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<DIV class=article-heading>
<DT>Nature</DT>
<DT><ABBR
title="Digital Object Identifier">doi</ABBR>:10.1038/nature.2014.14546</DT>
<DT> </DT></DIV>
<DIV class=article-heading><FONT size=5><STRONG>Frequency of extreme El Niños to
double as globe warms</STRONG></FONT></DIV>
<DIV>Climate models agree on projections of changing rainfall patterns from
future warming of the tropical Pacific Ocean.</DIV>
<DIV class=popup-parent data-role="popup-parent"><SPAN class=vcard><A class=fn
href="http://www.nature.com/news/frequency-of-extreme-el-ni%C3%B1os-to-double-as-globe-warms-1.14546?WT.ec_id=NEWS-20140121#auth-1"
data-popup-width="estimate">Jeff Tollefson</A></SPAN></DIV>
<DIV class=pubdate-and-corrections><TIME datetime="2014-01-19" pubdate>19
January 2014</DIV>
<DIV class=pubdate-and-corrections><A
href="http://www.nature.com/news/frequency-of-extreme-el-ni%C3%B1os-to-double-as-globe-warms-1.14546?WT.ec_id=NEWS-20140121">http://www.nature.com/news/frequency-of-extreme-el-ni%C3%B1os-to-double-as-globe-warms-1.14546?WT.ec_id=NEWS-20140121</A></DIV>
<DIV class=pubdate-and-corrections></TIME></DIV>
<DIV class=visually-hidden>Global-warming’s impact on the tropical Pacific Ocean
has been hotly contested, but an analysis now suggests that powerful warming
events in the eastern equatorial region, known as El Niños, are likely to double
as greenhouse-gas emissions rise this century.</DIV>
<DIV class=section>
<DIV class="content no-heading cleared main-content">
<P>The study, published today in <I>Nature Climate Change</I><SUP><A
id=ref-link-1 class=ref-link
title="Cai, W. et al. Nature Clim. Change http://dx.doi.org/10.1038/NCLIMATE2100 (2014)."
href="http://www.nature.com/news/frequency-of-extreme-el-ni%C3%B1os-to-double-as-globe-warms-1.14546?WT.ec_id=NEWS-20140121#b1">1</A></SUP>,
focuses only on extreme events such as the 1997‒1998 El Niño, which affected
weather across the globe. Climate models have long differed regarding
global-warming’s precise impact on El Niño and its sister effect, La Niña, which
cools the same area. But the current analysis finds agreement when it comes to
major rainfall trends caused by the most intense El Niños.</P>
<P>“The present day’s moderate El Niño becomes an extreme event in the future,”
says lead author Wenju Cai, a climate modeller at the Commonwealth Scientific
and Industrial Research Organization in Aspendale, Australia.</P>
<P>The key, Cai says, was to essentially redefine extreme El Niños and focus on
the weather rather than the condition of the ocean itself. Instead of using the
standard definition, which focuses on the difference in ocean surface
temperatures between the eastern and western equatorial Pacific, the researchers
focused on rainfall on the eastern side of the basin.</P>
<P>The team identified 20 climate models — half of those available — that were
capable of simulating extreme rainfall. They then used the models to compare the
occurrence of extreme El Niños in a control period, 1891 to 1990, versus a
warmer period extending from 1991 to 2090. Although the total number of El Niño
events decreased, 17 out of the 20 models predicted more major El Niño events,
with the average frequency increasing from once every 20 years to once per
decade.</P>
<DIV class="related-stories-box box">“I’ve been at this long enough to know that
you have to look at everything five times before you are entirely convinced, but
I like the paper,” says David Neelin, a climate scientist who studies
ocean‒atmosphere interactions at the University of California, Los Angeles.
“It’s a very promising analysis.”</DIV>
<P>The models suggest that the eastern tropical Pacific is likely to warm more
than the west, and that extra warmth effectively primes the pump for major
storms. As such, even smaller El Niño events — as defined by the temperature
gradient across the basin, with warming in the east — can have larger effects on
rainfall.</P>
<P>The most immediate impact would be on neighboring countries such as Peru and
Ecuador, but Cai says that major El Niños could affect the weather in far-flung
locales, from southeast Asia to the American Southwest. “It’s really a massive
reorganization of atmospheric circulation,” he says, noting that the 1997‒1998
El Niño inflicted tens of billions of dollars in damage and killed thousands of
people around the globe.</P>
<P>More research will be needed to assess the global consequences, but the study
nonetheless advances El Niño research in a way that is more relevant to society,
says Shang-Ping Xie, a climate modeller at the Scripps Institution of
Oceanography in La Jolla, California. “It kind of steals attention away from the
traditional definition of El Niño and focuses on a more useful and relevant
variable like rainfall,” he says.</P></DIV>
<DL class=citation>
<DT><A href="javascript:;" jQuery164014777521623137235="8"><STRONG><FONT
color=#000000>References</FONT></STRONG></A></DT></DL></DIV>
<DIV id=references class="section expanded">
<DIV class=content>
<OL class=references>
<LI id=b1>
<P><SPAN class="vcard author"><SPAN class=fn>Cai, W.</SPAN></SPAN> <I>et
al</I>. <SPAN class=source-title>Nature Clim. Change</SPAN> <A
href="http://dx.doi.org/10.1038/NCLIMATE2100">http://dx.doi.org/10.1038/NCLIMATE2100</A>
(<SPAN class=year>2014</SPAN>).</P></LI></OL></DIV></DIV></FONT></BODY></HTML>