Air Carbon Capture Storage: Not the Answer to Keeping the Lid on at 1.5 degrees Celsius – Part 1
As we live the reality of climate disruption and weather extremes, the widely accepted goal is that the average global temperature rise must be limited to 1.5oC to avoid catastrophe. The analysis of the Intergovernmental Panel on Climate Change (IPCC 2021) states that we have a remaining “carbon budget”: the world can burn a few hundred billion tons more of fossil carbon and still keep to that temperature limit. That seems to accord with the fact that global temperature rise to date is about 1.1oC. The good news is that that understanding is right; the bad news is that it is also wrong.
That 0.4oC margin is real, but it hides a very difficult reality. By themselves, greenhouse gas levels are already high enough to drive the average global temperature up by 1.5 degrees Celsius. The reason that the thermometer doesn’t show that the Earth has such a high fever is that pollution, mainly sulfur dioxide aerosols and nitrogen oxides from fossil fuel burning, is producing a net cooling effect amounting to 0.4oC. In other words, a combination of non-greenhouse-gas pollutants is keeping the planet cooler, masking about one-fourth of the heating impact of greenhouse gas concentrations. This is very clear from the chart in the IPCC report reproduced below (IPCC 2021, pdf p. 9).
So, what is to be done? Clearly, we can’t continue using coal and fossil fuels; not phasing them out essentially completely by or before mid-century is a recipe for even worse disasters. To keep the temperature lid at 1.5oC we will need to eliminate fossil fuels AND simultaneously do more to compensate for the shredded cooling mask created by pollution.
There are already substantial hurdles to achieving zero emissions because the technologies ready to hand to eliminate emissions completely or nearly so from difficult sectors, such as air travel and steel and cement production are, in the main, expensive at the present time. Deforestation, more extensive forest fires, and increasing carbon and methane releases due to permafrost melting also point to the need to go beyond eliminating fossil fuels.
Fortunately, we can do more as we get rid of fossil fuels. Unfortunately, most of the attention and vast sums of money have been focused on just one approach: carbon capture and sequestration (CCS). It comes in two unpleasant flavors:
- Extract CO2 from the atmosphere where its concentrations were as high as 418 parts per million on February 22, 2022 according to NASA, preferably at a location where it could be directly injected underground for sequestration; this more precisely called “air capture” of CO2 followed by sequestration.
- Capture CO2 at the point of fuel use, for instance, from exhaust gases at coal-fired power plants and steel and cement plants; transport it in pipelines for scores or hundreds of miles to a suitable location; and inject underground in a geologic medium that could hold it down for eons – in other words, sequester it from the atmosphere. This is point-source CO2 capture as distinct from air capture.
I’ll focus here on the first, air capture, in this blog post and cover point source CCS and “use” of CO2 in the next. In the third of this series, I’ll propose approaches that could address the problem much better both from the economic and ecological points of view.
On the face of it, it seems reasonable to focus on CO2 capture; it is the most important greenhouse gas emitted by human activities. But at about 0.042 percent, it’s concentration in the atmosphere is very low. Trying to extract it mechanically or chemically means thousands of tons of air have to be handled to separate a single ton of CO2 from it. It takes a lot of energy to do it.
It will also take a lot of money.
Each part per million of CO2 in air has a mass of almost 8 billion metric tons, roughly 20 times the weight of all the men, women, and children in the world. The 418 ppm of CO2 in the atmosphere add up to about 3.2 trillion metric tons; about a third of that is due to human activities. That’s not the amount we have emitted; it’s the amount that remains in the atmosphere. Much of the CO2 we’ve put into the atmosphere is dissolved in the oceans and is acidifying it.
Human activities have been adding an average of about 2.3 ppm of CO2 to the atmosphere each year since 2005 – amounting to 18 billion tons of CO2 a year. One estimate of current costs of air capture is $425 per metric ton (see p. 9 of Bill Gates, Financing the Clean Energy Revolution). At that cost, it would take about $8 trillion to remove a single year’s increase in the atmosphere’s CO2. Even if the cost is brought down to $100 per metric ton, as proponents hope, it would still cost almost $2 trillion, which is more than the Gross Domestic Product of all of Sub-Saharan Africa. Sectors where it is difficult to economically eliminate CO2 emissions like steel and cement account for about 15 percent of CO2 emissions. If air capture aimed to remove most of their CO2 – say about 10 percent of the annual increment, that still adds up to cost almost $200 billion per year , after the costs of air capture are drastically reduced.
