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Environment

El Niño Odds Boosted Again: Now Exceed 65% By Summer

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Cross-sectional views of five-day-average temperature in the top 300 meters of the Pacific Ocean in February, March, and April 2014 compared to the 1981-2010 average. (Images: Climate.gov. Animation: Tom Yulsman) El Niño's a comin'... Probably. The latest update on the climatic phenomenon that has the potential to strongly influence weather around the world has just been posted by the Climate Prediction Center. The verdict: By summer, the chances of an El Niño developing will exceed 65 percent — up from 50 percent in the CPC's previous update in early April. And many forecasters are saying that it could be a big one. Really big. The CPC issued an El Niño "watch" back in March, and that continues — for now. This means the conditions of the ocean and atmosphere in the tropical Pacific region are favorable an El Niño developing within the next six months. When an El Niño develops, warm water in the western tropical Pacific shifts to the east, carrying lots of rain with it. This, in turn, triggers a chain of weather effects. More about those in a minute. But first, what has been happening in the Pacific that is raising the odds of an El Niño? For one, over the past few months a gargantuan blob of abnormally warm water has been working its way beneath the Pacific Ocean from west to east. You can see this "Kelvin wave" in the animation above. The animation consists of three cross-sectional views of the Pacific down to 300 meters, from the middle of February, March and April respectively. The colors indicate how the temperature of the water departed from the long term average. (One caveat: The surface map and ocean-depth cross-section in the animation are not to relative scale.) As the animation illustrates, the blob began in the western Pacific in mid-February; by mid-April, it had shifted way to the West and was close to the surface. According to today's Climate Prediction Center update, the upper portion of warm water has in fact reached the sea surface. That by itself does not mean an El Niño has begun. But when the monthly average sea surface temperature in the eastern Pacific is 0.5° Celsius or more above average, and other conditions are met as well, the CPC will declare that an El Niño is in progress.

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Source: Climate Prediction Center Normally, trade winds blow from east to west, which pushes warm surface waters away from South America and toward Indonesia. This allows cool water to well up to the surface from the ocean depths off the coast of South America. But as an El Niño develops, those trade winds tend to slacken, and even reverse. This allows warm water to slosh back from the western side of the Pacific toward the eastern side. (Click on the thumbnail for an animation showing a warming of surface waters in the eastern half of the tropical Pacific Ocean.) In fact, the Climate Prediction Center notes that weak, anomalous westerly winds developed in the western Pacific during April. Moreover, storminess was enhanced over the west-central equatorial Pacific. "These atmospheric and oceanic conditions collectively indicate a continued evolution toward El Niño," according to the CPC. What typically happens when an El Niño develops? Peru experiences dramatically increased rainfall, with the potential for devastating flooding. In winter, Southern California and the southern United States tend to experience wetter than normal conditions, while the Pacific Northwest gets drier. Meanwhile, Alaska and Western Canada typically experience unusual warmth. Meanwhile, on the western side of the Pacific, El Niño typically brings drought — and sometimes devastating brush fires in Australia.

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Source: NASA/GISTEMP There is usually a very significant global effect as well. The warmth that El Niño brings to many areas of the world is typically added on top of the background, human-caused warming of the planet. As a result, El Niño years tend to be particularly warm globally. In fact, the super El Niño year of 1998 was among the three warmest on record. And 2010, which saw a moderate El Niño, tied with 2005 for warmest ever. (Click the thumbnail graphic above for an illustration illustrating this phenomenon.) Independently of the Climate Prediction Center, Klaus Wolter of NOAA's Earth Systems Research Laboratory monitors conditions that give rise to El Niño and its opposite, La Niña. The two climatic phenomena are part of what's known as the El Niño-Southern Oscillation, or ENSO. Wolter released his latest ENSO assessment yesterday. He notes that there are still signs in parts of the Pacific Ocean basin of a lingering La Niña, but also evidence of a developing El Niño as well. As part of his assessment, Wolter looked to the past to see what has happened during times when conditions evolved as they have done during the past two months. Here's what he came up with:

Of the 10 cases selected in this fashion, two (1984, 2001) remained either neutral or dropped back to at least weak La Niña status within the year. Of the remaining eight, seven ended up as bona fide El Niño events (1951, 1957, 1965, 1991, 1994, 2002, and 2009), while one ended up as a short-lived one (2012).

In other words, it is possible that an El Niño may not develop, or if it does, it could be a dud. But don't bet on it. Wolter's conclusion:

While the overall assessment remains ENSO-neutral, change is obviously on its way, and I expect to see a further shift towards El Niño-like anomalies by next month.

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