Potential ozone depletion from satellite demise during atmospheric reentry | Hacker News Reader

Potential ozone depletion from satellite demise during atmospheric reentry

agupubs.onlinelibrary.wiley.com

181 pointsnobody9999116 comments

The Japanese have already been concerned by this problem for a few years.

Their solution has been to develop satellites made mostly of wood, which will burn completely upon reentry.

The first such wooden satellite is planned to be launched in September. It is intended mainly for collecting data about the behavior of wood in the outer space, e.g. on wood expansion, contraction and degradation, along with internal temperature and electronic equipment performance.

An alternative to wood would be the use of synthetic polymers, but those are typically more sensitive to radiation, so more research would be needed for finding a suitable plastic and appropriate additives to decrease the radiation sensitivity.

Wood or plastic would not be suitable for ships hosting humans, because they are not hermetic, but they may be an acceptable choice for satellites with a short lifetime and with much more relaxed constraints for the composition and pressure of the internal atmosphere (which may not be needed at all, e.g. when the internally produced heat reaches the external radiant cooling surfaces through solid paths or through pipes with circulant liquid).

That would be so awesome! Reminds me of the sci-fi book “Children of Time”

From the science we do on spider silk, who knows...we could one day see a Spider(Portiid)-derived hull cladding to fit around the lumber!

Yeah, the book has thought-provoking take on evolution

What about something like carbon fibre?

It is used quite a bit in the space industry already. But it is more expensive so it is usually confined to applications where you really need the weight savings, or you need something with a more controlled coefficient of thermal expansion. Thermal expansion of carbon fiber is small so you get less mismatch when you use it with things like optics or as part of solar panels.

And a common place you find carbon fiber in the space industry is actually carbon fiber skinned aluminum honeycomb panels. Very light and very stiff.

https://www.rockwestcomposites.com/shop/plates-panels-angles...

Fibreglass? I'm surprised raw material/machining cost is a significant concern when you're making satellites.

So the Hearthians' timber ships made sense after all

> Their solution has been to develop satellites made mostly of wood, which will burn completely upon reentry.

"When finishing the surface of your wooden satellite you must, of course, use an orbital sander."[1]

[1]: https://www.metafilter.com/203958/Yes-they-wood-build-a-sate...

Could just send it into the astral plane.

Just don’t use a random orbital sander or you may lose your satellite.

Nanocrystalline cellulose (NCC) could be a great constituent component of a composite material. Not only would it burn, but anything that doesn't burn and makes it to the surface is biodegradable; there's lots of stuff that eats cellulose. NCC can be formed into highly strong and rigid structural pieces, or combined with carbon fiber, fiberglass, hemp, or other fibers to create ultra strong and durable composite material.

   high mechanical strength, with a tensile modulus of approximately 150 GPa and a modulus of elasticity ranging from 18 to 50 GPa. CNCs also exhibit excellent thermal stability, undergoing gradual thermal transitions and decomposition between 150 °C and 600 °C

> Their solution has been to develop satellites made mostly of wood, which will burn completely upon reentry.

I like how the Google image search for "japan wooden satellite" (https://www.google.com/search?q=japan+wooden+satellite&udm=2) is gummed up with garbage AI generated images of satellites with wooden solar panels. This wooden Borg cube with off-kilter panels is my favorite: https://indianspacetechnology.com/wooden-satellite-lignosat-.... This one is also great: https://www.universetoday.com/161473/building-a-satellite-ou.... I guess the satellite went back in time to the Cretaceous period, where North America had an inland sea?

The future is looking bright, guys!

Kagi returns basically the same result set including the AI generated slop, which is disappointing.

I'm not sure how they could do any better. AI is enabling the degradation of the public web, and that's what they search.

Pretty soon the web's going to be one big Mikkelsen Twins ebook.

Well, here's an actual photo they could have used: https://www.japantimes.co.jp/news/2024/05/29/japan/science-h...

And here is an earlier rendering from 2021: https://www.japantimes.co.jp/news/2021/12/31/national/japan-...

And it only took a simple Google search to find, from a reputable news source.

This really says it all. Theres the right thing and then 1000 signs pointing every which way saying Eat At Joe's like a bugs bunny cartoon.

Blaming AI for the current trajectory of the Internet is like blaming the Internet for the current trajectory of public discourse & trust - they're both only instruments for the real reasons.

