#AMOC musings and global mean temperature GMT

Says here https://www.nature.com/articles/s41561-024-01568-1.epdf?sharing_token=O3cvnzvEWDHiaPGAV-CB3dRgN0jAjWel9jnR3ZoTv0M2PsD_MIel1A6mz6UbuhaTQSv4VfXkSU9okrbFGA0gy1etRpvwJw0P0tMsHg9ro8Nv1h-GiKg-3Km08jevWj3MVZ6uFzlIrUTv-X1bF8I0K8crc3qdtYsHtgUTx9fE2Zc%3D
(Original #Pontes etal 2024 https://www.nature.com/articles/s41561-024-01568-1 )

it takes 5 years for the Southern warming signal from AMOC slowdown to appear in the Atlantic near South Africa. And another 14 years for the signal to propagate from South Africa's coast to Brazil's.

So for 14 to 19 years, GMT can be expected to drop from the cooling from Greenland to St Petersburg.
(Yay, another told-you-so-moment for climate deniers!)

But then, when the warming Atlantic is seriously trapped in the South, for a while there, GMT will be stable.

Just goes to show how meaningless the concept of GMT really is. Civilisation will have disappeared in a puff of smoke, or maybe, in a blizzard. But GMT is stable. Yay.

This study looks at a few climate elements over 1000 years after fossil fuel cessation https://esd.copernicus.org/articles/15/1353/2024/esd-15-1353-2024.html
by #King et al 2024 "Exploring climate stabilisation at different global warming levels"

Among other continued regional climate changes, they find that Antarctic sea ice will continue to decline despite stabilisation of GMT🌡️ after CO2zero.

But the paper does not mention this:
continued Antarctic #seaice decline means that #Antarctic bottom water formation slows down. Which in turn changes the ocean carbon cycle and slows down AMOC.

Since they don't mention either, how trustworthy is the overall model result?
And can it also mean that a stabilised GMT is merely the result of an AMOC shutdown where cooling over North East Atlantic is balanced by warming everywhere else?

It did mean exactly that in #paleoclimate during the #LastGlacialMaximum, #LGM:
The bellwether for global mean temperature is a place called Ceara Rise off the coast of North Brazil.
It's surface temperature proxies stayed stable-ish with minuscule changes during known AMOC shutdowns in the last #IceAge
( #Westerhold et al 2020 https://www.science.org/doi/abs/10.1126/science.aba6853)

I'm not convinced that global mean temperature has meaning at all. Haven't been for a long time now. Especially because I see climate scientists on Twix, here or Bluesky mis-using GMT as proof for something to be irrelevant if it only has an impact of 0.05°C on GMT for example.

But regional impacts of something is where it hits us, our civilisation!

The chart shows temperature at Ceara Rise as white line. It's values are the originals, not in any way amended to fit the y-axis.
Greenland's d18O in light yellow is a proxy for temperature changes. When it goes up or down, it's likely that AMOC hickupped.
But Ceara Rise, the bellwether for global mean temperature, stayed a stable holiday destination for the Neanderthals throughout the Last Glacial Maximum, with changes of maybe 0.2°C .

A new paper on #AMOC

Prose summary by the authors https://theconversation.com/meltwater-from-greenland-and-the-arctic-is-weakening-ocean-circulation-speeding-up-warming-down-south-238302

Free ePDF https://www.nature.com/articles/s41561-024-01568-1.epdf?sharing_token=O3cvnzvEWDHiaPGAV-CB3dRgN0jAjWel9jnR3ZoTv0M2PsD_MIel1A6mz6UbuhaTQSv4VfXkSU9okrbFGA0gy1etRpvwJw0P0tMsHg9ro8Nv1h-GiKg-3Km08jevWj3MVZ6uFzlIrUTv-X1bF8I0K8crc3qdtYsHtgUTx9fE2Zc%3D

actual paper https://www.nature.com/articles/s41561-024-01568-1 #Pontes et al 2024

tldr: by adjusting #Greenland meltrate to actually observed accelerated rate which is underestimated in standard climate models, they are now able to explain the observed increase in SST and salinity in the South #Atlantic with a slowdown of the AMOC in the past decades , matching the slowdown rate calculated by #Rahmstorf 's former PhD student #Caesar 2018.
If you recall, that's the latitude in the S-Atlantic that #vanWesten etal 2024 found as prime location for early warning signal of an imminent AMOC collapse in their freshwater experiment.

By applying melt (but without the observed AND projected acceleration that #Greene et al 2024 notify us of https://www.nature.com/articles/s41586-023-06863-2 ), Pontes' model now projects a total slowdown of 30% by 2040.
(Also noteworthy maybe that the authors pull the 2degree milestone forward to 2040, while some papers I read in 2018 still saw 2C sometime in the 2050s. But they're not the first researchers doing so that I came across.)

Meltrate in Greenland is 30Mt of ice per hour... Did you know that 1kg of pizza equals 19kg CO2 which ultimately melts 12.3 t glacial ice?
1 cup of coffee is 400gr CO2 and melts 260 kg. (sources see #2)

Meanwhile, #COP29 news falsely report a global consensus in coal phase-out. A journalist on Bluesky dug into the actual agreement and the countries listed.
First, it's not a global agreement.
Then either, the countries have no coal energy, or they have already long ago planned the phaseout so nothing new from them, either.
The single country with a new development in this coal agreement is Australia which announced to close 3 coal power plants ... sometime in the future...