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Prof. Stefan Rahmstorf 🌏 🦣 Profile picture
@rahmstorf
Feb 25, 2021 • 13 tweets • 6 min read • Read on X
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Just out: our new paper affirming the unprecedented slowdown of the Gulf Stream System (aka Atlantic meridional overturning circulation, 𝗔𝗠𝗢𝗖) in Nature Geoscience! @NatureGeosci A thread. 1/11 Image
Lead author Levke Caesar compiled a range of different, published proxy data reconstructions of the AMOC - thanks to all their authors for sharing them. The longest ones go back 1600 years! They represent different AMOC facets: flow speed, water masses, heat transport. 2/11
These data consistently show an AMOC decline in the 20th Century, with the weakest AMOC state of the whole series in the last decades. This finding is statistically significant in 9 of the 11 time series. 3/11
This decline is as predicted by climate models in response to #globalwarming & responsible for a particular "finger print" pattern of sea surface temperature change including the northern Atlantic '𝗰𝗼𝗹𝗱 𝗯𝗹𝗼𝗯' or '𝘄𝗮𝗿𝗺𝗶𝗻𝗴 𝗵𝗼𝗹𝗲'. See realclimate.org/index.php/arch… 4/11
What the last IPCC reports said on the AMOC decline. We know IPCC is very conservative - let's see what they make of the new and stronger evidence in the next report. 5/11
Here I discuss a couple of further recent studies supporting an AMOC decline - one based on sea level data, the other based on salinity data from the South Atlantic. realclimate.org/index.php/arch…

Graph from @chrispiecuch nature.com/articles/s4146… 6/11
This 'cold blob' is another climate model prediction come true, and in the models it's due to human-caused AMOC decline. A discussion of various pro and con arguments (as of three years ago): realclimate.org/index.php/arch…
(The image of observed SST trends is from IPCC AR5.) 7/11
How much AMOC weakening do the latest (CMIP6) climate models predict by the year 2100? They find "the AMOC might decline between 6 and 8 Sv (34–45%) by 2100." 8/11 agupubs.onlinelibrary.wiley.com/doi/full/10.10…
And what about the risk of crossing the tipping point for an AMOC breakdown? I discuss that here: realclimate.org/index.php/arch… 9/11
Here's a nice Washington Post story on our paper, by @chriscmooney. washingtonpost.com/climate-enviro… 10/11
Since it mentions The Day After Tomorrow I've gotta add this clip... I reviewed the movie at the time it came out: pik-potsdam.de/~stefan/tdat_r… 11/11
Should read SAT trends of course. Surface air temperature.
Open access link to our paper:
rdcu.be/cfPxA

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More from @rahmstorf

Prof. Stefan Rahmstorf 🌏 🦣 Profile picture
Jul 5
Short thread with 2 basic facts you should know about this kind of flash flood. ⬇️
1. Extreme rainfall increases as global temperatures rise.
There’s a basic law of physics behind that (Clausius Claperon Law, known since 1834, see Wikipedia).
And numerous analyses of weather station data prove it. See e.g. ours.
nature.com/articles/s4161…
2. Global warming is caused by fossil fuel emissions. That is why it was predicted correctly before it was even observed. And even by scientists from fossil fuel companies like Exxon Mobil. But their bosses decided to tell you a different story.
Read 5 tweets
Prof. Stefan Rahmstorf 🌏 🦣 Profile picture
Mar 26
A new study by van Westen et al. shows that the #tippingpoint of the Atlantic overturning circulation #AMOC is also found in a high-resolution ocean model which resolves ocean eddies. A first, but no surprise to AMOC experts. 🧵
To find the tipping point you need to do a very slow, long hysteresis model run. That is so computationally expensive that it hasn't been tried before. All models which have tried show this tipping point - we published a first intercomparison in 2005. 🧵 agupubs.onlinelibrary.wiley.com/doi/10.1029/20…
So all kind of models since Stommel's 1961 box model show it, due to the destabilising salt transport feedback. The new model also shows the well-known sea surface temperature fingerprint pattern of an #AMOC shutdown: the 'cold blob', and warming along the American coast. 🧵 Image
Read 5 tweets
Prof. Stefan Rahmstorf 🌏 🦣 Profile picture
Mar 15
Zur Erinnerung: Kernfusion ist /keine/ Klimalösung sondern klimaschädlich. (Nur falls jemand auf die Idee kommt, diese Träume von Merz mit Klimaschutzgeldern zu subventionieren.)
Kurzer Thread in 5 Bildern. Image
Image
Image
Read 7 tweets
Prof. Stefan Rahmstorf 🌏 🦣 Profile picture
Jan 12
2024 war global das heißeste Jahr seit Beginn der Aufzeichnungen, mit 1,6 Grad über dem Temperaturniveau des späten 19. Jahrhunderts. Kleiner Thread mit Datengrafiken dazu. 🧵 Image
In Deutschland war es ebenfalls das wärmste Jahr seit Beginn der Aufzeichnungen - allerdings schon 3,1 Grad wärmer. Weil Deutschland ein Landgebiet ist, erwärmt es sich doppelt so schnell wie der globale Mittelwert, der 71% Meeresfläche enthält. 🧵 Image
Diese moderne Erderwärmung ist praktisch komplett vom Menschen verursacht. Natürliche Faktoren haben weniger als + oder - 0,1 °C beigetragen. Das ist eine Kernaussage des Weltklimarats IPCC. Eher - als +, weil die Sonnenaktivität etwas abgenommen hat. 🧵 Image
Read 7 tweets
Prof. Stefan Rahmstorf 🌏 🦣 Profile picture
Nov 19, 2024
Important new study shows that current climate models underestimate the human-caused slowing of the #AMOC (Atlantic Meridional Overturning Circulation), because they neglect freshwater influx from Greenland melt and other sources. /1
nature.com/articles/s4156…
The study shows "that accounting for upper-end meltwater input in historical simulations significantly improves the data–model agreement on past changes in the Atlantic Meridional Overturning Circulation, yielding a slowdown of 0.46 sverdrups per decade since 1950." /2
In our 2018 Nature article (Caesar et al.) we estimated ~3 Sv slowing since 1950, i.e. -0.4 Sv/decade, based on the observed 'cold blob' in the Atlantic west of Britain. /3 Image
Read 5 tweets
Prof. Stefan Rahmstorf 🌏 🦣 Profile picture
Nov 3, 2024
Latest NASA global temperature data.
Earth has never been hotter since Homo sapiens discovered agriculture in the early Holocene. Likely even since 120,000 years ago.
Fossil coal, oil and gas emissions caused it.
We need to stop making it worse.
Yes, we can if we want to. 🧵 Image
Here is the last 2023 years of data for CO2 (from Antarctic ice core data) and global temperature (from numerous sources of proxy data from around the world, such as sediment and ice cores). Check it out: pastglobalchanges.org/science/wg/2k-…Image
And here's global temperature for the past 24,000 years - since the last Ice Age! Earth is now warming 20 times faster than at the end of the last Ice Age.
(Ice ages are caused by the Earth orbit's Milankovich cycles - modern warming is not.)
Source: nature.com/articles/s4158…Image
Read 7 tweets

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