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How the Bering Strait influences Earth's climate

The Bering Strait is only 50 miles wide, but it has quite an influence on Earth's climate, say scientists.

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In the north Atlantic, warm water flows north from equatorial regions. As it cools between Iceland and Norway, this water sinks and, once at a certain depth, begins flowing back south.

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Scientists call this conveyor-beltlike flow the "meridional overturning circulation." And it's responsible for keeping Europe balmy compared to regions at similar latitudes elsewhere.

When the overturning is impeded, however, the transport of tropical heat to high northern latitudes slows, and the north Atlantic grows colder.

In other words, freshwater flowing into the north Atlantic can bring temperatures down in the region. Conversely, lessening the flow of freshwater into the north Atlantic can cause temperatures to rise. That's what the authors of this paper say happened repeatedly during the past 100,000 years.

Here’s the cycle: Cooling brought on by changes in Earth's orbit caused glaciers to grow and sea levels to fall. Eventually, the seas dropped far enough that the Bering Strait was closed off. The flow of relatively fresh water from the north Pacific to the north Atlantic stopped, or was dramatically decreased. Without interference from this freshwater, the meridional overturning in the North Atlantic strengthened — by about 13 percent. Parts of Greenland, northeastern North America, and Europe warmed by 2.7 degrees F. Glaciers around thenNorth Atlantic then began melting.

Meanwhile, as the northward flow of water in the Pacific was stymied, temperatures there dropped by the same amount — 2.7 degrees F.

In the end, however, this warming was self-limiting. As increased warmth melted glaciers around the north Atlantic, sea levels began to rise.

Eventually they rose sufficiently to again engulf the Bering land bridge. The flow of water from the north Pacific into the Arctic resumed. The meridional overturning in the north Atlantic again weakened. And the glaciers of the Northern Hemisphere again began advancing southward.

None of this bears directly on the current trend of human-induced global warming. But it does indicate that scientists, enabled by ever-more powerful computers and more complicated — some might say "realistic" — climate models, are improving their understanding of Earth's climate system.

It also highlights an important lesson: In complex systems (Earth’s climate), seemingly small changes, such as closing the 50-mile-wide Bering Strait, can have large consequences, like temporarily reversing a hemisphere-wide cooling trend.

Or, as we talked about last week, a little warming might cause a lot more.

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