming and\nthe brightening, or how they affect the rest of the climate system.\n\nEarth reflects about 30 percent of the incoming sunlight back into\nspace. Slight changes in the reflectivity, possibly caused by changes in\ncloud cover and air pollution, can have as much impact on the climate as\nheat-trapping greenhouse gases like carbon dioxide.\n\nSome scientists say that the dimming and the brightening might explain\nwhy for many years temperatures on Earth lagged what was predicted by\nmany climate models and then shot upward more recently.\n\n"I think what could have happened is the dimming between the 60's and\n80's counteracted the greenhouse effect," Dr. Wild said. "When the\ndimming faded, the effects of the greenhouse gases became more evident.\nThere is no masking by the dimming anymore."\n\nBut Dr. Rachel T. Pinker, a professor of meteorology at the University\nof Maryland who led the team that wrote one of the other papers, said\nthe picture might not be so simple. More sunlight should increase\nevaporation rates, leading to more clouds, and the additional cloud\ncover could then increase Earth's reflectivity, limiting the warming effect.\n\n"I think that's a complex issue," Dr. Pinker said. "There are many\nfeedbacks involved."\n\nThe findings of Dr. Wild and his colleagues are based on data through\n2001 from a network of ground-based sensors that directly measure the\nsunlight hitting the ground. But the sensors are not evenly distributed,\nwith the greatest number in Europe, few in Africa and South America, and\nnone covering the 70 percent of Earth's surface that is water.\n\nDr. Pinker's team analyzed satellite data from 1983 to 2001 that covered\nthe globe. Its findings about brightening, which basically agree with\nDr. Wild's, rely on computer models to estimate how much sunlight\nreaches the surface.\n\nFinally, a team led by Dr. Bruce A. Wielicki of NASA's Langley Research\nCenter in Virginia reports that measurements from the agency's Aqua\nsatellite show a slight decrease in the amount of light reflected off\nEarth since 2000, which corresponds to a brightening on the surface.\n\nThe NASA findings conflict with measurements, reported last year,\nsuggesting that Earth had resumed dimming since 2000. Those measurements\nlooked at the illumination of the dark side of the Moon by light\nreflected off Earth.\n\nDr. Philip R. Goode, a professor of physics at the New Jersey Institute\nof Technology who was one of the researchers behind last year's report,\nsaid it was not clear why the findings differed so markedly. "We've been\nworking with them to understand the origins of the differences," Dr.\nGoode said of the Wielicki group.\n\nDr. Wielicki said his data supported a report last month by a team led\nby Dr. James E. Hansen of the Goddard Institute for Space Studies in New\nYork. In a paper published on Science's Web site, Dr. Hansen and his\ncolleagues said much of the excess heat generated by global warming has\nbeen stored in the oceans. Even if no more greenhouse gases are added to\nthe atmosphere, they said, Earth will continue to warm by 1 degree\nFahrenheit over the coming decades, as the heat in the oceans is\nreleased into the air.\n\nDr. Wielicki said the amount of energy coming from the Sun matched the\ngain in heat in the oceans reported by Dr. Hansen. "It is consistent\nwith the ocean heat storage that the oceanographers are seeing," Dr.\nWielicki said, "and it is consistent with the climate models'\npredictions of what the heat storage should be."\n\nDr. Robert J. Charlson, a professor of atmospheric sciences at the\nUniversity of Washington and an author of a commentary that accompanied\nthe three papers, said, "This set of papers, taken together, calls\nattention for more emphasis on research in these topics."\n\nBut he added, "Unfortunately, impediments have come up." Four years'\nworth of data from the Earth Radiation Budget Satellite is unanalyzed,\nhe said, because there is no money for scientists to work with it.\n\nAnother satellite, the Deep Space Climate Observatory, which was\nscheduled to be launched on a space shuttle, awaits in storage. Proposed\nbudget cuts in earth science research at NASA could limit the analysis\nof data from other satellites, Dr. Charlson said.