Cool to see this research continued. I've spoken to the authors of a very similar paper, also based in Australia: https://onlinelibrary.wiley.com/doi/epdf/10.1002/adma.202105...

One thing I learned is that these experiments are generally done with a pure CO2 stream. The reactions taking place often compete with other molecules (especially O2), making this approach best for capturing carbon from tailpipes and smokestacks. There's still a lot of work to be done to get this sort of thing to work reliably for direct air capture (which IMO will be needed to actually draw down carbon from the atmosphere).

Anyway, this research is being commercialized via a company called LMPlus (https://lmplus.com.au). While I appreciate that the technology is being brought to market, it probably means that future breakthroughs will occur in private labs, protected by patents and trade secret laws.

We have a an urgent need to conduct more of this kind of research out in the open and to make breakthrough carbon capture technology available to everyone, for free. If you're interested in helping out on this front, please consider joining me in the OpenAir Collective discord (https://openaircollective.cc/).

> One thing I learned is that these experiments are generally done with a pure CO2 stream.

According to this comment three months ago [1] "they used 6%-20% CO2 mixtures with balance nitrogen and some water to try and approximate different exhausts including flue gas".

[1] https://news.ycombinator.com/item?id=28873458

I.e. no oxygen. It would probably not be suitable for direct air capture.

If you burn carbon, you can just decrease your air input to furnace. It is not done today because it causes lots of CO, which is very poisonous. If you don't care about CO like in this process, you an put O2 sensor (lambda sensor, used in all new cars to alter how much air is used) and almost eliminate oxygen from your output.

I wonder if it might be possible to add a separations stage (centrifugal gas separator perhaps) and redirect any remaining oxygen back to the furnace?

Technically yes, but practically no. It's much easier to just let in less air, you just set your blower to slightly less power, controlled by sensor.

It works fine for any degree of oxygen blend too, it just requires proportionally more Gallium. 400 times more or so for atmospheric blend. The problem is the energy required to then reduce the gallium.

But perhaps it will be possible to filter out oxygen by a different process and let the remainder gas be filtered.

It's quite simple: burn excess incoming O2 with a bit more carbon.

I wish it were this simple... but given that there's ~5250 O2 molecules for each CO2 molecule in the air, this will result in the production of 5250x additional CO2 molecules. Our CO2 capture process would then have to be 99.9999% efficient for this to pencil out.

One could mix the incoming air with hydrogen. Igniting that would capture the oxygen in the resultant water. This would allow precipitating it out prior to the mix hitting the gallium. Hydrogen could then be recaptured by using electrolysis on the byproduct water, exhausting the oxygen.

I don't imagine this would be particularly efficient, however.

We don't want to deplete oxygen in the atmosphere. Plants are much better suited to capturing CO2, IMHO, as they also produce oxygen.

CO2 is 0.04% of the atmosphere. Oxygen is 21%. We're not going to run out of oxygen.

I don't understand the downvotes. The idea of turning excess oxigen into CO2 which I replied to is plainly stupid just because of this proportion. How much coal (and oxygen) would we use up to bring down CO2 levels to 0.03?

I don't understand your question.

GP proposed to filter out O2 by burning carbon. This will create a CO2-rich gas, perhaps at about 30% (depends of the density of CO2 compared to O2).

GP didn't mean that we deplete oxygen in the athmosphere, but that this is an intermediate step inside the CO2 scrubbing apparatus. Perhaps that's why you got downvotes.

The burnt carbon will be gained back by the Gallium process, however this might not work out anyway because the process needs to be very efficient in filtering out CO2, as someone else already pointed out.

In my opinion the idea of burning hydrogen seems a lot better: https://news.ycombinator.com/item?id=29994000

>Plants are much better suited to capturing CO2

I do wonder if it would be much cheaper to capture CO2 by investing technology and capital into 'building' forests. What if we can irrigate Sahara and cultivate some fast-growing plants like bamboos there? Maybe that has ecological consequences but it doesn't seem to be much different than the agricultural land expansion that has happened in rainforests in the first place.

The sahara seems like a bit of a hassle compared to the taiga (russia to canada). The real problem with growing forests is that they do not store significant amounts of carbon after they reach maturity. They did during the carboniferous, but after fungi figured out how to decompose cellulose they haven't, and wont. Fast growing plants only capture carbon faster, but the total storage would be less per area.

However, we do know of how the deposits of fossil fuels formed in the first place, and most places newer than the carboniferous, formed at the bottom of deep lakes and especially oceans. They form from the anoxic compaction of marine snow. Either during massive algae booms, or more slowly from slightly larger corpses. This process is slow for several reasons, but a significant, in particular for the latter category, one is the lack of surfaces for attachment on the open ocean. The creation of large floating artificial coral reefs could provide this, and with it a highly productive rich ecosystem. We could further fertilize these, with iron in particular being rare, but also regular fertilizer.

Focusing scrubbing smokestacks (where large amounts of new CO2 is concentrated) should be exactly where the focus should be. Direct open air capture really only makes sense once we've learnt to deal with the low hanging fruit.

> One thing I learned is that these experiments are generally done with a pure CO2 stream.

That's probably why these kinds of things will likely only be super effective if taking the immediate exhaust of carbon fuel burning.

So...

1. Legally require all fossil fuel plants capture the carbon from their exhaust, which will have the knock on effect of increasing the economic cost of burning fuel, which means economic forces will naturally start to more strongly prefer carbon free sources, because they're cheaper.

2. Keep pushing for the migration to full BEVs and possibly have a similar requirement of carbon capture devices added to industrial vehicles that can't reasonably be EVs. I could see things like mining and construction vehicles go out with a tank full of fuel and return with a tank full of captured carbon to leave at a dump.

> it probably means that future breakthroughs will occur in private labs, protected by patents and trade secret laws.

This does well to incentivize the inventors; perhaps they could be purchased rather than nationalizing the successful innovation models.

I would almost suggest that gov't should be funding this, but it is primarily private corps doing the polluting. Maybe have gov't fund it, then force polluters to pay gov't back from actual carbon tax?

Have government fund it, then limit or tax net emissions and now there is tech on the market to capture carbon to reduce your net emissions.

Ah.. independant invention without significant capital/money based support is very rare in the modern day world. So I'm sure it will support only inventors at an organizational level and at that level, there are lots of skewed incentives for the CXO level peeps to do more marketing that inventing and ensuring most value is captured for the organization than passed on.

Gallium is not cheap at scale. We can only produce trivial amounts, and it is cheap because we don't have many uses for what we produce. It does not form concentrated ores which means it cannot be mined in any conventional sense.

