2 New Studies - Odds Of Weakening Or Collapse Of N. Atlantic Current Higher Than Thought
The large, looping Atlantic Ocean current that keeps northwestern Europe fairly warm and influences sea levels along the U.S. coast is a key component of the Earth’s climate system. But because of global warming, it may be more likely to substantially slow down — or even collapse — than previously thought, according to two new studies.
If that current, called the Atlantic Meridional Overturning Circulation, were to slow down substantially, it could lead to chillier weather in northern and western Europe, starve economically important fisheries and cause waters to rise along the U.S. coast, leading to more so-called “sunny day” flooding and storm surge when hurricanes come ashore. It could also shift tropical rain belts, causing major disruptions to regional climate in Central and South America.
The new studies factor in elements that have been missing from previous projections of how likely the collapse of the current is. One study factors in the melting of the Greenland Ice Sheet, which is adding a pulse of freshwater into the North Atlantic, but is difficult to incorporate into current climate models. The other attempts to correct a bias in climate models that underestimates how unstable the AMOC really is. While neither study is close to the final word on what might happen to this crucial current as global warming continues, the second, in particular, “raises some serious concerns” about our understanding and points to the need to improve models, said Tom Delworth, a research scientist with the National Oceanic and Atmospheric Administration.
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More concerning is the bias in climate models addressed by the second study, published Wednesday in Science Advances. Effectively, models are missing the way an initial weakening of the current from ocean warming causes freshwater to build up, further weakening the overturning of the circulation. This relationship has been observed in recent direct ocean measurements, as well as paleo data. Fixing that bias in the models will take substantial efforts to improve the understanding of the physics of the current as well as more powerful computers. To see what might happen if that positive feedback was included, though, the researchers “kind of [put] a Band-Aid on the models,” Delworth said. They found that the AMOC was much less stable under rising greenhouse gas levels than models are currently capturing and that a doubling of carbon dioxide levels could eventually lead to the current’s collapse.
In their simulations, that collapse caused significant shifts in tropical rain belts and led to regional cooling over the northern Atlantic and nearby areas. Winter temperatures over parts of northern and western Europe were nearly 13°F (7°C) colder than present.
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http://www.climatecentral.org/news/potential-collapse-key-atlantic-current-21024
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