[OANNES Foro] Stalled El Niño poised to resurge

[Mario Cabrejos]

Studies of brewing weather event test understanding of past and future
climate.

Stalled El Niño poised to resurge

 
<http://www.nature.com/news/stalled-el-ni%C3%B1o-poised-to-resurge-1.15814?W
T.ec_id=NATURE-20140904#auth-1> Mark Zastrow

Nature 513, 15 doi:10.1038/513015a

02 September 2014

 

 When Julia Baum tried to fly to the remote Pacific atoll of Kiritimati with
a chest freezer in her luggage last month, her airline objected. Baum needed
it to store samples of the algae that underpin the atoll’s fragile coral
ecosystem. “It was a lot of smiling and begging,” she recalls. “‘It’s for
science! It’s for coral reefs! Help us!’” Airline officials let it go.

 

This year Baum, a marine biologist at the University of Victoria in Canada,
has an added incentive to head into the field: the weather pattern known as
El Niño is brewing, and she wants to see what the warming it brings to the
tropical Pacific Ocean will do to the algae that live in the reefs of
Kiritimati, part of the island nation of Kiribati.

Hers will be one of many teams watching this potential El Niño. A growing
array of satellites, moored and free-floating buoys and autonomous
underwater vehicles is tracking changes in ocean temperatures and
atmospheric conditions. Those data are flowing into climate models that try
to predict the strength and timing of this year’s El Niño event — the
erratic behaviour of which has already tested forecasters. If researchers
could learn to predict such events with precision, it would significantly
improve their understanding of the past and future climate.

The first signs of an El Niño came in January, when the east-to-west trade
winds that blow across the tropics suddenly weakened, and a burst of winds
from the west triggered a slow surge of warm water into the eastern
equatorial Pacific. In 1997, similar conditions helped to set in motion one
of the strongest El Niño events on record, which caused extreme rainfall
along the western coasts of North and South America and drought in Australia
and southeast Asia, resulting in thousands of deaths and tens of billions of
dollars’ worth of damage.

Sustaining an El Niño requires the ocean and the atmosphere to work
together. Normally, the warming in the eastern Pacific that presages such an
event strengthens wind patterns that push even more warm water eastward. But
this year, the atmosphere did not play its part. As a result, the ocean
cooled in May, June and July, and the El Niño stalled.

Anthony Barnston, a seasonal climate forecaster at Columbia University in
New York City, says the latest data show that winds from the west are again
forming — a second chance for a full-blown El Niño. His team estimates that
there is a 75% chance that a weak to moderate event will form by the end of
this year, just a bit later than researchers had thought. The predictions
are in line with those from the US National Oceanic and Atmospheric
Administration (NOAA), which puts the chance of a weak to moderate El Niño
at 65%.

Whatever transpires, the next few months will be an important test for the
latest generation of seasonal forecast models. Scientists struggled to
interpret the wildly divergent predictions provided by models before the El
Niño of 1997–98, but this time there is cause for optimism. When the warming
of the eastern Pacific started to slow this summer, the latest models —
which run at higher resolution and on more powerful computers than their
predecessors — predicted that El Niño would stall in the summer and then
resurge. “If we don’t see an El Niño this year, then we have a big black
mark on the model performance,” says Barnston.

Other scientists are trying to learn what they can about El Niño’s links to
future climate change.

Climate models disagree on whether global warming will alter El Niño’s
strength or frequency. But even if the general pattern of El Niño events
does not change, the warming produced by an individual El Niño in an overall
warmer climate could generate more extreme weather, says Wenju Cai, a
climate scientist at the Commonwealth Scientific and Industrial Research
Organisation’s Marine and Atmospheric Research centre in Aspen­dale,
Australia. “The world is not waking up to that,” says Cai, whose modelling
work suggests that by the end of this century, El Niño events could become
twice as common as they were for most of the twentieth century (
<http://www.nature.com/uidfinder/10.1038/nclimate2100> W. Cai et al. Nature
Clim. Change 4, 111–116; 2014).

Back in the tropical Pacific, Baum’s colleagues hope to gain a fuller
understanding of El Niño’s history by analysing the oxygen content, salinity
and temperature of water samples from Kiritimati and the Palmyra atoll, a US
territory roughly 680 kilometres away. Researchers will use the data to help
to calibrate records of past climate that are preserved in fossilized coral.
Shifting ratios of oxygen isotopes captured in coral layers can reveal
changes in ocean temperature, providing a record of El Niño events going
back thousands of years.

One thing is certain, says Michael McPhaden, an oceanographer with NOAA in
Seattle, Washington: however this year’s El Niño watch plays out, it will
influence research for several years. “Why has nature surprised us in this
startling way?” he asks. “Figuring it out is going to be really important.”

 



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