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Prof. Stefan Rahmstorf 🌏 🦣

@rahmstorf

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. 🧵

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. 🧵

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. 🧵

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Prof. Stefan Rahmstorf 🌏 🦣

@rahmstorf

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

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Prof. Stefan Rahmstorf 🌏 🦣

@rahmstorf

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. 🧵

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-…

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…

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Prof. Stefan Rahmstorf 🌏 🦣

@rahmstorf

Oct 21, 2024

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…

A third misunderstanding (that one promoted by climate skeptics) is that we do not need to reduce our CO2 emissions to zero in order to stabilize the concentration, because the ocean takes up 25% of our emissions. However, that is primarily just due to a temporary imbalance and will stop after a few decades, just like the heat uptake will. Much of the increased CO2 will actually remain for many tens of thousands of years in the atmosphere (unless our descendants actively pull it out of the atmosphere).

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Prof. Stefan Rahmstorf 🌏 🦣

@rahmstorf

Sep 14, 2024

Wie hängen solche Extremniederschläge wie derzeit mit dem Klimawandel zusammen? Kurzer🧵. 1/x

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…

Das nennen wir in der Forschung thermodynamische Effekte. Hinzu kommen Veränderungen in der Wetterdynamik, etwa dem Verlauf des Jetstreams oder der zunehmenden Dauer von Wetterlagen (relevant bei mehrtägigem Dauerregen). Das erklärt unser Kommentar. 3/x iopscience.iop.org/article/10.108…

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