Not true at all (or only in limited circumstances that do not apply

First, it was not the original energy expenditure that is the problem. The problem is that the CO2 CHANGES the solar energy exchange equation, by allowing ~the same amount of solar energy to the earth's surface, but REDUCING the earth's ability radiate that energy back to space. That newly captured energy VASTLY EXCEEDS the original energy that went into adding the CO2 to the atmosphere. That original energy spent has almost zero impact on climate change.

Next, capture requires none of the things you say.

— Carbon capture can be done by 'farming' high-uptake organisms, which has extreme leverage for energy expended. Examples include iron-seeding of water to make algae blooms, planting high uptake trees, etc.

— Carbon capture can be done by accelerating natural chemical processes, e.g., exposing rocks that react with water and CO@, or crushing those rocks and spreading them on fields (iirc, Google just contracted with a company doing exactly that)

— Carbon capture can be done by enzyme-driven processes that make the desired reactions happen with minimal artificial energy input

— Even if you want to use a chemistry that requires direct energy input, there is zero requirement to recover the original highly complex and energy-dense molecules previously used for fuel, it only needs to make a compound that can be captured. Still requires less energy than original used.

— Even if you insist on producing new molecules as energy-dense as the originals, there is vastly more energy available via non-CO2-outputting sources, such as solar, wind, etc. which often produce surpluses. Again, the energy of the process has almost zero to do with promoting climate change.

So, NO, it neither a bad joke, a process that requires breaking laws of physics, at fantasy, or a scam.

That's not true. You've got a requirement to reduce entropy but none to pack it back into energy dense fuel.

> You've got a requirement to reduce entropy but none to pack it back into energy dense fuel.

C'mon, this is laughable. What are we going to do with it? Fill-up massive balloons? Also, I have never suggested that the objective should be to pack it back into energy dense fuel.

You are trying to talk your way around violating the laws of physics. Look, it's OK if you want to believe this. However, this does not change reality. This is why every single so-called solution has failed and ultimately is discredited.

As I suggested to someone else. If you don't see the point, do this:

Go to the store and buy a 10 Kg bag of finely ground flour.

Walk around your office or home and start throwing flour everywhere. Coat every single surface and crevice with it. Make sure it goes into your TV, computer, air conditioning system, setup a few fans to blow it around.

Now go back and retrieve every single particle.

The time, energy and resources required is astronomical when compared to the damage you can cause in 30 to 60 minutes. Anyone with minimal critical thinking capacity can understand that it will take weeks, if not months, of a very serious effort and lots more energy to remove every grain of flour.

Note that there is no requirement to put it back into the bag. You can eat it, cook with it. I don't care. Yet, you must repair the damage you caused down to the last particle.

Are you suggesting you can clean the room/office using less time, resources and energy than that required to create the disaster? I hope not.

That's the problem.

You need to understand that small-scale hypothetical first.

Now expand it to a planetary scale, where you have CO2 floating around the atmosphere at all levels, over every continent and ocean. The mere suggestion that we can actually claw this back should be ridiculous to anyone who stops to really apply some thinking to this problem. It's a fantasy.

>>understand that small-scale hypothetical first

We understand it well enough to know that it does not apply. Flour in crevices is not a gas in a mix of gasses

Your problem is you must pick the right small-scale hypothetical.

For gasses, any single removing device operating faster than the input devices will eventually remove ALL of the target gas. Yes, the rate gets asymptotic, and yes, more devices are better than one, but every molecule will all by itself come out of every crevice, and eventually bump into the removal device. That will NEVER happen with your flour example.

This principle is already used for pretty much every air cleaning device in use both on the planet and in space.

I am disappointed to see that you are relying on vague reasoning by analogy instead of thermodynamic calculations or empirical performance figures from currently existing carbon dioxide scrubber systems in this conversation. Generally you are more intellectually rigorous than this.

There are significant and relevant differences between carbon dioxide and flour for this purpose; for example, carbon dioxide is a gas and therefore diffuses continuously through the atmosphere, so a scrubber in a fixed location can eventually remove all of it, which is common practice in submarines and space stations. Also, the amount of energy obtained by burning carbon is orders of magnitude larger than, and actually the opposite sign from, the amount of energy obtained by scattering a similar mass of solid particles around, and this is relevant because you are specifically and explicitly comparing the energy consumed by the emission and capture processes.

