[See the two updates at the end of the post]
This paper claims that ENSO is a following rather than a forcing of climate, but given what we’ve seen in the last two decades, it sure seems like ENSO El Nino events are in fact a forcing of the global climate, from which the Earth quickly recovers.
The paper: (paywalled)
Changes in ENSO Activity During the Last 6,000 Years Modulated by Background Climate State
Soon‐Il An, Seul‐Hee Im, Sang‐Yoon Jun
Various proxy records show that El Niño–Southern Oscillation (ENSO) activity has changed from calm to active during the last 6,000 years. However, it is so far unclear whether orbital forcing has solely induced such a dramatic change. In this study, we performed a transient run for the last 6,000 years using an Earth system model of intermediate complexity affected by orbital forcing only without changes due to other climate forcing, and then its time‐varying background states were implemented into an intermediate atmosphere‐ocean coupled model for ENSO. ENSO activity simulated by the intermediate atmosphere‐ocean coupled model during the last 6,000 years resembled the observed proxy data, inferring that orbital forcing mainly leads to changes in ENSO activity during the last 6,000 years. From additional sensitivity experiments, we found that a change in sea surface temperature background conditions is primarily responsible for the observed ENSO activity over the last 6,000 years through modifying the anomalous horizontal thermal advection of the mean SST gradient.
UPDATE BY ANTHONY: Commenter “frankclimate” has provided a URL for the paper:
Reading it, it all makes sense now, thanks to that mighty big word “may”:
[Update by Willis Eschenbach]
I trust that Anthony won’t mind my noting that I’ve said for some time that the El Nino/La Nina pump is indeed a “following rather than a forcing of climate”, to use Anthony’s words. To be more precise, it is another temperature-regulating emergent phenomenon, one which occurs when the Pacific ocean temperature and surface heat content get above a certain level. At that point, the winds spring up and push millions of cubic metres of warm ocean water towards the poles, cooling the ocean. See my posts below for a fuller discussion.
Best to all, and thanks as always to Anthony for providing this marvelous forum for scientific discussion.
The Tao of El Nino 2013-01-28
I was wandering through the graphics section of the TAO buoy data this evening. I noted that they have an outstanding animation of the most recent sixty months of tropical sea temperatures and surface heights. Go to their graphics page, click on “Animation”. Then click on “Animate”. When the new…
The Power Stroke 2014-02-27
I got to thinking about the well-known correlation of El Ninos and global temperature. I knew that the Pacific temperatures lead the global temperatures, and the tropics lead the Pacific, but I’d never looked at the actual physical…