Running AMOC: Climate Forecast for the North Atlantic

Any Gulf Stream Stall Would Likely Cause Spike in Severe Weather

Genevieve Jacobs May 19   ∙   Guest post

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The author is a longtime professor of Psychology and Communications. She landed in Vermont in 1987 after a decade of cruising under sail. She is a regular Loose Cannon contributor.

As if rising sea levels and ever more fierce, frequent, and freakish weather weren’t enough to worry about, there’s an underlying nightmare scenario of particular concern to sailors.

The Atlantic Meridonial Overturning Circulation (AMOC for short) is the northernmost feeder of the Gulf Stream, which flows like a warm salty oceanic river north along the Eastern Seaboard and then transatlantic to Europe before circling back around. This thermohaline circulation is the engine of our concept of seasons and the relative stability of sailing directions for both wind and water.

Sailors have fond feelings for the Gulf Stream when getting a nice boost north along the coastal USA, although anybody who has made that course while beating against contrary winds might not be so fond of the Stream’s infamous square waves, as the current’s set of up to three knots battles against the occasional Northerly blow.

AMOC is the part of the great conveyor belt located near Greenland, where such a rapid acceleration of glacial melt is occurring that the influx of fresh, cold water causes the thermohaline current to weaken, which may lead to wavering or even stalling of the Gulf Stream.

The feedback loop of the conveyor belt is a function of relative water density: both temperature and salinity. Colder, fresher water sinks; while warmer, saltier water rises. Cooler fresher heavy waters dive below, running in a direction opposite the warmer, saltier surface current. This complex dynamic interplay is what keeps the whole system in motion.

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Cold fresh water rapidly injected in great quantities into the AMOC from the melting polar regions is a serious threat to the dance. A few summers ago, an ominous “cold spot” of ocean water, which would normally join into the flow, was observed sitting stagnant in the North Atlantic. Superstorm Sandy was able to profit from the slowing down of AMOC, with it’s concurrent heating up of the waters along the East Coast, to barrel into New York at hurricane force.

The 2017 summer waters off Africa, where hurricanes breed, were unusually warm and covered an abnormally large area, several weeks before the spawning of Irma and Maria devastated the Virgin Islands and Puerto Rico.

These horrific storms were quickly followed by a hurricane that deviated so radically from any previously recorded storm tracks that NOAA’s graphics didn’t serve: the hurricane headed straight North from the African coastal waters for Western Europe and quickly went, quite literally, “off the charts” as it bowled for the U.K.

It may be cold comfort, but Mother Earth has been here before, the last time AMOC ran amuck, during the last interglacial period 118,000 years ago. Dr. James Hansen, who directed NASA’s Goddard Institute for Space Studies from 1981 to 2013, is a true Cassandra. The dire climate predictions he’s made since 1981 have essentially panned out.

EUObserver: If the AMOC Stops, Europe Will Experience Ice-Age Like Winters

Hansen considers the recent data and warns a “shutdown or substantial slowdown of the AMOC…will cause a more general increase of severe weather stronger than any seen in modern times.” He explains that the lower latitudes of the Atlantic will gather excessive heat which will drive superstorms of the magnitude which launched massive boulders onto the islands of the Caribbean so long ago.

If our CO2 fossil fuel emissions (now exceeding 400 ppm) could be cut back to 350 ppm we might be able to forestall the worst outcomes of this runaway “global weirding,” scientists say.

As for this year, hurricane gurus at Colorado State University anticipate that the 2026 Atlantic basin hurricane season will have somewhat below-normal activity due to a moderate or strong El Niño. NOAA will issue its outlook for the 2026 Atlantic hurricane season during a news conference on Thursday at the NOAA Aircraft Operations Center in Lakeland, Florida.