Modeling Shows Potential For "Burp" Of Heat From Southern Ocean - Absorbed Over Time, It Could Be Released Suddenly [View all]

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Now consider that the expansive Southern Ocean, which wraps around Antarctica, could one day do much the same thing. Since the Industrial Revolution kicked off, humans have dialed up the kettle to its max, adding extraordinary amounts of heat into the atmosphere, more than 90 percent of which has been absorbed by the sea. (It’s also taken up a quarter of our CO2 emissions.) Under climate change, the Southern Ocean has been storing warmth which, like your morning jolt, can’t stay there forever, and will someday return to the atmosphere.

New modeling suggests that this “burp” of heat — the scientists called it that, by the way — could be abrupt. In a scenario where humanity eventually reduces its greenhouse gas emissions and then goes “net negative,” finding ways to remove those planet-warming pollutants from the atmosphere, global temperatures fall. But suddenly the Southern Ocean belches its accumulated heat, leading to a rate of planetary warming similar to what humanity is causing right now. And the thermal burping would continue for at least a century. Put another way: According to this modeling, at least, humans figure out a way to reverse climate change, only to see the Southern Ocean essentially restart it. While there would be nothing our descendants could do to stop this — since the warming would be driven by already stored heat — the calculations are yet another urgent call to reduce that pollution as quickly and dramatically as possible.

This sudden eructation is not a sure thing, however — it’s the prediction of a model. But it’s a step toward understanding how the planet could respond as humans continue to manipulate the climate, both warming and cooling it. “The question is: How will the climate system, and specifically the ocean, react to scenarios where we remove CO2 from the atmosphere, and when we have a net global cooling effect?” said Svenja Frey, an oceanography PhD student at Germany’s GEOMAR Helmholtz Centre for Ocean Research Kiel and coauthor of the paper. The Southern Ocean may encircle the frozen continent of Antarctica, but it’s very effective at storing heat: It alone holds around 80 percent of the warmth that’s taken up by all the oceans. Some of this comes from currents that transport relatively toasty waters south, but also lots of upwelling in the Southern Ocean brings cold water to the surface to be warmed up.

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In the scenario the researchers modeled, the atmospheric concentration of CO2 increases by 1 percent every year until the total amount is double what the planet had before the Industrial Revolution. Then negative emissions technologies reduce the carbon concentration by 0.1 percent annually. (The study didn’t look a specific techniques, but one option is direct air capture of CO2, though this remains expensive and limited in scale.) In response, the atmosphere, land, and oceans cool. But something starts brewing in the Southern Ocean. Its surface becomes colder, but also saltier due to the formation of new sea ice: When sea water freezes, it rejects its salt, which is then absorbed into the surrounding waters and makes the surface layer heavier. “At the same time, we have these warm, deeper waters,” Frey said. “At some point, the water column becomes unstable, and that’s when we have the deep convection event.”

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https://grist.org/oceans/hey-so-one-day-the-ocean-might-burp-up-a-bunch-of-heat/