The Improbability of CO2 Removal from the Atmosphere


The Improbability of CO2 Removal from the Atmosphere

The concentration of carbon dioxide gas in today’s atmosphere is 417ppm (parts per million). There are 10^44 gas molecules in the entire atmosphere (78% diatomic nitrogen, 21% diatomic oxygen, 1% everything else), so 1ppm is equivalent to 10^38 gas particles. The 417ppm of CO2 represents a total of 4.17×10^40 molecules.

Some people hope for new technology to remove carbon dioxide gas from Earth’s atmosphere, and then forestall the advance of global warming, or even completely eliminate it. I see this as improbable because I think any such technology would be extremely inefficient at CO2 removal, and be energy intensive as well. The process of gaseous diffusion, as with the release of CO2 into the atmosphere, requires no energy; the gases just mix, spread and dilute, and the entropy of the atmosphere increases. It is an “irreversible process” in the parlance of chemical thermodynamics. This means that the spontaneous un-mixing of gases and their re-concentration into separate volumes has never been observed. Energy must be invested to effect any such desired separation of component gases in a mixture. To explore the possibility of CO2 removal, I have quantified my sense of improbability about it, and describe that here.

Consider a hypothetical CO2 removal machine that is a tube with a filter box in the middle. Air is fanned into the tube, flows into the filter box where some of its CO2 is removed, and then flows out of the tube to rejoin the atmosphere and to slightly reduce the global average concentration of CO2. Energy is supplied to entrain air into the device, and energy is supplied to power the unspecified process that effects the CO2 removal within the filter box. The machine would operate continuously so that over time all the atmosphere would be filtered and de-carbonized.

This would be a very large machine, and most likely be a large array of identical or similar units all over the world that would comprise a composite machine. I will describe this composite as if it were a single tube. [1]

Machine #1

This machine has a filter cross-sectional area of 10,000 km^2 (10^10 m^2) into which air is fanned through at 1meter/second (2.24mph). Producing that continuous mass flow from still air requires 16GW of power, assuming an efficiency of 40% (from raw power into moving air). The filtration process is assumed to consume 40GW (1% of the power used by the United States) and be 1% effective at CO2 removal. The anthropogenic emission of CO2, at its current rate of 35.5GT/year (giga metric tons per year), is assumed to continue indefinitely (the economy!), with the oceans absorbing 29% of those emissions (10.4GT/y).

At the end of 10 years of continuous operation Machine #1 would have cleared 3.26ppm of CO2 from Earth’s atmosphere, at a cost of 1.77×10^19 Joules of energy (4.92×10^12 kilowatt-hours). Reducing the CO2 concentration to the pre-industrial level of 280ppm would require 507.6 years.

Machine #2

Clearly, improvements are required for Machine #1. So, we assume that 10% efficiency of CO2 removal can be effected by investing 400GW (10% of the power used by the United States) into the filter box. Now, the power consumption is 416GW for Machine #2. After 10 years of continuous operation 31.5ppm of CO2 would be removed from the atmosphere (bringing the concentration down to 386ppm), at an energy cost of 1.31×10^20 Joules (3.64×10^13kWh). Reducing the atmospheric concentration of CO2 back to 280ppm would require 51 years. This might seem promising except for the fact that the assumed 10% efficiency is pure fantasy.

Machine #3, All Earth’s Lands

To regain a sense of reality, consider the actual performance of the entire land surface of the Earth (1.489×10^14 m^2) acting as a CO2 removal filter. This was the case in the clearing of 2500ppm of CO2 from the atmosphere over the course of 200,000 years during the geologically brief episode of explosive global warming 55.5 million years ago, known as the Paleocene-Eocene Thermal Maximum (PETM). I described the PETM and cited numerous public-access scientific references to it in [2].

Using the same rate of CO2 removal (the e-folding time) as occurred during the PETM, in my formulation of CO2 removal machines, it transpires that the efficiency of removal by the Earth-filter (rock weathering reactions in the long term) is 8.6×10^-8 (0.0000086%). After 10 years, this Earth-machine would clear 0.42ppm of the atmospheric CO2 (bringing the level down from 417ppm to 416.6ppm). That level would be reduced to 280ppm in 3,984 years.

Machine #4

Hope in technology springs eternal for some, so maybe our Machine #2 even with a realistic efficiency can better the clearing-time set by the Earth, natural Machine #3. We accept an efficiency of 1.474×10^-7 (0.00001474%), invest 1.31×10^19 Joules of energy every year at a rate of 416GW of continuous power, and after 10 years find 0ppm of CO2 removal! In fact however long we run this machine there will always be 0ppm of CO2 removal, because the rate of technological removal is equalled by the rate of anthropogenic emissions. Reaching 280ppm is literally infinitely far away.

Machine #5

Maybe by some technological breakthrough the efficiency can be raised by a factor of 100, to 1.474×10^-5 (0.001474%). Then in 100 years Machine #5 would have cleared 0.0478ppm of atmospheric CO2 (reducing the level from 417ppm to 416.95ppm) for an investment of 1.31×10^21 Joules (3.64×10^14kWh). Achieving 280ppm would require 348,577 years. It’s hard to beat the Earth at its own game.

Best Course of Action

It should be obvious by now that our best course of action is to apply our energy resources to the betterment of our many societies and the equalization of living standards worldwide, and to the transformation of our economic activities for minimal CO2 emissions. The current catch-phrase for this transformation is “degrowth.”

