The impact of direct air carbon capture on climate change | Hacker News Reader

The impact of direct air carbon capture on climate change

cognitivemedium.com

152 points_Microft140 comments

I'm not sure if this article hammers home the key point: extracting carbon from the air always takes more energy that was gained by burning the fossil fuel to make that carbon. This is inevitable due to the entropy cost of de-mixing CO2 from the air, and from the limited efficiencies of thermal power generation (~33-40% for a coal power plant, perhaps 20% in an internal combustion engine), and limited efficiency of the carbon capture technology.

So it only makes sense to spend energy on sucking CO2 out of the atmosphere, once you've already de-carbonised everything which you possibly can.

Maybe it has a future role (>2050? >2100?) to start using excess low-carbon energy to take CO2 levels back to their pre-industrial level, or to constantly offset hard-to-decarbonise technologies such as air travel.

> Maybe it has a future role (>2050? >2100?)

It absolutely must, or else it's basically already too late: https://www.vox.com/2016/10/4/13118594/2-degrees-no-more-fos...

> This image should terrify you. It should be on billboards.

> As you can see, in either scenario, global emissions must peak and begin declining immediately. For a medium chance to avoid 1.5 degrees, the world has to zero out net carbon emissions by 2050 or so — for a good chance of avoiding 2 degrees, by around 2065.

> After that, emissions have to go negative. Humanity has to start burying a lot more carbon than it throws up into the atmosphere.... Thus far, most demonstration plants of any size attaching CCS to fossil fuel facilities have been over-budget disasters. What if we can’t rely on it? What if it never pans out?

> If we really want to avoid 1.5 degrees, and we can’t rely on large-scale carbon sequestration, then the global community has to zero out its carbon emissions by 2026.

(emphasis mine)

My dad sees articles like this and he'll just say that maybe the damage needed to prevent warming is worse than the damage that will be done by the warming.

The cost to ordinary people would actually be relatively minor. You buy an electric car instead of a gasoline one. The average new car price in the US is ~$36,000. A new Nissan Leaf starts below $30,000, Model 3 only a little more than that. Replace coal with alternatives. We can do at least as well as nuclear, which is barely any more expensive than coal has been. Best case is that storage gets a lot cheaper than it is and then the price of electricity goes down from the historical norm.

Capture could cost as little as zero. Renewables inherently have to build over-capacity to compensate for intermittency, but that means there are days when they generate more power than there is demand. Use the rest for carbon capture and it's free.

The real "cost" to fixing it, and the big lobby against it, is that the oil and coal companies would take a nosedive. Literally trillions of dollars in lost revenue. It moves to alternatives. It isn't economic damage, it's displacement. But the specific people who own the oil and coal reserves stand to lose their shirts, and these are not people lacking in political influence. Everything you hear about the high cost -- it's only really a cost to them. To you it's just an upgrade to electric.

But we still have to actually do it. A carbon tax so that people do all buy electric cars and stop burning coal. It's a thing we can do but not a thing we have done yet.

The point of the Vox article is that just switching from gas to electric isn't going to be enough. The argument is that without large-scale carbon capture we will not hit the 1.5C goal.

Large-scale carbon capture is still untested. Reforestation is the only well established large-scale carbon capture but is very land intensive.

Spekboom (Portulacaria afra) is said to sequester up 10 times the carbon of a rain forest by area.

This is largely due to a special mechanism that continues photosynthesis at night.

And it grows best in semi-arid regions.

Where people don't live or farm.

interesting, the Portulaca Oleracea is edible, I wonder if it has the same property and whether we should plant a ton of it.

Wikipedia sais it does:

"P. oleracea is one of very few plants able to utilize both CAM and C4 photosynthesis pathways, for a long time believed to be incompatible with each other despite biochemical similarities. P. oleracea will switch from C4 to CAM pathways during times of drought and there is transcription regulation and physiological evidence for C4-CAM hybrid photosynthesis during mild drought."

Your dad is right.

If the wild alarmists are correct that the only way to prevent destructive climate change is to immediately dismantle all human economies and return to a life more like that of the middle ages, maybe we should just forget the whole thing and invest in sunscreen.

>It absolutely must, or else it's basically already too late:

This is solution bias though. "We need it to work therefore it will"

The universe doesn't owe us anything. DAC has been added to these scenarios as a sort of balancing element to make the models add up but that has no bearing on whether DAC is possible at scale.

> it only makes sense to spend energy on sucking CO2 out of the atmosphere, once you've already de-carbonised everything which you possibly can.

Except possibly when energy prices are negative due to wind and solar intermittency - although that is also a signal that you need more storage in the grid, additional storage may not be economic for some reason.