I don't buy the whole "tools are neutral, it's the people who are good or bad" responsibility-dodge argument. It's definitely true that many tools can be used for good or bad, certainly. But the people who create a tool should consider how they expect people will use their tool, and the ease at which people can use it for bad. This is pretty much Engineering Ethics 101.

When you zoom out though, this engineering problem is a cultural and political one.

If you are designing apps in an environment of scammers and shameless grifters, the options for the societies you can build are reduced.

Focusing on the core issue of "how can we stop people from destroying nice things" is critical for society-scale engineering, as it frees ethical engineers to create more magnificent tools.

Ignoring law / politics / etc, and solely focusing on "how can I design this given presence of grifters" is muted engineering.

Without AI you'd still be looking at dozens of artists' mockups of wooden satellites because they have to put something at the top of the blog post or news article to catch viewer attention.

Seriously - have people forgotten what so much of the Internet looked liked prior to just a few years ago? That is to say, exactly the same? SEO spam, quick artist mockups, mass-generated crap.

When it takes actual effort to create something, you tend to think about what exactly you are creating ahead of time. Time commitment and opportunity cost mean that the resulting work is a combination of both your raw mechanical effort and critical thought (both ahead of time and during the actual work).

> Without AI you'd still be looking at dozens of artists' mockups of wooden satellites

No, that's a false equivalence. The artists' mockups wouldn't be this bad. They'd either have gotten a real photo or based their artwork on one.

Now Google Images is flooded with images generated in two minutes from half-assed prompts.

> because they have to put something at the top of the blog post or news article to catch viewer attention.

They do not. That's just a current-year web design tic, which "AI" will probably kill.

> current-year web design tic

IIUC it's more that you do it to expand the page-inches on social media so that it's more likely readers will click through to your story, because social media displays the preview banner.

But sill wood usage does have an impact on the environment too

So does corn. In fact much of the wood used in construction in the US is grown like corn in a cornfield.

Everything you do does. Question is how much.

I assume you mean the high atmospheric particulate. It would be interesting to see how this compares

It's an interesting effort, but the supposed issue addressed in the paper is not that aluminum does not fully burn up during reentry. It generally does, just like wood. It's that, when it does so, it releases alumina.

Maybe this is better because the vaporized wood would. not release any alumina. But you'd then have to look at the impact of wood's combustion products when introduced directly to the upper atmosphere. I'm not sure anyone has seriously studied that question.

Burning pure wood doesn’t produce anything terribly exotic. We know what most of the byproducts do because they occur naturally and we’ve already studied their effects. Namely H2O, CO2, CO, and solid carbon with traces of nitrogen and sulfur oxides, along with metallic micronutrients (at a very small scale).

We already know how the major byproducts interact, I think it would be a question of modeling what happens when we start adding them to the mesosphere. Models aren’t perfect, but it’s not like we have absolutely no idea how the components interact.

Leave it to Japan to make a satellite out of wood. So cool. Their innovations in woodworking are very impressive. I’d love to see a picture.

Very interesting study. I guess putting things in orbit is absolutely going to cost us but I hope we will have this under control before it gets out of hand.

Unfortunately, just like green house gases, it requires the very people who benefit from ignoring these kind of problems to pay attention and well...

One of the main reasons we have governments is to solve those sorts of problems. That's how the ozone problem was successfully addressed before.

The Montreal protocol worked because it was focused on a limit set of changes. Something similar could also work again if metal satellites and uncontrolled hypersonic reentry spaceship metal parts were outlawed as well.

Unfortunately, the lack of a gradual set of limited changes is why the same process cannot be replicated for climate change remediation. Countries are trying to tackle the entire problem as an "impossible" monolith rather than breaking it up into separate industry and lifestyle practices to address incrementally.

The Montreal Protocol was nothing short of miraculous. It was the first international treaty to be ratified by all 198 members of the UN (including the Holy See), and it's been called "perhaps the single most successful international agreement to date" by former UN Secretary General Kofi Annan. It's one of history's greatest achievements of environmental policy and international cooperation.

The impact of CFC's on the ozone layer was first proposed in a scientific paper in 1973; the authors testified before the US House of Representatives in 1974 and significant funding was provided to study the problem. The Montreal Protocol was then signed in 1987 despite industry protests that the research was uncertain and there was no crisis that demanded urgent action. This was only 14 years (!) after the effect was first hypothesized. The discoverers of the effect won the Nobel Prize for chemistry in 1995.

I don't expect to see anything even remotely as successful as the Montreal Protocol in my lifetime.

