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What the article leaves to the conclusion is what needs to be stated up front and center: it's virtually impossible to do this efficiently, cheaply, or effectively because there's so little CO2 in the air, meaning

a) adding even a little bit more greatly affects the CO2 levels b) with a global ppm of ~400, it basically means that you need to filter 2500 molecules of air to get a single molecule of CO2, and that's assuming perfect binding and effectiveness. There is no magic powder we can mix that'll cause CO2 to precipitate out of the atmosphere and fall to the ground like snow; it's a grueling energy intensive process to filter that out of the air around us.

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It only has to do it cheaply now because there is NO COST to putting CO2 into the air.

Why are people surprised that if something is free (pumping CO2 into air) demand for it is high?

You are telling me that doing a charge of let's say $10 - $100/ton of CO2 wouldn't have a DRAMATIC impact on emissions? Is $10 - $100/ton too little for a supposed climate emergency?

There is so much funding and lawmaking and finger pointing and shaming - but still - dumping CO2 into the atmosphere if free and dumping remains high and people pretend to be surprised.

On energy: CA curtails (turns off) solar (and wind) power because there is not enough demand. In 2019 CA had 921,000 MWhs of curtailment.

Let's start by charging something for CO2 emissions.

You mean a Carbon Tax ?

The tax that applies to every single business, every single product, every single process, everything. The one that causes every single vested interest to come out of the woodwork and join together to make it politically toxic.

We tried this in Australia. It has killed every government that even dared to discuss it. And politically it is utterly impossible to defend e.g. "Carbon tax that raises power prices for pensioners".

Except many countries have carbon tax

Which ones would that be? I know of many which have a tax on various forms of energy consumption. And even then, industrial consumers are exempt or have a reduced rate.

Heres a document explaining things from 2017 issues by the Japanese government. I remember reading it a few days ago, interesting for the context: http://www.env.go.jp/en/policy/tax/20170130_greening.pdf

IMHO, the first step is to migrate coal power plants to capture and storage. It is much easier to drop emissions than to pull from the air. I would like to see more tax pressure globally incentivizing carbon release reductions. Instead you get weird stuff like Japan's carbon tax where coal pays the lowest carbon tax of gasoline and diesel.

Not all polluters are equal, some make huge gains while doing it.

Why not have the level of sales tax (VAT in the UK) vary depending on amount of C02 was used to create a product. The consumer would not pay any more on average.

... "will be used to offset costs for pensioners."

Our carbon tax worked at reducing emissions, and at being low economic impact. It was removed because we are a corrupt banana republic, not because it's unworkable.

don't call it tax, call it carbon dividend and give the collected money away to citizens.

This is the secret. The average citizen would actually come out ahead financially, making it a progressive tax, as opposed to the de-facto regressive taxes that have received popular opposition in other attempts.

"The Largest Public Statement of Economists in History": https://clcouncil.org/economists-statement/

> The average citizen would actually come out ahead financially

For a while. But if the carbon tax works and society switches to clean energy, then there is no more emissions and no more dividends pay to the citizens.

Goal achieved.

I suspect there will be always be use cases for fossil fuels; for instance, even when 99% of all cars are electric, I wouldn't want to deny auto enthusiasts muscle cars and the like, if they're willing to pay for the societal externality. The carbon tax can continue to go up to cover these cases.

Moreover, I think the same model can apply to other negative externalities (aka, Pigovian Tax [0]). But to the extent that the public will someday complain that their carbon dividend is going down: (a) I call that a good problem to have, and (b) because the collective action problem now points the other direction, there's no individual incentive to over-consume such that the dividend goes up again.

[0] https://en.wikipedia.org/wiki/Pigovian_tax

Squint a bit and Canada's carbon dividend looks like UBI.

Two birds, one stone.

This has been the Canadian model and the Right has still weaponized the worst kind of vitriol against it (despite a carbon tax being the most market friendly mechanism).

Opponents of carbon tax and similar measures need to decide which they like less... some lost profits, an escalating carbon tax, and reshuffling their investment portfolios -- or food riots, mass migration, the massive resurgence of left wing populism, and even civil war, once the effects of climate change become intense and obvious to the populace.

Canada is likely to be spared the worst effects of climate change due to geography so it might not seem like such a serious problem to them. Even under the worst case scenario, Canada will still be self sufficient in staple crops. And any mass migrations will have to pass through the USA first.

People living through massive record forest fires in B.C. and Alberta probably won't agree with you.