Some captured CO2 might be used with cheap electricity to make carbon neutral fuel - which is of course a form of stored energy itself. A pilot project in Germany is doing this[1]:

> The green hydrogen will be combined with carbon dioxide captured from the cement plant to produce synthetic methanol, which would then be refined into carbon-neutral synthetic kerosene (ie, aviation fuel), for use at the nearby Hamburg airport. The airport is hoping that 5% of all fuel used there will be carbon-neutral by 2025.

[1] https://www.rechargenews.com/transition/offshore-wind-to-pow...

Honestly, I suspect that long-term storage will be inefficient for a long time.

For example, batteries exceed 90% efficiency for storage, but they are only cost effective for day-to-day storage. (Charge when the sun is out, discharge at night.)

In contrast, charge during long summer days, and discharge during shorter winter days will probably be lower efficiency at first. For example, generating hydrogen by electrolysis is about 75% efficient (https://en.wikipedia.org/wiki/Hydrogen_production#Electrolys...), and then pressurizing it will also consume energy.

This means it may be more cost efficient to extract CO2 from the atmosphere as "storage" and then burn natural gas... At least until we find a better way to store energy than hydrogen!

Cheaper if you are planting trees/plants or algea for say diesel production

Exactly!

But even so, meaningful collective global action is seeming less and less likely. So I can imagine that some with surplus greenhouse-neutral energy could capture CO2 to offset emissions by others.

You're assuming perfect elasticity of energy supply which there absolutely is not.

There is quite a mismatch between solar and wind production and electricity usage patters which is why storage is such a hot issue. Already there have been brief periods where 100% of energy production in a few regions was renewable. Those will certainly only grow in frequency and duration.

You don't start working on this technology when everything else is ready for it, you start as quickly as possible so the tech is ready when the rest of the world is ready for it.

> extracting carbon from the air always takes more energy that was gained by burning the fossil fuel to make that carbon.

This sounds true at first glance, but is it always? It seems like it's obviously true for simple reactions like burning methane and converting it back to methane since the energy you get from it is equal to or less than the energy required to turn it back into methane, but might there be some other chemical reactions where you can turn it into something less energetic than the molecule it came from?

Yes, there are rocks that will "extract" carbon from the air on their own if crushed into sand. They are even reasonably abundant, so it seems like they would be a feasible tool for carbon capture. It would basically amount to speeding up the natural carbon cycle, which normally keeps carbon dioxide concentrations relatively stable in the very long run.

The rocks are called olivine, and are very common. They indeed look very promising for CO2 absorption.

https://www.betterworldsolutions.eu/is-olivine-the-solution-...

It's not true at all. Turning the CO2 back into fuel would take as much energy as burning it released, but simply capturing the CO2 from the air need not.

There is a well known relationship summarized in the Sherwood plot.

https://www.pnas.org/content/pnas/108/51/20428/F1.large.jpg

Your basic intuition is correct in that the more dilute something is, the more costly it is to extract/purify it.

A properly engineered DAC system will be much less expensive than the number they found.

https://www.cell.com/joule/fulltext/S2542-4351(18)30225-3

That paper only looks at the energy/cost balance of the plant, not the chemical feedstock. Production of that feedstock is energy intensive, the recycling is not 100% efficient per the paper (i.e. it will constantly have to be replenished), and the industrial infrastructure to produce those chemicals at the necessary scale to materially reduce atmospheric carbon simply doesn't exist.

Any cost model for large-scale DAC must include the capital and operational costs of new feedstock factories to keep the DAC supplied at scale. It won't be cheap. The pilots can ignore this because they rely on the excess capacity of existing industrial infrastructure.

Not at all -- the cost of makeup streams for chemicals are included in the O&M cost (table 2).

Not objectively true, as plants and even rocks grab CO2 out of the air pretty efficiently. From a thermodynamics standpoint, you can burn fossil fuels at 50-70% efficient (50% is not uncommon), and the actual theoretical lower bound of CO2 direct air capture is ~20 kJ/mol,[0] or about 1.7MJ/kg of elemental carbon, compared to 33MJ/kg for burning elemental carbon (same as high grade coal).

(Burning methane is even better as it releases much more energy per unit CO2 i.e. ~860kJ-per-mole-of-CO2 vs anthracite's ~400kJ.)

And as others have said, rocks actually are able to exothermally absorb CO2 permanently. It's possible to speed this up by grinding rocks to a powder, placing in water with a catalyst.

...none of this is to say I support relying on direct air capture and just go ahead and burn fossil fuels. We need to keep that in the ground and transfer the whole civilization to non-fossil fuels, otherwise if some populist jerks wer elected, they could just order the expensive direct air capture program to stop (can't do that if you're already transitioned to clean energy and all your wellheads and drills and coal mining equipment are rusted or melted down for scrap).

Source: [0] https://www.researchgate.net/publication/257177020_The_therm...

