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Prof. Stefan Rahmstorf 🌏 🦣 Profile picture
Prof. Stefan Rahmstorf 🌏 🦣
@rahmstorf
Professor of Physics of the Oceans & Head of Earth System Analysis at the Potsdam Institute. Public speaker. Dad. I don’t read comments here, I do at Bluesky.
22 subscribers
Aug 28 • 9 tweets • 4 min read
I was shocked when I first saw these results from standard climate models used in IPCC reports:
for high emissions, the Atlantic overturning circulation #AMOC shuts down in all 9 models that ran
past 2100, and is well on the way to shutdown by 2100.
Our paper is out today. 🧵 Image The latest climate model generation CMIP6 consists of models from institutes around the world.
The IPCC report found that the crucial Atlantic Ocean circulation #AMOC will weaken. Now
some of the models have been continued beyond year 2100 and reveal a high risk of full
shutdown.
Jul 11 • 6 tweets • 2 min read
We see here a self-styled "honest broker" with decades of experience in downplaying climate change presenting an age-old climate denial trope: using *annual* rainfall data as argument against an increase in *extreme* rainfall.
Does he *really* not know better?
Brief 🧵1/4 Image What scientists have predicted since the 1980s is an increase in heavy rain at the expense of days with light or no precipitation. And that is indeed observed. See @Knutti_ETH That is because warmer air can hold more moisture (Clausius-Clapeyron law). 2/4 nature.com/articles/nclim…Image
Jul 5 • 5 tweets • 2 min read
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…
Mar 26 • 5 tweets • 2 min read
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…
Mar 15 • 7 tweets • 2 min read
Zur Erinnerung: Kernfusion ist /keine/ KlimalÜsung sondern klimaschädlich. (Nur falls jemand auf die Idee kommt, diese Träume von Merz mit Klimaschutzgeldern zu subventionieren.)
Kurzer Thread in 5 Bildern. Image Image
Jan 12 • 7 tweets • 3 min read
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
Nov 19, 2024 • 5 tweets • 2 min read
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
Nov 3, 2024 • 7 tweets • 3 min read
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
Oct 21, 2024 • 4 tweets • 3 min read
One feature of global warming is the *energy imbalance* of the Earth: we are absorbing more energy from the sun than we send back to space in form of thermal radiation.
If Earth’s climate were in equilibrium, these two numbers would exactly balance.
The main reason they don’t is the thermal inertia of the ocean. Because the ocean takes a long time to warm up, the warming of the surface ocean lags behind the warming of the land areas.
So the ocean remains cooler and therefore emits less thermal radiation.
93% of the energy imbalance is due to that relatively cool ocean.
If the ocean surface warming didn’t lag behind the land areas, the imbalance would thus largely disappear.
I’ve seen some crazy claims, like: if the ocean did not absorb most of the energy imbalance, then that amount of heat would end up in the atmosphere, heating the Earth by 36 degrees Celsius.
That’s not how this works.
The ocean with its large heat capacity and therefore large heat uptake causes most of the energy imbalance of our planet at a time of rapid global warming. If the ocean didn’t do that, the Earth would only take up a fraction of the heat it does now. It would be a little bit warmer (a few tenths of a degree C) but nothing like 36 C! That misunderstanding of ocean thermal inertia, is linked to another one: That the Earth will keep warming for decades after we reach zero CO2 emissions, as the oceans catch up with warming. That’s also incorrect.
That idea is not fundamentally wrong, but there is a balancing effect: the CO2 uptake inertia. While the ocean continues warming for some decades, it will also continue taking up CO2 for some decades after we stopped emitting, because of a CO2 concentration imbalance between atmosphere and upper ocean. So the CO2 concentration will decline, and from the point where we reach zero emissions, the warming will likely stop right away.

carbonbrief.org/explainer-will…
Sep 14, 2024 • 9 tweets • 4 min read
Wie hängen solche Extremniederschläge wie derzeit mit dem Klimawandel zusammen? Kurzer🧵. 1/x Image Erstens enthält mit Feuchtigkeit gesättigte Luft pro Grad Erwärmung 7% mehr Wasserdampf. Das ist ein Gesetz von 1834, ich habe es hier erklärt:
Zweitens kommt mehr Wassernachschub durch Verdunstung, wenn das Mittelmeer wie derzeit wärmer ist. 2/x spiegel.de/wissenschaft/c…
Image
Aug 17, 2024 • 5 tweets • 2 min read
Wo macht ihr in der #Klimakrise lieber Urlaub? Izmir oder Menorca?

