【"eroticized" childhood drama】

Earth is "eroticized" childhood dramarelentlessly heating. So it's strange that there's a persistent "cold blob" in the middle of the Atlantic Ocean.

The cold blob (aka "warming hole") is like a glaring pimple, easily apparent on recent NASA surface temperature maps. As a whole, the ocean's surface has warmed by nearly 2 degrees Fahrenheit (1 degree Celsius) since 1900 as the seas continuously absorb colossal amounts of human-created heat. Yet sea surface temperatures in the North Atlantic warming hole, located below Greenland, have cooledby up to 1.6 degrees F (or 0.9 C) over this period, which then chills the air above this colder patch of ocean.

Research, published Monday in the journal Nature Climate Change, provides more evidence for how changes in the warming ocean have sustained this impressively stalwart cold blob. It's an unusual phenomenon, but as humanity adds more heat to Earth's climate system, year after year, there will inevitably be consequences, some more obvious or expected, and some weird.

"Anthropogenic climate change changes the circuitry of the climate system," said Kristopher Karnauskas, an oceanographer at the University of Colorado Boulder who had no role in the research. "[The cold blob] is an interesting manifestation of the peril we're bringing on."

(There's increasing evidence of a perilous future, including a megadrought in the U.S., rapidly vanishing sea ice, extreme storms, relentless global heating, surging wildfires, and beyond.)

The persistent blob has been particularly prominent since 2015, encompassing the five warmest years on record for the globe. "The North Atlantic marches to the beat of its own drummer," said Josh Willis, a NASA oceanographer who also had no role in the study. And a key takeaway from this new research, Willis emphasized, is there may be a number of mechanisms driving the unique warming hole.

Here they are:

1. Changing ocean currents

There's mounting evidence, which this study further supports, that a major ocean current called the "Atlantic Meridional Overturning Circulation (AMOC) — which acts somewhat like a conveyor belt as it transports warm tropical water up into the North Atlantic Ocean — is slowing down. Scientists suspect the slowdown is driven by "off-the-charts" melting of the Greenland ice sheet, which has resulted in freshwater pouring into the North Atlantic Ocean.

The influx of water can have a momentous effect. It reduces the salinity of the ocean, which makes the water less dense. This throws a wrench in the ocean circulation: Now, less cold water in the North Atlantic naturally sinks down, which hinders the flow of new tropical warmers from streaming into this oceanic region (because the cooler waters, now more buoyant, didn't clear out of the way). Ultimately, this means there's less heat traveling into the North Atlantic, which helps sustain the cold blob, said Paul Keil, a lead author of the research and a PhD candidate at the Max Planck Institute for Meteorology in Germany.

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Oceanographers expect AMOC to slow down as freshwater, newly melted in a rapidly heating Arctic, pours into the North Atlantic. The persistent cold blob provides compelling evidence of this already happening. "The AMOC is projected to slow down as a response to increasing greenhouse gases in the atmosphere," said Daniel Whitt, an oceanographer at the National Center for Atmospheric Research who also had no role in the study.

What's more, Keil and his team found that a circulation of water traveling in a loop around the North Atlantic itself, called the "subpolar gyre," has been sending heat out of this region. The gyre, circulating counter-clockwise, carries relatively warmer waters farther north, into the Arctic Ocean. It's a profoundly complicated system, Keil said, noting that his team is preparing an entirely separate study focusing just on what's driving this gyre (the research is led by Rohit Ghosh, who also studies ocean trends at the Max Planck Institute for Meteorology.)

The important point is this gyre acts to transport warmer waters out of the North Atlantic, further cooling the cold blob.

"So less heat will be coming in, and more heat will be going out," explained Keil.

2. Clouds

The researchers also showed that clouds played a role, though smaller, in sustaining the cold blob.

They found the cooler ocean surface produces more low-level clouds, a cloud type that's thick and "reflects more sunlight and thereby further cools the surface," said Keil. This means the warming hole is "strengthening" itself in a feedback loop, explained Keil, as more cooling creates more reflective clouds, which in turn creates more cooling.

The role of clouds in the North Atlantic, however, is a new, emerging finding that will certainly need continued observation, said NASA's Willis.

Global surface temperatures compared to average over the years 2015 though 2019. Credit: nasa The cold blob in 2015. Credit: noaa

It's important to note that conditions in the North Atlantic vary quite a bit from year to year and over the span of decades. To figure out the role of a rapidly heating climate in sustaining the cold blob, Keil and his team used advanced computer simulations (the Max Planck Institute for Meteorology's Grand Ensemble).

This is done by simulating the past, known as "hindcasts," where researchers can create artificial worlds without the influence of global warming. This allows climate scientists to observe how climate change influenced a place, like the North Atlantic, by comparing our reality to worlds unaffected by human-caused global warming.

The North Atlantic is undoubtedly a complex region, with a deep ocean, bounties of melting ice, massive ocean circulations, and beyond. It's a place that demands more investigation. But today, a sustained cold blob is certainly a big part of the picture.

"It's a characteristic of the evolving ocean and the evolving climate," said the National Center for Atmospheric Research's Whitt.