Not to mention the water supply of Calgary and many other western Canadian cities is glacier fed, and the Bow Glacier that provides to Calgary may not be able to meet demand within the next 30 years... a problem that will only get worse with climate change.

Yes, the great lakes region looks better than most. And it will look desirable to a lot of displaced people...

Carbon tax is not harder to implement than VAT. It's also the most effective tool against CO2 release.

Yes, people don't want any solution that would result in the slightest inconvenience in the present. So we'll have the end of civilization instead.

We need to think past that point: how will the world look like once civilization has collapsed? What will still exist? What will not?

> It has killed every government that even dared to discuss it. And politically it is utterly impossible to defend

Then pull it out of political discussion! We don't have political discussion about "how to hang people of color Q better" anywhere in the world (mostly) anymore because we've wrote it in the text of our f laws that violence and racial discrimination are forbidden! Not on the political menu anymore.

Same needs to happen with lots of stuff concerning climate, ecology, sustainability etc. - we need to restrict the political menu to only the right choices.

And use the states' monopoly on violence to enforce these choices.

I have some very bad news for you: there are lots of people actively trying to work to bring those back on the menu. It's almost impossible to put things "beyond politics" so long as someone wants to bring them back.

Once some things are off the menu, people need to work really hard to change things. And, more importantly, violence can be used against those people - I mean throw-them-in-prison type of violence, not more. Just like with freedom - in order to preserve it, you need to, "paradoxically", shut some toxic persons' mouths forcefully (eg. "hate speech").

Yeah, sure, you can philosophise in the most general terms but that's not how you get people and companies stop doing wrong things. You get them when the people/entities who want to re-bring the despicable things back into discussion can be fined / closed / put-in-prison etc.

I don't argue for eco-fascism. But with some things we need to be ruthless, especially in order to be able to carry on our peaceful, understanding and democratic discussions concerning all the other things!

Good luck convincing China to impose a carbon tax.

Given trade imbalance you could impose carbon tax on Chinese imports.

China has piloted a number of carbon pricing schemes since 2013. It is introducing a nationwide scheme this year. https://www.reuters.com/article/climate-change-china-idUSL3N...

You could but they already planning for a greener future. CO2 is the least of the problems with burning anything (including coal in power plants).

https://www.world-nuclear.org/information-library/current-an...

Given the extremely uneven distribution of money I suspect that you'd reach "couldn't afford exhaling" levels at one end before making anything resembling a dent at the other. I'm not against a carbon tax, far from it, but it's a difficult problem.

The most direct approach would be to levy the tax at the time buried carbon is taken out of its geological grave, but good luck enforcing that globally. The most realistic approach (still a total sci-fi fantasy, with plenty of room for a dystopian touch) would be a fundamental removal of resource extraction sovereignty, implemented through a combination of military force and buying out whoever is currently in charge of representing that sovereignty.

We need to treat climate change like the existential crisis that it is, and start spending like we're at war. If we can drop 2000 billion dollars on war in Iraq, why can we not do the same for something actually worthwhile like ensuring that our children and grandchildren inherit a livable planet?

We can. However that would fundamentally shift the economy off fossil fuels which is one of the largest lobbying groups in Washington and specifically the GOP.

Judging from the tone and rhetoric of the so-called "left" in the US Democratic party, it isn't limited to the GOP by any means. Watching a few minutes (all I could stand) of the South Carolina debate last night was depressing.

History will not look kindly on this epoch.

It's not an existential crisis. That's not what the science says. There's no evidence that climate change will make humans extinct or end civilization. If that's not what you mean by existential crisis, then don't use that word because that's what it means.

There’s plenty of evidence that a whole lot of other plants and animals will cease to exist, though.

That's just being pedantic and obviously not what the GP's post means. If it were, then walking in the garden is an existential crisis because you're bound to step on a bug and that individual will cease to exist.

It's anticipated that at least millions, more likely hundreds of millions of humans will die to the consequences of climate change including effects of extreme weather, flooding and (especially) famine. This won't extinct all of humanity but can be expected to severely impact civilization(s), with a chance of this impact being fatal to individual cultures.

For a prospectus of what could happen, I point to the large-scale devastation of (ancient) civilization attributed to the Sea Peoples (https://www.history.com/news/who-were-the-sea-peoples). They're believed to have toppled the Hittite Empire and severely weakened the Egyptian one. "some historians believe they had been displaced from their homeland by famine or natural disasters." -- the parallels to the anticipated effects of climate change should be clear.

Large-scale political unrest, very possibly including a WW3, is something I feel justified in considering "an existential crisis." Your mileage may vary.

