Six months ago, temperatures in the equatorial Pacific suggested that, after two years under the influence of La Niña, which tends to mean cold dry winters here in Southern California, that our ocean was turning towards an El Niño condition. Under that condition, warm temperatures and westerlies in the equatorial Pacific predispose those of us in California for wetter winters. This is what usually happens, after a long stay in one condition, that we transition to its counterpart.
But now it appears that, unusually, the predicted El Nino is "petering out," in the words of Kevin Trenberth, a leading climatologist. Even more curiously, the statistical and dynamicla models are in disagreement, as discussed by Robert Henson of the National Center for Atmospheric Research. Henson highlights a curious fact about this year's discussion of the controversial boy El Nino:
- In March, the dynamical and statistical models tracked by IRI agreed that neutral conditions were most likely to prevail by late 2012.
- By May, about half of the models called for a weak El Niño, while half still called for neutral conditions.
- And by July, more than 70% of the models were calling for an El Niño. However, a clear split was now evident. Most of the dynamical models were calling for El Niño to appear, perhaps even a moderate to strong one, while the statistical models leaned toward neutral conditions or a very weak El Niño.
The statistical method, used to establish a probabilistic baseline, is about as skilled as the dynamical model as a forecaster. But the IRC [International Research Institute for Climate and Society] points out that the statistical method, which looks at the past record, might not pick up changes -- perhaps including those brought on by global warming? -- that the dynamical model can. The dynamical model plugs ocean temps and other values into a climate/ocean model and runs a projection.
Here's an image of the rise and fall of ocean temps in the mid-Pacific this year, from Henson's excellent discussion:
As you can see, the fall-off in temps has been rapid. What is going on? Could this be part of a broader trend towards drought, as discussed in this paper in Nature by Aiguo Dai? (h/t: Dot Earth)
Have an assignment: Will try to find out, report back.