> Burning methane is even better

Actually, burning is probably the best way to deal with any excess methane. Methane has a significantly higher warming potential than CO2 does. So if there's any methane we're venting into the atmosphere, we should burn it to convert it into CO2. Bonus points if you can use the generated energy to capture the CO2 as well.

From what I can recall, landfills produce more methane than any other process. How about we build a carbon capture next to every landfill, divert the methane and burn it to run the DAC?

Landfills do collect and burn methane. Those pipe like structures you see sticking out of a completed landfill are part of the process.

https://archive.epa.gov/climatechange/kids/solutions/technol...

TIL. Now we just need to execute the second part of his plan to capture the carbon from the energy produced

Or capture the methane, upgrade it and run generators/cars/busses of it. It's existing tech

https://en.wikipedia.org/wiki/Biogas

This scheme is used in real life in Czech Republic

Why bother for landfills?

If the landfill can generate electricity that would otherwise be generated, it will convert the CH4 more efficiently than a bus and you don't expand energy upgrading it.

You can power the bus with the already high quality CH4 you extracted from the ground that you would have otherwise burned in to generate the electricity.

Buses have different power requirements than cars; they need a lot more range because they run throughout the day.

I was reading somewhere that in buses in cold climates, heating is actually what eats up all the energy in an electric bus. ICE buses just use the waste heat from a combustion engine.

Or you just burn the trash directly.

This.

Releasing CO2 and NOx.

From what I can see, yes, methane is abstractly a worse greenhouse gas. However its absorption band is within that of water vapor. Since water vapor is plentiful around the blue marble, methane doesn’t really cause any problems.

This is incorrect, it’s well established that methane is a more potent GHG. See the reply here: https://news.ycombinator.com/item?id=21485738

What’s not taken into conservation with that comment is that methane at those altitudes does not impact much because the energy is radiate back to space.

You have doubled down on a casual assertion ("methane is not a significant greenhouse gas") because you don't understand radiative transfer in the upper atmosphere. It's OK, radiative transfer is complex. Your options are to accept this consensus, or do a lot more study than you have.

With solar prices hitting negative rates for some periods in a day capturing carbon and converting into burnable fuel will probably start making sense in the next few years.

Think we could frack with corn syrup? Inject that carbon back into the ground?

Not corn syrup. That takes way too much CO2 and water to produce. Not even corn itself I suspect.

It's partly the problem alleged marshland and forest sequestration schemes face, alongside the assumption they're going to grow well in the changed climate.

(Limited experimental data suggests this works up to some 500 ppm as long as there's excess water and minerals. If the conditions are bad you lose capture potential. And what do you do with the methane releases from these systems? It's much more diffuse than from landfills.)

As long as there's still fossil fuel powered transportation, it would make more sense to use that excess power to charge batteries, since that converts electricity into motion more efficiently than taking the detour through synthetic burnable fuel.

Destroying fossil fuel powered transportation then replacing them with electric would actually produce more carbon. All new transportation should be electric but the already running transportation if can be run on captured carbon would result net carbon decrease.

'Populist jerks' meaning people who are democratic?

I think that you're thinking of the cost of turning the CO2 (and water) back into fuel, which can be argued along thermodynamic and irreversibility lines to show that unscrambling that egg always requires more energy than obtained from combusting. However, I don't think there is a similar thermodynamic argument on the energy costs of mere capture. It's not a priori impossible that a fractional distillation column with a clever configuration of heat exchangers, for example, could capture all the carbon released by the fossil-fueled plant that powered the column in the first place (and more).

Arguing that mere capture would require more energy than is released would be akin to arguing that cleaning the fireplace would require more energy than was released by the fire, on the mistaken grounds that ash removal took as much energy as regrowing the wood that was burned. Both the ash and the CO2 are in a lower energy state, so there's thermodynamic room to maneuver.

> So it only makes sense to spend energy on sucking CO2 out of the atmosphere, once you've already de-carbonised everything which you possibly can.

Not necessarily. I'm thinking of cold polar winters with no wind and no sun, people burning fossil fuels to stay warm. Meanwhile in deserts solar panels powering carbon capture machines to reverse the greenhouse gases back again. Maybe even the carbon capture creates synthetic coal which can be shipped to the cold regions.

Yeah, you can basically use the atmosphere as a chemical battery.

Also, a better example than heating homes with coal is aircraft. Long distance air plane travel is so far only doable via fossil fuels due to their energy density. And while you can run a electric line to a house and heat it with electricity, this is not possible for long range aircraft.

So the idea is you use hydrocarbons to run aircraft and then capture the CO2 produced and turn it into more hydrocarbons to run your airplanes. This of course requires clean energy source to work, but is perfectly doable. :)

Here's my vote for planting more trees and especially letting older forests grow and thrive.

