Future Tense

Cutting Carbon Dioxide Isn’t Enough

We have to invest in technology to remove the CO2 already in the atmosphere.

A thermal power plant in Changchun, China. Even as we try to reduce CO2 production, what happens to the CO2 already in the atmosphere?

Photo by STR/AFP/Getty Images

According to data being gathered at the Mauna Loa Observatory in Hawaii, which has been monitoring atmospheric carbon dioxide since 1958, the CO2 concentration in the Earth’s atmosphere officially exceeded the 400 parts per million mark last week, a value not attained on Earth since humans were first human.

This ominous milestone comes at a time when the evidence that human activity is resulting in unprecedented climate change is now overwhelming. More important, perhaps, even if all greenhouse gas production ceased immediately, this elevated carbon dioxide level would persist in the atmosphere for thousands of years.

Indeed, even moving relatively quickly toward a carbon-neutral economy will still result in a net increase in CO2 in the atmosphere for the foreseeable future. But that is moot, because we are nowhere close to moving quickly in this regard anyway. Fossil fuel reserves have effectively increased, due to improved technologies for extraction, and investment in alternative energy sources has been limited due to artificially low prices on carbon-based energy. As a result, 2012 was likely another record year for human-induced CO2 production.

So in addition to undertaking dramatic global efforts to reduce present and future CO2 emissions, we need a strategy for addressing the carbon already up there. Recently, a broad group of geologists, planetary scientists, climatologists, social scientists, and physicists convened at the Origins Project at Arizona State University, which I direct, to explore such strategies. (Disclosure: Future Tense is a partnership of Slate, the New America Foundation, and ASU.) As an upcoming paper being prepared by 15 of the participants* at the meeting will argue, we came to a broad consensus that there is an increasingly urgent need to seriously consider removing and sequestering CO2 directly from our atmosphere.

This effort should not be confused with ongoing efforts to capture CO2 and sequestering it at its source, for example, from outgoing flue gas from coal-fired power plants. That area is important, too, but it’s already being explored, and the technological demands are quite different.

Extracting CO2 from the atmosphere, even with its current level of 400 ppm, is very different—and in some ways more difficult—than extracting it from flue gas, where the CO2 concentration is much greater. But on the brighter side, extracting ambient CO2 from the atmosphere does not have to be anywhere near 100 percent efficient. Both of these factors imply different constraints on the extraction process that will affect its ultimate cost.

There are two parts to the extraction process. First, one removes CO2 from the air by using a sorbent, which is a material that can absorb gasses. Next, the CO2 has to be extracted from the sorbent and sequestered, presumably by pumping it deep underground at relatively high concentration or by binding it to minerals—a bit like how we handle nuclear waste. But another possibility includes actually converting it back into fuel. One particularly attractive possibility that has been proposed involves using an “exchange resin” sorbent which binds CO2 when dry and releases it when wet. In this way the evaporation of water could actually be used to help reduce the energy burden associated with binding and subsequently extracting the CO2.

Note that direct air capture is also not to be confused with so-called “geoengineering,” which attempts to lessen the impact of climate change using other global (and potentially environmentally hazardous) interventions, unrelated to the root cause. Put another way, direct air capture would treat the disease, not merely the symptoms.

Though there could be huge advantages to directly extracting carbon dioxide from our atmosphere instead of from its source, there has been almost no R&D funding to explore making it a reality. Meanwhile, literally hundreds of billions of dollars have been put into subsidies for fossil fuel exploration and production. If direct air capture proves economically competitive at all, it could potentially be scaled to control atmospheric concentrations with falling marginal cost. More important, from a political and economic perspective, it could perhaps be carried out by any country, independent of whether that country is a net energy producer or user, and it would not affect “competitiveness.”

At present, it is difficult to determine the cost of direct extraction. (See a recent piece in the Atlantic, in which my ASU colleague Daniel Sarewitz and the University of Colorado at Boulder’s Roger Pielke Jr. write that estimates range from $20 per ton of CO2 to two orders of magnitude higher.) By comparison, the current world production of CO2 is approximately 30 billion tons. But without R&D support to test several technologically viable proposals, it will be impossible to determine if this approach, including the feasibility of sequestering the extracted CO2, is at all practical, cost effective, and safe. If it is, the modular production of air capture units would result in economies of scale, and units could be shipped in standard containers anywhere in the world, away from population centers in dry wastelands.

Given the risks of increasing CO2 levels in the atmosphere, and the difficulty of slowing current production, at the very least some modest government R&D support of this important possible alternative seems appropriate right now to help safeguard our future.

The road to sustainability will be a long one. At best it may be decades before we are able to wean ourselves off of fossil fuels. The possibly drastic upheaval that climate change may bring for future generations as a result of the activities of present and past generations suggests that at the very least we should seriously consider cleaning up our own mess, and doing it now. Direct air capture may be one way to do that. Not funding research into this possibility even as we pursue other important research to address climate change seems, in this sense, negligent.

This article arises from Future Tense, a collaboration among Arizona State University, the New America Foundation, and Slate. Future Tense explores the ways emerging technologies affect society, policy, and culture. To read more, visit the Future Tense blog and the Future Tense home page. You can also follow us on Twitter.

*Update, May 13, 2013: The 15 participants in the paper are Lawrence M. Krauss, Kip Hodges, Ariel Anbar, Arjun Helmsath, Sander Van der Leeuw, and Manfred Laubichler of Arizona State University; Wallace Broecker, Klaus S. Lackner, and Scott Barrett of Columbia University; Jeffrey Severinghaus and Ralph Keeling of University of California-San Diego; J. Michael Hall (NOAA, retired); James Anderson of Harvard University; Ray Piierrehumbert of the University of Chicago; and James Hansen (NASA, retired).