The Atlantic Ocean is heading towards a tipping point, researchers warn, which could staunch the flow of heat to the northern hemisphere in what could be yet another consequence of climate change.
At the precipice is the ocean's churning network of cold and hot currents called the Atlantic Meridional Overturning Circulation (AMOC). As detailed in a new study published in the journal Science Advances, warming temperatures and melting ice sheets could cause this circulation to shut down within a century, causing entire continents to dramatically drop in temperature.
"People would see severe and cascading consequences around the world," the authors, hailing from the Netherlands' Utrecht University, wrote in an essay for The Conversation.
The beating heart of AMOC is a current called the Gulf Stream, which the authors describe as "the ocean's conveyor belt." In it, warm and salty water at the equator flows northward, passing through the Gulf of Mexico and the US East Coast and bringing heat to Europe, the authors explained.
As it continues heading north, the salty water cools down and becomes heavier. Then it sinks, pulling in more water from the surrounding Atlantic, and travels southward, starting the cycle all over again.
But global warming could dramatically disrupt that. As ice sheets and glaciers melt, the fresh water they release dilutes the density of the ocean's salty water. The less dense the water, the less it sinks. Without sinking — which sucks water into the current — the weaker the entire conveyor belt is. At a certain point, you can say goodbye to this vital pipeline of heat to North America and Europe.
"We found that once it reaches the tipping point, the conveyor belt shuts down within 100 years," the researchers wrote. "The heat transport toward the north is strongly reduced, leading to abrupt climate shifts."
According to their experiment conducted with a detailed climate model, Europe would be the worst affected. Parts of the continent, the researchers found, would cool at more than 5 degrees Fahrenheit per decade, with regions in Norway dropping by more than 36 degrees.
These extreme changes wouldn't happen uniformly, with some places getting colder than others, but on average both continents would cool by several degrees. Still, it's unclear when this tipping point will be reached. Some analyses have suggested that it could be as soon as several years, though the researchers note that there's great "uncertainty" over that forecast.
What we do know, however, is that AMOC's circulation has slowed since observations began in 2004. So whatever the timeline, we're steadily marching towards the precipice.
"It might seem counterintuitive to worry about extreme cold as the planet warms, but if the main Atlantic Ocean circulation shuts down from too much meltwater pouring in, that's the risk ahead," the authors wrote.
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