NASA/NOAA Study Finds El Niños are Growing Stronger

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Alan Buis 818-354-0474
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Jana Goldman 301-734-1123
National Oceanic and Atmospheric Administration, Silver Spring, Md.
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News release: 2010-277 Aug. 25, 2010

NASA/NOAA Study Finds El Niños are Growing Stronger

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-277&cid=release_2010-277

PASADENA, Calif. – A relatively new type of El Niño, which has its warmest waters in the central-
equatorial Pacific Ocean, rather than in the eastern-equatorial Pacific, is becoming more common and
progressively stronger, according to a new study by NASA and NOAA. The research may improve
our understanding of the relationship between El Niños and climate change, and has potentially
significant implications for long-term weather forecasting.

Lead author Tong Lee of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and Michael
McPhaden of NOAA's Pacific Marine Environmental Laboratory, Seattle, measured changes in El
Niño intensity since 1982. They analyzed NOAA satellite observations of sea surface temperature,
checked against and blended with directly-measured ocean temperature data. The strength of each El
Niño was gauged by how much its sea surface temperatures deviated from the average. They found
the intensity of El Niños in the central Pacific has nearly doubled, with the most intense event
occurring in 2009-10.

The scientists say the stronger El Niños help explain a steady rise in central Pacific sea surface
temperatures observed over the past few decades in previous studies—a trend attributed by some to
the effects of global warming. While Lee and McPhaden observed a rise in sea surface temperatures
during El Niño years, no significant temperature increases were seen in years when ocean conditions
were neutral, or when El Niño's cool water counterpart, La Niña, was present.

"Our study concludes the long-term warming trend seen in the central Pacific is primarily due to more
intense El Niños, rather than a general rise of background temperatures," said Lee.

"These results suggest climate change may already be affecting El Niño by shifting the center of
action from the eastern to the central Pacific," said McPhaden. "El Niño's impact on global weather
patterns is different if ocean warming occurs primarily in the central Pacific, instead of the eastern
Pacific.

"If the trend we observe continues," McPhaden added, "it could throw a monkey wrench into long-
range weather forecasting, which is largely based on our understanding of El Niños from the latter
half of the 20th century."

El Niño, Spanish for "the little boy," is the oceanic component of a climate pattern called the El Niño-
Southern Oscillation, which appears in the tropical Pacific Ocean on average every three to five years.
The most dominant year-to-year fluctuating pattern in Earth's climate system, El Niños have a
powerful impact on the ocean and atmosphere, as well as important socioeconomic consequences.
They can influence global weather patterns and the occurrence and frequency of hurricanes, droughts
and floods; and can even raise or lower global temperatures by as much as 0.2 degrees Celsius (0.4
degrees Fahrenheit).

During a "classic" El Niño episode, the normally strong easterly trade winds in the tropical eastern
Pacific weaken. That weakening suppresses the normal upward movement of cold subsurface waters
and allows warm surface water from the central Pacific to shift toward the Americas. In these
situations, unusually warm surface water occupies much of the tropical Pacific, with the maximum
ocean warming remaining in the eastern-equatorial Pacific.

Since the early 1990s, however, scientists have noted a new type of El Niño that has been occurring
with greater frequency. Known variously as "central-Pacific El Niño," "warm-pool El Niño,"
"dateline El Niño" or "El Niño Modoki" (Japanese for "similar but different"), the maximum ocean
warming from such El Niños is found in the central-equatorial, rather than eastern, Pacific. Such
central Pacific El Niño events were observed in 1991-92, 1994-95, 2002-03, 2004-05 and 2009-10. A
recent study found many climate models predict such events will become much more frequent under
projected global warming scenarios.

Lee said further research is needed to evaluate the impacts of these increasingly intense El Niños and
determine why these changes are occurring. "It is important to know if the increasing intensity and
frequency of these central Pacific El Niños are due to natural variations in climate or to climate
change caused by human-produced greenhouse gas emissions," he said.

Results of the study were published recently in Geophysical Research Letters.

For more information on El Nino, visit: http://sealevel.jpl.nasa.gov/ .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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