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."
"Averaged across the equatorial Pacific, there is a far larger than normal amount of heat, which is a necessary precondition for an El Niño. At the moment, the amount of heat is comparable to that prior to the extreme El Niño of 1997-98."
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.
'System is ripe'
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.
"Averaged across the equatorial Pacific, there is a far larger than normal amount of heat, which is a necessary precondition for an El Niño," he told NBC News in an email. "At the moment, the amount of heat is comparable to that prior to the extreme El Niño of 1997-98."
In addition, trade winds that typically blow east to west across the equatorial Pacific have started to pulse strongly in the opposite direction. Strong westerly winds can push up to the surface the reservoir of warm water lurking at depth, which would trigger an El Niño, Cai said. That water, he noted, is more than 10 degrees Fahrenheit above normal in places.
"The system is ripe for an El Niño event," he said, adding that the current conditions are in line with those outlined in his research for the formation of an extreme event. "The debate is whether it is going to be a huge one, like the 1997-98. The fact that we are seeing these features earlier really indicates the potential for such a big one."
Halpert noted that predictions of a monster El Niño are largely extrapolated from the similarity in subsurface warmth prior to the 1997-98 event. "That is a sample size of one," he said.
"While we expect the surface to warm over the next couple of weeks, months, for it to actually take hold and really develop you will need to see the atmosphere respond to those changes,” Halpert said.
Also taking a cautious interpretation of the current conditions is Stephen Zebiak, a senior research scientist at the International Research Institute for Climate and Society housed at Columbia University in Palisades, N.Y., who is a pioneer in the creation of models used to forecast El Niño and La Nina events.
"The system is ripe for an El Niño event ....The debate is whether it is going to be a huge one, like the 1997-98. The fact that we are seeing these features earlier really indicates the potential for such a big one."
The models, he said, are certainly detecting changes in ocean warmth and winds that are a precondition for El Niño. But those conditions are just starting to evolve. The pulses of westerly winds and pool of warm water beneath the ocean surface could quickly disappear. "It is not a time of year when El Niño usually has a large expression. The noise is more of the whole story," he said.
If a monster is brewing, the models will know by the end of May, early June, he added. At that point, large scale patterns in the ocean and atmosphere "lock together and start to build a significant El Niño or La Nina event … as you start to move into that season and you get something going, it is much more likely that it will keep going into the future."
If it comes, be prepared
Even Wolter, who is convinced an El Niño will form this year, said he is hesitant to "pin the label super" on it at this point. A promising event as recently as 2012 fizzled by summer, he said. "We won't know for another two months at least before there is more certainty about that and it makes a difference for places like California. That is why people are concerned."
If, indeed, the models do show a significant event on the horizon — the effects of an El Niño are often felt most strongly during the winter months — Halpert said the Climate Prediction Center will be "getting the word out as loud as we can."