> I am disappointed to see that you are relying on vague reasoning by analogy instead of thermodynamic calculations or empirical performance figures from currently existing carbon dioxide scrubber systems in this conversation. Generally you are more intellectually rigorous than this.

I have presented detailed calculations in the past only to be met with the same mindless brutalization via downvotes, comments and flagging. The HN masses are just as intellectually lazy as masses can be in any other context.

This is no different from recent events in the political spectrum, such as nearly the entire political and media machinery telling the world that Biden was just fine (and a bunch of other lies). Only those of us who managed to think outside the indoctrination seemed to have understood --years ago-- the sad reality that the poor man was being used and abused by the political machinery. Only when reality became inescapable did they start speaking the truth. In fact, it was worse than that, they actively attacked the man and popped him out of the system like a painful puss-filled pimple. The end result? They gave the leadership position to a candidate so flawed that billions of dollars and massive amounts of support from luminaries could not get her elected.

The point is: The truth always has a way to come out, sooner or later. Sometimes with undesirable consequences.

Climate change became a religion a long time ago. The domain is supported by the indoctrinated masses who love to regurgitate what they are told to think. Researchers fear going against the grain because their funding and careers depend on it. The powerful and those making money with this madness actively promote it and make sure they have support for insane projects. Frankly, it would be far easier to join them, regurgitate the nonsense and make millions of dollars per year by being a member of this dishonest club. Not my style. Sorry.

Regarding the flour analogy. You are reading too much into it. This was not a model of the planet and our atmospheric system. I only use these kinds of analogies to show how it takes far more effort, resources and energy to reverse damage that can be done in mere minutes. That's all.

Lot's of commenters on HN do not seem able to (or willing to) exercise critical thinking. Some might not have the requisite scientific background or real-world experience to understand what are otherwise simple arguments rooted in physics. One of the common comments goes something like: If we polluted it in X years we can clean it up in X years or less.

Of course, this is ridiculous. The example of flour spread all over the office is simple enough to illustrate just how silly this idea actually is. And, if someone cares enough to think it through a bit deeper, it also illustrates just how much more energy and resources is required than a sack of flour.

That's it. It isn't a model of a planet and its atmosphere. It's there to say: You cannot fix a problem with less energy, resources or time than what went into creating it in the first place. Nothing else.

> a scrubber in a fixed location can eventually remove all of it

That would be nice if it were possible. Sorry, this is another fantasy. Once again, things fail in a violent manner once considered at a global scale. You cannot filter air at a planetary scale, this is simply preposterous starting with the reality of building these kinds of systems every 10, 20, 50 or 100 miles throughout the planet, the scale, energy, resources and realities of air processing all work against you. These systems are far more likely to "filter" the same air over and over again than to actually "remove all of it".

In a prior life I was involved in large systems installations requiring the construction of clean rooms of varying scales, from small 20 x 20 foot labs to massive aerospace-level clean rooms (think Home Depot scale).

What works well in a smallish environment (a room, submarine, space station) quickly fails at larger scales. In the end, you cannot create a clean room by filtering the enclosed volume. That's not how it is done except for very specific applications (spacecraft, submarine, space station and that's it). The only way is to inject clean air and create positive pressure such that nothing is able to come in from the outside. Scrubber systems in the corner-case applications where this isn't an option are incredibly expensive and complex. They do not scale well at all.

Of course this isn't to suggest that we can bring in clean air into our atmosphere. My point is that the idea of filtering our entire atmosphere (or a substantial enough portion of it) only works on paper, research grant applications and proposals for funding by politicians eager to continue the narrative that drives unthinking masses to vote for them. Who wants to vote for someone who says "The emperor has no clothes"? Nobody. Far easier for the machinery to convince everyone that the naked man in front of them is wearing the finest garments every conceived. Sadly, that book [0] covers climate change with great accuracy.

