I really enjoyed the book, honestly. It’s somewhat less rad than it could be given that the problem eventually gets solved by the UN doing weird crypto banking shit to create “market based incentives,” but yeah the Children of Kali do incredibly based stuff. The plot of “we might have secretly infected some number of cows with a prion disease–you won’t know which ones or how many until it’s way too late and people start dying, so you might as well just stop doing large-scale beef farming” is a badass idea.

I quit “real” academia. I teach this stuff at a university-attached high school for super smart kids now.

Yeah, this is correct. You’d need to dim things a lot more than what’s possible with aerosol injection like this before photosynthesis failure would start to be the dominant problem.

This is the kind of scenario I expect, honestly, though I’d be mildly surprised if it turned out not to be a member of (or a multinational corporation/billionaire) making the first move as a result of deciding it will hurt their rivals more.

Depends a bit on what compound we end up using. Sulfur dioxide is the one that gets the most attention in the literature because it’s the easiest to make and work with (sulfur is the 5th most abundant element on Earth), but it’s also an especially risky one. Not all of the aerosols would precipitate out–some would break down in the stratosphere, and many of the decomposition byproducts of sulfur dioxide are really bad for the ozone layer, so that problem might crop back up again. There’s some risk that the precipitation itself might lead to a resurgence of acid rain, though that part probably wouldn’t be too bad given the quantities and elevation. Sulfur dioxide was a major driver of acid rain in the 20th century, but that was largely because it was being injected into the low troposphere as a result of industry and coal combustion. This would be an injection of much smaller quantities at much higher elevations, so that element of the risk is probably low. There are also other candidate compounds that aren’t nearly as risky in that respect (generally calcium-based), though those are much less well-studied. Again, though, there’s a lot of uncertainty here which is bad for things like this.

it would be like handing a nation or group of nations a whole new style of nuke

Or some guy! Or an oil company!

That’s an interesting question. My educated guess is that it shouldn’t have much of an impact, because the intervention is on albedo–the reflectivity of the atmosphere to incoming radiation, which is concentrated around the visible spectrum and UV–and even there, it’s not much. We’re talking about an adjustment of only a few (low single-digits) percent of the overall planetary albedo, which would be undetectable to human eyes and shouldn’t be terribly hard on anything else either. It would be a very, very slight dimming of the light that makes it down to the surface; we’re talking a few watts per square meter. It probably wouldn’t meaningfully impact photosynthesis or vision. I don’t know if that question has ever been explored in detail, though. I’ll look into it.

I think between this angle, the potential to put pressure on increasingly “uppity” parts of the Global South (and China), the ability it would lend us to kick the can down the road while still looking like we’re doing “serious climate change policy,” and the absurdly low price, it’s pretty much a guarantee that this is going to happen.

If someone could figure out a way to make carbon capture and sequestration work at scale, it would actually be a great part of a meaningful climate policy portfolio and likely would have no significant side effects. We can do it now (and the Earth does it naturally as part of the carbon cycle), but we haven’t figured out a way to do it at levels that would be sufficient to fix the problem on the time scales that are relevant yet. Direct air capture is probably a pipe dream for thermodynamic reasons (removing and sequestering a gas with a concentration of ~450 parts per million is really hard and energy intensive), but something like enhanced weathering could work.

The scale we’d need to run it at would basically look like the fossil fuel industry run in reverse, though: we’d need that level of mining, processing, distribution, and collection of some candidate mineral (calcium carbonate or the like), which is also energy intensive. If we seized every fossil fuel company, forced them to start using all of their infrastructure for this, and also forcibly converted all (or nearly all) global energy production to renewable, that might work. That’s pretty much my preferred policy portfolio, but it ain’t gonna happen.

When we start the injection, we immediately create a warming deficit of however much we’ve reduced the temperature by. Even if that’s only 2°C to start with, that much warming in 18 months has the potential to be incredibly destabilizing to weather and ecosystems–possibly more so than just sitting at a +2°C anomaly. We don’t really know what the impacts would be, because it’s totally unprecedented. My prediction is that the longer it goes on, the worse the snapback will be, even if the warming debt isn’t substantially larger. The more adapted things are to one equilibrium, the more violent and disruptive the transition to a new one will be.

we’d only reap the normal amount of warming we’d have gotten anyways (not 4 degrees C over that limited span) though which could still be bad as the change in temperatures would be harmful to various ecosystems I’d imagine and the stress of going from warm to cool to even warmer again could be devastating to a lot of things.

Right! By starting this, we immediately create a warming deficit. Even if it’s only something like 2°C, getting that much warming in 18 months would be incredibly destabilizing. We actually have no idea what the impacts would be, which is terrifying. The longer it goes on, though, the worse the snap back looks. One of my colleagues compares it to starting a heroin regimen.

This is why I’ll be shocked if we don’t try it in the next 15 or 20 years.

There’s an upper limit to how much we can do this, at least with this method. Above a certain concentration (probably an offset of around 8°C), the aerosol particles will start sticking together into macroscopic droplets and just precipitating out. It’s not the kind of thing we could just do forever to offset arbitrarily high amounts of warming, which is either good or worrying depending on your perspective.

It wouldn’t need to be that much. A change of 1-2% in planetary albedo would likely be enough for the foreseeable future.

It would actually probably be a net positive for the US, at least in most places (and at least if you ignore the blowback from the rest of the world). We’re less likely to get hit by major precipitation changes, have the technology to shift our agriculture practices to compensate for what changes we do see, and the capital to adapt. A significant (>2°C) temperature reduction is likely to have enough positive effects for us to make it at least a wash. The same is not true for the rest of the world. We all know how much that matters to us, though. This is part of why I’m not optimistic about us keeping this particular genie in the bottle.

Primarily precipitation pattern shifts. Stratospheric aerosol injection (SAI) is highly likely to result in less precipitation falling globally overall, but it’s really the distribution that’s worrying. Our natural model for this–the eruption of Mt. Pinatubo in the 1990s–caused an almost perfect inversion of global precipitation patterns: places that usually get a lot of rain turned dry, and places that are usually dry got a lot of rain. The effect was detectable for more than two years, and appeared and disappeared right along with the temperature reduction signal.

Here’s the precipitation anomaly and Palmer Drought Severity index data for 1991 and 1992, immediately after the eruption. Warmer colors mean less water:

Computational modeling of SAI has indicated that this was not a fluke, and that the degree of change will likely increase with more aerosols in the stratosphere. Both elements of the switch are bad: if you’re used to dry conditions, excess precipitation brings flash flooding, erosion, and mudslides. If you’re used to rainy conditions, a lack of precipitation brings drought, famine, and fire. SE Asia–and other places that rely on a stable seasonal monsoon–are likely to be especially hard hit, and we have every indication that the shift would be permanent for as long as we kept up SAI. That’s why I said it would set off the worst refugee crisis in the world’s history.

Yeah, I’ll put together an effort post tomorrow.

I’d prefer not to dox myself directly, but I can certainly put together an effort post tomorrow.