Aug 12, 2024 • 4 tweets • 2 min read
Vor 22 Jahren - am 12./13. August 2002 - fiel eine nie zuvor in Deutschland innnert 24 Stunden gemessene Regenmenge: 312 mm. Bald stand Dresden unter Wasser, es gab über 11 Milliarden € Schaden. Mein Welt-Interview von damals. 🧵
pik-potsdam.de/~stefan/welt-i… Inzwischen ist die von mir erwähnte Zunahme der Extremniederschläge noch viel deutlicher in den Messdaten der Wetterstationen hervorgetreten.
Die Häufung liegt inzwischen weit außerhalb der historischen Schwankungen. nature.com/articles/s4161…
Jun 16, 2024 • 15 tweets • 6 min read
Talkshows sollten gut Ăźberlegen, ob sie allen Ernstes 2024 immer noch Klimaskeptikerdebatten fĂźhren wollen. Kleiner Thread mit Faktenchecks zu den Behauptungen von @Axel_Bojanowski. 1/x In dem Clip behauptet Bojanowski, er habe nicht bestritten, dass der Meeresspiegelanstieg sich beschleunigt. Hier ist dokumentiert, dass er das z.B. in der SZ sehr wohl getan hat (Zitat: "...also keine Beschleunigung").
2/x scilogs.spektrum.de/klimalounge/me…
Apr 13, 2024 • 7 tweets • 3 min read
Short thread on the Atlantic Meridional Overturning Circulation #AMOC, which brings a huge amount of heat to the northern Atlantic.
If it slows, the region west of Britain cools. And the Gulf Stream moves closer to the US coast, causing warming there.
Both are already happening, as satellite data show. 1/6Image Also air temperature data show: remarkably, the northern Atlantic is the only part of the world which has cooled since the 19th Century. 2/6 Image
Apr 12, 2024 • 7 tweets • 3 min read
Kurzer Thread zu meinem neuen Paper. Es geht um die Atlantikzirkulation (#AMOC genannt), die riesige Wärmemengen in den nÜrdlichen Atlantik schafft. Schwächt sie sich ab, kßhlt sich der Atlantik westlich der britischen Inseln ab. Und der warme Golfstrom rßckt näher an die US-Kßste, dort wird es besonders warm. Beides passiert bereits, wie Satellitendaten zeigen. 1/6Image Auch in den Daten der globalen Lufttemperaturen sieht man: der nÜrdliche Atlantik ist die einzige Weltregion, die sich seit dem 19. Jahrhundert abgekßhlt hat! 2/6 Image
Feb 9, 2024 • 6 tweets • 2 min read
New study: the Atlantic overturning circulation AMOC “is on tipping course”.

The paper by Dutch colleagues adds more weight to recent warnings, such as the OECD Climate Tipping Points report of 2022 and the Global Tipping Points report published 2023.

realclimate.org/index.php/arch… Most-viewed Guardian story. Image
Jan 25, 2024 • 9 tweets • 3 min read
Nicht veräppeln lassen: der "Strippenzieher der WerteUnion" Markus Krall verbreitet Klimaleugner-Lügen. Dieser Eisbohrkern aus Grönland von Richard Alley endet im 19. Jh, vor Beginn der modernen Erderwärmung. Alley hat sich längst in der NYTimes gegen diesen Fake gewehrt. 🧵1/4 Image Mit solchen Lügenmärchen passt Krall gut zur WerteUnion, die Klimaforschung als "Müll-Wissenschaft" diffamiert. (Sie könnte ja auch stolz sein, dass Forschung aus 🇩🇪 auch auf diesem Gebiet Weltklasse ist...) Zum Klimamanifest der WerteUnion ⬇️ . 2/4 spektrum.de/kolumne/das-kl…
Nov 23, 2023 • 4 tweets • 1 min read
"Wenn die auf sozialen Medien bei mir kommentieren blocke ich die einfach. Es ist alles hundert mal widerlegt worden, und wir haben einfach nicht Zeit uns damit jetzt noch aufzuhalten." Dabei geht’s natürlich nicht um andere Meinungen - die sind immer ein normaler und wichtiger Teil des wissenschaftlichen Diskurses.
Es geht um falsche und unbelegte Behauptungen, gefälschte Grafiken, VerschwÜrungstheorien und Beleidigungen.
Nov 13, 2023 • 4 tweets • 3 min read
For all interested in the tipping point of the Atlantic overturning circulation : here's Henk Dijkstra's recent talk.
The tipping point has been confirmed in a state-of-art climate model, and a novel early warning indicator suggests we're heading there.
buff.ly/3QU5dtZ


Image
Image
Image The novel early warning indicator is based on a diagnostic I proposed in this paper in 1996: pik-potsdam.de/~stefan/Public…
Oct 30, 2023 • 4 tweets • 1 min read
There's more happening to weather extremes now than can be explained by thermodynamics, i.e. everything getting warmer, evaporation increasing, the atmosphere holding more energy and water.
Also changing: jet stream, polar vortex, planetary waves & Atlantic ocean circulation.

Image Some commentators (surprise!) didn’t get the key point: that climatologists distinguish between ‘thermodynamic’ and ‘dynamic’ effects of climate change. So far we’ve mostly seen thermodynamic effects on extremes, but we argue there’s more: we can now also see changes in dynamics.
Aug 17, 2023 • 5 tweets • 2 min read
Kann’s nur wiederholen:
Extremregen nimmt durch die Klimaerwärmung zu.
Physik ist verstanden.
Weltweite Datenauswertung bestätigt es.
buff.ly/47BSFO1 Studie: nature.com/articles/s4161…