We extract it from aluminum (and zinc) refinery waste because it is relatively convenient in an industrial process sense, but the amount that can be produced this way is inconsequential. The gallium in all the known aluminum ore reserves is measured in kilotons. For this application, we would need something closer to gigatons. We could produce the necessary quantities if that was the sole objective, but the cost per gram would be closer to gold which is not great when you need gigatons.

The alloy is completely reusable as per TFA, I'm not sure why gigatons are needed...

The throughput of carbon sequestration per unit of time is a direct function of the quantity of gallium and the time it takes to execute a complete reaction cycle. Whether or not you recycle the gallium, the time it takes to complete the process cycle limits the number of iterations you can execute per year, which in turn limits the amount of carbon a ton of gallium can sequester per year.

If you need to remove tens of gigatons of carbon per year, you are going to need similar scales of gallium to have enough reactant operating concurrently.

How fo you turn gallium oxide back into gallium?

Hiw do you separate it from carbon or from indium?

From wikipedia, "Ga2O3 is an intermediate in the purification of gallium."

https://en.wikipedia.org/wiki/Gallium(III)_oxide

So we'd turn the gallium oxide back into gallium the same way we did in the first place, when we made the gallium. I'm guessing we can also come up with chemical reactions for the other two.

However, you're right that gallium production is quite low. It's a byproduct of zinc production from bauxite, and we get only a few hundred tons per year. Wikipedia doesn't say what the potential might be if we gallium were the main product.

https://en.wikipedia.org/wiki/Gallium#Production_and_availab...

You would still need to spend a lot of energy for the process, which brings us to the beginning. This could maybe be used when we have fully renewable enegry in excess to pull some carbon out of atmosphere.

Can we do it while it's still mixed with indium?

Is gallium oxide dissolved in EGaIn?

> How do you turn gallium oxide back into gallium?

electricity? Cathode and Anode?

Hmm.. i was wondering how cheap it actually was .. Can we re-use the Gallium used in this process?? Can we recover it?? Sorry I haven't yet had time to deep-dive on the article.

Yep

ca 720t in 2019

Its not fraudulent, its a good idea, and likely useful in niche large chemical plants. It is also useless against climate change.

The the paper uses a simple input of CO2 and nitrogen. Though O2 could be added as well, as the gallium will simply react with it too. After all, More energy is released by gallium reacting with O2, than by carbon reacting by O2, or it would not happen in the first place. In the atmosphere, CO2:O2 is say 400:1 meaning you need 400 times more gallium.

The next step would be to separate the gallium from the gallium oxide, which is energy intensive, though this can be climate neural using nuclear. To do so would require hundreds of times the global energy production from coal, oil, and gas. And if you have built these, why not just use them instead, global warming would already be effectively stopped.

It also cannot be used in car catalyzes, providing an anoxic reaction chamber which can collect and separate the outputs simply isn't feasible at small scale. The carbon would be in a fine powder, likely to spontaneously react with O2 if exposed to air, either slowly, or if given a spark, very rapidly indeed. The gallium also should not be released into the environment. Not only would large scale use of this tech make it very expensive, gallium is also mildly toxic. However, because it is rare in our environment, there are few if any studies on the impact of long term low dose gallium poisoning. As a result, its a comparable to lead, a few decades ago. Not saying its as deadly, just saying its a metal we are rarely if ever exposed to, known to be mildly poisonous in the short term. And this is before you add the problems of contaminants in fuel, and partial combustion. For similar reasons it also cannot be used in aviation.

At first I ignored the entire HN submission because I've been taught that carbon sequestration will never be a solution to atmospheric carbon.

On a whim I clicked on the comments though expecting the first comment to be, "This will never work, because..." So I was happy to see that the top comment was actually positive! Then I saw your response.

I get that pain -_-'

One of the things which I've seen but feel is rarely talked about is that the planet is sequestering a large amount of CO2 and this increases positively proportionally to CO2 concentration. Over longer periods of time, the CO2 levels drop, and sudden shocks such as volcanos and cataclysmic massive forest fires, are parried by the increase, quickly returning to previous levels. This proves that sequestration does work which is nice. There are many problems with this. At historic CO2 levels on human timelines the natural sequestration is effectively in balance with CO2 production. So its not enough to sequester the additional modern human production, and the prop increase is less than 1, so it wont be. Two, at least some of the systems which are sequestering are doing so as a side effect of severe to catastrophic ecological damage. For rare events this isn't a problem, but our current production is not one year in a century.

It does mean that if we stop using fossile, CO2 levels will revert on their own. Though it will take a long time.

Exactly. If we go carbon neutral and stop the CO2 production shock to the system, nature will take care of what we've already put out (though it may take a few centuries, depending on which of the IPCC atmospheric CO2 level half-life estimates you go by).

This still is pretty positive- it seems like it can be used as carbon capture inside of existing plants that produce CO2 as a byproduct. It isn't going to solve climate change but it could give us another tool to use.

Just think of how much money your could make selling the carbon as 100% eco-friendly charcoal...

Most farmers do just that^^

Getting C out of CO2 require more energy than burning C to get CO2, otherwise you'd get perpetual motion. So, if you want to reduce CO2 emissions, you're better off not burning the C to begin with rather than trying to split the CO2 after the C was burnt.

Even if capturing uses more energy than emitting, it can still be useful since we can Maxwell's Demon the whole process.

We can decide only to emit CO2 at the times when we don't have clean energy ready to use and decide to recapture CO2 when we do have clean energy to use.

Unfortunately we have collectively decided that solving hashes is a better use for clean energy

Maybe we could start minting coins or NFTs from captured CO2?

There is already similar stuff being done as part of tracking for carbon credits. i.e https://www.forbes.com/sites/forbestechcouncil/2021/08/16/th...

This would be an interesting approach! Not sure how it would work in practice, but it's a fun thought...

And there could be inherent value there, especially as a carbon capture tax credit. Instead of proof of work or proof of state, it's proof of capture. You'd have to put together some kind of distributed capture hardware, but... That's maybe possible with current tech?

Unfortunately the fact that it has a clearly measurable value means it's price is pegged to that value.

If this token gets you $100 worth of carbon emissions, it's hard to justify a price higher than $100. If the token gets you absolutely nothing, then the value is absolutely arbitrary - enabling spectacular rise

What if you tied it to a desktop carbon capture device (understood that these don't really exist currently)? Doesn't even have to be particularly efficient, nor tied to carbon credits.

The reason we don't have clean energy ready to use is that the cost of renewable generation plus storage is currently higher than the cost of burning natural gas. If you add the cost of capture to the cost of natural gas, that's plausibly not going to be the case anymore. And then it's more cost effective to build storage than capture.

