Sign In or Create an Account.

By continuing, you agree to the Terms of Service and acknowledge our Privacy Policy

Climate

Why It’s So Hard to Predict a Climate Tipping Point

There’s disagreement about when the Atlantic Ocean current will collapse.

The ocean.
Heatmap Illustration/Getty Images, Nature Communications

For a while now, something weird has been happening in the Atlantic Ocean.

The ocean’s circulatory current, a system called the Atlantic Meridional Overturning Circulation, or AMOC, seems to be slowing down. Scientists have long worried that what used to be a steady exchange of warm and cold water between the tropics and the North Atlantic is being disrupted by cold freshwater from melting Arctic ice, and could even shut down entirely, sending Northern Europe into a deep freeze and causing even more extreme heat to hit tropical regions.

What scientists haven’t agreed on, however, is when the AMOC might stop, though the latest report from the Intergovernmental Panel on Climate Change, or IPCC, predicted it should hold out through the end of the century. A new study, published Tuesday in Nature Communications, says otherwise: the AMOC, its authors say, will reach its “tipping point” by the middle of this century, and could collapse sometime between 2025 and 2095. If it does, it would bring rapid changes to the world’s climate of a type that haven’t been seen in over 12,000 years.

“When we first got these results, we didn't believe them ourselves,” said Susanne Ditlevsen, a mathematician at the University of Copenhagen and co-author, with her brother Peter Ditlevsen, of the new paper. “We were thinking that there's something wrong in what we're doing because we got estimates that are so off compared to the IPCC.”

It’s a striking study, and it can make us feel like catastrophe is not only looming but irreversible. But in many ways, this study is a microcosm of the many challenges that come with trying to predict — and speak definitively about — how our planet will change in the future.

“I personally think it’s very hard to say [a shutdown] is going to happen in the next 50 years,” said Zhengyu Liu, atmospheric sciences director at the Ohio State University. “There are lots of uncertainties.”

The IPCC report’s prediction, which it issued with “medium confidence,” is based on climate models that use supercomputers to simulate the physical processes that will change as the climate changes. Looking at those models, we see a gradual weakening of the AMOC over time rather than a sudden tipping point that leads to a collapse. But it’s possible, Liu said, that those models may present a world that is a little too stable. The influx of freshwater from melting glaciers is difficult to account for, and it’s possible the models used by the IPCC are too conservative.

To sidestep the issue of uncertainty over freshwater inflows (and, similarly, to avoid having to model for how the world responds to climate change over the next century) the Ditlevsen study instead used statistical modeling based on historic temperature records to study how the ocean’s temperature has fluctuated over time. They then predicted how those fluctuations might become increasingly unstable in the future. The bigger those fluctuations become, Ditlevsen said, the closer the AMOC gets to total collapse, and those fluctuations have recently been growing ever larger.

Temperature is a useful fingerprint when studying the AMOC, Liu said, but it’s just one fingerprint of a system that has only really been studied in earnest since 2004, when a network of sensors began collecting data on everything from temperature to salinity to ocean pressure. It’s difficult to say, with such limited data, whether extrapolating from just one fingerprint alone can truly predict a tipping point for the AMOC.

The big question, said Tom Delworth, a senior scientist at NOAA’s Geophysical Fluid Dynamics Laboratory, is the physics of how such a tipping point would work.

“Our models generally aren't showing these tipping points, and they’re based on our best physical understanding of the system,” Delworth told me. “So my question would be: what is missing from the models?”

Still, Delworth and Liu said, the Ditlevsen study is compelling, and it’s one of the first to attempt to put a timeline on the collapse of the AMOC. It’s also, as these studies tend to be, yet another reminder of the urgent need to reduce our dependence on fossil fuels and dramatically cut down on emissions.

The study’s authors intend to run their analysis again in five years, when they will have more data and should be able to come to a stronger conclusion on when exactly the AMOC could collapse. “We could have said, okay, let’s wait five years to publish this because maybe we are wrong, but I think we have the obligation to actually publish it now, because we believe that it’s correct.” Ditlevsen told me.

“I hope we are wrong,” she continued. “I hope we are wrong.”

Neel Dhanesha profile image

Neel Dhanesha

Neel is a former founding staff writer at Heatmap. Prior to Heatmap, he was a science and climate reporter at Vox, an editorial fellow at Audubon magazine, and an assistant producer at Radiolab, where he helped produce The Other Latif, a series about one detainee's journey to Guantanamo Bay. He is a graduate of the Literary Reportage program at NYU, which helped him turn incoherent scribbles into readable stories, and he grew up (mostly) in Bangalore. He tweets sporadically at @neel_dhan.

Sparks

Nuclear Energy Is the One Thing Congress Can Agree On

Environmentalists, however, still aren’t sold on the ADVANCE Act.

A nuclear power plant.
Heatmap Illustration/Getty Images

While climate change policy is typically heavily polarized along party lines, nuclear energy policy is not. The ADVANCE Act, which would reform the nuclear regulatory policy to encourage the development of advanced nuclear reactors, passed the Senate today, by a vote of 88-2, preparing it for an almost certain presidential signature.

The bill has been floating around Congress for about a year and is the product of bipartisanship within the relevant committees, a notable departure from increasingly top-down legislating in Washington. The House of Representatives has its own nuclear regulatory bill, the Atomic Energy Advancement Act, which the House overwhelmingly voted for in February.

Keep reading...Show less
Blue
Technology

AM Briefing: America’s Long Bake

On Equatic’s big news, heat waves, and the Paris Olympics

Ocean-Based Carbon Removal Is About to Take a Big Step Forward
Heatmap Illustration/Getty Images

Current conditions: Tropical storm warnings have been issued for Texas and Mexico • Parts of southwestern France were hit with large hail stones • The temperature trend for June is making climate scientists awfully nervous.

THE TOP FIVE

1. Lengthy heat wave threatens nearly 80 million Americans

About 77 million people are under some kind of heat advisory as a heat wave works its way across the Midwest and Northeast. In most of New England, the heat index is expected to reach or exceed 100 degrees Fahrenheit. What makes this heat wave especially dangerous is its “striking duration,” Jake Petr, the lead forecaster with National Weather Service Chicago, toldThe New York Times. Temperatures are projected to stay exceptionally high for several days before beginning to taper off only slightly over the weekend. According toThe Washington Post, temperatures could be up to 25 degrees higher than normal for this time of year. And forecasters expect it to be unseasonably hot across the country for at least the next three weeks. Below is a look at the NWS HeatRisk projections today (top) and Thursday (bottom). The darker the color, the warmer the temperature and the higher the health risks.

Keep reading...Show less
Yellow
Economy

Crux Is Getting Some Powerful New Backers

The New York-based startup aims to create a market for clean energy tax credits.

Green energy and money details.
Heatmap Illustration/Getty Images

One of the least-noticed changes in the Inflation Reduction Act may be one of the most important.

For years, the government has encouraged developers, power utilities, and other companies to build clean energy by offering tax credits. But those tax credits were difficult to transfer to other companies, meaning that complicated financial instruments had to be created to allow them to share in the wealth.

Keep reading...Show less
Green