Look, the scenario today is no different from what it has been for the last, 50 years or more. This articles [1] is an interesting compilation of predictions over time. All crazy nonsense. Yet, at the time, taken seriously and used to set policy and more.

Who would dare go against the likes of Nobel Prize winners, Ted Turner, Al Gore and other merchants of FUD? From a career standpoint, as academics, media or politicians, it would have been suicidal. Anyone can understand this. And yet, all of these and many others were selling pure unrefined bullshit. I mean, crap like this, quoting:

"A senior UN environmental official (Noel Brown) says entire nations could be wiped off the face of the Earth by rising sea levels if the global warming trend is not reversed by the year 2000."

(1970) "Air pollution may obliterate the sun and cause a new ice age in the first third of the next century if population continues to grow and earth’s resources are consumed at the present rate…"

"Harvard biologist and Nobel Prize winner George Wald, speaking at the University of Rhode Island in November 1970: “Civilization will end within 15 or 30 years unless immediate action is taken against problems facing mankind.”"

"In April 2008, media mogul Ted Turner provided far more detail than either Gore or Pachauri, emphasizing the consequences of climate inaction. “Not doing it will be catastrophic. We’ll be eight degrees hotter in ten, not 10 but 30 or 40 years and basically none of the crops will grow. Most of the people will have died and the rest of us will be cannibals. Civilization will have broken down. The few people left will be living in a failed state like Somalia or Sudan, and living conditions will be intolerable. The droughts will be so bad there’ll be no more corn growing.”

(2019, AOC) "The world is gonna end in 12 years if we don’t address climate change"

When I say that this domain has become a sad joke, a religion, an incredible farce supported by those seeking political and financial gain, rather than real science, well, there's ample evidence to support this statement going back over 50 years. In other words, it is far more likely that this is all a big smelly pile of bullshit than otherwise.

[0] https://en.wikipedia.org/wiki/The_Emperor%27s_New_Clothes

[1] https://www.agweb.com/opinion/doomsday-addiction-celebrating...

> Lot's of commenters on HN do not seem able to (or willing to) exercise critical thinking. Some might not have the requisite scientific background or real-world experience to understand what are otherwise simple arguments rooted in physics.

Sure, that's true, but are those the people whose opinion you care about? If you tailor your argument for them and leave out all the reasoning, you'll look like one of them, and people who are able and willing to exercise critical thinking on the topic will write you off. Don't tempt people to confuse you with dumbfucks like Ted Turner and Noel J. Brown.

> You cannot filter air at a planetary scale, ... These systems are far more likely to "filter" the same air over and over again than to actually "remove all of it".

You might be right that you need more than a single giant inverse volcano sucking carbon dioxide out of all of the air.

The diffusivity of CO₂ in air is 16mm²/s, or 1.6 × 10⁻⁵ m/s in SI units. Suppose, conservatively, that there are no jet streams or any other wind, so you have to rely entirely on diffusion, and that you've reduced the CO₂ around your scrubber to the pre-industrial 280ppm (0.012mol/m³), while the opposite side of the planet, 20000km away, is still at 400ppm (0.017mol/m³). If the concentration gradient were constant, it would be 0.25 nmol/m³/m over that distance. Using the given value of the diffusivity, this results in 4 × 10⁻¹⁵ moles per second per square meter flowing over that gradient. The atmosphere is in effect about 8 km tall, so at the halfway point of this flow, the great circle halfway along the path, you have 320000 km² of cross-sectional area, through which your flow is about 0.000128 mol/s. If you're trying to clean up the air over, say, 20 years, that works out to about 800 kilomoles, only about 36 tonnes of CO₂.

But we had to remove 2.3 gigatonnes of the atmosphere's 7.8 gigatonnes of CO₂, not 36 tonnes. We need a system that's 64 million times more powerful, which means that instead of being 20000 km away from the farthest points on the planet, it needs to be about 20000/8000 = 2.5 km. (Also, the above is assuming that the gradient remains constant, which of course it can't; you'll have a much stronger cross-sectional gradient around anything like a point sink or source of carbon, because the same mass flow is spread over a much smaller area. I don't know the exact solution for diffusion on the surface of a globe, but I'm confident the above is in the ballpark.)

