zlacker

And that was a reasonable prediction at that time. Since than climate models have improved significantly, computing power has increased by several orders of magnitude, and policies and technology has changed—both as a response to the climate crises, and as technology and infrastructure improves around the world.

Today’s models predict 1.5°-2.0° C by 2040, and 4° C by 2100 if no additional climate mitigations (not even promised or pledged) are implemented. The 4° C scenario is generally regarded as unrealistic so most climate models have another prediction which accounts for some additional climate mitigation which most countries have promised and pledged and put the increase at 2°-3° in 2100.

>>runarb+(OP)
It sounds like the only reason why the 4 degree Celsius scenario is deemed unrealistic is that people don’t like it. So they have come up with hopium about as of yet imaginary solutions and veracity of carbon pledges.

>>jgilia+k6
I think I agree with you. 4° is much more likely IMO than 1.5° given how governments tend to align them selves with the interest of the rich above all else. However I think at some point continuing climate inaction will not only become politically infeasible but also economically infeasible. However at that point we will have acted to little too late, and will be looking at a 2-3° warming.

Climate optimists will have you believe that 2-3° is actually not that bad, however I believe this sort of climate optimism amounts to climate denial, 2-3° is definitely a horror scenario effectively destroying our current way of life. Millions of people will die, millions more will be forced to flee—and they won’t be accepted as refugees, wars will break out, our economy will collapse, and the poor will starve in a 2-3° scenario.

>>runarb+(OP)
> The 4° C scenario is generally regarded as unrealistic

Why? It sounds like you might mean that, by about +2 °C (~double today's avg warming) we start to notice the impacts a little too acutely and take more action, am I reading that right?

>>lucb1e+Yi
4° C is an extrapolation from current trends. Straight up extrapolations are seldom good predictions. There are usually some feedbacks and feed forwards in a complex systems. It is not unreasonable to assume that governments will follow through with at least some of their promises and pledges, especially as the effects of the climate disaster becomes more apparent. And doubly so as new industries pop up around climate solutions with enough money to influence governments over what the dying fossil fuel industry.

That said, I'm under no disillusion that 2° C warming is not a horror scenario and that if governments actually cared about human lives they would limit warming to 1.5° I know they don't and the won't

>>runarb+Et
Ah, unrealistic because it's a plain extrapolation without accounting for any behavior change or indeed feedback effects. That makes sense, thanks!

> It is not unreasonable to assume that governments will follow through with at least some of their promises and pledges

FWIW, it actually looks like we're on a path to 2.5-2.9 °C of warming with current policies, and nearly another 1°C reduction with current pledges which are indeed much less likely to fully materialise. Via https://en.wikipedia.org/wiki/Climate_change#/media/File:Gre... which appears to use 2021 data. The "no climate policies" scenario is shown as having the lower error margin actually above +4°C

>>runarb+Mh
How do you know all that will happen in your second paragraph? Is there a model making such a prediction for society in the 2-3° scenario? If skeptics of such societal projections are denialists, then are you a doomer?

There's another possibility. Society will adapt and things won't be nightmarish, because 2-3° warming isn't extreme enough to break down society, when people will have decades to adapt.

>>goatlo+Lz
> How do you know all that will happen in your second paragraph?

We have barely reached 1.5° C and people are already dying by the thousands, people are already fleeing by thousands more—and people are already not accepted as refugees. There are entire areas which are become more and more inhospitably which are experiencing disproportionately more famines, coups, and even wars (namely the Sahel region in Africa).

Yes I am a climate doomer, but I believe doomerism is the reasonable reaction to our climate reality.

>>lucb1e+gu
> FWIW, it actually looks like we're on a path to 2.5-2.9 °C of warming with current policies.

This is true, I actually used 2° C as a shorthand for 2° C - 3° C. I shouldn’t have done that. I actually believe we are more likely to be closer to 3° C at the end of this century than 2° C.

>>goatlo+Lz
2-3 C will probably break society. I have heard opinions about Earth's carrying capacity being 1B people at 4C, imagine that possibility.

At 2 C a cascade of tipping points might start:

https://climatetippingpoints.info/2022/09/09/climate-tipping...

>>runarb+(OP)
> Today’s models predict 1.5°-2.0° C by 2040

From when 1990, or 2023?