EL NI脩O, the reversal of ocean currents across the Pacific that
periodically disrupts the world鈥檚 weather, has won another round in its
cat-and-mouse game with climate modellers by sneaking up largely unseen.
In the past two months, waters in most of the tropical Pacific have warmed
dramatically, by up to 2 掳C in places, as surface water from the western Pacific
and storm systems that normally remain over Indonesia have migrated eastwards.
The events herald the onset of a new El Ni帽o, according to an alert
issued earlier this month by the US National Oceanic and Atmospheric
Administration (NOAA).
鈥淭he consequences will probably be felt worldwide over the coming year,鈥� says
David Parker, an El Ni帽o tracker at Britain鈥檚 Meteorological Office in
Bracknell. The new El Ni帽o will increase the risk of serious drought in
Australia, India, Brazil and East Africa. It will also heighten the danger of
torrential rain and floods in American deserts from Peru to California, and of
forest fires in Indonesia.
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On past form, the event will also add to global warming. 鈥淪o far, 1997 is
already the second warmest year ever, so we could see a new record,鈥� says
Parker. The warm surge will probably peak at the end of the year鈥攋ust in
time for the climax of negotiations at a meeting of the UN Convention on Climate
Change in Japan in December, which is scheduled to agree tough new emissions
standards for greenhouse gases.
Many climate modellers who have prided themselves on predicting El
Ni帽o up to a year ahead have been caught out this time. 鈥淲e are
scratching our heads as to why our models didn鈥檛 anticipate it,鈥� says Stephen
Zebiak of the Lamont-Doherty Earth Observatory at Columbia University in New
York. Zebiak and his colleague Mark Cane, widely regarded as the world鈥檚 top El
Ni帽o forecasters, successfully predicted the onset of the last two major
El Ni帽o events, in 1987 and 1991.
But they failed to predict that the 1991 El Ni帽o would remain for an
unprecedented three years, rather than the normal nine months or so. And now the
latest event has eluded them鈥攍ast November, their forecast was for
鈥渃ooler-than-normal conditions through July 1997鈥�. 鈥淥ur most recently revised
model still isn鈥檛 seeing it,鈥� says Zebiak. 鈥淚t is predicting an El Ni帽o
for 1998.鈥�
He has one hope, though: 鈥淚t is just possible that this will prove to be a
false start. Sometimes, it looks like an El Ni帽o is beginning and then it
falters, returning for real the following year. Otherwise, it鈥檚 back to the
drawing board. We鈥檒l need to look in detail both at the model and the data we
put into it.鈥�
Most other teams of El Ni帽o forecasters are in the same position.
NOAA鈥檚 review of models published last November in the Climate Diagnostics
Bulletin concluded by predicting 鈥渁 continuation of present [cool]
conditions through May 1997鈥�. NOAA鈥檚 own modellers did predict 鈥渁 trend towards
slightly warmer-than-normal conditions [in the tropical Pacific] over the next
nine months鈥�. But it stopped short of an El Ni帽o forecast.
The failures suggest a hard task ahead for a new International Institute for
Climate Prediction being set up by NOAA, with collaborators from Australia,
Brazil, Japan and Taiwan. The institute鈥檚 first task is to improve the
forecasting of El Ni帽o.