But we do have wind; to take the most extreme example, the jet streams travel about 50m/s, so any parcel of air in them circles the globe about once a week. So if you set up your antivolcano near a jet stream and create a locally very low CO₂ concentration, CO₂ will diffuse rapidly out of the jet stream as it travels through your area and diffuse rapidly back into the jet stream on the other side of the planet three days later.

So if you have winds that bring all of the atmosphere within 2.5km of your antivolcano at some point within those 20 years, you can scrub it all. All of it.

https://www.usgs.gov/news/volcano-watch-global-reach-volcani... says of Mount Pinatubo:

> Notable eruptions in recent years appear to have affected climate. One example is the 1991 eruption of Mount Pinatubo in the Philippines, which injected nearly 20 million tons of SO2 into the stratosphere that became dispersed around the globe in about 3 weeks. The recorded effect was a 0.5 degrees C (0.9 degrees F) drop in temperature for the following two years.

So in practice the timescale on which an antivolcano's CO₂-scrubbing effect would reach the air on the other side of the planet is only a few weeks, not the hundreds of millions of years that the naïve diffusion calculation suggests.

You say:

> In the end, you cannot create a clean room by filtering the enclosed volume.

I haven't tried, but I'd venture to guess that that's because dust, like flour, doesn't diffuse through air (at human temperatures on human timescales). It's a thousand times denser than air, so it can settle on surfaces and get trapped in certain kinds of airflow patterns. Carbon dioxide doesn't behave like that. It behaves like water vapor.

> Scrubber systems in the corner-case applications where this isn't an option are incredibly expensive and complex. They do not scale well at all.

Unlike cleanroom filters, scrubbers, which are gas-exchange devices used for removing unwanted gases from air, are actually very cheap and simple, and they scale extremely well; they are already being operated at many-megawatt industrial scale, which is how we ended the acid rain problem caused by coal power plants. A CO₂ scrubber can be as simple and low-tech as a wall painted with whitewash, though soda-lime scrubbers (a few percent of lye added to the whitewash, which is balled up in little beads to let the air pass through) are much more common because they are so much more compact. They are in wide use for general anesthesia, scuba diving, and decompression chambers. On the order of a million recreational scuba divers own their own scrubbers. You can buy a bottle of 5 liters of soda lime for €32 at https://www.diveavenue.com/en/high-pressure/1860-chaux-spher... if you stick a porous breathing tube into the bottle, it becomes a scrubber, although you'd probably die if you tried diving with it.

Other kinds of gas scrubbers are available as disposable cartridges from 3M for their respirator masks, so it's absolutely not true that they're "incredibly expensive and complex", but let's stay focused on CO₂ scrubbers here, since that's what's relevant to climate change.

The disadvantage of lime CO₂ scrubbers is that, although they are very simple, regenerating the lime requires heating it up to 900°. People have been doing this for 12000 years (it's probably literally the oldest human chemical process) but it takes a lot of energy compared to other sorbents like triethanolamine, which is why amine scrubbing is currently the mainstay of both submarine CO₂ scrubbers and point-source CO₂ capture pilot projects. There's a nice process flow diagram of a submarine CO₂ scrubber at https://sites.psu.edu/mooneypassionblog2/2022/03/22/how-subm....

As for scaling, lime burning, in the slightly altered form of portland cement making, is one of the world's largest-scale industrial processes, producing 4 billion tonnes of cement per year and emitting 1 billion tonnes of CO₂, which you'll notice is about 2½ years for the mass of the carbon dioxide we have to remove. (Portland cement, unlike Neolithic-style lime cement, only reabsorbs a fraction of that CO₂ when it sets.) So we already know we can scale lime kilns up to the requisite levels; we just have to capture their carbon dioxide output. There are also a bunch of startups trying to scale up amine scrubbing and other processes to direct air capture, but I'm skeptical that their supply chains will be able to compete for scale with the world limestone-and-other-calcareous-stone industry.

> My point is that the idea of filtering our entire atmosphere (or a substantial enough portion of it) only works on paper, research grant applications and proposals for funding by politicians eager to continue the narrative that drives unthinking masses to vote for them.

