The flawed appeal of unilateral Direct Air Capture programs to prevent climate change

For the past 20 years, UN-led climate change negotiations have failed to produce an accord that halts the rise of global GHG emissions. Given this track record, it’s easy to see the appeal of the idea proposed in a recent New Republic article: that the US alone could prevent climate change by investing heavily in large-scale carbon dioxide removal (“CDR”) deployments.

The idea in the article goes something like this: the US (and/or some of its developed country allies) would fund a “Manhattan Project” for Direct Air Capture (“DAC”) systems. DAC systems scrub CO2 from ambient air; the resulting CO2 can then be buried deep underground, where it would be trapped in impermeable rock formations. If DAC system costs fell substantially, the US alone could fund massive “artificial” forests that offset large portions of global GHG emissions.

Unfortunately, there are three major problems with this plan:

Problem #1: The hypothetical costs of the “mature” DAC systems described in the article are likely an order of magnitude too low. The article claims that:

“If $30/ton were indeed possible, the U.S. government could construct huge forests of “artificial trees” in American deserts and absorb 30 percent of 2013’s carbon emissions for about $90 billion per year…”

The problem here is that the author is quoting figures in $/t Carbon (and not $/t CO2) as is done in the rest of the article: 30/t Carbon translates to a price of less than $10/t CO2 (as a CO2 molecule weighs over three times as much as a molecule of pure C). Today, simply injecting CO2 underground and making sure it doesn’t come back up — a relatively mature process thanks to decades of enhanced oil recovery efforts — costs around $10/t CO2. Even the biggest proponents of the field say that DAC systems are unlikely to cost less than $50-$100/t CO2 even when mass produced. Asking the US to pursue a $0.5-$1T unilateral DAC program seems significantly less feasible than the <$100B program outlined in the article…

Problem #2: The reliance on the “silver bullet” of DAC systems. There are numerous proposals for CDR systems, nearly all of which are expected to cost less than DAC systems:

CDR Supply Curve

Above: curve assumes midpoints of estimates of costs and supply levels from analysis by: Lomax and Addison (Virgin Earth Challenge), Ciais, et. al. (UN IPCC)

This isn’t to say that we shouldn’t invest in developing cost-effective DAC systems, but rather that we should invest in a broad portfolio of CDR approaches alongside other GHG mitigation techniques such as renewable energy and energy efficiency. Instead of a Manhattan Project for DAC systems, a better recommendation would be to scale up ARPA-E, SunShot, and other existing applied research programs in a way that incorporates CDR approaches and can find the most cost-effective portfolio of solutions to mitigating climate change. Which all leads to…

Problem #3: The biggest problem of all with the article is the the framing that a CDR research program would be a “hedge” against international climate negotiations not working. Instead, a robust CDR research agenda could serve as a major enabler of the success of international climate negotiations. Unilateral investments in CDR and other GHG mitigation techniques can help parties signal that they are committed to making significant GHG emission reductions, and will not free-ride off of other countries’ efforts. The article claims that climate change is not a “repeatable” game, but climate change negotiations are such a repeated game. Signaling individual commitments and building trust are then critical for the players in this “prisoners dilemma” to cooperate, and investments in CDR should be seen as a complement, not a hedge, to enable this cooperation.

Bottom line: the idea of massive “artificial forests” may be an intellectually appealing way of preventing climate change, but the reality of the situation is that a broad portfolio of CDR and other GHG mitigation approaches developed through international collaboration still looks more promising — even with the disappointing failures of this approach to date.


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