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Dispatch #4 

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September 15, 2004

The science of this workshop is focused around the climate phenomenon known as El Niño, or more formally ENSO (El Niño Southern Oscillation). We heard from climate forecaster Tony Barnston of Columbia University’s International Research Institute (http://iri.columbia.edu/) about the latest in El Niño forecasting and climate prediction (NOTE: the audio stream for this session is not available).

The biggest news is that earlier in September, NOAA (http://www.noaanews.noaa.gov/stories2004/s2317.htm) announced that a “weak” El Niño has developed in the east-central tropical Pacific (http://iri.columbia.edu/climate/ENSO/currentinfo/update.html). When climate scientists say weak, they mean that the warming of sea surface temperature that characterizes El Niño is relatively small. For this current El Niño, the ocean temperature is an average of 1 degree Centigrade above normal just to the east of the dateline in the tropical Pacific. As this warmer water on the sea surface spreads eastward toward South America, it can impact weather in the U.S. and around the globe, creating wetter-than-normal or drier-than-normal conditions (in California, we get higher rainfall in the winter during El Niño years).

Predicting El Niño
This is a late-developing El Niño, Tony Barnston says, and took many of us by surprise. Usually they pop up in late spring and may persist for about a year. “My confession is that we’re not good at predicting the onset of El Niño but we’re pretty good at knowing about how long they will last once they get started,” he says. That’s fine for the U.S., which usually feels the impact of El Niño six months after it develops. “But people in India, Australia, and Africa’s Sahel desert probably think we’re dumb because they start experiencing impacts much earlier, from June through August, just as the El Niño usually begins, and have no time to prepare.”

Why is El Niño so hard to predict? It comes down in part to the difference between weather and climate, Barnston says. When scientists say weather, they’re talking about the short-term changes in the atmosphere that lead to rain, wind, clouds, and changing temperature on a day-to-day basis. Climate is the long-term or seasonal average of temperature and precipitation that happens over months or years. “We’re good at weather forecasting, there are computer models that provide lots of details about storms, winds, fronts, and pressure conditions out to about five days in the future.” Predicting climate is another matter. Longer-term climate conditions are subject to many factors working together, and the system is very sensitive to initial conditions. That means that a small change in atmospheric pressure, wind patterns, or ocean temperatures and currents can have a large impact on weather for any particular day in the future beyond the fifth day. Still, knowing about likely changes in seasonal average temperature, rain, or snow patterns is very useful for farmers, water and utility companies, and folks thinking about repairing their roofs. That makes scientists like Tony Barnston accountable to people on the ground (or “users” in the vernacular of this workshop), motivating many in the field to develop more accurate climate forecast models and to make their results more understandable and useful to the public.

Impacts of El Niño
After getting a handle on what El Niño is, the rest the day was spent talking about what El Niño does. Scientists estimate that 25% of the earth’s land surface is affected by El Niño in some way or another. Here is a sampling of some of the impacts:

  • Increased cyclone activity in tropical Pacific Islands
  • Drought in parts of Australia affecting farming
  • Collapse in fisheries in eastern Pacific, off the coasts of Peru and Ecuador
  • Micronesia has a combination of droughts and floods
  • Rice crop in the Philippines can see much lower yields
  • In flooded areas, health effects include more possibility of mosquito-borne diseases, and lack of fresh crops affects nutrition.

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