100's of millions is not necessarily an existential crisis because it already happened in the 1900's due to war, disease, and famine. Even if that absolute scale of deaths happens again because of climate change, it will be proportionally smaller due to the global population being an order of magnitude larger.

Do you have a reference to that prediction of it probably killing 100's of millions of people? On it's own, it doesn't really mean much because what time scale and what's the no-climate-change number to compare to?

Famine, meteorites, large scale war, atomic bombs, infectious disease, the plague - all survivable by society at large. With your definition almost nothing qualifies as existential crisis.

As you write, plants can do this quite efficiently via photosynthesis. So there is at least one working example where CO2 capture is resource-efficient (even solar-powered). From photosynthesis we get sugar. From sugar we can get to raw (solid) carbon for long-term storage.

Forests are not the only option. Imagine large installations with tanks of algae under a white canopy. I imagine the economies of scale are huge once this is ramped up to industrial levels.

The question is who will pay for it. Nobody wants to indirectly subsidize coal plants on another contintent.

The mechanisms for us (people everywhere) to begin paying for it is crucial, as there are a number of technologies on the cusp of being useful for tackling this problem, however they are not cheap. Cheap solutions to CO2 are rare and tend to only apply to point sources at best.

Large scale solutions that help mitigate the existing CO2 are going to require some significant capital and operational expenditure.

The cheapest large scale solution actually requires less money, and more legal / willpower. But I’d argue it’s also harder to measure concrete impact and “monetise” oceanic surface iron enrichment. It’s harder to convince people to pay for estimated results even ones based on measurement and science, than results containing physical outputs, like actual solid/liquid/gaseous CO2.

AFAIK tree sequestration is marginal compared to the amount of co2 to be captured. Also, trees rot, and the decomposition process reverts a chunk of the process (releases co2)

"a worldwide planting programme could remove two-thirds of all the emissions from human activities that remain in the atmosphere today" https://www.theguardian.com/environment/2019/jul/04/planting...

> AFAIK tree sequestration is marginal compared to the amount of co2 to be captured

Nope. Tree sequestration is extremely effective on a global scale. That's why it's so important that we prevent deforestation.

"Intact forests and those re-growing after disturbance (like harvesting or windthrow) sequestered around 4 billion tonnes of carbon per year over the measurement period — equivalent to almost 60% of emissions from fossil fuel burning and cement production combined."

http://theconversation.com/explainer-how-much-carbon-can-the...

Well, the study considers already existing forests. Is it feasible to eg. increase global forestation by 100% to offset 60% of emissions? Not sure. Also, it considers a limited timespan. While it is not that relevant for undisturbed forests that usually have a stable ecosystem (trees born and die gradually), it may be an issue with disturbed ones; trees will tend to have about the same age and the same duration; this will cause release spikes related to decomposition. Also, "planting trees" usually is a placeholder response that largely ignores the impact of monocultures in the soil, subterranean water reservations and propagation of forest fires, plus the fact that co2 tends to concentrate higher in the atmosphere, way above the average tree line.

In summary: its not as bad as I thought when I wrote the previous reply, sure. But it is still far from feasible.

> plus the fact that co2 tends to concentrate higher in the atmosphere, way above the average tree line

I looked this up and seems it's the opposite. I'd politely suggest you check your assumptions are correct.

https://www.quora.com/Is-there-less-carbon-dioxide-at-higher...

https://667-per-cm.net/2015/08/04/atmospheric-concentration-...

The efficiency of photosynthesis isn't all that great.

There's a reason energy based on organic matter has gotten a bad reputation. It's just not a very efficient way of getting energy from the sun compared to e.g. solar.

The calculation for carbon storage will be a bit different, but not by that much.

Photosynthesis manages to convert about 1% of the sunlight into chemical energy. I wouldn't call that efficient. The big benefit of plants is of course that they're relatively low maintenance. You still need to cut them down and turn them into charcoal if you want to capture that carbon for good.

Now look at the gigatons of coal we already dug out of the soil and burnt. That's a lot of forests you need to plant, cut down, and turn into charcoal. It might be doable, but it certainly won't be cheap or easy.

(I wrote the post) This is good feedback that this is buried in the appendix -- I pulled that section up and made it inline with the flow of the post. Does that help?

Section "How to take CO2 out of the sky"

> Briefly: there are plant-based, mineral-based, and chemical options.

Where are cryocooling-based options?

