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<div class=Section1>
<p class=MsoNormal><b><span lang=EN style='font-size:18.0pt;font-family:"Arial","sans-serif"'>El
Niño tests forecasters<o:p></o:p></span></b></p>
<p class=MsoNormal><span lang=EN style='font-family:"Arial","sans-serif";
color:#333333'>As hints emerge of a major weather event this year, poor data
could thwart attempts to improve predictions.<o:p></o:p></span></p>
<p class=MsoNormal><span class=vcard><span lang=EN style='font-family:"Arial","sans-serif";
color:#333333'><a
href="http://www.nature.com/news/el-ni%C3%B1o-tests-forecasters-1.14972#auth-1">Jeff
Tollefson</a></span></span><span lang=EN style='font-family:"Arial","sans-serif";
color:#333333'><o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN style='font-family:"Arial","sans-serif";
color:#333333'>NATURE, 02 April 2014<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN style='font-family:"Arial","sans-serif";
color:#333333'>http://www.nature.com/news/el-ni%C3%B1o-tests-forecasters-1.14972<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN style='color:#333333'><o:p> </o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>The first sign of a
brewing El Niño weather pattern came in January, as trade winds that normally
blow from the east reversed course near Papua New Guinea. Barrelling back
across the tropical Pacific Ocean, they began to push warm water towards South
America. Now climate scientists and forecasters are on high alert.</span><span
lang=EN style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#333333'>
<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>A major El Niño event
— a periodic warming of waters in the eastern equatorial Pacific —
could boost temperatures and scramble weather worldwide. The most recent major
event, in 1997–98, was linked to thousands of deaths and tens of billions
of dollars in damage from droughts, fires and floods across several continents.
Yet more than 15 years later, forecasting the timing and intensity of El Niño
remains tricky, with incremental improvements in climate models threatened by
the partial collapse of an ocean-monitoring system that delivers the data to
feed those models.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>El Niño often emerges
during the Northern Hemisphere summer and peaks around December; forecast
models can do a reasonable job of predicting its eventual strength by July,
when the changes in ocean circulation that give rise to the weather pattern
have become pronounced. But scientists are working feverishly to provide
earlier forecasts, to allow governments more time to prepare for potentially
devastating weather patterns.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>In 1997, the emergence
of a record-breaking El Niño caught scientists by surprise, despite hints in
wind and sea surface temperature data (see <a
href="http://www.nature.com/news/el-ni%C3%B1o-tests-forecasters-1.14972#warm">‘Warming
up’</a>). The European Centre for Medium-Range Weather Forecasts in
Reading, UK, was reluctant to issue early warnings because its forecast model
was untested. And the model that had best predicted earlier El Niños —
developed by scientists at Columbia University’s Lamont–Doherty
Earth Observatory in Palisades, New York — foresaw neutral conditions.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>“We were in the
early days in forecasting,” says Michael McPhaden, an oceanographer at
the US National Oceanic and Atmospheric Administration (NOAA) in Seattle,
Washington. “Now we are much more systematic.”<a name=warm></a><o:p></o:p></span></p>
<p class=MsoNormal align=center style='text-align:center;line-height:17.85pt;
background:#ECECEC'><span style='border:none windowtext 1.0pt;padding:0in'><a
href="http://www.nature.com/news/el-nino-jpg-7.16543?article=1.14972"><span
style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#5E5E5E;
text-decoration:none'><img border=0 width=630 height=594 id="Imagen_x0020_2"
src="cid:image001.jpg@01CF4E60.C2BAE950"
alt="http://www.nature.com/polopoly_fs/7.16543.1396374158!/image/el-nino.jpg_gen/derivatives/landscape_630/el-nino.jpg"></span></a></span><span
lang=EN style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#333333'><o:p></o:p></span></p>
<p class=credit style='background:#ECECEC'><span lang=EN style='font-size:7.5pt;
font-family:"Arial","sans-serif"'>Source: NOAA<o:p></o:p></span></p>
<p class=MsoNormal style='line-height:17.85pt;background:#ECECEC'><span
lang=EN style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#333333'><a
href="javascript:;" title=Expand><span style='color:#5E5E5E;border:none windowtext 1.0pt;
