El Viejo, (the old one) is an alternative name developing for the La Niña phase of the El Nino Southern Oscillation, ENSO. Much has been written on the impact of ENSO on global temperature, and many are coming to understand the importance of the Pacific Decadal Oscillation, PDO, in both controlling the likelihood of Nino/Viejo events in the ENSO subcycle and in affecting global temperature directly.
Here I have plotted Jim Hansen’s land +ocean data available at GISS against a remarkable PDO index from Caining Shen et al that I found while bushwhacking through the National Climate Data Center site. This index goes back to AD 1470 and it correlates very well with the more familiar Mantua and NCDC multivariate indices.
The Pacific oscillations, PDO and ENSO, result from the unequal and alternating upwelling of deep water pumped in to the Pacific by the thermohaline circulation. Alex Van de Sande did a beautiful all-ocean view of the thermohaline circulation available under a creative commons license.
The bottom water in this circulation mixes so poorly with shallower waters that it can be isotopically identified in the Pacific after travelling 25000 miles from the North Atlantic, down to Antarctica, around the circum- Antarctic current, and up.
Fewer appreciate that the bottom water upwelling in the Pacific oscillations today is about a thousand years old. It was sinking in the North Atlantic during the Medieval Warm Period while the Vikings were settling Greenland (and wreaking havoc in Europe).
The big dog is an old dog, maybe a third of the oceans by volume, and whatever else may force global temperature, there is a thousand-year supply of this cold water already in the pipeline, a supply with a temperature and chemical signature imprinted when it first sank in the North Atlantic.