Stratospheric warming, SRM and aerosol injection events

[Gideon Futerman]

Hi all,

Do people know of the impact of stratospheric warming that SRM causes on the injection of other aerosols into the stratosphere, say from wildfire events or volcanic eruptions? Like, how does a warm stratosphere effect how these aerosols rise into the stratosphere and the dynamics of them within the stratosphere

Best Wishes

Gideon

[Adrian Hindes]

I'm not an expert on atmospheric dynamics, but am aware of some relevant papers in that general direction.

Gao et al. (2021) looked at "practical" SAI using solar powered lofting from black carbon particles, partly inspired by the dynamics seen from large bushfires: https://www.science.org/doi/10.1126/sciadv.abe3416

More broadly related, Christian et al. (2019) looked at the radiative forcing and stratospheric warming impacts of pyrocumulonimbus clouds: https://doi.org/10.1029/2019GL082360

Along the same lines, Peterson et al. (2021) looked specifically at the Black Summer bushfires in Australia from 2019-20: http://www.nature.com/articles/s41612-021-00192-9

Similar methods from those studies would presumably be applicable to studying SAI injection, and/or the potential dynamics between artificially injected sulphur (or other) aerosols with stratospheric warming events, pyroCb clouds and the like. I imagine there would be quite a lot of complexity with potentially compounding effects, maybe increasing aerosol lifetime, mixing and regional hydroclimatic changes, etc.

Speaking of which, Simpson et al. (2019) specifically looked at the regional hydroclimatic effects of SAI, and how stratospheric heating plays into it: 10.1029/2019JD031093. 

My understanding from reading that paper and others is stratospheric heating dynamics of SAI is one of those areas where there's still quite a lot of uncertainty, and an area of active research. Maybe other folks in the group here who have more experience with ESMs and atmospheric dynamics can comment further. I know the perspective paper by Ben Kravitz and Doug MacMartin on uncertainty in solar geo research picked out stratospheric heating impacts on tropospheric and surface climate as one of the key outstanding uncertainties.

[Govindasamy Bala]

Besides the effects on stratospheric circulation and chemistry, stratospheric warming caused by sulfate aerosols reduces the effectiveness of what we are trying to achieve. The main intent is to increase sunlight reflection. Part of this cooling effect is offset by stratospheric warming. In a 2019 ESD paper, we show this by prescribing volcanic aerosols at 16, 19, and 22 km. In all these 3 cases, there is stratospheric warming. However, in the case of 16km which is close to the troposphere, the stratospheric warming leads to more water vapor in the stratosphere which could further offset the originally intended cooling. 

https://doi.org/10.5194/esd-10-885-2019

Cheers,

Bala

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With Best Wishes,

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G. Bala
Professor
Center for Atmospheric and Oceanic Sciences
Indian Institute of Science
Bangalore - 560 012
India

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[Andrew Lockley]

My understanding is that current consensus is that adding black carbon to the stratosphere would be a bad idea, so the paper proposing using it for lofting is unlikely to be implemented.

But what if we used forest fires as a natural(ish) source of black carbon for lofting? Are there enough such fires that this could be a viable option for lifting sulfur to the stratosphere, without deliberately adding more? 

Andrew 

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[Douglas MacMartin]

Why?

 

Option 1) Build a modest number of airplanes that can get to desired altitude, like 20km, without any need to spend much time at altitude, and then use them continuously.

 

Option 2) Build 10-100x as many airplanes as option 1 because you’re only going to use them when there might be fires, and while they won’t need to get as high, they’re still dedicated aircraft, and they’ll need to be able to fly long distances to get from wherever the air base is to wherever the fire might be… and while you’re at it, you lose the ability to decide latitude of injection and seasonality.

 

Option 1 sure seems a lot easier from a cost perspective regardless of how many massive fires there are

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[Andrew Lockley]

We already have lots of low level tankers. We have no true high level tankers.

If we need to do geoengineering at the same time as a large global war, we might have a problem with tanker supply. But  then we'd have lots of other problems, too. 

A