[wcoenen]

> a temporary thing for a few centuries, after which the climate goes back to what it used to be

Reduced or even zero emissions are not negative emissions. By what processes and at what time scales will 100% of the surplus accumulated CO2 go away? I am not so sure this can happen in just a few centuries.

[skissane]

This is what the IPCC predicts [0]:

"According to the IPCC's 2021 projections of global temperature under different emissions scenarios, peak temperature could be anything from 1.6 ºC in around 2050 (if the globe hits net zero emissions by then), dropping to 1.4 ºC by 2100; to, with emissions still climbing, 4.4 ºC at 2100, with the peak still to come."

The IPCC's own predictions are that temperatures will peak and thereafter fall due to reductions in anthropogenic CO2 emissions. The question is when it will peak and how big the peak will be, which all depends on how quickly emissions are cut.

[0] https://www.nature.com/articles/d41586-023-01702-w

[wcoenen]

> The IPCC's own predictions are that temperatures will peak and thereafter fall due to reductions in anthropogenic CO2 emissions.

Yes, but it's important to understand why. I believe it's because the oceans and atmosphere would not be in equilibrium when we reach zero emissions, and so the oceans would continue to absorb CO2 for a while. This reduces atmospheric CO2 concentration and temperature in the short term (at the cost of further ocean acidification).

But what happens after the oceans and atmosphere reach equilibrium? Where does the excess CO2 go?

I think it can only go away through the very slow process of bicarbonate formation. And I'm not convinced this can completely remove the excess CO2 in just a few centuries.

[silverquiet]

I believe James Hansen’s latest paper about long-term feedback effects actually predicts 10 degrees Celsius as the new equilibrium after a few centuries which seems… apocalyptic?

[skissane]

The IPCC views many of Hansen’s predictions as unlikely.

I don’t know who is right, but I think for someone who isn’t an expert at this, there is an argument for preferring the mainstream consensus to the views of a single controversial researcher-especially if one hasn’t spent the time to understand the details of that researchers’ work (I haven’t)

[silverquiet]

I fairly recently re-read some of Hansen’s work from the 80’s and it was quite prescient of the current state of the world (done in a time when a super computer would be firmly outmatched by a cheap cell phone of today), so I’m inclined to give him some consideration. Certainly his past performance makes no guarantees about his present work; I think he’s in much more of a mentor/managerial role these days anyway, but then again, I don’t think anyone can really tell you with certainty and precision what the future holds. That’s just the way it is.