Especially when people now think the ozone hole was a hoax and use that as justification for doing nothing about co2 emissions

Some people ...

You might as well say people now think { vaccines are clot shots | earth is flat | 9/11 was an inside job } and use that as justification to do nothing about AGW.

I've heard the same said about acid rain. Another case of an actual major problem that was quickly solved by multilateral action.

People don't understand that those problems were peanuts though in comparison.

I couldn’t see a quantitative estimate of how much ozone would be depleted in a typical year as a result of the extra catalyst being present. If it’s only ~hundreds of tons, that seems both immaterial (there are about 3 billion tons of ozone in the atmosphere currently) and potentially easy to replace (fly up there and dump some fresh ozone).

I think it says its a catalyst, for some chlorine reaction. So its not out of the question 300 tons (per year) could effect ozone concentrations.

There's absolutely no estimation of the impact. Your 300 tons of activated chlorine per year idea is as baseless as the GP's 300 tons of ozone, but the GP is aware that his number is a complete invention.

Any exercise in making numbers out of nothing is completely useless.

(Besides, is chlorine activation really a bottleneck in ozone depletion? AFAIK it gets activated by UV light quite quickly.)

GP never implied the amount of ozone just the amount of aluminum oxide. All I know is catalysts can speed up reactions by orders of magnitude. CFCs actually created a hole in the ozone layer so its not like human activities haven't accidentally created problems before. Probably something that at least needs to be ruled out.

Correct. That's the same way I read that comment.

More fundamentally, chemical catalysts by definition are not consumed by the reactions they catalyze.

Think: a cheese grater. It doesn't react with the cheese, so a few ounces of grater could make hundreds of pounds of grilled cheese.

A hypothetical 300 tons of catalyst is not limited stoichiometrically to how much substrate it would affect.

If starlink thinks it may have 40,000 satellites at full capacity[1] .. and we expect at least 1 if not 2 competitors..

With a 5-year lifespan for an LEO sat, that's potentially 120,000 deorbits every 5 years...

That will add up quickly... I don't know the science of aluminum oxide increase to ozone depletion.. but this can certainly warrants more research and consideration

1: https://starwalk.space/en/news/spacex-starlink-satellites-ni...

https://www.antipope.org/charlie/blog-static/2024/05/on-mist...

Can't they spray some ozone as they deorbit?

No, but I imagine they could include some other solid mass that has a counter effect.

Chemtrails!

The satellites are typically much smaller than historic satellites. I think ~50-60 are launched in a fairing that would house 1 or two older-style satellite.

Does the mass make a difference?

All of those starlinks are designed to burn up though. And there will be many thousands more of them then there ever was of those older larger satellites.

Starlink satellites have gotten big. The V2 Mini they are launching now is 1600 lb, and they fit only 20 some on Falcon 9. The V2 for Starship will be 2700 lbs.

Why would the number of satellites be pertinent here? It’s a mass problem, and starlink satellites are tiny compared to most of the satellites that are up there.

Many little number make big number. Mhmmm.

And SpaceX boasts to have launched more mass than the rest of the world combined...

Im guessing it would make sense to release more pro ozone catalyst. It may even be an option to release more it from the ground, as an inverse to CFCs.

NOx is also has a global cooling effect, taking the edge off climate change.

NOx and VOCs from power plants and diesel vehicles produce ozone.

Catalysts don't get consumed by the reactions they facilitate, so the weight of the catalyst compared to the ozone doesn't say much about the effect.

For example, consider that a car exhaust catalyst contains ~5 grams of platinum, and AFAIK, that doesn't really "wear out".

SpaceX put up 1,238 tonnes in 2023. So let's say about 2000 tonnes globally. I don't know the Al fraction of a satellite, but assuming it's very high. Estimates are 15,000 to 220,000 tons of meteoritic material entering earth annually. Assuming 1.2% Al in a meteor (from the paper) that's 180 to 2604 tons of Al.

So the range of human impact is somewhere from 2 to 10 times the meteoritic material in Al. That's quite surprising, assuming that my math and research is correct.

Switching to steel should make the environmental impact negligible, considering that the Fe content of meteorites is quite high.

meteoritic material source: https://adsabs.harvard.edu/full/1994IAUS..160...45B

Switching to steel means satellites don't demise and hit the ground in larger chunks, something that the FCC has actively avoided in their constellation licensing for fear of hitting things.