That's the point though? You use carbon-capture as energy storage (when you have excess clean energy), and you can release CO2 when you don't have enough clean energy. In an idealized process, you basically produce coal as a form of "energy storage".

No. That doesn't follow at all, and I wish people would stop repeating this overclever "proof".

Burning fossil fuels for energy: hydrocarbon + O2 -> atmospheric CO2 + other stuff

Sequestration: atmospheric CO2 -> not-amospheric-CO2 e.g. solid C + other stuff

Notice that those are not exact reverses of each other, so there is no requirement that the energy released in one be the same quantity as the energy absorbed in the other.

Hydrocarbon fuels have very high Gibbs free energy. Solid carbon does not. We're only trying to get the CO2 out of the atmosphere, not return it to the form of the original fuel that was burned. Therefore, sequestration can potentially require less energy than was originally released from burning the hydrocarbons.

Combustion is an energetic oxidation. The primary chemical energy change is combining the oxygen with other stuff to produce stuff-oxide. If you want the stuff back out in its pure form you absolutely do have to put in more energy in to remove the oxygen than the combustion result produced. Now, depending on the chemical reaction, sometimes the "more energy in" is "waaay more energy in", which can certainly be improved with catalysts and the like, but that can only create improvements like 100x to 1.1x, which is great!, but always >1.

It's not a general rule for all capture processes, but on the case of solid carbon you do need to put back most of the energy yo get by burning the fuel.

Solid carbon is basically coal. It has more usable energy per mass than any hydrocarbon, and just a little bit less per carbon.

> you do need to put back most of the energy yo get by burning the fuel.

And we can get this energy from sunlight.

Well, we can. But it would make no sense to deploy something like this before our electricity generation is decarbonized. Other capture processes do not share that issue.

But nobody is planning on deploying something like it currently anyway.

Sure, but dont underestimate the inefficiency of power production and sequestration.

Take take the gallium example, for atmospheric levels of CO2, is 400:1. Add the thermodynamic minimum to reverse GalliumOxide to Gallium and O2, and its 800:1, at an absolute minimum. This crushes the difference to methane.

More importantly its a pointless argument, we have practically endless nuclear fuel available, enough to supply the world with power entirely for millions of years. So it does not matter if its inefficient, its climate neutral anyways as long as we stop being idiots and use what we have better. That said there are way simpler more cost effective methods than using a rare earth metal.

You're on to something.

To make it concrete, let's look at methane, the hydrocarbon with most hydrogen.

One kg of methane contains 0.75 kg of C and 0.25 kg of H. When it burns it realeases 55.6 MJ (per wikipedia [1]). Carbon's energy density is 32.7 MJ/kg, so the 750 g release 24.6 MJ. More importantly, you could in principle split the CO2 for the cost of 24.6 MJ and be left with a net of 31 MJ. Q.E.D.

Well, except in real life nothing is done with 100% efficiency. You can't just use all the 55.6 MJ released by burning CH4, you first convert it to electricity, and the best you get is 63%, so you make 35 MJ of electricity. If you get 70% efficiency in splitting CO2, you get exactly the 24.6 MJ you need. But you don't get that efficiency. But let's just say you get even more than that, let's say you get a whooping 85%. That means you need 30 MJ for the splitting, and you are left with a net of 5 MJ of electricity. Which is another way of saying you increased the cost of electricity you generate by a factor of 6 (=30/5), this ignoring altogether the capital cost associated with the splitting of CO2.

But all is not lost.

If we get back to 1kg CH4 = 0.75 kg C + 0.25 kg H2, burning the CH4 we get 55.6 MJ, burning the C and H2 separately, we get 24.6 MJ + 35.5 MJ = 60.1 MJ, which is 4.5 MJ more. That's a different way of saying you need 4.5 MJ to split CH4 into C and H2. That reaction is called methane pyrolysis [2]. Let's say you manage to deliver this with only 30% efficiency, i.e. for 15 MJ. You are left with 35.5-15=20.5 MJ net energy. If you convert this to electricity you get about 13 MJ, which is not that great. But hydrogen is valuable in itself. If we move towards the hydrogen economy, this method of generating hydrogen may be the winner.

[1] https://en.wikipedia.org/wiki/Energy_density

[2] https://en.wikipedia.org/wiki/Pyrolysis#Methane_pyrolysis_fo...

Agreed, the only way this can be useful is to do both: stop burning carbon; use processes like this to recover the carbon from processes where there isn't a good alternative to producing CO2 output. Cement production, perhaps.

There are a number of marine processes which permanently bind carbon, and they do increase with increased CO2 concentration. Problem is that they are overwhelmed by current production. If we reduce CO2 production to zero, the earth will mostly bounce back on its own in a century or two.

Yes, recapturing CO2 at the powerplant is pointless because of conservation of energy. It's always better not to burn the carbon in the first place.

But recapturing CO2 from air isn't pointless - because we can use surplus renewable energy to do so (and then burn C later as fuel). Basically it would use air as infinite capacity (but low-efficiency) rechargeable battery. I've seen estimates of about 13% efficiency over the whole cycle (capturing + burning).

Is there any known or predicted capture technology that does this more efficiently than by growing plants or algae and then burying them underground and/or using them as biofuels?

Inducement of massive algea blooms is extremely cost effective, can store massive amounts of carbon very quickly, and horrendously damaging to large lake, and ocean ecosystems, where you can use them. There are two problems, the first is that its only effective as storage if you make it damaging enough to ensure mostly anoxic decomposition, so the damage is required. Its reusable though, so if you waste a huge lake, there is no reason not to do this over and over again. The second problem is that if you do it in oceans, then ensuring it sinks to the bottom, becomes key, though this is straightforward if you do it on a scale to solve global warming in a single sweep. Though you would sacrifice an ocean and everyone living nearby for decades. The one time someone tried it, it was a far more massive success than anticipated, but also killed the fishing and tourism industry on several nearby, and not so nearby islands, for several years.

A slower variant is to build artificial floating reefs, increasing the amount of marine snow. That improves the ecosystem, but requires significant investment.

According to this guy [1] in less than a decade it will be cheaper to produce hydrocarbons out of air and water + surplus renewable energy than by pumping them out of ground. Which is in turn cheaper than biofuels.

[1] https://caseyhandmer.wordpress.com/2021/11/01/scaling-carbon...

Yes. CO2 can be frozen out of the air as snow at sufficiently low temperatures.

This could be done at scale in central Antarctica using enormous refrigerating complexes[1], but it would be the most ambitious engineering project ever undertaken by humanity.

Generally this is not seriously discussed by experts as a solution to global warming not because it is not feasible, but because it would diminish the sense of urgency and discourage the much more prudent and affordable approach of simply reducing emissions.

[1] https://journals.ametsoc.org/view/journals/apme/52/2/jamc-d-...