> So it only makes sense to spend energy on sucking CO2 out of the atmosphere, once you've already de-carbonised everything which you possibly can.

The actual point is much narrower than that. It doesn't make sense to spend energy on sucking CO2 out of the atmosphere, unless:

1) You use an energy source that produces less carbon than the amount you're taking out; and

2) You're not displacing demand that must then be satisfied by an energy source that produces more CO2 than you're taking out.

In other words, it doesn't make sense to burn coal to capture CO2, but it doesn't also make sense to use nuclear power to capture CO2 if that means that some other demand will have to be satisfied with coal instead of nuclear power.

But it goes too far to say that the above criteria only hold "once you've already de-carbonised everything which you possibly can."

For example, if you build a surplus of renewable power (which we have in some cases, where instantaneous generation exceeds what the grid can use at that moment), it makes sense to use that to suck out CO2, even if, for example, you haven't replaced ICE vehicles with electric vehicles.

As a practical matter, we need carbon capture much earlier than 2050 or 2100 to keep below 1.5C or 2C. For example, China plans to ban EVs by 2040: https://www.forbes.com/sites/energyinnovation/2018/05/30/chi.... Even if they stick to that plan, they will put out hundreds of millions of ICE vehicles on the road until that time. Even by 2025, official goals will leave 60% of new Chinese vehicles as ICE.

If you look at the mitigation pathways for 1.5C, they require the whole world hitting net zero emissions by 2050 and often going net negative soon after that: https://www.ipcc.ch/site/assets/uploads/sites/2/2019/05/SR15...

That will not happen. Indians and Chinese aren't going to stop building high-speed rail (which puts out a huge amount of carbon due to the concrete used), skyscrapers, etc. Nigeria's population is going to balloon to 400 million. We're going to need to build a large number of nukes and offshore wind to capture all that new CO2.

> if you build a surplus of renewable power … it makes sense to use that to suck out CO2

Although it's unclear that resources to build carbon capture infrastructure wouldn't be better spent on (say) energy storage.

> China plans to ban EVs by 2040

I think they plan to require EVs by 2040...

Sure, but does it matter? If we decide that's a better use for the energy, then we spend it that way. And can't we capture any carbon generated through that process instead of releasing it as further emissions?

Not a word about the most effective, cheapest strategy: reduce emissions?

Most Americans could reduce their emissions by 75% while improving their standard of living by buying less junk, wearing a sweater in the winter, eating more healthy, and other low hanging fruit that will make them more active, healthy, connected to their communities, etc.

Reduce consumption by half. There, I just saved us $300 million.

How is reduction not our top priority and activity??

Because it’s also the least effective strategy. The reality is getting nearly everyone to change their behavior just isn’t gonna happen.

Even if everyone in America went vegan, showered once a day and biked everywhere wouldn’t change much with impoverished countries coming out of the third world. If you can’t get them to change then it doesn’t really matter.

Big problems require big, comprehensive solutions. For that you need government to function effectively regulate, make climate bills countries can stick to.

We already have the tools we need to get climate change turned around but we don’t have the political will.

Wait. Does the average American shower more than once daily? Is water consumption/heating for showering even a measurable component of GHG emissions?

Not at all, we need to cut back on emissions everywhere. That also applies to Americans, who emit 3-4 times more per capita than what is sustainable.

> Even if everyone in America went vegan

> we don’t have the political will.

Something tells me that achieving the first would more easily lead to the second. For a politician whose constituency is mostly vegans, their work on climate change will determine whether they keep their seat. If their constituents are pickup-truck-driving, McMansion-owning suburbanites, it's not going to be a priority.

I recognize that getting everyone to go vegan isn't possible or maybe even desirable. But let's not pretend that willing personal sacrifice isn't at least part of the solution.

Don't forget, the military is the biggest emitter on the planet. We should rapidly downsize all militaries immediately.

Wearing a sweater instead of heating my home improves my standard of living? What kind of bizarre doublespeak is this?

We’re already over the safe threshold. And as a practical matter we won’t be at zero tomorrow, so we’re going to go even further past it.

We’ll need to do both: reduce emissions to zero, and then suck more out.

Jimmy Carter tried this and got vilified for it. You don't get into positions of power by telling Americans how to do more with less. You get there by telling Americans "More, more, always more, more for you. More, more, more. I promise."

Personal choice is a very small aspect here. Americans can not choose to have lower carbon cement, steel, manufacturing, shipping, airliners, etc. Yes, we can do a lot by not flying ourselves, buying less items, eating less meat, but at the end of the day: MOST of our solutions are going to come from corporations and government.

Exactly. An individual can live their entire life taking short showers, abstaining from meat, and generally living like it's the 15th century and all of their efforts are erased when the Keystone XL pipeline sprays 300,000 gallons of oil over North Dakota.

https://time.com/5731775/north-dakota-keystone-pipeline-spil...