For example the 4 reaction control wheels for attitude adjustment where you actually want mass, were specifically moved to Al on starlink so that they _would_ burn up on reentry.

I don't know how you weigh the risk of environmental effects vs occasionally landing a sat on something, or someone. I guess an actuary somewhere has a table for that.

I would think it depends heavily on the degree of control they have over where it lands, which is perhaps something that could be optimized for?

I still think it’s a political non-starter, though. People will be terrified of being randomly struck with a satellite, and it would be an enormous international crisis if an American satellite deorbited and took out a skyscraper in Beijing or vice versa. Heaven forbid one accidentally hits the Pentagon or similar, it would probably start world war 3.

It would be interesting to see if the current constellation reentries are in any way grouped over specific areas. My understanding is spacex don't have exact control due to the relative weakness of the ion thrusters and the unpredictability of aerodynamic drag on the big flat surfaces (1). Say only 1% of reentries were completely uncontrolled and random then you're right, that could shift the odds from just acceptable to meh. (1/10.000 -> 1/1.000.000)

1 - https://api.starlink.com/public-files/technology_v2mini_back...

If aluminum is the issue, could steel and plastics be a solution? Especially with Starship coming online, weight should be less of an issue.

Anything’s possible but the mass of the satellite won’t cease to be something they need to optimize, even with a heavier booster. Those little satellites use thrusters themselves when they’re in orbit.

There's also magnesium alloys, but if MgO is any better in the stratosphere is anyone's guess

There's a lot of really smart people that understand chemistry at a much better level than the typical reader on an internet forum. Do we really need to "guess"? Seems like we could study this to actually determine what would happen with controlled experiments. One might go so far as to call that the scientific method.

Nope, it is unknowable because ginko doesnt know /s

The thrusters are to offset atmospheric drag, which accumulates with surface area, not mass.

Weird half-true comment. Imaging satellites change their orbits, satellites operating in constellations station-keep, etc.

Station keeping is for drag, which is the only thing the vast majority of satellites maneuver for.

There are some oddities here. The least interesting is that drag is not the only reason satellites station keep and I can't imagine why you'd say it is. The weirdest is that we're actually having an argument about whether satellite mass continues to matter once the satellite is in orbit.

More interestingly, the majority (perhaps not yet "vast majority" [0]) of active satellites right now are Starlink satellites. Those things actually maneuver all the time in the interest of collision avoidance, and the rate at which they maneuver is predicted to increases as the number of satellites increase for obvious reasons. [1]

[0] https://www.visualcapitalist.com/who-owns-the-most-satellite...

[1] https://www.space.com/starlink-satellite-conjunction-increas...

More mass still means you get less velocity out of your fuel, even if the drag stays constant.

But you also lose less velocity with the same drag.

Since Starship itself is made of steel, it seems possible that the satellites could be as well.

Assuming it's overall heavier, you have to carry more fuel, and then the rocket equation kicks in and you have to carry more fuel than that. That's all extra weight that makes your launch more expensive. But if your cost to launch is $30/lb instead of $1200/lb, you've got the budget for it.

But it's not just the cost of the launch, its also going to be the cost of the satellite itself.

More mass means you need larger reaction wheels (or CMGs) to control the attitude of the spacecraft, larger reaction wheels means you need more power to control those reaction wheels, more power means you need more solar arrays/batteries, more solar arrays means more mass and moment of inertia...which means you need larger reaction wheels and on and on and on.

Often people talk about the "tyranny of the rocket equation" but many other things on a satellite are the "tyranny of other non-linear systems"

You can end up seeing that in companies like K2 Space. Their goal is to take advantage of cheaper launch costs with large, cheap satellites. But if you read in the article [0] they had to do things like develop new reaction wheels in house because "there was not a suitable supply chain for spacecraft bus like Mega Class". Starting from scratch on mechanisms like that for space is not super cheap.

https://spacenews.com/k2-space-plans-first-launch-as-company...

These are good points, but I still think it's technically feasible to make non-aluminum satellites, and reasonably economical even if it costs somewhat more. If the only alternatives are giving up on large satellite networks or destroying the ozone layer, then switching away from aluminum seems like the way to go.

I'm not claiming steel is the best option though. Other metals, or even non-metal materials as mentioned in other comments might be better.

I don't think needing new components is really a downside except in the very short term. With much cheaper launch at much higher volume, we're going to be doing a lot of that anyway. We're going to have all sorts of new applications that weren't economically feasible before.

