If the Gulf Stream slows down

 

The Daily Mail has the article first:

The real-life Day After Tomorrow? The Gulf Stream is weakening thanks to climate change - and it could plunge Europe into a deep freeze if it collapses, scientists warn

You can read that. However, let's find the actual study it's based on. 

Deeper and stronger North Atlantic Gyre during the Last Glacial Maximum

And here's the full abstract:

"Subtropical gyre (STG) depth and strength are controlled by wind stress curl and surface buoyancy forcing. Modern hydrographic data reveal that the STG extends to a depth of about 1 km in the Northwest Atlantic, with its maximum depth defined by the base of the subtropical thermocline. Despite the likelihood of greater wind stress curl and surface buoyancy loss during the Last Glacial Maximum (LGM), previous work suggests minimal change in the depth of the glacial STG. Here we show a sharp glacial water mass boundary between 33° N and 36° N extending down to between 2.0 and 2.5 km—approximately 1 km deeper than today. Our findings arise from benthic foraminiferal δ18O profiles from sediment cores in two depth transects at Cape Hatteras (36–39° N) and Blake Outer Ridge (29–34° N) in the Northwest Atlantic. This result suggests that the STG, including the Gulf Stream, was deeper and stronger during the LGM than at present, which we attribute to increased glacial wind stress curl, as supported by climate model simulations, as well as greater glacial production of denser subtropical mode waters (STMWs). Our data suggest (1) that subtropical waters probably contributed to the geochemical signature of what is conventionally identified as Glacial North Atlantic Intermediate Water (GNAIW) and (2) the STG helped sustain continued buoyancy loss, water mass conversion and northwards meridional heat transport (MHT) in the glacial North Atlantic."

Yes, and so what does that have to do with the possibility of the Gulf Stream slowing down?

Back to the Daily Mail for that.

"He adds: 'There is the subtropical loop—that the Gulf Stream is part of—and a subpolar loop, which carries heat further northwards into the Arctic.

'During the last ice age, our findings show that the subtropical loop was stronger than it is today, whereas the subpolar loop is thought to have been weaker.'

One of the biggest concerns is that warming global temperatures will disrupt the engine which drives that subtropical loop.

As ocean water meets ice around Greenland in the sub-polar North Atlantic it rapidly cools, becoming extremely dense and salty.

This causes the water to plunge downwards, pulling hot water in behind it and creating a vast circulation pattern.

But as freshwater from Greenland's Ice sheet melts it is diluting these cold salty waters and making them less dense."

Now, one thing that isn't mentioned here, though it may be in the paper, is that the Gulf Stream supplies the salty water that when cooled off becomes the dense water that sinks.  That's called deepwater formation. 

So the next excerpt from the article is, ahem, chilling.

"Likewise, the authors of this paper point out that recent studies indicate climate change is already weakening the strong North Atlantic winds which help drive the Gulf Stream."

So, weaker winds mean weaker Gulf Stream flow, which means less salt into the north Atlantic, which combined with more fresh water from the melting Greenland ice (and nearby) means less dense surface waters, which means less deepwater formation. And that leaves more cold air at the surface, which means a European cooldown. 

And that could mean more views like this: