Problem Child El Niño Has Returned
By Phil Berardelli
ScienceNOW Daily News
9 July 2009

Batten down the hatches! The disruptive weather pattern known as El Niño has
developed once again in the central Pacific Ocean, the first time since 2006,
scientists announced today. Satellite instruments have recorded a band of
telltale warming in surface waters of about 1°C. That could mean damaging
storms this winter in California and across the southern half of the United
States, as well as heavy rains in Central and South America, drought in
Southeast Asia and Australia, and less productive fisheries in the eastern
Pacific. On the positive side, El Niño's return also tends to moderate the
Atlantic hurricane season and bring milder winters to North America.
For more than a century, ship captains and fishers have been aware of a
recurring pattern in the weather in the eastern Pacific, which tends to repeat
itself every 3 to 4 years. The pattern is known as El Niño--or "The Boy
Child"--because its effects seem to be felt the most around Christmastime.
Scientists now understand that an El Niño period begins when a narrow but
well-defined band of surface water, at least 0.5°C warmer than normal,
accumulates in the eastern equatorial Pacific and spreads westward during late
spring and early summer (see diagram). Satellite data have now confirmed just
such a pattern, report scientists at the U.S. National Oceanic and Atmospheric
Administration (NOAA).

What isn't yet known is how strong an El Niño will eventually develop and how
long it is likely to last. That's because the data collected so far are
insufficient to determine those factors. But NOAA's Climate Prediction Center in
Camp Springs, Maryland, estimates that for the next several months the overall
effect across the United States should be mild. Whether El Niño will stick
around for longer and bring destruction remains undetermined.

The previous El Niño, which occurred in 2006–2007, produced relatively tepid
effects. But one of its recent predecessors, in 1997–1998, was considered the
strongest ever recorded. It caused the average sea-surface temperature in the
central Pacific to rise as much as 5°C above normal and warmed average global
air temperatures temporarily by about 2.5°C --some five times higher than an El
Niño normally generates. That episode also more than doubled 1997–1998
seasonal rainfall over Southern California, washing out roads and bridges and
causing landslides.