11
Mai
2005

Earth Lightens Up - Why the Sun seems to be 'dimming'

I have to say it's interesting reading these two articles together. I've attached the additional article from January '05 entitled "Why the Sun Seems to Be Dimming" - which many of us will remember seeing posted. Now they are saying the Earth's surface is actually brightening.

Anna


Earth Lightens Up

Richland WA (SPX) May 06, 2005

Earth's surface has been getting brighter for more than a decade, a reversal from a dimming trend that may accelerate warming at the surface and unmask the full effect of greenhouse warming, according to an exhaustive new study of the solar energy that reaches land.

Ever since a report in the late 1980s uncovered a 4 to 6 percent decline of sunlight reaching the planet's surface over 30 years since 1960, atmospheric scientists have been trying out theories about why this would be and how it would relate to the greenhouse effect, the warming caused by the buildup of carbon dioxide and other gasses that trap heat in the atmosphere.

Meanwhile, a group led by Martin Wild at the Swiss Federal Institute of Technology in Zurich, home of the international Baseline Surface Radiation Network (BSRN) archive, had gone to work collecting surface measurements and crunching numbers.

"BSRN didn't get started until the early '90s and worked hard to update the earlier archive," said Charles N. Long, senior scientist at the Department of Energy's Pacific Northwest National Laboratory and co-author of a BSRN report in this week's issue (Friday, May 6) of the journal Science.

"When we looked at the more recent data, lo and behold, the trend went the other way," said Long, who conducted the work under the auspices of DOE's Atmospheric Radiation Measurement (ARM) program.

Data analysis capabilities developed by ARM research were crucial in the study, which reveals the planet's surface has brightened by about 4 percent the past decade.

The brightening trend is corroborated by other data, including satellite analyses that are the subject of another paper in this week's Science.

Sunlight that isn't absorbed or reflected by clouds as it plunges earthward will heat the surface. Because the atmosphere includes greenhouse gasses, solar warming and greenhouse warming are related.

"The atmosphere is heated from the bottom up, and more solar energy at the surface means we might finally see the increases in temperature that we expected to see with global greenhouse warming," Long said.

In fact, he said, many believe that we have already been seeing those effects in our most temperature-sensitive climates, with the melting of polar ice and high altitude glaciers.

The report's authors stopped short of attributing a cause to the cycle of surface dimming and brightening, but listed such suspects as changes in the number and composition of aerosols—liquid and solid particles suspended in air—and how aerosols affect the character of clouds.

Over the past decade, the ARM program has built a network of instrumentation sites to sample cloud characteristics and energy transfer in a variety of climates, from tropical to polar.

"The continuous, sophisticated data from these sites will be crucial for determining the causes," Long said.

Long also pointed out that 70 percent of the planet's surface is ocean, for which we have no long-term surface brightening or dimming measurements.

//www.pnl.gov/news/2005/05-33.htm

--------


Why the Sun seems to be 'dimming'

1/13/05

By David Sington

They have reached the disturbing conclusion that the amount of solar energy reaching the Earth's surface has been gradually falling.

Paradoxically, the decline in sunlight may mean that global warming is a far greater threat to society than previously thought.

The effect was first spotted by Gerry Stanhill, an English scientist working in Israel.

Cloud changes

Comparing Israeli sunlight records from the 1950s with current ones, Dr Stanhill was astonished to find a large fall in solar radiation.

"There was a staggering 22% drop in the sunlight, and that really amazed me." Intrigued, he searched records from all around the world, and found the same story almost everywhere he looked.

Sunlight was falling by 10% over the USA, nearly 30% in parts of the former Soviet Union, and even by 16% in parts of the British Isles.

Although the effect varied greatly from place to place, overall the decline amounted to one to two per cent globally every decade between the 1950s and the 1990s.

Dr Stanhill called it "global dimming", but his research, published in 2001, met a sceptical response from other scientists.

//news.bbc.co.uk/2/hi/science/nature/4171591.stm
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