True, it's definitely feasible to make non-aluminum satellites. I do tend to go get up on my systems engineering soap box when people just talk about launch cost as it's a conversation I have too frequently in my job as well.

The mass consideration has certainly changed things in general. One of the things we have seen is a shift from aluminum honeycomb panels to just machined aluminum plates which weigh more for the same stiffness but are easier and faster to manufacture.

Steel might also drive more spacecraft to have to do a controlled re-entry (something the Starlink satellites are not currently designed for) as with the higher melting point and more mass it is more likely to survive re-entry. Although it does have a lower specific heat capacity than aluminum so I'm not quite sure on that one but usually the things I have seen that we expect to survive re-entry are titanium tanks and large glass mirrors. They also have the benefit of being in the center so there is a bit of an ablative shield.

What do you think might be the most promising substitute for aluminum? And what do you think of the Japanese idea of using wood?

Or visiting satellites to be deorbited and encapsulating them inside a re-entry vehicle with refractory tiles.

> We find that the population of reentering satellites in 2022 caused a 29.5% increase of aluminum in the atmosphere above the natural level, resulting in around 17 metric tons of aluminum oxides injected into the mesosphere...

On the scale of the planet, that's incredibly tiny. 17 metric tons of aluminum oxide can be made by oxidizing a cube of aluminum about 1 meter on a side. The catalytic action must be incredibly potent!

Wolfram helpfully tells me that the mass of the mesosphere is on the order of 10^12 tons, so that's on the order of parts per trillion.

It's tiny, but it may be enough if the wind currents are concentrating it, as happened with CFCs doing away with the ozone layer over the South Pole.

It’s tiny compared to the mass of natural debris which enters the atmosphere as well. This is just SpaceX NIMBYism tbh.

Uh, a 30% increase beyond natural levels suggests that it's not tiny

The mass of human contributed CO2 is tiny compared natural CO2 emmission and still it's bad for us.

More is bad that's the bottom line.

One option is to make the satellite survive re-entry rather than burn up. Then just re-enter over a desert like australia or the sahara so you can go find and collect the junk.

Single-use heat shields for smallish things like satellites are quite easy I believe, although fold-out items like solar panels would need to be designed to fold-in again.

It’s not all desert here mate.

Privatize the profit (and government helps pay for development) then socialize the cleanup costs.

Why doesn't every messy industry like this have to pre-pay massive insurance fees ahead of time for known and unknown damages?

Note X isn't the only one with thousands of satellites, there are several startups that are launching their own thousands. Soon we'll have debris and burnup of dozens a day, that will add up.

It's kind of like the industrial revolution. I don't think anyone knows what will happen (it's the classic human behavior of kicking the problem down the road), but the collective human mind has decided we want global connectivity now that it's cheap.

I can't see the cat going back into the bag (or reengineered) unless there have been proven negative results like the ozone hole directly linked to CFCs.

Please fine the companies who did this. This is a global problem that affects everyone, but especially those of us in Australia.

Just so you know, the comment immediately below yours proposes a solution where satellites are designed not to burn up at all and are aimed at Australia during reentry.

> One option is to make the satellite survive re-entry rather than burn up. Then just re-enter over a desert like australia or the sahara so you can go find and collect the junk.

So be careful what you wish for!

Parent post: won't someone please think of Australia!!!!

Global military industrial complex: Now that you mention it...

Is there even an estimate of the impact on ozone in the paper?

You don't need a science paper to end up with "letting satellites burn up in the atmosphere results in burned satellite dust in atmosphere", do you?

I would have liked an estimate of the natural sources to compare.

It's in section 3.3.

- Natural Al estimated at 141.1 metric tons / year not varying.

- Human-made: 2016: 5.36 tons, 2022: 41.7 tons, "future" could be 912 tons, i.e. more than 6x natural.

I think the last figure is based on many planned large satellite constellations being deployed.

Other work on this from January but focusing on temperature in stratosphere: https://arc.aiaa.org/doi/abs/10.2514/6.2024-2169

Cosmic dust dumps about 30 tons a year of aluminum into the atmosphere already

How about just not letting them burn up? Give the core an organic heatshield (wood?) and let it crash into the ocean. Even thousands of them each year would be nothing compared to the amount of waste regularly dumped into the oceans, an acceptable compromise over ozone depletion.

If thousands of intact satellites crash to Earth yearly, they will hit and kill people, even just over the oceans.

People will also be upset about the environmental damage, real or imagined.

