It used to be simpler. Whenever the surface waters of the equatorial Pacific turned warmer than normal in summer, climatologists would expect an El Niño year, then forecast when and where droughts, floods, and hurricanes might occur. But that was before a study by Georgia Tech scientists, led by Hye-Mi Kim, deciphered the effects of another pattern in which high temperatures are confined to the central Pacific (Click this link to expand the graphic). Now the already difficult field of atmospheric forecasting has become even trickier.

 

Called El Niño Modoki (Japanese for “similar but different”), it joins El Niño and La Niña, a cold-water phenomenon, as major climate swings that emerge every few years. A Modoki cycle triggers more landfalling storms in the Gulf of Mexico and the western Caribbean than normal, and more tropical storms and hurricanes in the Atlantic than El Niño does. Another difference: Modoki’s precipitation patterns are the reverse of El Niño’s—making the American West, for instance, drier rather than wetter. In 2009, despite early signs of a Modoki year, El Niño prevailed, producing the fewest named Atlantic storms since 1997. —Tom O’Neill