> it would diminish the sense of urgency and discourage the much more prudent and affordable approach of simply reducing emissions.

If air capture costs more, then simple economics will keep us more focused on reducing emissions. If it somehow costs less, then doing the air capture is a win.

Most likely, air capture will cost more in some cases (power plant emissions), and less in other cases (long-haul jets). Ideally we'd set a price on carbon, award credits for verifiable air capture/sequestration, and let the market sort all this out.

> Generally this is not seriously discussed by experts as a solution to global warming not because it is not feasible, but because it would diminish the sense of urgency

Let us say it is not being discussed because it is not feasible. Unless of course we build massive nuclear power plants in Antarctica with all what that entails. We are not any time soon in a position where we can produce any nontrivial amount of solar or wind energy in the hostile environment of that continent, plus it's dark night down there for half a year each year. Meaning the only remaining option would be to ship coal or oil down there to burn it so we can cool air to –140°C, obviously a non-starter if there ever was one.

> and discourage the much more prudent and affordable approach of simply reducing emissions.

This. The entire plan is madness: you'd burn two tons of oil and coal to get rid of part of what burning one ton of oil and coal leave behind in the atmosphere. It is not clear to me at this point if it is at all feasible to use fossil fuel to get more CO2 out of the atmosphere than burning it puts into the atmosphere in the first place. Because in this household we obey the laws of thermodynamic. And if it's possible at all it's not easy to see why continuing to burn oil and coal and capturing the CO2 at other sites should be better than not burning part of those fuels and capturing the CO2 right at their point of emission should be the better option. It is a hare-brained plan.

> Let us say it is not being discussed because it is not feasible. Unless of course we build massive nuclear power plants in Antarctica with all what that entails.

Maybe it really is because it's not feasible, I concede that's not something I can really know. But nuclear power plants are not necessary. As the paper sets out, there is abundant wind energy in Antarctica. Setting up a medium-size (1200 MW) wind farm on the Antarctic coast is actually not a crazy proposal, since the construction can be undertaken by ship alone.

Moreover it's very clear that the energy required to freeze one ton of CO2 is substantially less than the useful energy obtained by its combustion (this is intuitive from the magnitude difference between heat of combustion and enthalpy of sublimation: combusting one mol of pure coal to CO2 liberates 393 kJ, freezing one mol of CO2 out of the air consumes 26 kJ). In no way does that violate thermodynamics; the CO2 still exists, it just isn't doing any harm.

This project would not just ameliorate global warming, it could allow useful exploitation of all the remaining global fossil fuels.

Maybe perpetually shaded area would work even without active refigeration? Sun never rises overhead in Antarctica. But yes it's still about building a megastructure in very harsh environment.

I'm not sure if it's more efficient than the methods you mentioned, but Project Vesta makes some pretty bold claims using the carbonate-silicate cycle. More details:

https://news.ycombinator.com/item?id=20403570

https://www.vesta.earth/

> surplus renewable energy

is where you lost me. Hell coal is projected to get burned by the megaton for another half century or so because China and India have those resources and that demand. Mankind does not currently have surplus renewable energy.

There isn't a single global account of electricity generation and expenditures. If your windmills are humming in Montana, and demand for electricity relatively nearby right now is already met, you have surplus energy to either use or store; China doesn't factor into it.

Maybe if you were allocating resources across the world's economies, it would be better to invest in solar panels in Shanghai than capture carbon in Billings, but that's not the actual situation.

> Mankind does not currently have surplus renewable energy.

On the contrary - we have a lot of surplus renewable energy, and it's a problem [1].

Energy isn't fungible. 1 MWh in Texas at 12:00 on 4th July is not the same as 1MWh in London at 23:30 on 25th December.

Energy consumption vary a lot through the day and year. Energy production of solar and wind vary a lot as well, and these variances aren't correlated with each other.

Most big scale energy grids are created with the assumption that every millisecond energy produced == energy consumed. When this isn't true - frequency in the grid rises or drops. If it drops too much you just have blackouts, if it rises too much - devices blow up AND you have blackouts until you replace the blown up devices.

Even if a grid as a whole has energy deficit - it's often true that one part of the network is producing too much but the power lines between them might not be "thick" enough to transfer all that energy to the part of the grid that has deficit at the moment.

If we moved completely away from fossil fuels towards renewables - to serve energy needs of customers we would need a lot of overcapacity (because you can't count on sun and wind producing at 100% power all the time). Usually the overcapacity for wind is 2x and for solar is 10x compared to traditional sources. Better batteries might change that, but it still won't be 1x. So when there's a very good weather grids with a lot of renewables will by definition produce too much energy.

There's a lot of factors, and in practice even in countries with less than 50% renewable power installed - often they have too much renewable energy. This will only get worse as we replace more energy production with renewables.

Big batteries like the one in Australia are very profitable and solve short-term (sub-hour) balancing, but aren't big enough to shift the solar production peak in the noon to the consumption peak late evening.

So indeed we have a lot of surplus renewable power already that gets wasted every day and causes problems, and it will only get worse.

[1] https://www.sierraclub.org/sierra/what-do-we-do-too-much-ren...

Yeah, I was about to say... as great as this seems like it may be, surely turning CO2 into coal isn't a net gain versus not burning the coal.

But there are plenty of point emitters of CO2, so if we imagine a grid that's actually renewable sure. Capture though? It could always be paired with another capture method to concentrate it first, it's usually cheap to concentrate things a little and expensive to concentrate them a lot.

Even if we stop all emissions right now, the CO2 already in the air will stay there for a while. We need some way to recapture it if we want to return to pre-industrial levels.

And that might take centuries to do, so we'll probably end up doing some kind of geo-engineering to interrupt the buildup of heat to give us time to extract the carbon.

Or, pessimistically, we’ll do the geo-engineering step without ever reigning in the new emissions and call it done.

As someone who has been growing plants for years underwater (aquascaping) IMO geo-engineering is the only answer. We are already doing it by proxy, we need to have it front and center though. Every action has a reaction. We cannot consider a single project for its merits without the context of the larger whole. We need to not only stuff more air into that supercharged engine, we also need the correct mix of fuel, strong spark, and correct timing.

The natural way to of carbon sequestion on a planetary scale is - life ( plants / organisms / microbes etc). The catch is that if we fuck it up, and you know we will, we will pay a hefty price (like we do now with red tides, dead zones, bleeching). The added bonus is that we just do not sequester carbon, but we supercharge all the plantatary processes.

You reminded me of a "midnight thought" on the topic. I wonder if Tesla starlink process could be used to create satellites with sails that block sunlight opening/closing as needed until we can remove enough carbon to do it right? The ring of satellites could be some distance above our current satellite flight paths.