padding:0in'>Expand</span></a><o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>This year, NOAA issued
its first forecast on 6 March, estimating a 50% chance that El Niño will
develop this summer. But that early projection, and others from weather
agencies and research institutions around the world, comes with lots of
uncertainty. Fickle tropical winds in spring can easily quash a brewing El Niño
— or strengthen it.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>Researchers say that
real progress in forecasting has come from systematically comparing the outputs
of groups of models, with each simulation run under a range of possible climate
conditions. “Combining these various predictions — doing some
crowd-sourcing, if you will — tends to lead to more reliable predictions,”
says Gabriel Vecchi, a climate modeller at NOAA’s Geophysical Fluid
Dynamics Laboratory in Princeton, New Jersey. Averaging the results of several
different forecasting models tends to cancel out flaws in an individual
program, he says.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>The sensitivity of the
simulations is also increasing. Global climate models divide the planet into
grids, like a computer screen divided into pixels, and represent climate
variables such as temperature as averages in each cell. Modellers increase the
resolution of their calculations by reducing the size of the cells.
Vecchi’s lab, for example, has shifted its model from a grid with cells
200 kilometres across to one with cells 50 kilometres across, thereby increasing
the number of cells by a factor of 16. In theory, this allows for more-accurate
representations of the microphysical processes and interactions that drive
weather and ultimately climate. Forecasters also continuously fine-tune how
they incorporate environmental-monitoring data and represent complex interactions
between air and ocean circulation.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>During the spring, when
forecasting is most difficult, such improvements have given climate models
based on physical processes a leg-up over less sophisticated statistical
models, which compare the current weather-system trends to those of past years
and essentially estimate the likelihood that history will repeat itself.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>Almost all of this
year’s initial forecasts suggest that a moderate to severe El Niño or
neutral conditions will emerge in coming months. None predicts El Niño’s
sister effect, La Niña, in which upwelling currents from the deep ocean bring
cooler waters to the surface off the Pacific coast of South America.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>In the coming weeks,
scientists will watch to see if warm water continues to flow across the Pacific
into the area off South America where El Niño forms. But in a potential blow to
the ongoing effort to improve forecast accuracy, their ocean-temperature data
will get progressively worse. A US-funded system of data-gathering buoys known
as the Tropical Atmosphere Ocean (TAO) array has started to break down as a
result of budget cuts that have hobbled its maintenance (see <a
href="http://doi.org/q72"><i>Nature</i> http://doi.org/q72; 2014</a>). NOAA has
committed to restoring most of the system by the end of the year, but that aid
will come months after crucial El Niño forecasts are issued. Scientists will be
forced to supplement the buoy data with satellite observations of water
temperature and sea level, which can serve as proxies for the depth of the wave
of warm water.<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>The stakes are high.
Since 1998, the eastern Pacific has been in a cold phase that is associated
with La Niña-like conditions, but every 15–30 years, as part of a cycle
known as the Pacific Decadal Oscillation, that trend flips. Kevin Trenberth, a
climate scientist at the US National Center for Atmospheric Research in
Boulder, Colorado, has theorized that a major El Niño could help to push the
ocean back into a warm phase, which studies have linked to more frequent El
Niños and more rapid global warming (see <a
href="http://www.nature.com/uidfinder/10.1038/505276a"><i>Nature</i> <b>505,</b>
276–278; 2014</a>).<o:p></o:p></span></p>
<p style='line-height:19.8pt;background:white'><span lang=EN style='font-size:
11.0pt;font-family:"Arial","sans-serif";color:#333333'>But all of that depends
on what happens as warm water washes across the Pacific in the next couple of
months. “The system is primed,” says Trenberth. “Will it wimp
out or really take off?”<o:p></o:p></span></p>
<p class=MsoNormal><span lang=EN><o:p> </o:p></span></p>
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