Of all the ways in which our broken planet is preparing to kill us — tropical diseases gone wild, swarms of water refugees, frozen methane rising from the inky depths to smother us in prehistoric microbe farts — the general public has become most fascinated with the possibility that melting Greenland glaciers will shut down the Gulf Stream, plunging northern Europe and much of North America into a new ice age. People have clung to this specific possibility partly because of its contrarian appeal — global warming causing local freezing? where’s my snowball? — and partly because it’s been part of the plotline of certain Hollywood blockbusters.
Recently, the media gave the issue a bit of attention when a pair of papers in Nature last month indicated that the Gulf Stream is now slower than at any time in the past 1,600 years. As the Voice’s Lara Zarum remarked when one especially alarming story from the Guardian showed up in the office Slack, “It’s never a good sign when you use a still from The Day After Tomorrow to illustrate your climate story.”
The Voice contacted several leading climate scientists who study ocean currents, who offered some good news: Any effect on the Gulf Stream from the slowing of the Atlantic Meridional Overturning Circulation — or AMOC, the “conveyor belt” that helps drive ocean currents via the sinking of cold saltwater in the North Atlantic — is probably not that dire, at least not yet. The less good news: Everything else is extremely dire, especially for coastal cities like New York.
Asked if end-of-the-world AMOC scenarios are overblown, Susan Lozier, an oceanographer at Duke University who is an expert in oceanic circulation, replies, “I think it’s a distraction from the other end of the world. New York City has more to worry about in terms of sea level rise than about AMOC anytime soon.”
The threat of an Atlantic deep freeze is relatively simple to picture, at least as complex climate-related systems go. As the Gulf Stream sweeps up from the Gulf of Mexico toward the North Atlantic, it brings warm water and warming temperatures to Western Europe, while drawing cold air down from the north to cool the U.S. East Coast. (This is one reason why Madrid is so much toastier than New York, despite being at the same latitude.) Once it gets there, the water cools and sinks, then flows back southward along the ocean floor to start the process all over again.
That’s how it’s worked for the past 10,000 years. The worry — which was already being raised before The Day After Tomorrow hit theaters in 2004 — is that Greenland’s rapidly melting ice cap is releasing a blob of cold freshwater into the North Atlantic, which will sink more slowly since freshwater is lighter than saltwater. As a result, that would stall the AMOC, and eventually could slow down or stop the Gulf Stream altogether.
Not so fast, says Lozier. “Unlike sea level rise or global warming or Arctic sea-ice loss, where there’s broad consensus in the scientific community,” the models predicting what will happen to the Gulf Stream are far less certain, she says. “The latest IPCC” — the reports regularly issued by the Intergovernmental Panel on Climate Change to track our impending doom — “says AMOC is more stable than we thought it was,” she notes, predicting only that the AMOC is expected to decrease in strength by between 11 to 34 percent by the year 2100, which is still a little ways off.
“There’s a lot going on in the climate system, and to think there’s only one mechanism is oversimplifying the climate system,” adds Amy Clement, a climate scientist at the Rosenstiel School of Marine and Atmospheric Science at the University of Miami, who has authored papers on AMOC. “Ocean circulation variability is one thing in what’s happening in ocean sea level.” Some of the other factors, as scientists like to say, are not well understood: “There are definitely some mysteries: We have had a tripling of sea level rise here in Miami and the Florida Straits, and we basically don’t really know the specific cause.” (One leading suspect: The North Atlantic Oscillation, an El Niño–like climate pattern that can accelerate or slow sea level rise for years at a time.)
The problem with the recent spate of Day After Tomorrow stories, notes Lozier, is that “the headlines really exaggerated things.”
In any case, what we can be sure of is scary enough. Lozier says that regardless of what the Gulf Stream does, we are likely to see more late-winter storms in the Northeast and general shifts in precipitation patterns. (Pro tip: Don’t move to Arizona.) A less publicized but potentially even scarier issue is ocean acidification, in which the world’s oceans absorb about 25 percent of the anthropogenic carbon dioxide in the atmosphere. That’s good news for the atmosphere, she notes — more carbon in the oceans means less in the air — but bad news for the ocean, where the carbon forms carbonic acid, the same mechanism that sent the trilobites and other prehistoric sea creatures on a path to extinction after a run of 270 million years.
“Plan for sea level rise,” says Clement. “Plan for storms. We have a very good theoretical understanding of the connection between the intensity of storms and how the impacts change as sea level rises and as the atmosphere gets warmer and wetter. All those things we know.” The Gulf Stream issue, she says, “is a real scientific debate — but the fact that the sea level is rising is not up for debate.”