Iceland’s relatively mild climate is shaped by a crucial network of currents that winds its away around the Atlantic Ocean transporting heat northward — without it, the island would be much icier and stormier. As evidence mounts these currents could be on course for collapse, Iceland’s government has made the unusual move of designating the risk a national security threat, prompting a a high-level response into how to prepare for this “existential threat.”

“Our climate, economy and security are deeply tied to the stability of the ocean currents around us,” said Jóhann Páll Jóhannsson, Iceland’s Minister for Environment, Energy and Climate.

The Atlantic Meridional Overturning Circulation — known as the AMOC — is a looping system of currents that works like a giant conveyor belt, pulling warm water from the Southern Hemisphere and tropics to the Northern Hemisphere, where it cools, sinks and flows back south.

When scientists are asked which potential climate impact terrifies them most, the collapse of the AMOC is often top of the list.

A growing body of research points to the AMOC slowing down, as higher global temperatures disrupt the delicate balance of heat and salinity on which its strength relies. The science is still unsettled on the likelihood and timing of any collapse, but some studies have projected it could be on course to happen this century.

A shutdown of the AMOC “cannot be considered a low likelihood risk anymore in view of the evolving science over the past years,” said Stefan Rahmstorf, a physical oceanographer and climatologist who has studied the AMOC at Potsdam University in Germany.

The impacts would be catastrophic — ushering in huge global weather and climate shifts, including rising sea levels in parts of the US and Europe, disrupted monsoon systems affecting countries in Asia and Africa, and a winter deep freeze in Europe, with sea ice potentially creeping southward as far as the United Kingdom.

Iceland “would be close to the center of a serious regional cooling,” meaning the country could be surrounded by sea ice, Rahmstorf told CNN.

It’s an “an existential threat,” Jóhannsson told CNN. The AMOC regulates Iceland’s weather, and its collapse could devastate infrastructure, transport and vital industries including fishing, he said.

Jóhannsson briefed the government on the latest science after research published in August raised “grave concerns” about the AMOC’s future stability. In September, Iceland’s National Security Council designated the current’s potential collapse as a national security risk, marking the first time a climate impact has received this designation in the country.

The decision “reflects the seriousness of the issue and ensures that the matter gets the attention it deserves,” Jóhannsson said. In practice, the designation will mean a high-level, coordinated government response to understand the threat and work out how to prevent and mitigate the worst consequences, he said.

Rahmstorf commended Iceland for its decision and said other countries should follow suit. The impacts of an AMOC collapse would be felt across the globe. Scientists are trying to understand the full range of potential impacts on societies and economies, but research has pointed to destroyed crops and catastrophic flooding.

Iceland’s decision marks a shift in how the country understands climate risks, Jóhannsson said.

“What we do know is that the current climate might change so drastically that it could become impossible for us to adapt,” he said. “In short, this is not just a scientific concern — it’s a matter of national survival and security.”