TAMPA, Fla. (WFLA) — If you remember the movie "The Day After Tomorrow," starring Jake Gyllenhaal in 2004, weather patterns became so out of whack that New York City got flooded by a huge tsunami and gigantic tornadoes that ravaged the land.
The plot is outlandish - but like so many science fiction plots - the movie is based on something real - the Atlantic Meridional Overturning Circulation (AMOC). In the movie, the Atlantic Ocean's giant ocean conveyor belts abruptly shut down, tripping a switch in the climate system that throws climate patterns into complete chaos.
While the movie's special effects were way over the top, a shutdown of Earth's most important ocean current system may soon not be science fiction. In fact, there is a growing scientific body of evidence suggesting that the AMOC may very well collapse - and some of the newer papers suggest it may be within a few decades. This June 2024 paper says perhaps by or before 2050, and so does this one published days ago— just two examples of recent papers warning of a somewhat imminent collapse.
If that were to happen, Earth's climate patterns would be thrown completely off-kilter. Although tsunamis would not ravage New York City and gigantic tornadoes would not descend on cities, the widespread impacts would be, by far, the biggest and most systemic changes modern humans have ever experienced.
Paleoclimate tells us that the AMOC has collapsed a few times in the very distant past after the end of the last ice age. So we know it can, and has happened. The reason the collapse happened in the past was likely due to large infusions of fresh water from crumbling-melting glaciers in or near the Arctic circle as Earth naturally warmed out of the ice age.
That is why science is concerned that it could happen again because we are now warming the planet at a much faster pace - 10 times faster than any time in millions of years. This is due to the burning of fossil fuels, the release of heat-trapping greenhouse gases, and the mowing down of forests.
The AMOC is a system of currents in the Atlantic responsible for 25% of the northward transport of global heat. Since Earth is heated much more near the equator than the poles, the planet needs a way of redistributing heat. The AMOC is one mechanism.
The AMOC takes warm-salty surface water from the Caribbean and the Gulf of Mexico - employing the Gulf Stream east of Florida - northward into the North Atlantic near Iceland.
When it reaches that area the water naturally cools and sinks downward, like a slow-moving waterfall due to the density of the cold-salty water. The overturning is the vertical component of the circulation.
In recent decades the AMOC has slowed by at least 15%. Scientists theorize the recent slowdown is due to less sinking because the the water is becoming less salty, more fresh, and thus not as dense or heavy.
The reason for the freshening of the water is three-fold.
First, Greenland is melting due to climate heating and that is pumping cold, fresh water into the North Atlantic, diluting the heavier salty waters. Second, there is less sea ice due to warming. When sea ice forms it leaves salt behind in the water increasing the salinity, but with less ice, the water is less salty. Lastly, a warmer climate means more rain and differing wind patterns in the northern polar regions, once again resulting in fresher water.
So what happens if 25% of the northward global transport of heat abruptly stops? The impact would be huge - exactly how huge is difficult to know considering this has never happened before in recent history. But there are some impacts that seem clear.
Because of the lack of warm water being transported north, Northern Europe is likely to see a dramatic drop in temperatures, perhaps several degrees or more on average, which could wreak havoc with agriculture.
Sea level rise along the U.S. East Coast would accelerate, adding to an already faster-than-average pace of increase, and weather patterns in the Atlantic would be thrown off-kilter.
Rain patterns in the Amazon and the Indian Monsoon, both incredibly important climate systems, could experience large shifts, impacting both the natural environments and also the people who rely on them.
Lastly, with more heat being stored in the tropical waters, ocean temperatures in that zone would inevitably rise and storm systems would respond to those changes, in ways science is just starting to scratch the surface of.
Bottom line: Impacts would be life-changing for humanity and it's not something we should take a chance on.
To help us better understand this topic, for today's Climate Classroom, we are interviewing one of the world's number one experts on the AMOC, Dr. Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research.