Oil pipeline spills make me furious, but they don't have the exact same effects as carbon emissions. It's not a useful comparison.

I would have liked to see https://projectvesta.org/ commented on in the article.

They claim to be able to sequester carbon by scattering olivine rock in an active and warm coast. The cost of the rock is $25/ton now, with the prospect of $10/ton in the future. Plus whatever it costs to break it up and scatter it.

That makes it at an interesting price point if it works as advertised.

Even more interesting to me is that the absorption happens in the water. Meaning that it can counteract ocean acidification near the coral reefs that are the most vulnerable.

I would aggressively vote and promote a us presidential candidate who stated they would negotiate an arrangement to do this for financial compensation on coastal equator countries- and failing that, a hostile military invasion to force it upon them.

Probably no need for the latter, but having it on the table makes the former easier to negotiate.

This process could release deadly nickel into the water. It probably would harm the coral reefs more than help... but I really feel like much of the ocean is pretty f*ed longer term anyway. Also the countries most poised to do this are the ones most at risk from climate change both in terms of heat, tidal forces, and horrible storms.

I feel it would be a powerful platform. It makes an optimistic message out of an otherwise negative concept- and it makes America the hero saving the world. Who wouldn’t vote for that?

> and failing that, a hostile military invasion to force it upon them.

Eco-fascism! I mean, once you're willing to murder people to reduce carbon emissions, there are simpler ways to do it. But make sure you've got suitable carbon offsets for the invasion and the crematoriums.

> optimistic message

"Good news: America is going to improve the world at gunpoint again!"

I know people won’t like it, but the alternative is a Mad Max world. We’re told the whole planet will be either an ocean or a desert unless we return to the Stone Age. Therefore we need to follow the Georgia monument and reduce the global population to 500 million. Anything less than the total dissolution of human rights in the name of environmental protection is a death sentence anyways. At least we can use the benevolence of democracy to pick winners and losers.

> Eco-fascism! I mean, once you're willing to murder people to reduce carbon emissions, there are simpler ways to do it. But make sure you've got suitable carbon offsets for the invasion and the crematoriums.

I think this disingenuous. I am fully aware this is not a virtuous path (noting again that I think it could be done easily and more preferably with economic solutions). From a utilitarian perspective it is massively moral. It would likely minimize suffering of the target populations too.

Yes yes killing billions would reduce carbon emissions but that’s clearly not a good solution and not comparable. Using military might to force coastal equator nations to comply with what is plausibly our only chance at saving the planet is very low on the scale of shit countries have done for self betterment.

Crematoriums imply killing is a first order goal. Killing is a bad thing in the eyes of this plan that is trying to be minimized.

I believe this type of project is referred to as geo-engineering, which is a bit more controversial as it's typically assumed that the side effects are somewhat unknown.

They're targeting a pilot within the next 5 years on a single beach, which should help towards figuring what side effects exist.

They also note there exist naturally occurring green sand beaches (https://en.m.wikipedia.org/wiki/Papakolea_Beach), though those are tourist spots and probably haven't been deeply studied.

I would worry about nickel and chromium pollution.

Why is that? I couldn't find any reference to that on their homepage. Is it a byproduct of the process?

Olivine rock usually contains those elements.

And the scheme would involve many gigatons of olivine, so the release would be very large.

"mineral processing approach using carbon dioxide to promote mineral alterations that lead to improved extractability of nickel from olivine ((Mg,Fe)2SiO4)"

"main products of the carbonation reaction include quasi-amorphous colloidal silica, chromium-rich metallic particles, and ferro-magnesite ((Mg1−x,Fex)CO3)"

https://www.mdpi.com/2075-4701/5/3/1620/htm

If you're going to continue to burn fossil fuels, it seems better to burn it in a plant that inherently captures the carbon then trying to wrangle it back after it's release. The interesting part of the Allam cycle for power generation is that supercritical co2 is the working fluid for the turbine, and when you burn the fuel it increases the mass in the closed circuit. Both the size and the efficiency of the plant also purportedly improve with the Allam cycle too.

https://en.wikipedia.org/wiki/Allam_power_cycle

https://www.netpower.com/technology/

That would be true, if the power plant has high capacity factor, and if it stationary, and if it is located near a place where the CO2 can be sequestered.

But if you (say) have peaking turbines that are intended to take over when renewables or short term storage are not available, they may have very low capacity factor. It could be economical to have them release the CO2 into the atmosphere, then steadily scrub that CO2 back out again, especially if that scrubbing could be done in a location with extremely cheap solar energy (like, say, Chile).

I'm for pursuing both options really. There are likely solution areas where both would be a win. And we really know not enough about the end direct cost of either until sufficient numbers are built out - and we should build out both to at least 10x what the prototypes do. The real problems are governmental policy, and then financial policy to get the attention and scaling going on any of these solutions.