During this pandemic year of 2020, the U.S. GDP shrank by 33%, and the CO2 emissions by the United States also shrank by the same proportion. Worldwide CO2 emissions shrank by 17%. Zero emissions require zero GPD, as we now know it.

Global warming will advance and its consequences will add great stresses to many human, animal and plant populations. This geophysical process could be experienced as “the collapse of civilization,” or it could be taken as a collective challenge to advance human civilization by bonds of solidarity, and the restoration of its reverence for the natural world. If we put our energy into fashioning that imperfect utopia, we would live through global warming with a justifiable sense of pride, and even have fun.


[1] Stream Tube CO2 Removal Machine
8 August 2020
Stream Tube CO2 Removal Machine

[2] Ye Cannot Swerve Me: Moby-Dick and Climate Change
15 July 2019


The Political Realities of Science Work

The author at work, 1983

The author at university, ~1970


The Political Realities of Science Work

Josue De Luna Navarro had an article published (in two parts) in the 4 and 7 October 2019 editions of Counterpunch, on how fossil fuel companies are distorting the orientation of engineering and science education to their favor by making large funding grants to universities to promote the idea that geo-engineering schemes can make it possible to continue with fossil fuel extraction and burning indefinitely:

How Fossil Fuels Pollute STEM Education

Geoengineering is a Scam

I agree with Navarro’s criticisms completely, and I add the following.

Mr. Navarro points out a fact that has always been true of the engineering profession (and also most other highly refined professions) that its students, first seeking education, and then as graduates seeking employment and lengthy careers, are destined to serve monied patrons, the Golden Rule: “those that have the gold make the rules.” Four to five millennia ago those patrons would have been called “Pharaoh,” and later “king,” “caesar,” “emperor” and “queen,” and in more recent centuries “the company” and “the corporation.” Professional expertise, like high art, has a dependency on patronage by the wealthy without whose largesse professional ambitions would be nearly fruitless (for there are always some successful independent scientists, like Charles Darwin).

My engineering education and physics career (1968-2007) was funded (besides by my parents paying my tuition and living expenses during my undergraduate years) by U.S. government money (the public) funneled through the military. Most decent paying options for employment after schooling were with manufacturing, electronics or energy corporations, defense (war industry) corporations, and government agencies. A tiny fraction of engineering science jobs were in academia. In any case, all such engineering science employees were servicing the aims of the Big Money: profitability for the corporations, greater military power through advanced technology, and the combination of both as greater global political power for the policy-making elite of the nation. Same as in Khufu’s day.

Because America’s militarism-backed capitalism is fossil fueled, both in my time and Navarro’s the oil and gas industry has been a major buyer and owner of engineering and science talent, as Navarro states. The great challenge for any engineer and scientist working in today’s government-funded paradigm of science professionalism is to try to keep body and soul together through corporate and government (and academic) employment while at the same time trying to produce work that is as much in the public interest as possible. A very difficult ideal to achieve, and not all engineers and scientists even try to. Our engineering professors were reluctant to talk about the political realities of our profession, and our economic captivity by the Big Money and its Capitalist Government, because they saw no alternative to it.

Navarro is right to excoriate the fossil fuel industries’s efforts to corrupt the intellectual integrity of the engineering and physical sciences, by urinating money on our professions’s training academies to drench them in the odor of the narrowly self-serving corporate mindset of fossil fuel burning forever, and for the endless profitability of oil and gas (and coal) extraction. Even so, it is up to each individual engineer and scientist to learn the facts about global warming and climate change and environmental degradation, and the unfortunate political realities governing the economics of their profession, as a matter of professional ethics and personal integrity. This is the necessary first step for them to have any possibility of producing work for the public good.

Navarro is correct to call geo-engineering to attenuate global warming a scam. It’s like trying to design a more effective helmet that would allow you to continue playing Russian Roulette. The most energy efficient, cost effective, socially beneficial and rapid solution to the fundamental problem is to simply stop the damaging behavior, which in the case of climate change is greenhouse gas emitting capitalism. But, that would be economically leveling and fatal to militarism, so unacceptable to the courtiers of capitalism, in all their national factions.

Like all engineers, I like machines and gizmos and gadgets, and I especially like flows of energy. But the best use of such engineered mechanisms are as adjuncts in harmony with the workings of nature for the beneficial maintenance of a sustainable society. There are so many delectable challenges to be enjoyed in the fashioning of a non-fossil fueled civilization, a Green New Deal, that operates within the natural tolerances for the continuation of a stable and benign (interglacial) global climate, that all the 21st century engineers could be fulfillingly employed for their lifetimes to help fashion and maintain that kind of world society. The immediate challenges are twofold: transform energy systems and industrial and food production operations to eliminate greenhouse gas emissions and toxic chemical pollution, and stop environmental damage and engage massively in environmental restoration of lands and the oceans. Planting trees and cleaning up plastic pollution are just two examples of specific tasks that easily come to mind.

So I circle back to the same conclusion as always: our problems are not technological but political. So long as our politics are bad — our economics held captive by fossil fueled capitalism and militarism, to the general detriment of the public — our technologists will be directed by the self-interests of the Big Money and the War Industries, and not by the public good of engineering and managing a decent society in harmony with Nature.