Last Updated: Friday - 09/24/2010
Week of June 7, 2004
Dimming sun threatens climate
Relatively unknown threat is turning down sun beams
By SUZANNE ELSTON
I had a feeling that something had changed. For as long as I can remember, long before mounting concerns about ozone depletion and increased levels of ultraviolet radiation, I've been extremely light sensitive. As a kid I could never go out without wearing good quality sunglasses, even on overcast days.
Earlier this year it struck me that daylight was somehow different. I noticed it one brilliant spring afternoon when I ventured outside. Although the sun was shining in a cloudless blue sky, I didn't have to immediately reach for my ever-present sunglasses. It was almost as if the sun had been turned down a few notches. Faded.
Global dimmingIt may be a coincidence, but there is increasing scientific evidence that the Earth's surface is receiving much less sunlight than it did when I was a kid. Atsumu Ohmura, a researcher at the Swiss Federal Institute of Technology, first detected the phenomenon known as global dimming, almost 20 years ago. Ohmura noticed that the recorded levels of sunlight throughout Europe were almost 10 per cent lower than had been recorded three decades earlier. His discovery was so astonishing that when he published his discovery in 1989, "It was ignored," he said.
Using a simple measuring instrument called a radiometer, other scientists have made similar findings, and their discoveries have also pretty much been ignored. Then in 2001, Dr. Gerald Stanhill and Dr. Shabtai Cohen began collecting their own data. Their results confirmed that the amount of sunlight reaching the Earth's surface has decreased from between 0.23 and 0.32 per cent per year from 1958 to 1992.
And now new research by Dr. Beate Liepart, a climatologist at the Lamont-Doherty Earth Observatory at Columbia University, is finally beginning to attract some attention.
The problem, not surprisingly, appears to be caused by pollution, the same kind of pollution that is causing global warming. Some sunlight is being bounced back into space by air born soot and other particulate pollution, caused primarily by the burning of fossil fuels. This same pollution causes greater condensation of water droplets, which in turn leads to thicker clouds, which block even more sunlight.
At first glance, it would appear that the effects of global dimming might actually mitigate the impact of global warming by creating a net sum gain, and tidily ridding us of what many consider to be the greatest threat to the future of the planet. Not so. What scientists do know about this phenomenon is that it may actually worsen the impact of climate change.
One of the problems is that darker, cloudier skies inhibit photosynthesis, the conversion of sunlight and carbon dioxide into oxygen. While the science of global dimming is very new, Cohen notes that for every one per cent decrease in solar radiation, there is a corresponding one per cent drop in photosynthesis.
While Atsumu Ohmura's research suggested that overall there has been a 10 per cent decrease in solar radiation in the last 30 years, areas of the former Soviet Union have witnessed a 20 per cent drop, while the heavily polluted skies over Hong Kong have caused a 37 per cent drop in sunlight. What this means for the health of the world's forests, the carbon sinks of the planet and our greatest hope against climate change, nobody knows.
Global dimming will also impact renewable energy technologies, such as solar and wind power. The effect not only means less sunlight, hence a reduction in the available fuel for solar collectors, but some predict it will also calm global winds. This will increase our use of fossil fuels for power generation and further exacerbate climate change.
If you feel like you've missed something in all of this, you're not alone. Even the Intergovernmental Panel on Climate Change, (the world's scientific authority on global warming), has yet to include global dimming on its agenda. "The IPCC is the group that should investigate this and work out if people should be scared of it," said Cohen.
Wake up, scientistsWhile the theory of global dimming remains controversial, the mounting body of evidence suggests that it is a real phenomenon that warrants our attention. For now, it's a question of waiting for the scientific community to sort this mess out. Let's hope they don't wait too long.
Recommended websites:The science of global dimming is so new that there is not a lot of information available. Check out Columbia University's Lamont-Doherty Earth Observatory at www.ldeo.columbia.edu. There is also some limited information available at www.wordspy.com/words/globaldimming.asp.
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