Ready for a ’90s El Niño flashback? Researchers are keeping a close eye on a giant pool of abnormally warm water in the Pacific Ocean that some think could trigger another El Niño of epic proportions if it rises to the surface, sending weather patterns into a tizzy around the world. That could mean heavy rains in drought-stricken California, dry weather across the Midwest and East Coast, and parched landscapes in Australia and South Africa while it pours in South America. The phenomenon is linked to the periodic warming of surface waters in the eastern tropical Pacific Ocean. “Given the drought that California is in the middle of right now, that is really where the heightened interest is,” said Mike Halpert, acting director of the National Oceanic and Atmospheric Administration’s Climate Prediction Center in College Park, Md.

“It turns out that the odds increase for California to be wet the stronger the event is.” For now, the monthly update on the oceanic conditions that drive El Niño and its sibling, La Nina, put out by the Climate Prediction Center is mum on the potential size of the event. “In our view, there is not a 100 percent chance there will be an El Niño,” Halpert said. The center’s latest outlook, issued on April 10, just gives better than even odds that one of any size will form.  Other experts are more bullish on the prospects for an El Niño, including Klaus Wolter at the National Oceanic and Atmospheric Administration’s Earth Systems Research Laboratory in Boulder, Colo. He independently tracks El Niño conditions using an index based on observations of six variables such as sea surface and air temperatures as well as winds and clouds in the tropical Pacific Ocean. The index has pointed toward El Niño formation since last December. The index, he said, reinforces what a battery of computer models say: that it looks increasingly likely that there could be a large-scale El Niño. In fact, the majority of a type of model based on conditions in the ocean and atmosphere “say that this looks bigger; this doesn’t look like just your small event that is not going to produce that much impact.” Another researcher bullish on the prospects of another El Niño is Wenju Cai, a climate scientist at the Commonwealth Scientific and Industrial Research Organization in Australia who is the lead author of a paper published this January in Nature Climate Change that predicted the frequency of extreme El Niño events will double this century. More