From: Mike Lorrey (mlorrey@yahoo.com)
Date: Mon Mar 24 2003 - 10:24:43 MST
http://www.space.com/scienceastronomy/sun_output_030320.html
Sun's Output Increasing in Possible Trend Fueling Global Warming
By Robert Roy Britt
Senior Science Writer
posted: 02:30 pm ET
20 March 2003
In what could be the simplest explanation for one component of global
warming, a new study shows the Sun's radiation has increased by .05
percent per decade since the late 1970s.
The increase would only be significant to Earth's climate if it has
been going on for a century or more, said study leader Richard Willson,
a Columbia University researcher also affiliated with NASA's Goddard
Institute for Space Studies.
The Sun's increasing output has only been monitored with precision
since satellite technology allowed necessary observations. Willson is
not sure if the trend extends further back in time, but other studies
suggest it does.
The recent trend of a .05 percent per decade increase in Total Solar
Irradiance (TSI) in watts per meter squared, or the amount of solar
energy that falls upon a square meter outside the Earth’s atmosphere.
The trend was measured between successive solar minima that occur
approximately every 11 years. At the bottom, the timeline of the many
different datasets that contributed to this finding, from 1978 to
present.
"This trend is important because, if sustained over many decades, it
could cause significant climate change," Willson said.
In a NASA-funded study recently published in Geophysical Research
Letters, Willson and his colleagues speculate on the possible history
of the trend based on data collected in the pre-satellite era.
"Solar activity has apparently been going upward for a century or
more," Willson told SPACE.com today.
Significant component
Further satellite observations may eventually show the trend to be
short-term. But if the change has indeed persisted at the present rate
through the 20th Century, "it would have provided a significant
component of the global warming the Intergovernmental Panel on Climate
Change reports to have occurred over the past 100 years," he said.
That does not mean industrial pollution has not been a significant
factor, Willson cautioned.
Scientists, industry leaders and environmentalists have argued for
years whether humans have contributed to global warming, and to what
extent. The average surface temperature around the globe has risen by
about 1 degree Fahrenheit since 1880. Some scientists say the increase
could be part of natural climate cycles. Others argue that greenhouse
gases produced by automobiles and industry are largely to blame.
Willson said the Sun's possible influence has been largely ignored
because it is so difficult to quantify over long periods.
Confounding efforts to determine the Sun's role is the fact that its
energy output waxes and wanes every 11 years. This solar cycle, as it
is called, reached maximum in the middle of 2000 and achieved a second
peak in 2002. It is now ramping down toward a solar minimum that will
arrive in about three years.
Connections
Changes in the solar cycle -- and solar output -- are known to cause
short-term climate change on Earth. At solar max, Earth's thin upper
atmosphere can see a doubling of temperature. It swells, and denser air
can puff up to the region of space where the International Space
Station orbits, causing increased drag on the ship and forcing more
frequent boosts from space shuttles.
Solar max has also been tied to a 2 percent increase in clouds over
much of the United States.
It might seem logical to assume tie climate to solar output, but firm
connections are few. Other studies looking further back in time have
suggested a connection between longer variations in solar activity and
temperatures on Earth.
Examinations of ancient tree rings and other data show temperatures
declined starting in the 13th Century, bottomed out at 2 degrees below
the long-term average during the 17th Century, and did not climb back
to previous levels until the late 19th Century. Separate records of
sunspots, auroral activity (the Northern Lights) and terrestrial
deposits of certain substances generated in atmospheric reactions
triggered by solar output, suggest the Sun was persistently active
prior to the onset of this Little Ice Age, as scientists call the
event.
Solar activity was lowest during the 17th Century, when Earth was most
frigid.
Large-scale ocean and climate variations on Earth can also mask
long-term trends and can make it difficult to sort out what is normal,
what is unusual, and which effects might or might not result from
shifts in solar radiation.
To get above all this, scientists rely on measurements of total solar
energy, at all wavelengths, outside Earth's atmosphere. The figure they
derive is called Total Solar Irradiance (TSI).
Heating up
The new study shows that the TSI has increased by about 0.1 percent
over 24 years. That is not enough to cause notable climate change,
Willson and his colleagues say, unless the rate of change were
maintained for a century or more.
On time scales as short as several days, the TSI can vary by 0.2
percent due to the number and size of sunspots crossing the face of the
Sun. That shift, said to be insignificant to weather, is however equal
to the total amount of energy used by humans, globally, for a year, the
researchers estimate.
The study analyzed data from six satellites orbiting Earth at different
times over the 24 years. Willson ferreted out errors in one of the
datasets that had prevented previous studies from discovering the
trend.
A separate recent study of Sun-induced magnetic activity near Earth,
going back to 1868, provides compelling evidence that the Sun's current
increase in output goes back more than a century, Willson said.
He said firm conclusions about whether the present changes involve a
long-term trend or a relatively brief aberration should come with
continued monitoring into the next solar minimum, expected around 2006.
=====
Mike Lorrey
"Live Free or Die, Death is not the Worst of Evils."
- Gen. John Stark
"Pacifists are Objectively Pro-Fascist." - George Orwell
"Treason doth never Prosper. What is the Reason?
For if it Prosper, none Dare call it Treason..." - Ovid
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