El Niños are growing stronger

NASA/Jet Propulsion Laboratory: 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."…

Deviations from normal sea surface temperatures (left) and sea surface heights (right) at the peak of the 2009-2010 central Pacific El Niño, as measured by NOAA polar orbiting satellites and NASA's Jason-1 spacecraft, respectively. The warmest temperatures and highest sea levels were located in the central equatorial Pacific. Image credit: NASA/JPL-NOAA