Dr Pedro DiNezio - an Associate Professor at the University of Colorado’s department of Atmospheric and Oceanic Sciences - calls the phenomenon “the most important unanswered question in climate science”. What’s been dubbed a “cold tongue” stretches off the coast of South America. “That part of the eastern tropical Pacific, a huge swathe of the Pacific Ocean from Chile to the Equator almost halfway through the Pacific, all that part of the ocean has been cooling despite almost the rest of the world warming. We’ve been trying to figure out what’s going on out there.”…
“I know it can be confusing, but the Pacific Ocean is a third of the Earth’s surface, so it’s a huge area of the planet that has been cooling while the rest of the planet has been warming.
“That part of the Pacific, the climate models are telling us that actually it should be warming faster than the rest of the surrounding ocean, so that’s even more puzzling. We’re trying to figure out why.”
“For a while we thought it was just a natural fluctuation,” DiNezio said, such as phenomenons like El Niño and La Niña. “It’s been going for a while, so now we’re starting to question that explanation.
Also from the article… Scientists have been researching the cooling ocean east of New Zealand for a while, but more recently it has really been getting attention.
Something doesn’t make sense. We are reportedly in an El Niño condition right now. That is supposed to be a warmer eastern Pacific. Where exactly is this “cold tongue” ? If it is east of New Zealand, that could put it south of where the El Niño is occurring. But “from Chile to the Equator” sounds like it extends more north.
I think they meant toward the equator. Remember, New Zealand goes as far south as Tierra del Fuego and Chile stretches over 2,600 miles north to south. So, there is a lot of room for a large cold blob south of the El Niño region.
“That’s one of the explanations,” DiNezio said. “…There’s some ideas that propose that that cooling can be transported by winds and ocean currents into the eastern side of the Pacific and then expand all throughout the tropical Pacific, producing what we see, but that’s not crystal clear, because we don’t have a climate model that simulates what we’re observing.”
Interestingly, the cold tongue first appeared between 1.8 and 1.2 million years ago. Its appearance was probably in response to a general shrinking of the tropical warm water pool caused by general climate cooling driven by changes in Earth’s orbit.