Earth is warming faster. Scientists are closing in on why (2024)

Thank you for this response. Of those that replied to me, yours seems the most balanced and scientific, and I learned the most from. I wish more often people engaged on HN like you have here.

Given your expertise in this, I'm curious what your take is on CO2 capture, not in terms of economic viability, but in terms of climate risk...

For example, if we were to discover a process that removed CO2 from atmosphere and converted it into a product profitably such that there was an economic incentive/positive feedback loop to remove CO2.

My intuition is that if we removed the CO2 too quickly or too much of it we may have unwanted consequences, but if the rate was managed and we slowed down and stopped at a certain equilibrium, would this be a theoretically ideal way to address the problem?

It's the aerosol levels that "snap back" (although that takes months to a few years, not weeks).

The effect that has on the climate depends on how much CO2 is in the atmosphere at the time.

If during the time we were doing the aerosol program we've also continued increasing CO2, using increasing aerosol releases to prevent that from causing warming, then when we stop with the aerosol we get that deferred warming over a few years or less.

We end up at the roughly the same place we would have been if we had not done the aerosols at all, except instead of getting from where we are now to them over several decades we get their over a few years.

Let's say that is 3℃ above current average temperature. A 3℃ rise over 2 years is a lot harder to handle than a 3℃ rise over 30 years.

Worse, if we started aerosols a lot of countries might decide that it is OK to keep increasing emission rates, so if we ever stop the aerosols were are looking at a rise to much higher than we would have had if we had not used aerosols.

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Some things to consider.

First, what is "too quickly" with reference to CO2 removal from the atmosphere? At present, human civilization emits over 40 gigatons - or 40 trillion kilograms - of CO2 per year. And that increases the atmospheric burden by about 2.5 parts per million per year. So today, before you even start _reducing_ atmospheric CO2, you need to be sucking down at least 40 trillion kilograms of CO2. I struggle to imagine a scenario outside of total science fiction where that would be remotely possible.

Second, the equilibrium climate response to changes in greenhouse gas forcing take on the order of decades or centuries to realize. This is because the dynamics of the climate system are heavily buffered. For example, the ocean acts as a giant heat capacitor that slowly interchanges with the atmosphere. Were you to instantaneously halve the CO2 in the atmosphere, you'd likely see a pretty classic exponential decay in global average temperature (and other more nuanced responses); in the present climate, it's not clear we have already passed specific "tipping points" that would induce that hysteresis I described in the previous comment (in fact - one could read "climate tipping point" as a synonym for dynamical system hysteresis). Theoretically, one could try to "dial in" some particular equilibrium climate state, but it's not obvious over what timescale you'd have to intervene and what the cost of such an intervention would be.

The cool thing is none of this needs to be purely "theoretical." You could simulate all of this _today_ if you had a setup to run a global climate model. A "4X CO2" experiment where you branch from an equilibrium spin-up climate state and immediately apply a global quadrupling of CO2 has been a completely standard experiment as part of CMIP for over two decades. The opposite experiment is an established protocol for both the Carbon Dioxide Removal Intercomparison Project [1], which features an annual ramp down of CO2 at a 1% per year rate, and the Cloud Feedback Model Intercomparison Project [2], which features a more direct counterpart, with an abrupt decrease of atmospheric CO2 by 50%. There is a large body of literature discussing the results of these classes of experiments, but this is outside of my primary research focus and I can't turn you to particularly good papers off-hand. But they're easy enough to find.

[1]: https://www.geomar.de/en/cdrmip [2]: https://www.cfmip.org/experiments/cfmip3cmip6

go find it and analyze it and publish your findings

until then, you can read the papers of scientists who have analyzed it and published their findings