Thousands of small rocks fall from space every year, have done so for a very long time. Human deaths are almost unheard of.

Not only this, but they fall in a randomly-distributed fashion. Most satellites are still under control and steered to a predetermined area for reentry over the South Pacific.

> Most satellites are still under control and steered to a predetermined area for reentry over the South Pacific.

This is not true, most satellites do not perform controlled re-entry. In order to perform controlled re-entry, you need to have enough thrust to perform the final de-orbit maneuver in a short amount of time before you get so low that you start to lose attitude control of the spacecraft and wouldn't be able to guarantee you are firing your thrusters in the correct direction. To do this in a short amount of time means you need a high thrust system, in other words a chemical propulsion system and not electric propulsion.

All of the Starlink satellites use electric propulsion to do their de-orbit so they are performing uncontrolled re-entry. NASA's Orbital Debris Mitigation Standard Practices (ODMSP) say that you can perform uncontrolled re-entry if the probably of casualties on the ground is less than 1 in 10,000. There are NASA analysis tools that are used to do that assessment of what kind of debris would survive re-entry. This is likely getting updated in the near future to be more conservative though as there was recently a piece of an old ISS battery they thought would burn up hit someone's house in Florida:

https://spacenews.com/uncontrolled-reentry-of-space-debris-p...

I had to check, but you're not wrong - only 47% of total are controlled re-entries. (https://en.wikipedia.org/wiki/Spacecraft_cemetery#cite_note-...)

I thought I recently read about a law requiring a de-orbit plan for anything launched. I would assume if most of the mass doesn't burn up (Starlinks mostly burn up), it would require them to hit the South Pacific patch or similar.

That is closer than I expected, and is specifically 47% of the re-entry mass (which is what we care about here) is from controlled. I would expect if you were just looking at # of satellites the numbers would be much more skewed as lots of little satellites would probably burn up and its the big ones that we need to worry about surviving to the ground.

True, but consider this:

People tolerate when natural processes kill very few people.

But they get very upset when human activity kill very few people.

Manufactured outrage.

Maybe or maybe not. I want to know what "significant" means in terms of stratosphere effects in DU/km^2 per kg of aluminum oxide.

I think as we continue to expand our use of space, it is crucial to consider the environmental impacts!

I'm no chemist but I noticed this other researcher wanted to dump literal tons of another oxide into the atmosphere to counteract global warming.

https://iopscience.iop.org/article/10.1088/1748-9326/aae98d/...

An oxide is just a molecule with one oxygen atom and one other element. Different oxides would have different effects on atmospheric chemistry.

"Nitrous oxide best oxide." -- Dominic Toretto

As a lifelong addict, I literally cannot live without my regular dihydrogen oxide. Even a day without is painful.

See "Snowpiercer"

see https://news.ycombinator.com/item?id=37344251

To geoengineer or not to geoengineer, that is the question. Can we build models that six nines assure us of a small stable improvement that stays near linear behavior, or asymptotic better yet?

My prediction: a country which has the political and technical ability to do so and is located somewhere where global warming starts being a major threat to it. Likely candidates: India and neighbors (wet bulb events depopulating large area) or China (inundation of the biggest population centres). This country eventually says "fuck it" and just does it, international opinion be damned. Everyone else in the world will proceed to performatively freak the fuck out. But, they'll all be watching closely and if it works, they'll all be doing it fairly soon. Again, if it works, in the eventual biopic, it'll be mentioned as an aside that they weren't 100% sure if the atmosphere would be destroyed or not, but they forged ahead.

The good news, since an internet forum's commentariat opinion isn't relevant to whether it happens or not, is that humanity is a couple of teratonnes into a 200-year experiment of many kinds of atmospheric modification and nothing critically non-linear has happened yet. Though we certainly don't have many sigmas of confidence that it isn't going to go non linear (but in the "hot" direction) at some point!

We're even doing a cute little cross-over trial specifically on atmospheric sulphur dioxide injection (just entered the second placebo phase)

In the scenario that China and India barrel into atmospheric experiments, they may be able to secure group funding from the larger island nations with high levels of buildup near the coast. I think you make a good point that we are centuries into an experiment (or longer if one wants to group all anthropogenic change like megafauna extinction) and I think that people living in places that have a high coastline to area ratio will be more likely to see it this way - perhaps even considering themselves primary subjects.

Don't look now, but humans dump a lot of oxides in the atmosphere. Millions and millions of tonnes. Gigatonnes if you incude dioxides.

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