Atlantic Ocean Currents Weakening, And Yes You Should Care

Map of departure from normal temperatures were in 
2020 globally. Red is warmer than normal, meaning
almost the whole Earth. Notice the blob of cool
southeast of Greenland, though. It's one sign that
the Gulf Stream in the Atlantic is slowing down.

Constantly, huge amounts of warm water northward toward Europe and keep that part of the world relatively mild, at least for as far north as they are. 

Cities like London, Paris and Berlin are further north than Vermont, for instance, but are milder than the Green Mountain State, at least during the winter.  

It's called the Atlantic Meridional Overturning Circulation or AMOC. It's basically the Gulf Stream.

It brings massive amounts of heat energy northward, and is critical for the relatively stable - sort of - climate in the northern hemisphere. Screw that up, and you really have some problems on your hands.

New research says the AMOC is indeed getting screwed up.  The latest science builds on previous research that says this massive northward motion of ocean warmth is slowing, largely due to climate change. 

According to The Guardian:

"Computer modeling and theory predict a steady reduction in the strength of the AMOC and its heat delivery service in response to human-induced changes in rainfall, river runoff and the melting of the Arctic sea ice and Greenland ice sheet."

There has already been a 15 percent reduction in the AMOC's strength since the late 1880s, and is at its slowest pace in at least 1,000 years. 

Before you start saying you don't really care of western Europe stays warm and damp in the winter, consider this from The Guardian:

"A reduced AMOC is projected to bring colder weather overall to the UK and northern Europe with much more intense winters and storms off the Atlantic, as well as reduced summer rainfall and crop productivity and a greater likelihood of extreme weather events such as the 2015 European summer heat wave.

The impacts are not limited to this side of the Atlantic, either. Increased sea levels are predicted on the U.S. eastern seaboard with the associated risk of flooding and potentially increased hurricane intensities."

The reason why the slowdown of the AMOC would accelerate sea level rises along the United States East Coast is that the northward momentum of the water in the Atlantic deflects and pushes water away from North America.

As the AMOC slows, water wouldn't be shoved away from the East Coast so much, so sea level rise would be faster there. 

Hurricanes might drift closer to the United States coastline too, because warmer water would drift closer to the coastline too instead of heading off toward Europe and keeping them mild. 

The whole system works like this; 

The massive northward current of warm water is a result of differences in density of ocean water. As ScienceDaily.com explains:

"Warm and salty water moves from the south to the north where it cools down and gets denser. When it is heavy enough the water sinks to deeper ocean layers and flows back to the south. Global warming disturbs this mechanism: Increased rainfall and enhanced melting of the Greenland Ice Sheet add fresh water to the surface ocean. This reduces the salinity and thus the density of the water, inhibiting the sinking and weakening the flow of the AMOC."

The slowing of the AMOC has been previous predicted by climate models.  Effects of this slowing are becoming more obvious.  There's been a pretty persistent "cold blob" in waters of the North Atlantic southeast of Greenland and west of Great Britain.  

That persistent cold blob is seen as a precursor to climate disruption caused by a slower or stopped AMOC.

I've seen a number of media reports that raise the hit climate disaster movie "The Day After Tomorrow." In that movie, climate change spirals pretty much instantly out of control, in part because the Gulf Stream stops. Frigid superstorms encase the populated Northern Hemisphere in a thick ice age.

The movie is obviously fiction. Nothing like that is in the offing. 

If the AMOC were to shut down completely, western Europe could end up facing a "Day After Tomorrow Lite."  Northern and western Europe would cool dramatically in the winter (think central Canada).

It would probably be stormier on the East Coast, too. Even without the hurricanes, the warmer water encroaching closer to the coastline would create greater contrasts with winter cold waves coming in from the northwest.

Bigger contrasts can lead to bigger storms. 

This is all another reason why the preferred term is not "global warming" but "climate change."  It doesn't just warm up nice and evenly.  You get all kinds of surprises.