But isn’t El Nino a “zero sum” phenomenon? It isn’t really a warming per se, but a shift in the location of warmer waters from the western Pacific to the eastern Pacific.
I recall talking to an Aussie rancher about all of that, and Aussie ranchers pay a lot of attention to that oscillation because when we have an El Nino, which brings wet, cool weather to the central U.S., it brings hot, dry weather to Australia. The reverse is also true.
I can certainly imagine El Nino creating the appearance of warming if the measuring stations in the U.S. are more numerous than those in the southwest Pacific. Far and away most of the southern hemisphere is ocean, and one wonders whether temperature studies there are as numerous and well-monitored as they are in, say, North America.
Also, El Nino conditions cause cooler summers but warmer winters in my part of the country. La Nina conditions cause hot, dry summers and bitterly cold, dry winters.
I wonder about the degree to which those things are taken into account.
Then there’s the Atlantic gyre, or whatever they call it, which is another 'temperature switch" phenomenon.