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Comment by AndrewKemendo | Hacker News Reader

This is wild:

> The amount of radiative forcing could lead to a doubling (or more) of the warming rate in the 2020 s compared with the rate since 1980 with strong spatiotemporal heterogeneity. The warming effect is consistent with the recent observed strong warming in 2023 and expected to make the 2020 s anomalously warm. The forcing is equivalent in magnitude to 80% of the measured increase in planetary heat uptake since 2020.

Truly, all bets are off for being able to predict the climate going forward

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The numbers in this study need to be interpreted carefully, the way the authors presented them doesn't really help this.

The warming rate they quote (0.24K per decade) is the instantaneous warming, which decreases over time. The warming over 10 years is actually about half of this (0.12K). While still significant, it's not a doubling of the warming rate (which is around 0.19K per decade).

The forcing being equal to 80% of the heatuptake is also interesting, but we have not seen such a large step change in energy imbalance in the Earth system. This doesn't mean they are wrong about the forcing estimate, but it does not mean that 80% of the warming since 2020 has been due to ship fuel regulations either.

This wasn't unpredicted, at least not in principle. Sulfur aerosols have been a component of climate models for decades, and were already known to be a major negative forcing term counteracting something like 1/3 of human-caused warming. See for example [1], an IPCC report from 2021 that shows sulfur aerosols contributing 0.5 C of cooling in the industrial era.

Deliberately adding such aerosols to the upper atmosphere (where they're less harmful than ground-level pollution), which volcanic eruptions already do, is one of a few major geoengineering proposals to counteract climate change.

[1] https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6...

But the mechanism is different, so far as I understand. The sulfur rich fuels supports marine cloud brightening and ship tracks. (Low clouds reflect heat, while high clouds absorb) The loss of the ship tracks accounts for a big jump in the warming effects of shipping.

https://ntrs.nasa.gov/api/citations/20220015136/downloads/Yu...

The mechanism is different from the impact of sulphur in the stratosphere (where there are no clouds), but it is the same as the mechanisms that have caused the majority of the aerosol cooling (a brightening of clouds).

The same ze of the cooling has long been uncertain though. It depends a lot on assumptions you make about the pre-industrial atmosphere,something that we don't have great observations of.

> Deliberately adding such aerosols to the upper atmosphere

Sulfur in the atmosphere causes acid rain. We can deliberately seed clouds much less damagingly than by encouraging sulphur emissions.

Artificial volcanic winters, that's something.

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