Goodbye El Niño, Hello La Niña
by Mark Hoover
The numbers are in. A recently-released NOAA review confirms that the latest
incarnation of El Niño was, indeed, the weather event of the century.
Compared with the previous title-holder in 1982, the 1997 El Niño
started earlier, grew faster, and amassed more energy. And then, in the
parlance of the researchers who study it, "it got legs," maintaining its
prodigious dimensions for months longer than in 1982.
Not content to just fade away, the El Niño in its endgame rewrote the
record books again, as it receded at an unprecedented rate. El Niño's
sea-surface temperature anomaly "just dropped like a rock. It was a hell
of a signal," says Mike McPhaden, who directs NOAA's tropical Pacific
monitoring program from his laboratory in Seattle. "We've never seen anything
like it." He should know. Using one of the largest scientific instruments ever
built—the Tropical Atmosphere/Ocean Array, a network of buoy-mounted
across the Pacific from Peru to Australia—it's his job to watch for changes
in that swath of the Pacific that is the womb of Earth's weather.
But now, finally, El Niño is gone, and as winter approaches, people
the world can breathe a collective sigh of relief...right? Unfortunately not.
True, the giant pool of abnormally warm water in the tropical Pacific that
made last year's weather so difficult has gone away. But in its place, an
abnormally cold pool of water has appeared, and it seems to have its own
mischievous agenda. The hot and cold extremes are both avatars of the El
Niño phenomenon, more properly called ENSO, or El
a name that reflects
its dual nature.
Pool of cold water (blue) off coast of South America.
El Niño's dramatic turnabout may portend yet another year of
weather ahead. As El Niño has transformed itself with lightning speed
its own opposite, the past year's weather disruptions may have been queued
up to be played again, but with a twist; what was baked will be frozen,
what was drenched will be parched, what was spared will be slammed. This
"cold phase" sometimes brings weather that is the mirror image of El
It's not a perfect symmetry, points out Michael Glantz, of NOAA's National
Climate and Atmospheric Research center in Boulder, Colorado. The
mechanics of El Niño's cold cycle are fundamentally different from the
cycle. "The rule of thumb is that the cold events don't get as cold as the
warm events get warm. If you heat the ocean, you get lots of rain, way
above normal. But if you cool the ocean, the most that happens is you shut
off the rain. Once it's shut off, you can't get negative rain."
Still, even Glantz thinks this year may be exceptional. "The other shoe may
be about to fall," he says. "Together, a strong El Niño and a strong
Niña can pack a climatological one-two punch second only to the change
seasons as a shaper of Earth's weather." Warning signs are already
abundant. Consider the following:
So when can when we expect the tropical Pacific to return to normal? The
surprising answer is basically, never. Normal is an average, but averages don't
tell us much about actual conditions. If you stand with your feet frozen in a
block of ice and your head in a pizza oven, your "average" body temperature
might be 98 degrees, but you will be not survive. Likewise, although we know
that year-in, year-out, the tropical Pacific on average is neither overly warm
nor overly cold, there are very few times when, like Goldilocks' porridge, it's
"just right." Most of the time, tropical ocean temperatures and currents are
see-sawing in slow motion toward one extreme or the other, in a natural and
recurrent cycle that takes years to complete. "We have to stop thinking of El
Niño as an event, and start thinking of it as part of the Earth's
breathing," says Princeton's George Philander. "It's as natural for the Earth
to have El Niño as it is for a bell to ring." In a word, it's normal for
the ocean to be abnormal.
- During a May and June that seemed more like August, much of the US
sizzled for weeks in temperatures 10, 20, even 30 degrees above
- The Southern plains and the Southeast broiled all summer long under
record heat. Texas and New Mexico in particular were hit by relentless strings of plus-90
and plus-100 degree days throughout June, July, and well into August. Rain
was sparse, and crop losses quickly mounted.
- Florida, wracked earlier in the spring by a rash of tornadoes, was next
blackened by fires consuming its dried-out forests and grasslands as the
rains failed in early summer. Although the rains finally returned, so did
the threat of a hyperactive hurricane season.
- The Atlantic hurricane season got off to an early start, and changes in
upper-level winds over the Atlantic have made conditions ideal for
hurricane formation. NOAA's Mississippi-based Hurricane Hunter storm
fliers have stayed on alert as the warm waters off the African coast have
generated tropical depressions like clockwork every three or four days.
- The year of torrential El Niño rain along the Pacific coast of South
America ended in late spring. Taking its place is the haunting specter of a
year of drought. It may easily be a full year before a single drop of rain
falls in parts of coastal Chile.
- In June, fires burning out of control in drought-stricken central Mexico
created massive clouds of acrid smoke, easily visible from space. Part of
the burned area was a critically important biodiversity reserve, a last
stand for numerous endangered species. Each day of fire brought
extinctions. Then, like a flipped switch, torrential rains came late in the
summer, and brought a new nightmare: flooding. The burnt land was further
scarred by erosion, without plants to soak up the water. Many people died as
rivers left their banks and inundated surrounding lands.
- California may face a fire peril of its own. El Niño rains
lush growths of desert brush (called chaparral) on coastal mountainsides.
Now, La Niña threatens a desiccating drought that will turn the
into a tinderbox by late autumn. Uncontrollable fires are possible,
perhaps likely. There's more: chaparral ash leaves behind a waxy film on
the soil, which will prevent winter rains from soaking in, resulting in
Just as morning gives way to afternoon, then to night, then to morning once
again, El Niño always gives way to the next part of its cycle—and so
up the conditions for its eventual return. In 1985, Philander coined a
name for this "next part" of El Niño, calling it La Niña, or
to go with El Niño's "Little Boy." The name stuck.
The La Niña half of the phenomenon is even less understood than the El
Niño half, in part because something has suppressed La Niña
formation for the past 20 years—precisely during the time instruments
monitoring it were developed and deployed. Scientists want to find out what
that "something" is, especially because that "something" seems to be
loosening its hold, indicating long-term changes in the climate system.
Some think global warming may involved; some think a larger oscillation
involving the entire ocean is to blame. No one can say yet.
Whether it's a boom or bust, one thing can be said with certainty about the
upcoming La Niña; it's going to crush a lot of cherished theories. With
dozen or more computer models predicting everything from Armageddon to a
no-show, "its time for natural selection to do a little weeding of our
theories" says McPhaden. As happened with the models that tried to foresee
El Niño, there will be some predictions right on the money, and some
See El Niño Scorecard to find out how the predictions stacked up
Photos/Illustrations: (1) NOVA/WGBH; (2,3) NOAA;
(4,5) ©Dr. John D. Cunningham/Visuals Unlimited.
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