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<P><EM></EM> </P>
<P><EM>Science</EM> 24 July 2009:<BR>Vol. 325. no. 5939, pp. 460 -
464<BR>DOI: 10.1126/science.1171255</P></TD>
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<H2><FONT size=4>Observational and Model Evidence for Positive Low-Level Cloud
Feedback</FONT></H2>
<DIV></NOBR><NOBR>Amy C. Clement<SUP>1</SUP><SPAN id=em0><A
href="mailto:aclement@rsmas.miami.edu">aclement@rsmas.miami.edu</A>,</SPAN>
<SCRIPT type=text/javascript><!--
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</NOBR> <NOBR>Robert Burgman,<SUP>1</SUP></NOBR> <NOBR>Joel R.
Norris<SUP>2</SUP></NOBR> </DIV>
<DIV><SUP></SUP> </DIV>
<DIV><SUP>1</SUP> Rosenstiel School of Marine and Atmospheric Sciences,
University of Miami, Division of Meteorology and Physical Oceanography, MSC 362,
4600 Rickenbacker Causeway, Miami, FL 33149, USA.<BR><SUP>2</SUP> Scripps
Institution of Oceanography, University of California-San Diego, La Jolla, CA
92093–0224, USA.
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<P>Feedbacks involving low-level clouds remain a primary cause<SUP> </SUP>of
uncertainty in global climate model projections. This issue<SUP> </SUP>was
addressed by examining changes in low-level clouds over<SUP> </SUP>the Northeast
Pacific in observations and climate models. Decadal<SUP> </SUP>fluctuations were
identified in multiple, independent cloud<SUP> </SUP>data sets, and changes in
cloud cover appeared to be linked<SUP> </SUP>to changes in both local
temperature structure and large-scale<SUP> </SUP>circulation. This observational
analysis further indicated that<SUP> </SUP>clouds act as a positive feedback in
this region on decadal<SUP> </SUP>time scales. The observed relationships
between cloud cover<SUP> </SUP>and regional meteorological conditions provide a
more complete<SUP> </SUP>way of testing the realism of the cloud simulation in
current-generation<SUP> </SUP>climate models. The only model that passed this
test simulated<SUP> </SUP>a reduction in cloud cover over much of the Pacific
when greenhouse<SUP> </SUP>gases were increased, providing modeling evidence for
a positive<SUP> </SUP>low-level cloud feedback.<SUP> </SUP></P></DIV>
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