I'm not sure what this is? You might be thinking of solar radiation management or other "geoengineering" techniques to try to make the earth shiner and reflect more sunlight, making us cooler at a constant CO2 concentration. Theres a ton of interesting topics within that to write about, I mention it briefly as "things I didn't include"

having not read the article (yet), i the OP is referring to “cooling down air until it liquifies then using fractional distillation to pull out the CO2”?

You don't want to do unnecessary transformations, to preserve as much energy as possible (so the turbine, which is needed for cooling, should work on small pressure difference). So, no air liquification - just let CO2 separate and send cleaned air back to the heat exchanger.

> to preserve as much energy as possible

Aren't there plenty of places where energy is so plentiful that you don't need to care that much?

Not really?

No, the idea is something similar to this - https://sesinnovation.com/ .

You carefully compress incoming air. Separate water vapors (and liquids, and hopefully not solids) from it. Cool this air in thermal exchanger - at this point CO2 falls off. Then you pass that air through turbo detander, which returns you some energy, and get a pre-liquified air, which pass to the thermal exchanger. Clean air of normal temperature is released to atmosphere.

You have to compress the air - but you also cool air, so compression is easier, and you also get some energy from the turbine where you decrease the pressure. Subject to optimizations. How much energy will you need?

Ah, thanks! I haven't seen this before. Will look into it.

> How much energy will you need?

A lot.

Air compression is not cheap, energetically. Chilling is also energetically expensive. You'll need to do both. This would be pretty much the "brute force" method, like O(n!) in software engineering. The concept would be to bring half the planet's atmosphere down to near its liquid temperature. Currently in most US homes, Air Conditioning (air cooling) contributes the majority of each home's energy use. This would be much greater than that, it requires chilling air to -140 °C to get CO2 to "drop out".

In contrast, seeding the ocean with iron would be fairly close to O(1). However, potential side effects of this process concern some scientists greatly. Googling 'Russ George' may provide more insight.

Side note: The press material for sesinnovation also says the outlet stream is nearly 100% nitrogen...that means they're using a stream which already has oxygen removed from it (likely because the air was just used for combusting fuels). Air is roughly 21% oxygen so you can't take air, only remove CO2, and get 100% nitrogen out. Generally these "Carbon Capture" technologies only work on feed streams with high CO2. So hey're placed at industrial outlets, where fuel/coal is being burned. These streams can be > 10% CO2. Often they don't work as well, or at all, on diffuse streams like 0.04% atmospheric CO2. The technical reasons why this is the case deal with "partial pressures" as well as general entropy.

> Air compression is not cheap, energetically. Chilling is also energetically expensive. You'll need to do both.

Not exactly.

The idea is that you don't just compress air - and let the heated compressed air cool to the atmosphere in order to then expand it so it would cool some more, and then just release whatever's left back to the atmosphere. No, you use those leftovers to cool the incoming air - so you need to compress air spending less energy - and you also get the expanding air to help you to compress incoming air.

The principal point where you have non-reversibility is that extra cooling - making compressed cold air to do the work - which you need to reach necessary temperature. And you only need that temperature to separate gases; after that you can use the cold products to help with compression.

So - without colorful metaphors - I'd like to figure out how much energy will you need.

I see the approach of SES with flue gases. I'm not sure how it will look like with regular air.

Yes, it does.

GREAT work.

Two (small) comments: - Perhaps the review of the re-forestation option could mention that this has a number of positive side effects (outside of carbon capture), for example on rainfall and wildlife.

- as there is a time constraint on co2 capture (e.g. 2050), and as the various co2 capture solutions are not all at the same stage of maturity, it could be useful to have a table/chart that summarizes which co2 capture options are deployable now vs. at some stage in the future

If you can capture the CO2 using transient power from wind or solar and use it to make a synthetic fuel, then you have a potentially viable option. Carbon Engineering in Squamish BC is doing this for $100 a tonne. Their synthetic fuel costs about $2/L to make - still too expensive, but not if the carbon price rises to about $100/T.

That’s way better than I thought it would be, aren’t some European countries fairly close to that mark?

This morning I paid about 1.68 euro/L as a consumer for plain gas/petrol here in the Netherlands.

The World Bank has compiled a database that you can query [1]. Sweden's carbon tax is USD $121, the highest in the world. Next best is Switzerland and Lichtenstein tied at $97, followed by Finland at $68.

Sweden's tax covers 40% of emissions from that country. Finland covers 36%. Switzerland covers 33%.

British Columbia's tax is lower, but it covers 70% of carbon emissions - a very broad-based tax. It will be USD $38 in 2021.