Have you ever seen the shadow of a satellite passing overhead?

For that matter, if it did work, would the satellites not reflect IR back to Earth? They might even hurt more than they help because they would be blocking sunlight on one side of the Earth only but would be blocking IR escaping on both sides.

Read about solar radiation management. Space based approaches aren't necessary. You can put the equivalent of sunblock in the upper atmosphere or seed more low clouds. It's relatively cheap but there is a lot of opposition to the science.

@dr_shiv & @DemocracyFTW (I don't recall if HN notifies of mentions)

Is the "opposition" mainly that the process as stated isn't reversible? Is there a way to improve the original idea to make it reversible in a short order?

Well, marine cloud brightening is small scale and involves lofting salt water in the air. It is immediately reversable.

The opposition comes from political signaling and tribalism.

Read more:

https://www.nature.com/articles/d41586-021-02290-3

Thank you so much - very helpful

That's not "opposition to the science", that's a sane response to a madman's proposal to intentionally f*k with the biosphere at the grandest scale.

Considering the psychological effects of no sunlight, this is a terrible idea.

It doesn't require darkened skies --a reduction in incoming light is all you need. 10% reduction would be a lot.

Oh, you'll still get sunlight, assuming you pay your monthly sunlight bill to spacex.

My response isn't a HN "appropriate" comment, more Reddit - but this is gold! Made me laugh thinking of it.

I was suggesting, more like.... if they were programmed (for instance) to open over deserts, or barren U.S. lands, etc for short periods of time. Some parts of the globe might have some small amount of light blocked for 10 mins, 1 hour, etc - whatever. It would be like a cloudy "hour", etc.

Not sure how to phrase this, but: Are you aware of clouds? (The ones in the sky, not at FAANG...)

That outcome isn't necessarily bad. It's somewhat arrogant of us to assume that we understand enough about a system as complex as the Earth's biosphere and atmosphere to know for sure a larger percentage of CO2 will necessarily be bad long term. It's feasible that it could be better, even if only after a painful transition.

I for one find the future where we're not actively managing the Earth's climate in some way to be the more pessimistic outcome. It indicates that civilization has failed to continue advancing, probably isn't spacefaring, and that the light of consciousness will eventually twinkle out once the Earth becomes uninhabitable in about 500 million years.

We'll see.

We know that, at least, thousands of species, including many not catalogged, will be driven to extinction, that large currently inhabited areas will become uninhabitable, that tens or hundreds of millions of those inhabitants will be converted to refugees unable to provide for themselves, and the influx of those refugees will drive temperate nation governments to fascism. If that is not bad enough, I can go on.

The "everything is so uncertain, we must do nothing" line has worn out its welcome. It was dishonest 30 years ago, and is reprehensible today.

Rather as in the pandemic, the attention paid to models is remarkable. You can cherry pick a model to suit your predilections. They certainly cover a wide range of possibilities. I do wonder what your view is of the utter lack of any concerted action by countries in response to these models? If we're off to hell in a handbasket, it does seem that few in power, with access to the best authorities available, are really concerned. How is that? Extinction Rebellion are certainly logical on the basis of their belief in the views of some climate scientists. They sound and act rather like people who'd say yes to O'Brien's question in 1984 when he asks Winston if he's prepared to do some pretty horrible things in pursuance of the objective of overthrowing Big Brother. But when it comes down to it, no one is convinced. Example: Coal is now back on the menu when power shortages loom.

I'm pretty sure the models are right, and that we will hit +4C on time, that politicians are aware of this, and they wont do much about it. They want to, but all real solutions have massive conflicts of interest, and they are aware voters dont really care much about global warming compared to other issues like house prices and jobs.

In forums like this, where everyone has a well paying job and fuck you money, it is important to preserve the planet, just not enough that more than 1% here would approve a build permit for a windfarm next door to their house. Arguably we mostly care about preserving the nice nature we now enjoy for free, and this is as good as it gets. The vast majority of people who specifically feel climate change is important still dont think the near guarantee of climate change is more important than the negligible risks of nuclear power.

Basically, politicians are representing the true interests of the population, which to be fair is their job. We just arent who we want to pretend we are.

Alarm about climate is overwhelming greater among voters than politicians. But US politicians (and the US Supreme Court) have arranged not to need to care if voters are alarmed, so long as lobbyists are not.

The two party system of the US occlude the matter so lets look at the rich well functioning democracies of Europe instead. Better education means there isn't anything resembling the climate denial movement of the us, and on average people are place climate concerns higher on their list of priorities. Every single one of these countries has a green party or similar whose primary purpose is the preventing ecological damage and climate change, and most argue it can be done without or with a minimum of loss of wealth and productivity. Not a single one of these countries is in a majority and most are around 10%. The ones which acknowledge that preventing a 4C rise requires massive investments and outright forced unpleasant changes will be required usually fail to go above 5%. And this is in the richest countries, the poorer countries dont give a rats ass about it, and the green parties are token efforts that idealists vote for knowing that their representatives will mostly make the others feel bad, while helping pass policy which supports the economy at the cost of eg climate as long as a token effort to minimize the negatives are used.

This shows that the vast majority of people in these countries, while publicly concerned, and privately mildly alarmed about climate change, prioritize other things and that their politicians are responding to their constituent priorities. Why would this be different in the US? everything from median education to city planning, predicts that US population cares much less about environmental impact. Poor people living on welfare in some Nordic country sometimes care about climate change, but mostly dont, certainly much less so than average citizens. The number of poor in the US who prioritize climate change over saving 5 bucks on gas so their kid can eat that night is zero.

When people aren't lying to themselves, its easy to see that preventing climate change is a policy favored by, and forced upon the public, by elites. Speaking as one, if of the lowest possible level, obviously we should do it. I'm certainly willing to sacrifice the poor both abroad and at home, but I think tigers are cool, that nature is nice to look at, and I would like to keep it that way. On the rare occasion I happen to meet some of my old friends turned politicians, I naturally point this out. And they listen, far more than they should, given neither my phd nor my career is in an applicable field. The few times I meet 0.001%ers, they have been more concerned than I. They haven't needed to status signal for decades, certainly not in private to someone like me, and they all had significant interests in industry which would be negatively affected.

This changes the story of who is preventing such policy and of if its democratic. There isn't a conspiracy by the elite to prevent climate change from being solved, if anything its the opposite, and the problem is that common people aren't stupid enough to let us get away with it.

With enough counterfactuals, you can support any claim.

The argument loses all interest, but the questions remain why the argument is being made, and who wants it made.

