Stratospheric aerosol injection hasn't been tested at any kind of scale, so we do not know whether it would be harmful (e.g. acid rain) or not. It would also be very expensive, so it's not really a practical solution at the moment. It may pan out, but stating "actually safe" is not yet known.

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BurningFrog 2 days ago | parent [-]

The Mt Pinatubo volcanic eruption in 1991 actually did inject huge amounts of SO₂ to the stratosphere, and it disappeared over the next few years.

While it remained, northern hemisphere temperatures lowered by ~0.5°C.

USGS report: https://pubs.usgs.gov/pinatubo/self/

Since the stratosphere is far above the rain cycle, it's very hard to imagine a mechanism whereby this could produce acid rain, and even if it did, acid rain is a much smaller problem than global warming.

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0x000xca0xfe 2 days ago | parent | next [-]

> acid rain is a much smaller problem than global warming.

In fact it used to be a common occurence during the heavy industrial pollution in the 20th century. So much that after the pollution stopped, farmers had to start applying sulphur to their fields as nutrients for some crops (I learned about this after unsuccessfully trying to grow tomatoes in alkaline soil).

	▲	nozzlegear 2 days ago \| parent \| next [-]
		> In fact it used to be a common occurence during the heavy industrial pollution in the 20th century. I remember watching news reports about acid rain in the 90s and being terrified that any ominous rain cloud might be full of acid rain which would melt away my town and family.
	▲	2 days ago \| parent \| prev [-]
		[deleted]

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ndsipa_pomu 2 days ago | parent | prev [-]

Yes, volcanoes are relevant data points, but that's also very different to proposed methods of seeding. It does raise the question of whether someone will decide to set off bombs in fault-lines to try and set off an eruption - I recall Trump asking why hurricanes couldn't be disrupted by the early use of bombs.

> acid rain is a much smaller problem than global warming

Possibly, but acid rain can devastate marine ecosystems and cause issues with soil quality, so I'm not convinced that we can just hand-wave it away.

I can foresee greedy capitalists rubbing their hands together over being paid to seed SO2 into the stratosphere and then being paid to clean it up too. There's probably a lot of money to be made selling clean air if we can pollute the atmosphere enough to cause health problems for people.

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BurningFrog a day ago | parent [-]

The SO₂ cleans up itself in ~2 years.

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ndsipa_pomu 19 hours ago | parent [-]

I'm not sure what you mean by "cleans up itself" as it doesn't just disappear. What is likely is that it gets distributed through various ecosystems and thus is no longer in the stratosphere. What concerns me is our lack of knowledge about that process and secondary effects on ecosystems.

Humanity has a track record of making assumptions about complex systems and treating them like a simple engine.

	▲	BurningFrog 11 hours ago \| parent [-]
		The process is well understood: https://acp.copernicus.org/articles/25/3821/2025/acp-25-3821...