Michael Nielsen, the author, also wrote a multi-part intro to neural networks (http://neuralnetworksanddeeplearning.com) which really cleared up for me the inner-workings and mathematics of machine learning quickly but without skimping on details.

I'm very excited to read what he has to say here.

I've been interested in these types of technologies lateley.

>that many people are extremely pessimistic about climate change. They can’t imagine any solution – often, they become mesmerized by what appears to be an insoluble collective action problem – and fall into fatalistic despair.

More and more, I find this description matches my thoughts on climate change. I'm really beginning to think the problem might require building carbon capture solutions on a huge scale. We might have to engineer our way out, because it doesn't appear we are slowing down emissions fast enough.

We are geoengineering already, so we are going to have to deliberately geoengineer our way out of the problem.

>we are going to have to deliberately geoengineer our way out of the problem

Agreed, I'm really starting to think this will be the only way.

I'm totally with you. Reducing carbon intensity is possible (and almost easy) up to a point, but once you've converted 80-90% of the power grid to renewable sources and electrified most transportation there is still significant carbon emissions occurring for high value operations, like air transportation. Plus we still have to deal with the elevated levels we are at today.

Having viable large scale carbon capture technology, gives us another advantage though- It gives us a really solid economic foundation for pricing those remaining carbon emitting operations. Entities can just regulate or tax carbon emissions at that point, and let the market figure out what activities and operations are still worth emitting for.

Fast-growing trees, which are then burnt to charcoal (and some energy), which is then put in the soil as biochar. Could be very cheap/low-tech and at the same time improve soils.

Or, buried wholesale as part of a Hügelkultur.

yes this could be even cheaper, though I'm not sure if perhaps the co2 is released quicker as the trees decompose- charcoal can keep the carbon locked up for centuries.

Either way, these methods greatly improve the land-use efficiency of growing trees for carbon capture/storage, as it is stored in the soil over many years, not only in the living trees. "putting coal back in the ground" as it were.

Just plant trees. They're cheap, solar powered, and convert CO2 to building materials.

They use too much land.

That's why you cut them down and build stuff out of them!

But, yes, in time we can probably build something more efficient.

To be specific, arable land. Not all land is fertile. And as the old saying goes, they arent making any more :)

Then there is the time aspect. They dont grow as fast as one would like.

"The need for arable land to feed human populations and the needs of wildlife have been in tension for millennia. One can look to Easter Island to see what the end game of man's resource overexploitation can lead to. Currently more than 1.4 billion hectares of land have been committed to agriculture. As human populations swell, especially in lower latitudes, even more forests will be cut, surface water and aquifers tapped, fertilizers applied, and pesticides broadcasted—all of which threaten insects and other biodiversity either directly (e.g., land conversion and pesticide exposure) or indirectly (e.g., water use and nitrogen and phosphorus pollution). Savannahs, prairies, and grasslands, with their deep fertile soils, lend themselves to immediate use for crop and pasturelands, and as consequence are collectively among the most threatened biomes on the planet. The clearing of tropical forests for farming and pastureland is happening at alarming rates and will have especially grave consequences for insect species diversity"

https://www.sciencedirect.com/topics/earth-and-planetary-sci...

Start by protecting existing forests. We're still losing rainforests ever more rapidly.

Planting more trees will reduce pressure to cut down existing forests.

In the case of rain forests, they're usually not cleared for the wood, but to open up farmland.

Existing forests don't do much in terms of CO2 reduction.

Interesting side effect is it makes the planet warmer because trees are dark.

OK to shout Eureka when you figure this out:

I have a website where I explore the idea of "not emitting fossil fuel CO2." www.lowco2america.com

Instead of thinking in terms of "cost of extracting CO2" I have sort of stumbled on the idea of "recapitalizing America around social systems that do not emit CO2."

My scheme has a payment of $394 per metric ton of CO2 not emitted. The payment from govt. funds is a prompt no bank account required electronic transfer payment. What it can purchase is a continuing free share of the electricity generated by the workplace parking lot, or an electric car, where the car is free is provided the driver carries 2 or 3 workplace commute riders. The car runs with an average load of 1 driver and 2 or 3 riders. The payment can pay for other things or be redeemed for cash, optionally.

The ancient Chinese Tao Te Ching poem Verse 80 describes a happy society that might sound a little bit like an America that figures out how to live well with 2 mt per person CO2 emissions, maybe in 40 years?

I really like the way the author tries to ballpark orders of magnitude and compare against known-budgetary-things for frames of reference. That said, talk of 10/tonne is pure fantasy, the real band is between 100 and 1000, so the analysis here is a full decimal place naive (of course, IMHO).

