UKH

https://www.theguardian.com/environment/2023/jul/25/gulf-stream-could-colla...
 

not in a good way

One the one hand, the collapse of global food production. On the other, decent winter conditions. It's a toughie.

When the North American ice sheets melted the giant pool of water (where the great lakes are now) was held back by an ice dam. When the dam broke loads of cold fresh water hit the gulf stream changing the salt content and therefore density as well as the temperature and shut off the gulf stream. Greenland melting today is very different. Melt water flows straight into the Atlantic constantly in more manageable amounts rather than one massive hit. Most predictions suggest that the gulf stream should be able to cope with this. Now, I'm a geography teacher not a paleoclimatologist so someone might be along shortly to provide some more up to date ideas but I'm not panicking (about this particular climate threat) just yet.

The problem (advantage?) for most gen Xers is that we've been living with multiple existential threats our entire lives and this particular one's not even new.

Is "Imminent Armageddon Fatigue" an actual thing?

Its interesting as the simple "Gulf stream collapses we go cold" scenario is more complex.

This piece from around 2006 calls it a myth.

http://ocp.ldeo.columbia.edu/res/div/ocp/gs/

While this piece published recently gives a more nuanced view

https://www.livescience.com/planet-earth/climate-change/gulf-stream-current...

"If the statistics are robust and are a correct/relevant way to describe how the actual modern AMOC behaves, and the changes relate (solely) to changes in the AMOC, then this is a very concerning result," David Thornalley, a professor of ocean and climate science at University College London, told Live Science in an email. "But there are some really big unknowns and assumptions that need investigating before we have confidence in this result." 

Other climate scientists have gone so far as to pour cold water on the findings, suggesting it is "wholly unclear" that observed surface temperature evolution of AMOC can be linked to the strength of its circulation. 

Scientific understanding of this topic has moved on a long way since 2006. 

You may be interested to read this piece, which discusses the potential collapse of the AMOC:

https://www.realclimate.org/index.php/archives/2023/07/what-is-happening-in...

I think the likelihood of the collapse happening by 2025 is very (vanishingly) small, but the likelihood of collapse by the end of the century is quite possible. 

Thanks, climate modellers actually don't ever think about basic high school geography. /sarcasm. The entire point of this prediction is that the Gulf Stream* can't "cope" with this, and will be altered - i.e. changing our current understanding.

*pedants corner: the paper is actually about AMOC, which is part of, but not the entire, Gulf Stream - but the latter term is more media-palletable. 

That's not quite right. The Gulf Stream is a near-surface current, mostly driven by winds. The AMOC is a large-scale overturning motion of the entire Atlantic, from the Southern Ocean as far north as Iceland and Greenland. If anything, the Gulf Stream could be described as part of the AMOC. 

True. I was under the impression (which may be wrong) that this prediction was an outlier compared to other recent models though?

Shows my rusty knowledge of ocean circulation! Thanks for the reminder.

Thanks for that link. Very interesting.

I think another part of this is not just the cold for us on land but also the effects of nutrients in the ocean and the impact on ocean life.

was taught to use North Atlantic Drift rather than Gulf stream back at school..

I wonder if Priti Patel and Suella Braverman would be sure to take a legal route to refugee status if Britain disappears under an ice sheet

Is this chap on Twitter wrong then?

https://twitter.com/globalecoguy/status/1683956619892121600?s=46&t=6hl_...

(Genuine question!)

And I thought it was a gyre, but I'm a virologist so not used to this scale

I don't know. What is he saying?

He agrees with Ian, that the Gulf Stream is the “big system” and the AMOC is a tiny sun-stream?

If that is what he is saying, he is wrong. 

https://www.metoffice.gov.uk/weather/learn-about/weather/oceans/what-is-the...

"The Gulf Stream is a small part of something called the Thermohaline Circulation or Atlantic Meridional Overturning Circulation. This is a large, global-scale ocean conveyor belt driven by differences in temperature and salt content."

Cheers, will have a proper read.

As Harry says, the Gulf Stream is part of the system. Oceanographically, the Gulf Stream is the western part of the North Atlantic subtropical gyre. It starts at southern tip of Florida where waters coming from the Gulf of Mexico meet waters coming from the Atlantic North Equatorial Current. The Gulf Stream then travels north along the east coast of the USA then separates from the coast at Cape Hatteras. It continues northeasterly, meandering and shedding eddies, until it splits southeast of the Grand Banks of Newfoundland. This is the formal end of the Gulf Stream.

The southern branch carries on eastward and then southward to become the broader, slower Azores and Canaries currents and recirculating round to the North Equatorial Current. This circulation of the North Atlantic subtropical gyre is wind driven - easterly trade winds north of the equator and westerly winds at mid-latitudes.

The northern branch from the split off the Grand Banks is called the North Atlantic Current and is the current that wanders over to the UK then up between Scotland and Iceland to the coast of Norway and into the Arctic Ocean. A branch - the Irminger Current - goes up to Iceland and then over to Greenland and some of the North Atlantic Current circulates north of Iceland and ends up coming south along the east coast of Greenland. 

Off Greenland there are two areas of convection where waters cool enough to sink. In the Labrador Sea - between southern Greenland and Labrador - is a gyre where water sinks to become the Labrador Intermediate water. East of northern Greenland, the cold waters sink deeper and become North Atlantic Deep Water. It is these two areas that draw the North Atlantic Current and so, should convection cease, because the water is either not cold enough or is too fresh, it is the North Atlantic Current that would be most affected and could possibly shut down. I don't really have any idea of the likelihood of that happening though.

I accept that the Gulf Stream is often used to describe the current system from Florida to the UK and further north. The above is for anyone who would like to know a little more detail about the system. I'm hoping it hasn't dated too much in the 25 years since I studied North Atlantic circulation. 

I do love a good ocean current, they are fascinating.