Your claim is that politicians prioritize global warming less than their constituents. If this was true, then in countries with multi party systems we would expect to see green parties become larger than parties which prioritize other issues. However in reality, most green parties get fewer votes than other niche voter issues like anti immigration. They are much much smaller than parties which focus on issues the voters actually prioritized, such as economy, jobs, and welfare.

People in power expect to be dead before the chickens come home to roost. They didn't get where they are by caring about what happens to anybody else. Provided civilization doesn't wholly collapse before then, they are insulated from all consequences.

All the accepted models point in the direction of mass extinctions to varying degrees.

Arrogant? It's arrogant?

You might want to read up on the effects of higher CO2 levels on human cognition. It's not pretty. And it completely blows your comment out of the water.

We already know that the CO2 levels that are forecast this century are going to be catastrophic. This isn't a "we'll see" situation anymore. We have seen. The only question is whether we will do something about it before it is far, far too late.

You need to worry about the next 50 years before you start worrying about 500 million years.

> It's somewhat arrogant of us to assume that we understand enough about a system as complex as the Earth's biosphere and atmosphere to know for sure a larger percentage of CO2 will necessarily be bad long term. It's feasible that it could be better, even if only after a painful transition.

That's the problem. Maybe it's better, maybe it's worse, and there is only one way to find out. But if it's worse, finding out is very bad. And there is no way to know ahead of time.

I think we can and should be confident about the short-medium term negative effects of high CO2 on human civilization. You can always spread doubt about anything that's long-term(say more than 2 decades) but it doesn't help to hope long-term it works, and short-term let it hurt as much as possible.

> And that might take centuries to do

How many efforts at international cooperation have survived for centuries?

A lot of the comments upthread seem to be assuming that we live under some kind of World Government.

> We need some way to recapture it if we want to return to pre-industrial levels

To return we probably need to capture well below the "safe" boundary of 350 ppm of CO2, to engage all the feedback loops that will refreeze the arctic etc.

But also, why bother? Biggest problems from climate change are due to the fast change, which causes destruction of ecosystems (including human habitat). Even if we refreeze, we won't revert these losses.

That's why we do solar radiation management first (e g., Marine cloud brightening), to prevent the rapid change. Then we try to fix the atmospheric carbon balance. That will take a while.

> solar radiation management first [...] Marine cloud brightening

you mean, like, throwing a spanner into a machinery we hardly understand and see whether "it sticks"? Give me a hundred planets and start the trials!

Maybe read about it: https://www.nature.com/articles/d41586-021-02290-3

That's a good reason not to apply this technology to smokestacks, since that would make a power plant into a power consumer.

However, in some cases it's quite difficult to stop burning C. Long-haul jets are one example. So for those, it makes sense to make carbon-neutral liquid fuels, even though there's an energy penalty. Pull CO2 from the atmosphere, use renewables or nuclear as an energy source to turn it into fuel. CO2 emissions from steel plants might be another good application.

Ideally we might be better off using clean energy sources to displace fossil plants, but that doesn't happen as fast as we'd like for all sorts of political and economic reasons. So we might as well get started now on other reductions, because it'll still help some, and we can get it scaled up by the time we've decarbonized the energy grid and want to decarbonize everything else.

We don't burn pure C to make CO2 though. We burn hydrocarbons. I am not sure what the effects of the longer carbon chain is. But I feel certain the other extra parts of hydrocarbons leave more energy on the table.

The output might be quite low. But I doubt it would be negative.

Coal is pure carbon more or less. You are right that the math is a bit different for gas and oil.

He's not talking about perpetual motion. The input energy into this hypothetical spherical-cow process is concentrated reflected insolation. Unfortunately, getting the Ga2O back to being liquid Ga is probably the problem.

How is it smelted from ore in the first place? Quick look suggests that it starts out as an oxide, and is a byproduct of aluminum production.

> getting the Ga2O back to being liquid Ga is probably the problem

guess, the same way we got it - bath, electricity, cathode and anode

Luckily there are these rocks which get hot just lying around, more so if you concentrate them, and we have millions of years of current power consumption of those to use. Perfectly CO2 free too.

Unless you're Australia, where we shut down our geothermal trials after some early success.

Ignore those rocks that are already hot, let's keep digging up these black ones and burning them!

There are some industrial processes like blast furnaces where it's hard to come up with a better heat source than fire. That might be a place where this tech could help.

I think a better example might be cement production. For a blast furnace you don't just need heat, you need to chemically react some reducing agent with the iron ore. Generally that's either coal coke or methane reacting with the iron oxide to produce iron and carbon dioxide. There's technologies on the horizon that could enable electrolytic refining of iron much like how aluminum is refined. With cement production there's no potential method to eliminate the carbon dioxide. You still have the extreme heat of the process so natural gas and coal are a pretty good fit but even if you sidestepped that and heated it through other means, you're ultimately taking calcium carbonate and calcining it to calcium oxide. Even if you eliminated all coal usage you'd at best cut the amount of CO2 released by half. With a good carbon capture system connected to cement kilns you could actually use concrete to capture CO2 from the air. Concrete naturally forms calcium carbonate over time as it ages so you could use it to have concrete production effectively be a net negative for atmospheric CO2. Concrete production currently accounts for 8% of CO2 emissions globally and direct atmospheric capture has been something that's historically difficult due to the low concentration of CO2 in the atmosphere so you could kill two birds with one stone.

> With cement production there's no potential method to eliminate the carbon dioxide.

Please have a look at Limestone Calcined Clay Cement: https://lc3.ch/

This is only one of the cement alternatives I believe.

Either way, point stands: there are industrial processes that are very carbon-intensive in ways that are difficult to replace with electrical power. Carbon-capture in the exhaust system sounds like an excellent solution for these.

Are there any chemical carbon configurations more stable than CO2 which are solid?

Yes, carbonates of alkaline earth metals (e.g. magnesium and calcium) are solids at STP and more stable than carbon dioxide. See section 7.2.2 "Chemistry of mineral carbonation" in this IPCC report:

https://www.ipcc.ch/site/assets/uploads/2018/03/srccs_chapte...

Even at the low partial pressure of atmospheric CO2 and at ambient temperature, carbonation of metal oxide bearing minerals occurs spontaneously, though on geological time scales (Robie et al., 1978; Lasaga and Berner, 1998). Limitations arise from the formation of silica or carbonate layers on the mineral surface during carbonation that tend to hinder further reaction and to limit conversion (Butt et al., 1996) and from the rate of CO2 uptake from the gas phase in the case of aqueous reactions. The challenge for mineral carbonation is to find ways to accelerate carbonation and to exploit the heat of reaction within the environmental constraints, for example with minimal energy and material losses.

A lot of people think carbon capture and storage has the potential to save us from climate change, but that idea ignores the scale of the situation.

