Collapse of key Atlantic current could have catastrophic impacts | Hacker News Reader

Collapse of key Atlantic current could have catastrophic impacts

livescience.com

44 pointsBrajeshwar12 comments

Just finished the 'Forty Signs of Rain' series of books that explores Atlantic stream cessation, or at least the ocean circulatory part of that. No spoilers, but I thought it was a little too optimistic in how humanity would respond in a giant collective effort. We are on a road with the pedal to the metal, and big business only wants us to don the peril sensitive sunglasses.

That was written when the effect of big tech's attack on the information landscape hadn't been digested yet. Now it's much more clear. The current future is correspondingly much more grim.

This claim has been around for a while, but it's unclear if it really is a concern. First, even if large freshwater injections had significant climate impacts at the beginning of this interglacial period c. 12k years ago, it doesn't necessarily mean that Greenland ice melt will have the same effect today as the state of the system is very different. Second, the Gulf Stream is a western boundary current driven by physical forces like gyre circulation that are due to the rotation of the Earth and midlatitude coriolis effects, it won't be shut down under warming.

See also recently published reports that don't seem to support the idea:

(2021) Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation

https://www.nature.com/articles/s41467-021-23350-2.pdf

In particular rapid warming of the North Atlantic shelf on the North American side seems to be overwhelming many other trends, due to increased heat transport northwards from the tropical Caribbean, leading to subsurface nutrient depletion and fishery collapses, and probably overriding any Greenland-melt-induced cooling:

(2021) Changes in the Gulf Stream preceded rapid warming of the Northwest Atlantic Shelf

https://www.nature.com/articles/s43247-021-00143-5

You don't back up your claim with any evidence: "Second, the Gulf Stream is a western boundary current driven by physical forces like gyre circulation that are due to the rotation of the Earth and midlatitude coriolis effects, it won't be shut down under warming."

The experts are not saying what you are claiming here. You provide links which are not directly related to AMOC collapse. I call cherry picking.

It's just basic oceanographic physics, that's how midlatitude gyres work. Since you ask:

> "The trade winds create the equatorial currents that flow east to west along the equator; the North Equatorial and South Equatorial currents. If there were no continents, these surface currents would travel all the way around the Earth, parallel to the equator. However, the presence of the continents prevents this unimpeded flow. When these equatorial currents reach the continents, they are diverted and deflected away from the equator by the Coriolis Effect; deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. These currents then become western boundary currents; currents that run along the western side of the ocean basin (i.e. the east coasts of the continents). Since these currents come from the equator, they are warm water currents, bringing warm water to the higher latitudes and distributing heat throughout the ocean."

https://rwu.pressbooks.pub/webboceanography/chapter/9-1-surf...

The issue is that increased poleward Gulf Stream heat transport could easily overpower the effect of Greenland ice melt outflows into the North Atlantic. This raises other problems, it could still decrease deep ocean ventilation and push the increasing oceanic hypoxia trend.

For those of you that don't understand the climate impact of this on Europe...

Go look at the latitude of frigid-cold Minneapolis-St.Paul or the Upper Peninsula of Michigan, and compare it to Europe. It goes right through central France, almost down to the Mediterranean coast. Spain is on the same latitude as Chicago. Iceland is quite temperate, but it is parallel with central Alaska.

The entire country of England is basically in same latitude as Canada, and not the southern parts of Canada. We think of England as a rainy but temperate country, not some frigid hellscape.

Now it will probably weaken and not collapse... probably...

There probably is huge moderation of temperatures due to the oceans and seas surrounding Europe in general, but the Gulf Stream pumps an unfathomable amount of heat into the area.

one wild card is the warming of the deep ocean suficient to cause the physical expansion of that water,driving sea level rise this is happening now,and is causing localised sea level rise,in the gulf of mexico something not fully accounted for is that the ice in the arctic is bieng formed from an increasingly fresh water top layer,it freezes fast.....and works as an insulative layer,locking in heat a more complicated source of heat is bieng generated in the greenland ice cap,where the surface melt water creates enough frictional heat as it falls through the miles of ice,to melteven more water,this is basic physics...as described by Mr Watt,james there are now enough positive inputs pushing sea level rise,that we now have multiple non zero chances at an ultra extream event,toggling the whole world ocean into different paterns the thing is that there are NO negative inputs and the full list of positive inputs is long,and all of those inputs are growing at an accelerating pace

Would such collapse, by cooling Northern Atlantic, refreeze some of the sea around there and reduce Earth's albedo?

I'm sure I'm not the first one to think about it

I saw other places all it means is some parts of Europe may be cooler then what would be expected with the Temp Rise, but still warmer than say it was 100 years ago. Eventually Greenland will still loose its ice.

The whole picture will be far more complex. In any case, we will go from the mostly stable system we had for the last 15-20k years to an increasingly more unstable one.

As it happens, this just came out:

"Impacts of Atlantic meridional overturning circulation weakening on Arctic amplification" - https://www.pnas.org/doi/10.1073/pnas.2402322121

And the abstract:

“Enhanced warming of the Arctic region relative to the rest of the globe, known as Arctic amplification, is caused by a variety of diverse factors, many of which are influenced by the Atlantic meridional overturning circulation (AMOC). Here, we quantify the role of AMOC changes in Arctic amplification throughout the twenty-first century by comparing two suites of climate model simulations under the same climate change scenario but with two different AMOC states: one with a weakened AMOC and another with a steady AMOC. We find that a weakened AMOC can reduce annual mean Arctic warming by 2 °C by the end of the century. A primary contributor to this reduction in warming is surface albedo feedback, related to a smaller sea ice loss due to AMOC slowdown. Another major contributor is the changes in ocean heat uptake. The weakened AMOC and its associated anomalous ocean heat transport divergence lead to increased ocean heat uptake and surface cooling. These two factors are inextricably linked on seasonal timescales, and their relative importance for Arctic amplification can vary by season. The weakened AMOC can also abate Arctic warming via lapse rate feedback, creating marked cooling from the surface to lower-to-mid troposphere while resulting in relatively weaker cooling in the upper troposphere. Additionally, the weakened AMOC increases the low-level cloud fraction over the North Atlantic warming hole, causing significant cooling there via shortwave (sw) cloud feedback despite the overall effect of sw cloud feedback being a slight warming of the average temperature over the Arctic.”

Why not use the brine from desalination plants in Europe to increase salinity in the Iceland region as a way to combat AMOC collapse?

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