Forty-Four Leading Climatologists Warn of “Devastating & Irreversible Impacts” if North Atlantic Current Collapses

A global warming-triggered collapse of the North Atlantic current “would have devastating and irreversible impacts” to the global climate, according to an open letter sent to Nordic policymakers by forty-four of the world’s leading climate scientists, with the more immediate effect of plunging northwestern Europe—especially Scandinavian countries—into an irreversible deep freeze. While the United Nations’ Intergovernmental Panel on Climate Change (IPCC) only has “medium confidence” that such an event might happen, the authors of the open letter say that the IPCC is underestimating the likelihood of the shutdown of this crucial component in the network of global ocean currents.

“Such an ocean circulation change would have devastating and irreversible impacts especially for Nordic countries, but also for other parts of the world,” the letter, sent to Nordic Council of Ministers, states.

As part of the network of currents that comprise the Atlantic meridional overturning circulation (AMOC), the North Atlantic current—more commonly known as the Gulf Stream—zig-zags northward from the west coast of Africa across to the Caribbean where it picks up warm tropical waters, and then tracks northeast towards northern Europe.

Under normal circumstances, the warm water from this southern stream cools when it meets the currents flowing south from the Arctic, causing the water to sink into the depths where it joins another current that runs southward, deep under the Atlantic, to continue its three-year journey through the world’s oceans. However, the accelerated melt of glaciers in Greenland has already caused a large amount of fresh water to flood into the ocean where this downward convection takes place, and this fresh water, being less dense than salt water, inhibits the sinking of the current’s waters, slowing the flow of the entire system.

The immediate effect of such an interruption to the AMOC would be that warm water from the south would no longer be delivered to the waters of northwestern Europe, a state that would cause local temperatures to drop—hence the paper’s concern for Nordic countries—of which already have comparatively low average year-round temperatures; a drop by just a few degrees in temperature “would potentially threaten the viability of agriculture in northwestern Europe.”

The letter’s authors also call out the IPCC’s most recent synthesis report, which states that “there is medium confidence that the Atlantic Meridional Overturning Circulation will not collapse abruptly before 2100”; according to the letter, more recent research “does suggest that the IPCC has underestimated this risk and that the passing of this tipping point is a serious possibility already in the next few decades.”

Evidence that a slowdown of the AMOC is already underway exists in the form of a “cold blob” that has been forming in the North Atlantic between Greenland and the United Kingdom, with waters across the area recorded as being cooler than normal while the rest of the Atlantic, especially the waters off of the U.S. east coast, are consistently above normal.

Concern that little is being done in the U.K. to prepare for the severe climate disruption that an interruption of the North Atlantic current would cause was voiced in a report released jointly by the Institute for Public Policy Research and the University of Exeter; the report’s authors point out that alongside the potential for the disruption to reduce the usable agricultural land to less than half than what is available now—a scenario that would cause “unimaginable and unprecedented impact on the global food system,” according to co-author Laurie Laybourn, a climate change risk assessment researcher with the Chatham House think tank— Britain’s infrastructure is built for a milder, AMOC-warmed climate, and would not withstand the harsh winters that the coming climate shift would bring.

“There’s been no full risk assessment of AMOC collapse,” Laybourn said. “Having lived through Covid, we now know that it affected everything and that there needs to be risk assessments of all the cascading consequences of another pandemic.

“There hasn’t been the same process for AMOC collapse. It could impact everything. It is probably the worst conceivable impact on food security that could happen right now.”

While northwestern Europe would be thrown into a deep freeze, a domino effect from the interruption of this key current would impact other parts of the planet, both up and downstream: for example, seasonal monsoons that typically deliver rain to the tropics would see the weather phenomenon shift to the south, causing monsoons in the Amazon, West Africa, India and East Asia to be shorter, potentially leading to drought conditions.

Upstream of the AMOC, warm water that would normally flow north from the Caribbean would collect off of the east coast of the U.S., fuelling ever-increasingly intense hurricanes, with their accompanying storm surges exacerbated by the region’s disproportionate sea level rise: in addition to the global increase in sea levels, without a northward route to flow into, waters off of the Eastern Seaboard—already expanding due to the excess heat it carries—will essentially begin to pile up, raising water levels beyond the global average.

“The purpose of this letter is to draw attention to the fact that only ‘medium confidence’ in the AMOC not collapsing is not reassuring, and clearly leaves open the possibility of an AMOC collapse during this century,” the letter states. “Even with a medium likelihood of occurrence, given that the outcome would be catastrophic and impacting the entire world for centuries to come, we believe more needs to be done to minimize this risk.”