Every engineering idea only works on paper until you build it. That's how engineering works: you make things work on paper, you validate your assumptions with prototypes, you learn from your mistakes, and finally you create something that never existed before. Your criticism here is a fully general criticism of every technical innovation in history; it doesn't distinguish between perpetual motion machines (which work on paper if you screw up your calculations badly enough) and any routine civil engineering project such as a bridge embankment.

As shown in https://news.ycombinator.com/item?id=42439752 my numbers above for the total atmospheric carbon dioxide load and the amount to remove are wrong by orders of magnitude. The total is 3.3 teratonnes, of which we will need to remove 1.1 teratonnes to get back to preindustrial levels, not just 2.3 gigatonnes. I believe this reduces the 2.5km number above (for the range over which diffusion alone would transport the necessary CO2 flux) to some 400m. Assuming I got the rest of the calculation right, which I'm uncertain of.

This also means that the world cement industry is not currently large enough to carry out the necessary direct air capture over a timespan of decades. You need a carbon dioxide capture industry 10 or 20 times larger; at current energy and material prices, this would cost on the order of 6 trillion dollars per year, about 6% of the world GDP of US$105 trillion per year, nominal, World Bank estimate: https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nomi.... World GDP has been growing about 3.9% per year, so rather than setting us back to the Stone Age, or even to the 18th century, this staggering expense would set us back to about the time Silicon Valley Bank collapsed, Hamas invaded Israel, OpenAI released GPT-4, and Microsoft bought Activision Blizzard.

This clearly demonstrates that it is technically feasible already, just not economically/politically. Rapidly falling energy prices thanks to the transition to super-cheap renewable energy will ease the economic difficulties, though the project may still require international diplomacy.

Also, https://earthscience.stackexchange.com/questions/994/how-lon... says, "The time scale of interhemispheric tropospheric transport is in the order of one year," not a few weeks. I assume that the difference from the Mount Pinatubo number is because the troposphere mixes more slowly than the stratosphere because in general the winds in the troposphere are slower. (However, the jet stream in particular is at the tropopause, where the two meet.)

I can't understand why you put so much effort into trying to justify your position with irrelevant analogies. You've tried to dismiss my point with a single line. There are several techniques for sequestering co2 pretty permanently that don't involve turning it back into fuel. Go and research them and stop being so dogmatic.

I used to think that too, but then I found out it wasn't true. It turns out that by instantly laughing at people who disagree with you, you lose the opportunity to learn the things they know that you don't.

Specifically, in this case, the standard enthalpy of formation of carbon dioxide is -393.5 kilojoules per mole (that's the energy you get when you burn coal). If you burn coal in a sealed 1-bar chamber to drive a heat engine (such as a steam turbine), and pump the exhaust gases through a passively-air-cooled 1-bar heat exchanger to cool them back down to room temperature, you have obtained those 394kJ/mol thermal, about 138kJ/mol electric, for only the cost of blowing the gas around, without releasing any carbon dioxide into the atmosphere. Blowing the gas around with blowers takes typically about three orders of magnitude less energy than the heat energy the gas carries, though this depends on things like gas temperature and duct length, diameter, and smoothness. So physics is no bar (heh!) to getting from the coal-and-atmospheric-oxygen state into the electricity-and-captured-carbon-dioxide state.

There is some necessary energy cost involved in atmospheric carbon dioxide capture, because the air is only 400 ppm carbon dioxide and 99.96% other things, so there is an entropic cost to unmixing it. That entropic cost is not where you get the energy from burning it; the mixing happens above your smokestack where you can't extract any energy released and, as demonstrated above, can be avoided entirely. I don't understand thermodynamics well enough to calculate the thermodynamically necessary energy to reverse that entropy, but my understanding is that even at 400ppm it is orders of magnitude lower than the fuel's heating value.