The world generates ~40 billion tons of CO2 a year, meanwhile the total mass of everything transported in the entire world is only around ~12b tons.

All of the carbon we put in the atmosphere was transported (oil, coal, etc) to the location where it was used so this rings false. Presumably the carbon will be pulled from the atmosphere on site and stored on site anyway.

Maybe something like building solar arrays in semi-arid regions and mixing up the resulting solid carbon into the local soil for some ecological engineering or filling up old mining pits.

The carbon gains 2 oxygens when combusted, tripling the weight of the original fuel

Presumably it also loses 2 oxygens when it is turned back into solid carbon.

Well we do move that 40 billion tons to the atmosphere. If we can do that, then in principle we can do the reverse. We just need an economic framework to pay for it.

It's certainly going to be cheaper, in most cases, to avoid emissions in the first place. But there will also be cases, like long-haul jets, where it may be cheaper to remove the CO2 later. Plus the CO2 is already above a safe level, so we'll have to draw it down somehow anyway.

We only move a small portion of the 40 billion tons. Most of the mass of CO2 is oxygen, which was already present in the atmosphere before we combined it with carbon.

Even assuming you can do some kind of reaction in-place, CO2 is over 25% carbon by mass. 10 billion tons is still a massive challenge.

But don't we only need to "first" remove just enough of that 10 billion tons to maintain where we are now, so that we can then remove more to "go back to levels earlier in modern time"?

Yeah, we need to go extremely carbon-negative, not merely carbon-neutral. It's so easy to forget this.

Why?

Why do we need to go carbon-negative? Because the atmosphere already has too much CO2, and reducing net emissions to 0 means that CO2 will stay there. We've emitted that CO2 in the course of (say) 300 years but need to pull it down in (say) < 50 years, hence we need to pull it down much faster than we emitted it.

Not sure if that answered your question or if you meant something else.

Yes, but what I wanted to know is if we kept the current concentrations would temeperature keep rising or would it stay basically the same as it is today.

It would stay the same. And nature would reduce current concentrations back to normal over the next few centuries.

Thanks - that did help me.

Related, for comparison: apparently planting 20B trees/year requires only $80M/year (!) and would pull down a trillion tons of carbon over 50 years (!): https://www.youtube.com/watch?v=QyQvfaW54NU&t=14m53s

But they would decay, unless something is done to sequester enough of the wood, and release much of it back into atmosphere, right?

Cross-laminated timber comes to the rescue. Plus the added benefit of being able to replace concrete, which is a huge bonus for decreasing emissions. And it's already in use.

https://en.wikipedia.org/wiki/Cross-laminated_timber

> unless something is done to sequester enough of the wood

I think that was the idea. He's viewing it as a mass transfer problem. You "harvest" CO2 with trees, then put it back in the ground.

I think the hard part is not hurting ecosystems in the process, but at this point honestly this might still be the best solution we have available.

Unfortunately, the people that plant trees have economic incentives to not put it back in the ground. Timber has considerable economic value, as fuel, or contruction materials or whatever. It's hard to imagine foresters cutting down valuable trees, and then discarding them in some lake.

I imagine it would need to be government funded, not for private enterprise. If the order of magnitude of the costs they mention are to be taken at face value ($80M/year), for the entire world, it would be absolutely trivial for the government to fund, so I don't think expect any commercial enterprise would necessarily be forced to align this with its mission.

> For the entire world, it would be absolutely trivial for the government to fund

Which government? Is that some hypothesised World Government?

The UK Government runs a lot of the forestry in this country. It is run as a commercial timber operation. The Brazilian and Indonesian governments appear to be committed to commercial exploitation of enormous amounts of old-growth rainforest timber. The Polish and Hungarian governments are also committed to logging old-growth.

There's no time left for this kind of dreaming.

> Which government? Is that some hypothesised World Government?

I meant the US government. But you can insert lots of other governments in there, including the UK like you mentioned.

> There's no time left for this kind of dreaming.

Nobody's dreaming. I'm just talking about the feasibility, not claiming anything about the likelihood.

I don't know what kind of construction materials your house is made of, but most wood construction doesn't just vaporize into the atmosphere as CO2 unless it's burnt down, which is considered an undesirable outcome to be prevented.

"then put it back in the ground" - throw it into a lake. Or artificial bogs. When its submerged, the lack of o2 causes the carbon to stay as it is. This is basically how coal comes into existence.

The whole lumber shortage thing makes me think that people are willing to sequester wood in their homes. (I know, I know, it was sawmill capacity or something. But still...)

Most trees are planted in order to be harvested as timber. Most of that timber turns back into CO2 in 100 years or so. Tree-planting is not a long-term solution to excess atmospheric carbon. Combined with carbon-trading, tree-planting is a rather obvious channel for greenwashing.

> Most of that timber turns back into CO2 in 100 years or so. Tree-planting is not a long-term solution to excess atmospheric carbon.

Do you have links to more reading on that? This is the first time I've heard of this particular reason why it might not work.

No I don't. But if wood lasted more than a couple of hundred years on average, then we would be neck-deep in old lumber. We're constantly cutting down trees, and yet the amount of wood in the lived environment isn't increasing noticeably.

Conclusion: all that old wood is either buried, or it's busy turning into CO2.

So I'm not impressed by claims of "carbon offsetting". On the contrary, I take such claims as evidence that the organisation in question is part of the problem.

Incidentally, how are you supposed to recycle chipboard? Like, for example a chipboard kitchen counter? For several decades, I had in my home a pair of oak side tables, that were made by my grandfather from the remains of a large oak dining table. You can't do that nowadays with chipboard.

I can't say I follow your logic at all unfortunately.

But regardless, I also don't get where you see a discussion of "carbon offsetting". This isn't about "offsetting" emissions or impressing you, this is about repaying "debt" that's already incurred. Pulling down old carbon is something we have to do regardless of what we do with our current emissions, even if we drive them to 0, because the current carbon in the atmosphere is already too much. Whether we do it with trees or machines or something else, it needs to happen.

Wooden things rarely last more than 50 years and end up being thrown in fire, or catching fire as a result of natural events. Additionally, decaying wood releases CO2.

It depends on how you use that wood. In old cities around the world, there are plentiful examples of wooden structures that have been around for up to 1000 years or more.

Does our current world really look like we're building thousand year long buildings ?

Well I believe we should be moving in that direction if we want to have any chance of sustaining society. Just like we need to kill fast fashion, we should kill "fast construction" too.

But only about 16% of that mass of CO2 was ever "transported" in the first place: the carbon atom. The O2 part appears for free because it comes out of the air the fuel is burned in. And that oxygen wouldn't be transported with carbon capture either, it would just be vented into the atmosphere again.