That is just the start of the cost problem. Using present-day energy sources would result in half a metric ton or more of CO2-equivalent emissions, to extract one metric ton of CO2 from the air. Most of the energy requirements would be in the form of heat for which the main energy sources today are fossil fuels, usually natural gas. I used estimates of energy requirements for air capture and sequestration cited by the International Energy Agency (IEA) to come to that conclusion. Thus, the net capture would be only half a metric ton or less of CO2-equivalent in terms of its warming impact. That effectively at least doubles the gross cost estimate, unless the process is done with nearly carbon-free energy sources. The IEA acknowledges the problem without putting a cost number to it: “The energy used to capture the CO2 will determine how net-negative the system is and can also be a significant determinant of the cost per tonne [metric ton] of CO2 captured. For instance, both solid and liquid capture technologies could be fuelled by renewable energy sources….”
Some processes would also use a great deal of water – as much as 1,300 gallons for every metric ton of CO2 extracted from the air, in one case study (inferred from Keith et al. 2018, p. 1590).
The cost of sequestration (or “storage”) in a geologic setting is even more uncertain. A National Energy Technology Laboratory (of the Department of Energy) report did a comprehensive look at the various sequestration sites and concluded there are a large number of potential locations; cost estimates ranged from a low of about $1 per metric ton to a high of about $1,900 per metric ton, with a mean of about $70 and a median of about $8 (NETL 2012, Table 3). In 2010, a federal government task force cited costs ranging from a low of only 16 cents per metric ton to $20. The wide range is understandable. There are enormous uncertainties about permitting, evaluating potential seismic risks, actually injecting tens or hundreds of millions of tons of CO2 into underground formations, where it could spread over hundreds of square miles, and then sealing CO2 repository to prevent CO2 from leaking out or even suddenly burping up. That can happen; a natural CO2 outgassing on an August night in 1986 in Cameroon killed more than 1,700 people. Finally, there is the complex problem of trying to characterize underground ecosystems that might exist in some sites, such as saline aquifers and how injecting vast amounts of CO2 might disrupt them.
In round numbers, it is fair to say the quest for net zero using air capture for just one-tenth of the annual additions to the CO2 in the atmosphere by air capture and sequestration would, in rough round numbers, cost $250 billion to $300 billion every year after the technology is fully developed and if it is done mainly with decarbonized energy.
How else could we use that much money? For one thing, in the 2015 Paris Agreement, wealthy countries promised $100 billion a year to developing countries to help with the transition. They have not delivered. Fulfillment of that promise could actually bring countries to make commitments to get to net zero emissions by 2050; they are very far from that at present.
Many scenarios could be devised for the rest. Some examples: $100 billion per year sustained over time could enable sustainable living in terms of energy, water, and sanitation for those the World Health Organization calls “the forgotten 2.6 billion”; they use kerosene for lighting and wood, coal, kerosene, or charcoal for cooking. It would reduce CO2 emissions and avoid billions of tons of organic matter such as fuelwood and cow dung now burned as fuel. Further, it would reduce soot, also known as “black carbon,” a warming particulate and save millions of lives now lost each year to respiratory diseases (almost four million a year, mainly women and children, according to the World Health Organization). Investing in a just transition for fossil fuel workers and helping island countries to adapt to sea-level rise are other examples where the need is great and coincides with justice and equity.
Air capture of CO2 is fighting Mother Nature in the worst way. Taking carbon created long ago by solar energy, greatly increasing entropy by burning it, and then expending vast amounts of money and energy to capture it and put it back into the ground is not a winning formula even without considering the high likelihood of negative consequences for EJ communities and/or countries in the Global South.
Will capturing CO2 from the stack before it is emitted to the atmosphere work better? That’s next.
Components of global temperature change and their net warming impact
Source: IPCC 2021, pdf, p. 9