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Press Release 04-130
Evidence Shaky for Sun's Major Role in Past Climate Changes
September 30, 2004
Arlington, Va.—Computer models of Earth's climate have consistently linked
long-term, high-magnitude variations in solar output to past climate
changes. Now a closer look at earlier studies of the Sun casts doubt on evidence of such cycles of brightness, their intensity and their possible influence on Earth's climate. The findings, by a solar physicist and two climate scientists funded by the National Science Foundation (NSF), appear in the October 1 issue of the journal Science.
"The relationship between the Sun's variability and its influence on climate remain open questions," according to Cliff Jacobs, program director in NSF's division of atmospheric sciences, which funded the research. "This study adds another piece to the puzzle and will spur efforts to unravel this complex relationship."
Scientists have attributed observed climate changes to a combination of
natural variations and human activities. Computer models of global
climate reproduced an observed global warming during the first half of
the 20th century when two solar influences were combined: a
well-documented 11-year sunspot cycle and decades-long solar cycles
now in dispute.
A more pronounced warming observed during the century's
last decades is attributed to greenhouse gases accumulating in Earth's
atmosphere and is not part of the study.
"Removing long-term solar cycles from the input to climate models
takes away about a tenth of a degree [Celsius] of early 20th century
warming," says Tom Wigley, a climate scientist at the National Center for
Atmospheric Research (NCAR) in Boulder, Colo. "This suggests that other influences on past climate changes may play a greater role than the solar one."
Peter Foukal of Heliophysics Inc., Gerald North of Texas A&M University,
and Wigley co-authored the paper.
The 11-year sunspot cycle is not questioned in the Science paper, but
its effect alone is "probably too little for a practical influence on
climate," the authors write. They also briefly consider possible
influences of ultraviolet and cosmic ray fluxes in Earth's climate.
The scientists think that long-term brightness variations of the Sun may
exist, but more convincing evidence is needed, they say. New
technologies now available can provide better data for understanding
Sun-climate relations, they conclude.
NASA co-funded the research.
-NSF-
Media Contacts
Cheryl Dybas, NSF (703) 292-7734 cdybas@nsf.gov
Anatta , NCAR (303) 497-8604 anatta@ucar.edu
Program Contacts
Cliff Jacobs, NSF (703) 292-8520 cjacobs@nsf.gov
The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2009, its budget is $9.5 billion, which includes $3.0 billion provided through the American Recovery and Reinvestment Act. NSF funds reach all 50 states through grants to over 1,900 universities and institutions. Each year, NSF receives about 44,400 competitive requests for funding, and makes over 11,500 new funding awards. NSF also awards over $400 million in professional and service contracts yearly.
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