Some of us no doubt remember the 2004 disaster film “The Day After Tomorrow,” in which the collapse of the Atlantic Ocean’s currents led to an ice-covered Northern Hemisphere in a matter of days. Great special effects but, as the filmmakers admitted, questionable science. Fortunately, a new ice age cannot be created in two or three weeks. Unfortunately, scientists have noted a serious problem with our planet’s circulatory system, one that could lead to disastrous if less immediately dramatic effects in our children’s lifetimes.

Last October, 44 oceanographers from 15 countries published an open letter warning of the potential collapse of the Atlantic Meridonial Overturning Circulation, or AMOC. For those whose last earth science class was a long time ago, AMOC is the “conveyor belt” of ocean currents that sends warm water from the tropics northward and gives northern Europe a much milder climate and longer growing season than it would otherwise have. As the warmer, saltier southern water passes further north into the Arctic, it cools and sinks, returning south as colder deep water that will in time rise to the surface and continue the cycle.

AMOC does not only moderate temperatures; the ocean currents carry nutrients and oxygen as well. The transfer of surface water to lower levels oxygenates the deep ocean and allows life to flourish there. Crucially, AMOC has also allowed the Atlantic to function as a carbon sink, with warm surface water absorbing atmospheric CO2 and sequestering it on the ocean floor once the cold water descends.

What concerns the ocean scientists is that AMOC is slowing. 2023 and 2024 saw the highest ocean temperatures ever recorded, with accompanying land-based heat waves in many parts of the globe. Melting glaciers and sea ice are sending freshwater into the North Atlantic, decreasing its salinity and density and disrupting the sinking process necessary for the current to flow. As less water is exchanged and less carbon goes to the ocean floor, the ocean’s ability to absorb carbon is diminished, resulting in more atmospheric CO2 and a feedback loop that is likely to slow the current even more. A study published on August 28 in Environmental Research Letters concludes that a collapse is no longer a low-likelihood event, with the tipping point likely to be reached sometime in the next few decades if global temperatures continue to rise.

So what does a collapse mean? AMOC has slowed and even collapsed in the past; the last collapse led to what is colloquially known as the Ice Age, which found everything north of what is now Cleveland covered in ice for many thousands of years. Fortunately, this scenario is unlikely, given the amount of CO2 in the atmosphere and the overall warmth of the ocean. Instead, the probable outcome will be greater weather extremes.

Europe in particular is likely to experience much colder winters, with temperatures 10 to 18 degrees Fahrenheit lower than recent averages, along with more intense summer heat waves and longer periods of drought. The same pattern would probably occur over much of North America as well, though not to the same degree. Growing seasons on both continents would be shorter, decreasing the human food supply. Tropical areas would likely see temperature increases and a change in rain patterns; one concern is that droughts in what are now rainforest areas could cause the collapse of those ecosystems, earth’s primary terrestrial carbon sink and home to much of its biodiversity. The loss of ocean species and fisheries is likely, and sea levels are predicted to rise as much as eighteen inches, with the Atlantic coast of the southern United States being particularly impacted.

This is not a desirable outcome, but it is one that we might be able to avoid. Stefan Rahmstorf, director of the earth system analysis program at the Potsdam Institute for Climate Impact Research in Germany and organizer of the October open letter, believes that we have not yet passed the tipping point for total AMOC collapse. In his view, reducing carbon emissions enough to hold the earth’s temperature increase to 1.5 degrees Celsius, the goal of the Paris Climate Accords, would minimize the threat to the ocean currents that control so many of the systems we depend on. The day after tomorrow need not be a disaster, but we have to act to create that future.

Rebecca Phillips is an emeritus professor at WVU Parkersburg and a member of Mid-Ohio Valley Climate Action.