I mean think about it, we can't be emitting more waste than we are transporting, because that waste comes from fuel, and the fuel itself is part of what we're transporting.

And then there's the fossil fuel dependency. We still need more than will be produced, even ignoring CO2 levels.

> This process runs at 200C and 1 Bar (=0.98 ATM).

Let's not be misleadingly precise. It runs at 1 atmosphere.

The process oxidizes the gallium, which then needs to be reduced. That's a lot of energy input.

There’s also a massive sun, which has alot of energy output.

So many of the comments here talk about using abundant solar energy as a solution to the atmosphric CO2 problem. But unfortunately, solar energy isn't even close to providing the energy we need for home-heating, transport and industry.

We have to start from where we are: we can't just warp into a future where Dyson Spheres are realistic. We have less than thirty years. I suspect it's actually already too late. Using solar to reduce Gallium, so we can use the Gallium to reduce CO2, while we continue burning hydrocarbons because the solar is all being used to reduce Gallium (or solve hashes), doesn't look to me like the way forward.

> solar energy isn't even close to providing the energy we need for home-heating, transport and industry.

It provides more than enough energy for these things in some places at certain times, we can build the CO2 extractors in these locations

So use that energy directly. Why burn carbon, release CO2, capture the CO2, and use the sun to turn it back into carbon?

It could be far more efficient than using batteries. Not round trip total energy efficient, but moving around carbon based fuel, refueling vehicles, energy density and cost to produce and retrofit generators

> So use that energy directly

This would use that energy directly. To sequester carbon.

> why burn carbon

I didn’t say anything about burning carbon.

This tech can only sequester CO2 without the presence of O2. Where does CO2 occur without O2? In the exhaust of power plants/engines/heaters that burn hydrocarbons.

If you didn't say anything about burning carbon, you weren't paying attention.

> This tech can only sequester CO2 without the presence of O2. Where does CO2 occur without O2?

Here is a system for collecting CO2 from ambient air and discharging a stream of pure CO2:

https://news.mit.edu/2019/mit-engineers-develop-new-way-remo...

> If you didn't say anything about burning carbon, you weren't paying attention.

Wrong.

The creation of solar cells to capture that sun takes time, and rare earth elements which have to be extracted from the environment. To use solar to capture carbon, you'd have to make enough solar panels to replace all the fossil fuel sources, then more. That's not happening any time soon, it can't.

Even if this works and this were marketable today, we still have to take into account the amount of time to scale up production capacities for the reactants and the devices which would to the extraction. On top of that the necessary subsidies to make it economically interesting to have it be deployed far and wide.

Don't get me wrong, if this works we HAVE to do this. I'm just not very optimistic that it could save us at this point. We'd still be fucked, just a little less so.

>We could start pulling more CO2 out of the atmosphere than we put in, and at that point we'd be pretty confident things won't get worse for the climate.

Not sure that would be terribly efficient to pull CO2 out of the atmosphere to pump through this setup.

Would be fine for many other reasons though. I wonder how it behaves with "non clean" CO2 sources. Like say at the output of a coal fired PowerStation.

You need a massive amount of energy to run the process. If you could make it 100% efficient, which you can't, you have to put in as much energy to turn the CO2 into C + gallium oxide, and complete the cycle by turning the gallium oxide back to gallium metal, as you got by burning the carbon. So if you still have people using coal for energy, you have to pay more than they got.

But if you could eliminate fossil fuel burning and use processes like this to reduce the amount of CO2 already emitted (a big "if" because you have to concentrate it somehow) it could be useful.

> But if you could eliminate fossil fuel burning and use processes like this to reduce the amount of CO2 already emitted (a big "if" because you have to concentrate it somehow) it could be useful.

It could be useful if we 'just' greatly reduce fossil fuel burning for electricity, even if we don't eliminate it and even if we still use fossil fuels for other things.

> Gallium is cheap (~$300/kg)

Please correct me if I get the numbers wrong but if that is the price, that means the price of 1 ton Gallium is $300,000 per ton

From [another comment](https://news.ycombinator.com/item?id=29990056) I got that the ratio of CO2 to Ga would be 1 to 2. So in order to reduce 1 ton of CO2 you'll need to spend $600,000. That seems insane. Especially when the damage done per ton of CO2 is usually valued at ~$200.

The Ga is a catalyst, so it’s a cap ex not op ex.

I’m dubious but open to try anything halfway plausible at this point.

The abstract says the process produces gallium oxide. We would need to recycle that into gallium, which is probably energy intensive.

Pretty sure the Gallium can be recycled.

It has to be endothermic. Otherwise you could run a coal plant and get net power while getting your carbon back. Second law says nope.

Could still work of course if it used solar heat or surplus industrial heat. If it was low maintenance you could deploy in places like the Sahara. Lots of free heat there.

Edit: gas on the other hand could in theory be burned without CO2. A lot of the net energy there is the hydrogens combining with oxygen to form H2O. You could use fuel cells for maximum conversion efficiency and then recover the carbon.

> We could start pulling more CO2 out of the atmosphere than we put in, and at that point we'd be pretty confident things won't get worse for the climate.

How much of the atmospheric CO2 can you actually capture with stations at ground level? I assume this isn't critical since I haven't seen anyone propose a Tower of Babel of carbon capture machines, but I'm not sure why it isn't.

The CO2 diffuses through the air. The same way you can make something crystallize completely out of water too, the concentration will want to equalize throughout the medium.

Of course it's going to be more efficient with more air flow, I don't know how turbulent the wind really is, how I could picture it in terms of something I understand like a bottle water, but I assume pretty turbulent?

Air moves.

All of the air from here to the Karman line moves over the spot you put your capture machine?

Yes, eventually. CO2 is referred to as a “well-mixed greenhouse gas” because its concentration is relatively stable across the entire surface of the earth. https://www.gfdl.noaa.gov/blog_held/6-transient-response-to-...

Eventually, yes.

If you have to put as much energy into splitting the C from the O2 as you got from burning the C in the first place, that means giving back all of the energy that was extracted by the fossil fuel economy for however much carbon you want to convert. That means not just stopping the fossil fuel economy but basically running it backwards enough to undo decades of its output.

Since fossil fuels are being burned as fast as ever and we can't even slow that down (Biden selling new coal leases in the US, etc.), running it at full speed backwards seems like a pipe dream. If we're going to be that utopian, we might as well think bigger and get started on a Dyson sphere.

> 319 μmol h−1

That's ... not a lot.

Gallium is not cheap. Indium is almost as expensive. As a way to extract small amounts of carbon, this does not look cost-effective.

Not cost effective now.

If you weigh it against the scale of death and destruction from climate change impact yet to come, that could change very quickly.