Global sea surface temperature anomaly in degrees Celsius. (NOAA)
The downward trend in El Nino forecasts continued on Thursday with the release of NOAA’s November outlook. The Climate Prediction Center has now decreased the El Niño chances to 58 percent this winter, which is a far cry from the close to 80 percent chances the center was forecasting back in July.
And yet again, the atmosphere is being blamed for the decrease in El Niño odds. “The ongoing lack of clear atmosphere-ocean coupling and the latest [model forecast] have reduced confidence that El Niño will fully materialize,” they write in the discussion of the forecast. “If El Niño does emerge, the forecaster consensus favors a weak event.”
In Climate.gov’s ENSO blog, Emily Becker writes about the difficulties in predicting weak El Niño events. “The shift toward weaker, more centrally located El Niños is more difficult for climate models to capture,” she writes. “The depth of the thermocline, equatorial winds, and sea surface temperatures are inextricably linked–and so the combination of certain factors results in changes in how well ENSO can be predicted.”
So maybe the climate models just struggle with weak El Niño events. But it’s also possible we do not have an excellent grasp on forecasting an El Niño embedded in widespread warm sea surface temperatures, like we have seen this year. El Niño is not simply the presence of warm ocean water in the equatorial Pacific. El Niño (and La Niña) is a connection between air and sea, driven by differences in temperature. And that is something that the Pacific Ocean decidedly lacks in 2014, where it’s not just the equator that’s warm.
Warm sea surface temperature – running anywhere from 0.5 to 4 degrees Celsius above average — extends far up the west coast of North America, all the way into the Gulf of Alaska. It can be blamed as both the cause and effect of the West Coast’s “ridiculously resilient ridge,” but it could also be putting the kibosh on this year’s much anticipated “super El Niño.” When the ocean surface is warm all over, there’s no strong temperature gradient for the atmospheric component to build from.
And most importantly, for El Niño’s purposes, the gradient in sea surface temperature is not strong across the equator from Australia to South America, either. This gradient – from cool in the west to warm in the east — drives winds across the equator, which in turn causes a stronger temperature gradient, and so on.
“Think of it as a chicken-and-egg problem,” said Michelle L’Heureux in an ENSO blog back in July, which sums up 2014′s wishy washy El Niño quite nicely.
