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WORLD METEOROLOGICAL ORGANIZATION REGION IV ADOPTS CONSENSUS
EL NIÑO AND LA NIÑA INDEX AND DEFINITIONS

NOAA satellite image of the conditions in the Equatorial Pacific Ocean taken April 26, 2005, where NOAA is currently observing and monitoring a transition from weak warm-episode (El Niño) conditions to El Niño/Southern Oscillation neutral conditions that will continue during the next three months.April 28, 2005 NOAA announced today that the 26 nations of the World Meteorological Organization's Regional Association IV have adopted a Consensus Index and Definitions of El Niño and La Niña conditions. By doing so, scientists and governments throughout the region can better define potential impacts from these short-term climate shifts and prepare for remedial action. (Click NOAA satellite image for larger view of the conditions in the Equatorial Pacific Ocean taken April 26, 2005, where NOAA is currently observing and monitoring a transition from weak warm-episode (El Niño) conditions to El Niño/Southern Oscillation neutral conditions that will continue during the next three months. Please credit “NOAA.”)

The Consensus was agreed upon earlier this year by the NOAA National Weather Service, as the U.S. representative, and its meteorological service counterparts in Canada and Mexico. In adopting the North American Consensus, the RA IV Member nations, located in North and Central America and the Caribbean, agreed that the index and definitions could be revised in the future based on further scientific research, and Member nations were urged to define local thresholds for impacts based on the index. The Consensus will now be known as the WMO RA IV Consensus Index and Definitions of El Niño and La Niña. The next step is to seek a worldwide consensus on this approach through the WMO.

"This is a historic achievement and demonstrates the truly global nature of our environment," said retired Navy Vice Admiral Conrad C. Launtenbacher, Jr., Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator. "By agreeing to the same operational definition for El Niño and La Niña events, members will be better able to collaborate on understanding risks and mitigating impacts throughout the region. From NOAA's perspective, this helps us meet a critical goal of helping the world understand and react to shifts in regional climate regimes."

"With this agreement in place, scientists can focus on whether observations of the measurable changes in Pacific sea surface temperatures will lead to changes in the rain and temperature patterns around the world," said former Air Force Brig. Gen. Jack Kelly, NOAA deputy undersecretary and current U.S. representative to the WMO. "Scientists are still cracking the code on these pendulum swings of short-term climate events. But these definitions focus more attention on these shifts and help governments in the region brace for periodic flooding or drought conditions. Being able to act in a timely fashion can save lives and help mitigate economic impacts."

Newly-elected WMO regional association president Carlos Fuller of Belize applauded the regional agreement for an El Niño/La Niña index and definitions. "We owe it to our public to reach agreement on terms, even as we improve our science and our ability to use this information at the national and regional levels," Fuller said.

As part of the agreement, the WMO Commission for Climatology has established an expert team on El Niño and La Niña definitions. Led by NOAA, the expert team will, among other duties, catalog El Niño and La Niña definitions in operational use globally to further assist improving analysis of local and regional impacts.

The index is defined as a three-month average of sea surface temperature departures from normal for a critical region of the equatorial Pacific (Nino 3.4 region; 120W-170W, 5N-5S). This region of the tropical Pacific contains what scientists call the "equatorial cold tongue," a band of cool water that extends along the equator from the coast of South America to the central Pacific Ocean. Departures from average sea surface temperatures in this region are critically important in determining major shifts in the pattern of tropical rainfall, which influence the jet streams and patterns of temperature and precipitation around the world. Operational definitions for El Niño and La Niña are:

  • El Niño: A phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño 3.4 region greater than or equal in magnitude to 0.5 degrees C, averaged over three consecutive months.
  • La Niña: A phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño 3.4 region greater than or equal in magnitude to 0.5 degrees C, averaged over three consecutive months.

NOAA is currently observing and monitoring a transition from weak warm-episode (El Niño) conditions to El Niño/Southern Oscillation neutral conditions that will continue during the next three months. ENSO-neutral conditions will likely prevail during the northern summer.

NOAA began using the index and definitions operationally for monitoring and predicting El Niño and La Niña conditions on Sept. 1, 2003. NOAA issues assessments of ENSO's status in the Monthly Climate Diagnostic Bulletin, the ENSO Diagnostic Discussion and the Weekly ENSO update.

NOAA, an agency of the U.S. Department of Commerce, is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation's coastal and marine resources.

Relevant Web Sites
NOAA Climate Prediction Center's El Niño/Southern Oscillation (ENSO) Diagnostic Discussion

NOAA Climate Prediction Center's ENSO Page

Media Contact:
Greg Romano, NOAA National Weather Service, (301) 713-0622 ext. 169