in case you need something big to worry about
- From: "Florida" <demeter547opine@xxxxxxxxx>
- Date: 25 Jan 2006 08:25:05 -0800
Baffled Scientists Say Less Sunlight Reaching Earth Robert Roy Britt
LiveScience Managing Editor
LiveScience.com
2 hours, 20 minutes ago
After dropping for about 15 years, the amount of sunlight Earth
reflects back into space, called albedo, has increased since 2000, a
new study concludes.
That means less energy is reaching the surface. Yet global temperatures
have not cooled during the period.
Increasing cloud cover seems to be the reason, but there must also be
some other change in the clouds that's not yet understood.
"The data also reveal that from 2000 to now the clouds have changed so
that the Earth may continue warming, even with declining sunlight,"
said study leader Philip R. Goode of the New Jersey Institute of
Technology. "These large and peculiar variabilities of the clouds,
coupled with a resulting increasing albedo, presents a fundamental,
unmet challenge for all scientists who wish to understand and predict
the Earth's climate."
Cloud changes
Earth's albedo is measured by noting how much reflected sunlight in
turn bounces off the Moon, something scientists call earthshine. The
observations were made at the Big Bear Solar Observatory in California.
The findings will be published Jan. 24 in Eos, a weekly newspaper of
the American Geophysical Union.
On any given day, about half of Earth is covered by clouds, which
reflect more sunlight than land and water. Clouds keep Earth cool by
reflecting sunlight, but they can also serve as blankets to trap
warmth.
High thin clouds are better blankets, while low thick clouds make
better coolers.
Separately, satellite data recently showed that while the difference
between high and low clouds had long been steady at 7-8 percent, in the
past five years, for some unknown reason, the difference has jumped to
13 percent. High, warming clouds have increased while low clouds have
decreased.
Research shows condensation trails, or contrails from jet airplanes,
fuel more high-altitude clouds. But they have not been shown to account
for all the observed change.
What about global warming?
Earth's albedo appears to have experienced a similar reversal during a
period running from the 1960s to the mid-1980s.
Goode's team says there may be a large, unexplained variation in
sunlight reaching the Earth that changes over the course of two decades
or so, as well as a large effect of clouds re-arranging by altitude.
How do the findings play into arguments about global warming and the
apparent contribution by industrial emissions? That's entirely unclear.
"No doubt greenhouse gases are increasing," Goode said in a telephone
interview. "No doubt that will cause a warming. The question is, 'Are
there other things going on?'"
What is clear is that scientists don't understand clouds very well, as
a trio of studies last year also showed.
"Clouds are even more uncertain than we thought," Goode said.
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