October 17, 2011 | Climate change is not expected to affect the extent or frequency of the El Niño/Southern Oscillation (ENSO) over the 21st century, but it could worsen its impacts. That’s the conclusion of a modeling study published in Journal of Climate in September.

ENSO events occur about every 4–12 years when surface waters warm anomalously in the tropical Pacific Ocean off the coast of South America. The phenomenon creates unusual weather patterns around the globe that can cause billions of dollars in damages from floods and droughts. Advance knowledge of ENSO’s behavior could help communities prepare for these catastrophes.

The research team, which was led by Samantha Stevenson (University of Colorado Boulder) and includes NCAR scientists Markus Jochum, Richard Neale, Clara Deser, and Gerald Meehl, used the NCAR-based Community Climate System Model (CCSM) to simulate the effects of climate change on ENSO over the 21st century. They found no significant changes in its extent or frequency.

However, the warmer and moister atmosphere of the future could make ENSO events more extreme. For example, the model predicts the blocking high pressure south of Alaska that often occurs during La Niña winters to strengthen under future atmospheric conditions, meaning that intrusions of Arctic air into North America typical of La Niña winters could be stronger in the future.

Stevenson, S., B. Fox-Kemper, M. Jochum, R. Neale, C. Deser, and G. Meehl, "Will there be a Significant Change to El Nino in the 21st Century?," Journal of Climate, 2011; DOI: 10.1175/JCLI-D-11-00252.1

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