Mastodawn

My favourite video-Climate journalist Nick Breeze speaks 30 minutes with Claudia Wieners from Utrecht about aspects in Solar Radiation Meddling SRM for avoiding the tipping of the #AMOC .

She finds it hard to get research and experiments funded because people find the topic "icky". But she explains, knowledge about what SRM would be doing and how, is not deep enough to assess it as a real option.
And she points out, once the real option looks like the lesser evil, it could already be too late – because the tipping point can be so close.

She splits the problem into two tipping points:
when convection in SubPolarGyre SPG South of Greenland grinds to a halt, and when the AMOC branch next to Europe collapses.
The SPG tipping is closer. And it might be an unavoidable chain reaction that, once SPG stopped, the right branch follows suit inevitably. Might. And might not.
If not, then injecting aerosols into the stratosphere could keep the European branch alive.

But at what cost, she asks. Teleconnections to for example the #Amazon do exist for both scenarios, cooling from SRM and a stopped AMOC.
Same goes for the Asian monsoon.

It's a half hour well spent to start forming an informed opinion about SRM.
#AMOC #Ocean #SRM #ClimateCrisis

"The Last Resort: Could Geoengineering Save the AMOC from Collapse?" – Dr. Claudia Wieners

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anlomedad

2/
That the two AMOC branches collapse at different times can be seen in this image.

The lines in the chart are a few proxy time series in 100 year resolution from 90ka to 300 years ago. The background shapes are Milancovic cycles.
#AMOC stopped and restarted multiple times, best seen in the white line which is a proxy for local Greenland temperature.

About 14.5ka, 14.5 on the x-axis, #Greenland temperature stops its upward race and drops very quickly. I think, this is the convection collapse in the Subpolar Gyre they talk about in the video.
It's when, from top to bottom in the chart: the bright red Andes Glacier index halts its downward slope and plateaus for the whole period of the collapsing and restarting AMOC;
the tentative Sahara greening is halted, blue line;
while noticeably, the dark red Asian monsoon and the pink CH4 methane line still increase.
These two only crash when Greenland feels the last dramatic, rapid temperature drop.

This last bottoming out takes 100 years, and lasts for 1200 years, from 12.8ka to 11.6ka.
Then it takes less than 100 years for temperature, methane and monsoon to climb back up to previous levels.

The bright red tropical Andes Glacier Index and the blue Sahara proxy stay unfazed throughout. But in the aftermath of all this atmospheric re-arranging, the Sahara proxy suddenly flickers, then it tipps – into a lush green Sahara!
(So when the blue line drops, it means that it rains a lot in the Sahara.)

On the side:
4,200 years ago, something called the 4.2ky event happens. The Sahara flickers. The red Glacier Index records a regrowth.
And from 2.9ka, the Sahara tipps. And dries out rapidly. And the glacier has another short, larger growth period.
The Asian monsoon also experienced a hickup 4,200 years ago.

Maybe that was a global event. Maybe. Although methane did not flicker – but this might an artefact of low time step resolution.

Anyway. That's how the last AMOC collapse went. In an Earth System that was crawling out of the last ice age.
It collapsed in 2 stages, first the Subpolar Gyre and Labrador Sea convection stopped. And much later, the European branch stopped too.
Again: In an Earth System that was crawling out of the last ice age. So not to be taken as blueprint for what we're setting into motion this time round.
#PaleoClimate #ClimateChange

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anlomedad 2h ago

That the two AMOC branches collapse at different times can be seen in Peltier's ice model of the last deglaciation https://www.atmosp.physics.utoronto.ca/~peltier/data.php
It's a coarse resolution of 500 year steps tho. But at one point, a coastal location in East Canada regrows its ice shield because the left branch of the AMOC has stopped. Meanwhile Scotland's ice is still melting because the European branch is still working. Only in the next 500 year time step does Scotland regrow its ice shield too.
A line chart at the end of the clip illustrates these 2 locations.