Just to contribute, another americanized version of the numbers: $100/tonne of a carbon tax works out to about $0.87 per gallon of gasoline. So if you assume carbon engineerings pilot plant estimates turn out to be right but on the high-end, at $232/tonne that's an almost perfect $2/gallon.

Which raises an interesting point to ponder... if anyone were capable of extracting carbon from the atmosphere at under $200/tonne... then all the oil companies would almost instantly switch to only building those plants. Why fight for drilling rights and production share agreement terms when air is everywhere.

To rephrase this article: The impact of direct air carbon capture will require enormous input of energy or enormous tonnage of materials such as limestone.

Another approach to reducing the human contribution to atmospheric carbon dioxide is to have each person adopt a low CO2 emission life style.

Just like a massive carbon capture technology, enabling individuals to adopt a low CO2 emission lifestyle is not a free proposition. How much to pay an individual to implement a specific low CO2 life style? Gasoline (the high emission variety 19.6 lb per gallon) at $3.50 a gallon produces a metric ton of CO2 for $393.

More detail at:https://www.lowco2america.com/2018/10/gasoline-co2-in-air-wh...

It's really nice to even see this discussed, I've been really interested in this topic.

It's true, at some stage we're going to have to reduce the carbon we've already injected into the atmosphere, so why not get started now. It's amazing how little funding this has received.

I'd actually be interested in paying for this like any other utility, as electricity prices get cheaper from renewable energy, I'd be happy to pay a carbon capture bill to survive and breathe cleaner air. I'd also hope this would be a temporary thing as we completely transfer away from fossil fuels.

Pay to clean up some of my own mess,makes sense.

I'd like to know the land use requirements of direct air capture technology. Will it use enormous amounts of land? What is currently on that land? Will this entail scalability issues?

An estimate I've seen repeatedly is that they'll take about 1/1000 as much land area as the same carbon capture with trees.

Very well written and balanced article. Thanks for sharing these insights. Looking forward to another "tiny corner" of your explorations of these technologies!

It's not mine but if you're interested in more of the author, follow @michael_nielsen on Twitter.

Agriculture can do DAC:

https://terraton.indigoag.com/

Don't vehicles emit other greenhouse gases too? Or would the carbon cover the overwhelming majority of effect?

You can do it to the tune of $15/person/year: https://automicrofarm.com/blog/2019/03/solving-climate-chang...

Does direct air carbon capture at scale even exist? Is there plausible reason to think it will exist in the next few decades?

The whole article seems like "If nuclear fusion cost $100 per MWHr, but if it only cost $10/MWHr..."

We need to stop callin it “climate change” and start calling it ”climate crisis”.

Good analysis, but fails to take into account the storage costs of whatever CO2 is sequestered (or the potential to offset those costs by selling the CO2 to whatever industry uses them).

The article does take storage cost into account (although it does kinda waive it away):

> If this impression is correct then the cost of capturing CO2 is likely to either dominate or in worst case be comparable to the cost of storage and utilization. Still, a more detailed analysis would be careful about this costing

> storage costs of whatever CO2 is sequestered

CO2 is not spent uranium.

No, but you do have to keep it somewhere where it won't leak back into the atmosphere again any time soon. Which means deep underground.

You know, I'm not sure I really need to hear from any more non-experts thinking out loud anymore. We've had enough of that. I want to hear from experts giving their carefully considered views.

If carbon capture is good then why do they encourage composting? Shouldn’t we be taking that organic material and burying it somewhere?

we should, preferably in shut down coal mines where the carbon came from, but that takes time, money and fuel.

Carbon capture is the dumbest and most expensive way to move forward. It would be cheaper to just turn every coal plant into a solar farm then it would be to capture the carbon out of the air so why even bother. Oh yeah, corporate interests.

True. Especially if nature already has the best direct carbon capture technology since hundreds millions of years for free: trees!

Plants convert at most 2% of incident light into chemical energy, and spend only a fraction of that binding carbon.

Trees are cheap but need a lot of space and water. People are cutting down forests because they want to use the space for something else.

Ocean surface algae also collect solar power and carbon, and there is little demand for ocean surface for other uses. Algae are limited by available trace minerals -- cheap ones.

Iron seeding of the oceans to increase producer activity is currently being done but on large enough scales to sequester enough CO2 to make a difference it's basically impossible.

Where is it being done, and by whom?

The only one ongoing I know of is Sahara dust being (naturally) blown out to the Atlantic ocean. Otherwise, just talk. Somebody who did an experiment had his results suppressed, crudely, with a false narrative promoted in its place. Why that was seen as necessary, and how it happened, seem even more interesting than the experiment.

