Prof. Stefan RahmstorfOct 5, 2023
We do understand the #globalwarming caused by fossil fuels - for four decades it’s been going as predicted.
But we don’t understand the surprise upward leap that is happening now.
And that worries me.
Show threadAlberto CotticaOct 5, 2023
@rahmstorf could it be that models tend to incorporate linearity assumptions by default?
Show threadAnne OminousOct 6, 2023

@alberto_cottica @rahmstorf

yes! why is it surprising that climate change is not linear?
i get that we dont know the exact cause of this dramatic & sudden rise, but i'd guess many assumptions have been made about proportional effects

and ofc, we're carrying more CO2 in the atmosphere than earth ever has... a look at the record shows that historically, it was a much hotter planet when CO2 levels were anywhere near this high. maybe things 'catch up' in fits and starts
https://earth.org/data_visualization/a-brief-history-of-co2/

A Graphical History of Atmospheric CO2 Levels Over Time | Earth.Org

As the most abundant greenhouse gas in our atmosphere, CO2 levels have varied widely over the course of the Earth’s 4.54 billion year history.

Earth.Org
Show threadKnud JahnkeOct 6, 2023

@rustoleumlove @alberto_cottica @rahmstorf

Because @rahmstorf has been part of the climate modelling community for decades and of course the models aren't in any way simplistic. If a central climate scientist says he is worried, because Earth got much hotter than expected and modeled ... then maybe it's worrisome. Extra worrisome.

Show threadAlberto Cottica
@knud far from me to criticize other people's expertise. As a modeller myself, however, I have oftentimes seen linearity assumptions being plugged into situations of theoretical ambiguity, where there is no reason to choose one functional form over another for a certain relationship. @rustoleumlove @rahmstorf
Oct 6, 2023 at 12:44pmWeb
Show threadKnud JahnkeOct 6, 2023

@alberto_cottica @rustoleumlove @rahmstorf

Sure, but one needs a decent argument to choose a quickly diverging function over a linear one, no? So yes, one might get surprises, but in the end this means a physical mechanism or coupling that wasn't on people's radar so far. To find and include that will be important.

Show threadAlberto CotticaOct 7, 2023
@knud @rustoleumlove @rahmstorf absolutely, you expressed it better than I could.
Show threadKnud JahnkeOct 7, 2023
@alberto_cottica @rustoleumlove @rahmstorf