Scientists hope to forecast the arrival of El Niños, the 800-pound
gorillas of the global climate, as much as two years in advance, thanks to a
new, improved computer model.
Until now, forecasters considered themselves lucky if they foresaw El
Niños -- which can turn California into a lake or drought land, depending on
the timing -- a half-year in advance. Now, though, U.S. and Chinese
scientists have unveiled a clearer crystal ball: a souped-up computer model
based on much older climate records.
They develop such models by turning a routine scientific method on its
head. As every science student learns, scientists test hypotheses by using
them to make predictions. For example, they predict that a solar eclipse will
occur at a certain time on a future date. If it doesn't, then they know
there's something wrong with their model of celestial motions.
By contrast, the U.S.-China team tested their climate model by
"predicting" events in the past -- that is, past El Niños, as far back as
1857. This method is known as "retrospective forecasting" or "hindcasting."
The team's findings are reported in today's issue of the journal Nature.
The leader of the U.S.-China team is Dake Chen, who is associated both
with Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y.,
and the Laboratory of Ocean Dynamic Processes and Satellite Oceanography in
Hangzhou, China.
Arthur Miller of Scripps Institution of Oceanography in La Jolla, who was
not connected with the Nature paper, called the team's results "astounding ...
absolutely amazing." But he cautioned that the new computer model is based on
statistical analyses, and statistics is a notoriously tricky business.
"Only time will tell if their procedure is superior to current
forecasting methods," Miller said.
El Niños begin when tropical Pacific waters warm, altering the flow of
ocean currents and redistributing rainfall. At worst, a severe El Niño can
ravage much of the planetary ecosystem, triggering droughts in normally wet
regions, floods in normally dry lands and famines that afflict millions. They
can also threaten fragile species and lessen biodiversity in usually lush
terrain.
Like Internal Revenue Service audits, El Niños tend to sneak up on you.
They can occur as frequently as once every two years, and as infrequently as
once per decade. The last El Niño to annoy California was a weak one that
burned out in 2002.
In that regard: The new computer model and several other, independent
computer simulations of the world climate hint -- just hint, mind you --
that another El Niño may be brewing in the Pacific, says one scientist who co-
authored the Nature article.
However, it's much too early to say whether the hint is just a mirage
that will vanish in coming months, warned the scientist, Stephen Zebiak. Most
of the world's climate simulations do not yet show any warming of Pacific
waters, he noted. Hence Californians -- who already have plenty of other
things to worry about -- shouldn't head for the hills just yet.
The Nature article is "first quality in every sense," said another
Scripps researcher, Guillermo Auad, who isn't connected with the U.S.-China
team. However, he added, the team's model contains a "weak point": It doesn't
do a great job of hindcasting the really, really big El Niños of history.
"This seems to be a common problem to all other El Niño prediction (models)
that I know of," he said.
