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Friday, September 30, 2005

Sun's Direct Role in Global Warming May Be Underestimated, Duke Physicists
Report

Study does not discount the suspected contributions of 'greenhouse gases'
in elevating surface temperatures

Durham, N.C. -- At least 10 to 30 percent of global warming measured
during the past two decades may be due to increased solar output rather
than factors such as increased heat-absorbing carbon dioxide gas released
by various human activities, two Duke University physicists report.

The physicists said that their findings indicate that climate models of
global warming need to be corrected for the effects of changes in solar
activity. However, they emphasized that their findings do not argue
against the basic theory that significant global warming is occurring
because of carbon dioxide and other "greenhouse" gases.

Nicola Scafetta, an associate research scientistworking at Duke's physics
department, and Bruce West, a Duke adjunct physics professor, published
their findings online Sept. 28, 2005, in the research journal Geophysical
Research Letters.

West is also chief scientist in the mathematical and information sciences
directorate of the Army Research Office in Research Triangle Park.

Scafetta's and West's study follows a Columbia University researcher's
report of previous errors in the interpretation of data on solar
brightness collected by sun-observing satellites.

The Duke physicists also introduce new statistical methods that they
assert more accurately describe the atmosphere's delayed response to solar
heating. In addition, these new methods filter out temperature-changing
effects not tied to global warming, they write in their paper.

According to Scafetta, records of sunspot activity suggest that solar
output has been rising slightly for about 100 years. However, only
measurements of what is known as total solar irradiance gathered by
satellites orbiting since 1978 are considered scientifically reliable, he
said.

But observations over those years were flawed by the space shuttle
Challenger disaster, which prevented the launching of a new solar output
detecting satellite called ACRIM 2 to replace a previous one called ACRIM
1.

That resulted in a two-year data gap that scientists had to rely on other
satellites to try to bridge. "But those data were not as precise as those
from ACRIM 1 and ACRIM 2," Scafetta said in an interview.

Nevertheless, several research groups used the combined satellite data to
conclude that that there was no increased heating from the Sun to
contribute to the global surface warming observed between 1980 and 2002,
the authors wrote in their paper.

Lacking a standardized, uninterrupted data stream measuring any rising
solar influence, those groups thus surmised that all global temperature
increases measured during those years had to be caused by solar
heat-trapping "greenhouse" gases such as carbon dioxide, introduced into
Earth's atmosphere by human activities, their paper added.

But a 2003 study by a group headed by Columbia's Richard Willson,
principal investigator of the ACRIM experiments, challenged the previous
satellite interpretations of solar output. Willson and his colleagues
concluded, rather that their analysis revealed a significant upward trend
in average solar luminosity during the period.

Using the Columbia findings as the starting point for their study,
Scafetta and West then statistically analyzed how Earth's atmosphere would
respond to slightly stronger solar heating. Importantly, they used an
analytical method that could detect the subtle, complex relationships
between solar output and terrestrial temperature patterns.

The Duke analyses examined solar changes over a period twice as long -- 22
versus 11years -- as was previously covered by another group employinga
different statistical approach.

"The problem is that Earth's atmosphere is not in thermodynamic
equilibrium with the sun," Scafetta said. "The longer the time period the
stronger the effect will be on the atmosphere, because it takes time to
adapt."

Using a longer 22 year interval also allowed the Duke physicists to filter
out shorter range effects that can influence surface temperatures but are
not related to global warming, their paper said. Examples include volcanic
eruptions, which can temporarily cool the climate, and ocean current
changes such as El Nino that affect global weather patterns.

Applying their analytical method to the solar output estimates by the
Columbia group, Scafetta's and West's paper concludes that "the sun may
have minimally contributed about 10 to 30 percent of the 1980-2002 global
surface warming."

This study does not discount that human-linked greenhouse gases contribute
to global warming, they stressed. "Those gases would still give a
contribution, but not so strong as was thought," Scafetta said.

"We don't know what the Sun will do in the future," Scafetta added. "For
now, if our analysis is correct, I think it is important to correct the
climate models so that they include reliable sensitivity to solar
activity.

"Once that is done, then it will be possible to better understand what has
happened during the past hundred years."