We’re at the point in the year where forecasting is hard, so the computer models used to try to get a handle on where this is headed are all over the map.
It’s the conventional wisdom the ENSO forecast community has been giving me for years, a sort of “pivot point” around this time of year when their forecast skill is weakest.
Then comes this draft paper from Jim Hansen and others:
We suggest that an El Nino is likely to originate in 2006 and that there is a good chance it will be a “super El Nino”, rivaling the 1983 and 1997-1998 El Ninos, which were successively labeled the “El Nino of the century” as they were of unprecedented strength in the previous 100 years.
(hat tip RP for the link to the Hansen piece)
Hansen goes on to “argue further that global warming has increased the likelihood of super El Ninos.'”
As it happens, I’ve been poking at this question as well because of the important relationship between ENSO and the climate here in the southwest. More/bigger (less/smaller) El Ninos means less (more) drought where I live. As Eric Guilyardi recently put it, “Predicting El Nino occurrence and amplitude… is a key societal need.”
The problem, as Hansen acknowledges, is that the global climate models are all over the map on this one.
Haiyan Teng and colleagues at NCAR just published a model intercomparison in GRL that looked, among other things, at the way a suite of global climate models handled ENSO under CO2 held constant at 2000 values.
In the present set of models, 9 out of 16 models show a committed El Nino-like response, while the rest have either a La Nina-like response or more uniform committed warming across the tropical Pacific. The reasons for these differing responses require further investigation.
That’s the paper that got me curious, which led me to Guilyardi’s paper in Climate Dynamics which also did a big model comparison. Again, the results tilted toward increased El Nino amplitude in a warmer climate, “though there is a considerable spread of El Nino behaviour among the models.”
I’m not a scientist, so I won’t try to evaluate Hansen’s claims, but were I a journalist trying to write about this and looking for the sweet spot where the bulk of the science lies, I’d have to explain to readers that Hansen is well to one side of it on both the question of what can be said now about what will happen in the coming year, and of what effect greenhouse warming might have on ENSO.