This argument is so naïve that I had to create an HN account (downvote ready comment for dissing HN commenters). Do note that I am not dissing the author. He did claim a lack of expertise, but I am sad to see the comments trying to analyze the directly presented facts than being detail driven. E.g. I saw some reference to Allum's process of reusing CO2. What it skips is the fact that it barely effects efficiency, but certainly sees that is better than excusing. I still don't understand how $ among is used to measure environmental impact is a relationship people can think is easy measure. Maybe because short term thinking is rewarded better, hence the success of capitalism (I'm not pro/anti, but that's the root of the philosophy). I am assuming that people understand that Carbon capture doesn't resolve environmental changes. It simply offsets a part of it - the global warming aspect. A LOT of impact is straight up coming from pollution/contamination of water and soil, recurring costs of restructuring landscapes, causing earthquakes to floods and terraforming from receding coastlines, destruction of habitats, leading from contaminated species to complete destruction is food sources. The cascading effect of environmental damages is like paying a loan. As humans we are known to be overconfident of "I can fix it". But remind me historically when THAT had worked? Almost in all cases, it had been "I can forget this". Except in this case, I think if we had to expend that sort of money to "solve the problem", then we might as well just find a new planet to squander. In 50 years, we would have spent trillions of dollars unanimously and probably got to Mars

[Edit] typos

Would love to know how many Trees/Algea farms/plants generally would need to do the job

Also growing plants and converting to fuel is exceedingly cheap for diesel

And before anyone gets worried about food prices going up.. it takes a surprisingly small amount of land mass to cover currect sneeds in energy, sorry no references no time..

Here goes for further downvotes...

The entire edifice of this "human caused climate change" hypothesis rests on the premise that carbon dioxide is /the/ control knob for this planet's temperature.

There is zero proof that this is true. Zero. So if I were you, I'd be very, very cautious before going ahead with capturing CO2, by any method.

It's way too early for this sort of thing. Vastly more research is required before taking a potentially disastrous decision to try to reduce the amount of CO2 - a gas which Earthly vegetation /needs/ in order to survive!

Can you provide anything beyond conjecture that there is any merit to what you've stated? My understanding is that the effects of CO2 as a greenhouse gas are pretty well understood at this point.

I can only ask that you read some Stuff From The Other Side Of The Argument...

http://www.drroyspencer.com/ is a good start on that.

I'm already being downvoted on here - proof that there are a substantial number of HN users who have Made Up Their Minds on this, and simply do not want to even consider that they have been bamboozled by various interested parties. I realise that no one likes to either admit they've been fooled by someone/a group of people, or simply that their view of the world around them is simply wrong - still, no reason to use HN's downvoting as a weapon against those who would otherwise try to post a contrary view. Still, it's fascinating to be downvoted simply for offering a contrary opinion.

As an interesting but connected sidenote: I've noticed on here that numerous HN submissions which tend towards CO2 demonization get upvoted and are filled with the Convinced, whereas the various articles I have submitted which tend to question this either get zero attention or are downvoted to obliviion. Whatever, and so be it.

Link looks a lot of garbage cherry picking of individual bad or flawed actors and arguments as misleading rhetoric that fallaciously implies the underlying belief is incorrect... as per usual...

Hint: capitalizing things and tossing about assertions about behavior of HN readers the way you do significantly undermines your credibility. If you really want to advance the argument you are making in good faith, you need to adjust your approach.

The problems with fossil fuels go way beyond climate change. If you told me that everything is a myth and it was just some government conspiracy involving almost every country on earth it wouldn't change anything. Even at 0.30€/kWh a used Kia Soul EV (small SUV) would pay for itself in gas savings compared to my 40MPG car. If climate change turns out to be true it will just be a nice bonus on top of all the other benefits you get by switching away from fossil fuels and if it doesn't, then everything is fine. You just can't lose by betting against fossil fuels. You know what the best part is? You get to avoid fuel taxes! The German government budget will shrink by 10% if we go all EV so if you hate taxation then EVs are the way to go!

Ugh, I shouldn't feed trolls...

1) AGM has hit the gold-standard of proof, it's not an open question at this point, and CO2 is the primary driver along with other GHG [1]

2) What exactly are the "potentially disastrous" consequences of going back to 300ppm, roughly where we were for 10k years?

[1]https://www.reuters.com/article/us-climatechange-temperature...

Being called a troll for questioning a false premise amuses me no end.

Have you ever read any of the other side's information, or do you solely read Reuters and other "CO2 is the demon!" mainstream media sources?

Thanks for your comments. A bit of fresh air. Really, I don't think that demonizing CO2 is the objective. Demonizing oil and other petrochemicals seems more likely. I think we are in a CO2 drought -- we know the planet (including corals) had an explosion of life at the 700+ ppm CO2 level.

> Vastly more research

We've done a vast amount of research. You've dismissed it. How much more research should be done to convince you, personally?

I guess you're not old enough to have noticed the seasonal temperature changes in your lifetime.

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