Recompressing the carbon dioxide to liquid form requires about as much energy as you got in mechanical form out of the turbine; carbon dioxide liquefies at room temperature at 60 bar, liberating its enthalpy of vaporization of 16.7 kilojoules per mole, 4.2% of the enthalpy of formation. 59 bar is 5.9 kJ/l, and at room temperature and 1 bar an ideal gas occupies 24.4 l/mol, so you need to put about 140kJ/mol into compression. But as I understand it (and correct me if I'm wrong) almost all of that energy comes back out as heat. In practice, atmospheric carbon capture systems use absorbents or adsorbents such as calcium oxide, zeolites, or ethanolamine solutions to avoid this complicated and inefficient compression step. They use a substantial amount of energy to regenerate the sorbents, but, as I understand it, much less than burning the fuel generates.

For example, https://cobblab.eas.gatech.edu/energy/Readings/rochelle2009.... (DOI: 10.1126/science.1176731) says that a monoethanolamine scrubber used for flue-gas treatment at a 450-megawatt power plant in the year 02006 used 0.37 megawatt hours per ton of CO₂ removed. Assuming they mean metric tonnes, that's 1.332 gigajoules per 22700 moles of CO₂, which works out to 59kJ/mol, which is 43% of the energy obtained from burning the carbon. (Although amine scrubbers have been used for capturing CO₂ from flue gas at a number of power plants since the 01980s, I'm unclear on whether this 59kJ/mol number represents measurements from an actually deployed system or the projected performance of a proposed design.)

You could argue that it's easier to remove CO₂ from power-plant flue gas where it's fairly concentrated (12% rather than 0.04%), but in fact sorbents like monoethanolamine and triethanolamine are also quite effective at removing CO₂ from breathable air in environments such as submarines and space stations. At room temperature, their vapor pressure of CO₂ is quite low indeed, so it's mostly just a question of needing to expose the sorbent solution to air over a longer period of time. It doesn't result in requiring a proportional increase in the energy consumption of the process.

A recent open-access survey of the direct-air-capture problem is https://pubs.rsc.org/en/content/articlepdf/2022/ee/d1ee03523... (doi 10.1039/d1ee03523a). (However, note that that's still from November 02021, at which point photovoltaic panels still cost three times as much as they do now, so its calculations of energy costs are inflated by at least a factor of three.)

So, no, the laws of physics don't require that removing CO₂ will require even as much energy as what went into adding it to the atmosphere, much less "massively more energy", as you claim.

Even if they did, though, that wouldn't make atmospheric carbon capture impractical or a scam. Burning methane (natural gas) yields 55.6 MJ/kg (https://en.wikipedia.org/wiki/Energy_density#Chemical_reacti...) which works out to 892kJ/mol, but each mole of methane only produces one mole of carbon. The other 892 - 394 = 498kJ/mol (HHV) comes from burning the hydrogen (water's enthalpy of formation is -285.83kJ/mol, and methane's is -74.6kJ/mol, so we get 497.1 kJ/mol extra after the rounding errors). So even if we had to pay back all of that 286kJ/mol from the carbon to stuff it back into a bottle, we'd still have 56% of the energy we got from burning the natural gas left over.

And, of course, photovoltaics and wind provide abundant energy we can use for atmospheric carbon capture without releasing any more carbon dioxide, and nowadays they do it far more cheaply than fossil-fuel power plants ever did.

There are also schemes for atmospheric carbon dioxide capture with biological photosynthesis, which I think are probably not feasible at the required scale due to the required area, and with enhanced weathering by pulverizing olivines, which are probably feasible but strike me as risky. In the olivine case, the energy required to extract the gas from the atmosphere was provided billions of years ago by the heat of the earth driving carbon dioxide and other volatiles out of the mantle, so we don't have to care how big it is.

The reason "every single proposal for CO2 removal has failed" is (1) most of them are pretty energy-intensive, and until five years ago, energy was expensive (and cheap energy still hasn't reached most places); and (2) there's no clear way to make money at CO2 removal at current carbon credit prices, which are in part because the carbon credit market is pretty corrupt but also because at this point there's still a lot of low-hanging fruit in the emissions-reduction sector.

> You do realize that removing CO2 will require massively more energy than what went into adding it to the atmosphere, right?

The reaction of CO2 with silicate rocks that pulls CO2 out of the atmosphere naturally (and is why the Earth is not like Venus with 90 bar of CO2 in the atmosphere) is exothermic. So, the energy needed is not just not large, it could even be negative.