The major Atlantic current that keeps Northern Europe warm could have new variations and tipping points

Northern Europe is relatively warm given its location on the globe. For example, London is further north than most of Canada’s major cities, yet it is warmer than all of them (even Vancouver, British Columbia). However, this warmth may be lost by the turn of the century due to global warming.

That could shut down a major ocean current called the Atlantic Meridional Current (AMOC), which flows from the Gulf of Mexico to around Svalbard in Norway. Currently, the AMOC carries large amounts of warm water into the North Atlantic, where it cools and sinks, then suddenly changes direction and travels off the east coast of Greenland, through the mid-Atlantic (under the northeast-flowing AMOC), and out into the South Atlantic. The heat released in the process helps keep northern European ports ice-free.

As global warming progresses, the salty northeastern AMOC mixes with the cold freshwater from the melting Arctic, causing increased precipitation. global warmingThis freshwater reduces the density and salinity of ocean currents, reducing their cooling and sinking in the North Atlantic, and therefore their southward flow.

In 1995, climate modelers Projected The AMOC circulation will cease by 2200. Observations have been conducted since 2004, and in fact, part of the AMOC Seems to be slowing down.

However, until now, climate models have not been able to look at the AMOC and its many flows, eddies, and inflows in detail.

Now, using climate models that make more detailed observations of the AMOC, scientists can better predict the AMOC’s future and discover details that previous models missed. In this new, clearer model, the AMOC collapses suddenly in some regions and increases unexpectedly in others. Their findings include: Published In the journal Physics Review Letter.

“Our high-resolution model study revealed a surprising development: the Atlantic Meridional Overturning Gyration (AMOC) can strengthen in the subarctic Atlantic due to warming,” said study co-author Gerrit Lohmann of the Alfred Wegener Institute at the Helmholtz Centre for Polar and Marine Research at the University of Bremen in Germany. “This contradicts the widely held belief that this important ocean current system is uniformly weakening.”

The large-scale global climate models used Climate change prediction Typically, for reasons of time and computing power, land and ocean areas are divided into regions of 100 by 100 kilometers. As a “low-resolution” model, it may miss small physical features such as: Vortex and Swirl In the ocean.

Roman and his colleagues used a recently developed high-resolution climate model called Community Earth System Model This reduced the previous grid size of 1° of latitude and longitude on each side to 0.1°, or about 17 kilometers.

They assumed that atmospheric carbon dioxide concentrations would increase rapidly. RCP 8.5 ScenariosCarbon dioxide concentrations are expected to increase rapidly during this century, reaching approximately 1,250 ppm by 2100.

Both high- and low-resolution models show an overall slowing of the AMOC, losing about 8 million cubic meters of water per second from 2000 to 2100, with a sharp decline near 2020. (By comparison, the AMOC’s total flow is estimated to be 15 to 20 million cubic meters of water per second, transporting about 13 trillion joules of energy per second.) But on smaller, regional scales, parts of the AMOC have suddenly collapsed, while other parts have even strengthened over time.

“Advanced climate models show that under extreme greenhouse gas emissions (RCP 8.5), the AMOC may decline sharply in some regions, while paradoxically increasing in the Arctic,” Roman said. “This unexpected strengthening in the region occurs despite an overall weakening trend in AMOC activity.”

In addition to regional variations and ocean eddies, the high-resolution model showed tipping points that were unclear in the lower-resolution study.

A tipping point is a sudden change of a system from one state to another; it is a threshold where a small change suddenly moves the system to a new state. For example, you can eat with your pants on, but at some point the bottom of your pants suddenly rips and you’re in a different state forever after. This is the tipping point of your pants.

sub-system There are tipping points in the climate systemFor example, research into the past of the Greenland ice sheet Estimation A tipping point will occur when the Earth warms by about 2.5°C above pre-industrial levels, at which point melting of the entire ice sheet may become inevitable.

On smaller scales, the scientists found that parts of the AMOC have tipping points that don’t appear in previous models of the general AMOC.

“Our findings highlight the urgent need to incorporate regional trends into AMOC projections, as regional variations can have significant effects on climate and marine ecosystems,” Roman said.

“As we face an uncertain climate future, these insights are Climate Model to predict and respond to dramatic changes in the Earth’s system.” Moreover, feedbacks between the AMOC as a whole and the small-scale AMOC “may change in the future,” he said.

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