Personally, I think it's better for governments to focus on total coverage rather than the price. The more broad-based the tax is, the more efficient it is in shaping the economic development of the region. You don't want carbon "leaking" into sectors where it's cheap to pollute - that's inefficient. Far better to have all sectors equally incentivized to decarbonize.

[1] https://carbonpricingdashboard.worldbank.org/map_data

There is exactly one technology that can affordably bind CO2 at scale and that is plants. We are just very, very far from measures to keep that carbon from reescaping back. And rightfully so, because burning carbon freshly captured by plants is infinitely less bad than burning carbon that has been nicely stashed away for geological timespans (the carbon captured by contemporary plants would recycle back into the air anyways, energy use is merely a minor latency reduction). Sequestration at burn site might be an improvement on that, but that still doesn't answer the question of where to put it. Geologically buried hydrocarbons are really hard to beat at keeping carbon out of the atmosphere, that is unless there happens an industrialization event...

> There is no magic powder we can mix that'll cause CO2 to precipitate out of the atmosphere and fall to the ground like snow; it's a grueling energy intensive process to filter that out of the air around us.

Why not to cool down air so that CO2 would fall off? Cooled air can be used for pre-cooling incoming "dirty" air stream?

I had the same thought as well. It's an option, but the energy required to cool air to the precipitation point of CO2 (-79C) is pretty large, and the cooling process itself will produce greenhouse gas, so you end up with a pretty small return.

How do you calculate how much energy is required?

You would use cooled separated products to pre-cool incoming stream of "dirty" air. CO2, having low concentration, won't fall off at -79C (or we'd have that effect in Antarctica today), but if you go to ~-140C, you'll have some results.

Why cooling process will produce greenhouse gas? You'd use energy from "green" sources to compensate for required expenses.

> You’d use energy from “green” sources…

This isn’t something you can just assert as if by magic.

By using this kind of technology, you increase the total power requirements of our civilization. That power has to come from somewhere. If you earmark green energy sources for it, something else will need to use a dirty energy source.

This remains true as long as green energy production falls short of planetary demand (modulo carbon taxes/credits/caps which change the math here a bit depending on specifics). The leftover slack will be met by burning fossil fuels.

That's why I'm trying to estimate energy requirements of such a process. Somebody experienced with gas liquification could perhaps help.

You have to build these cleaning devices, and you'll need to build energy sources for them. We do have both power and increase in power supply with time; the question is specific numbers, which I'm trying to estimate.

But that’s the problem. When you say you could just build new clean energy sources for these things, you’d be better off by only doing that.

Every kWh of clean energy produced is far more effective at addressing climate change when it replaces a kWh generated by fossil fuel than it is trying to remove the carbon from that fossil fuel after the fact.

> Every kWh of clean energy produced is far more effective at addressing climate change when it replaces a kWh generated by fossil fuel than it is trying to remove the carbon from that fossil fuel after the fact.

True. However, here are two significant, in my opinion, notes.

1) We already have a lot of CO2 in the air. We'd better get it out, and sooner.

2) We're proving every day our limited abilities in organizing focused efforts in fighting climate crisis, particularly by a single specific way. So, if we could reduce organizational problems by choosing a solution which has less of them, we could win in practice.

It's rather obvious that it's better not to get CO2 into the air in the first place. Looks like we can't avoid doing that now. So other options become interesting.

-140C only works for CO2-rich streams (> 10%). As the partial pressure of CO2 decreases, you'll need to get asymptotically closer to the melting point of oxygen/nitrogen. You'll also need to increase the pressure, but again that only gets you reasonable temperature gains if the partial pressure of CO2 is >>0mmHg. Currently it is 0.3mmHg @ 400ppm. In short, this is not a viable method for removing CO2 from the atmosphere.

For a fun take on some of this see https://wattsupwiththat.com/2009/06/13/results-lab-experimen...

> -140C only works for CO2-rich streams (> 10%).

The chart in the article by the link suggests -140C would work for pressure of 0,0004 atm.

How did you get that number - >10% ?

Antartica is -56C right now. Another 23C should be manageable. This doesn’t have to be done in the tropics.

https://wattsupwiththat.com/2009/06/13/results-lab-experimen...

I made some slightly more detailed posts elsewhere but this article addresses your point directly. Essentially, this is not a viable method for removing CO2 from the sky, because there's so little CO2 in the sky that it changes all the basic physics assumptions.

This is actually relatively basic undergraduate level napkin math from a chemical engineering perspective, but outside of that discipline most people understandably don't have experience with estimating physical states of mixed gases.

Plants can do it cheaply, why don't we just let them?

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