Cleaning Up the Excess CO2

Guest article by Professor William H. Calvin |  University of Washington  |  WCalvin@UW.edu |  WilliamCalvin.org

In climate science as in medicine, you become aware of irretrievable actions—say, learning that when the Amazon rain forest burns down, it won’t come back for a very, very long time. [1] Because of the uncommon way in which much of its rainfall is generated, plant succession will stay stuck at grasslands, so all of that biomass will not grow back. Most of its CO2 will remain, as the phrase goes, up in the air, causing heat waves around the world.

Burn locally, crash globally. And it’s bye-bye forever to perhaps half of the animal species caught up in the biggest mass extinction in, say, 65 million years. [2] Had the big drought of 1997 or the even more serious one in 2005 lasted longer, we could have lost the Amazon and many of its species. That is a terribly thin safety margin and the current El Niño has already exceeded, in some locations, the large temperature changes of the record 1997 El Niño.

While physicians are at least accustomed to patients with no moves left, the climate docs have only one patient. So when they contemplate that our profligate ways may have painted us into a corner, it is truly about the big picture, not an individual’s fate.

But it’s not as if we have run out of choices. Being appalled is reasonable but despair is premature. The usual menu of climate choices has been arbitrary pruned by the way in which the issue has been framed [3]. When you see the phrase “irreversible” in a climate discussion, you have to keep reminding yourself that they could have prefaced it with “If we do not remove the excess CO2 from the air, then….”

The framing was once quite logical and followed from the physics of heat. It resulted in an intervention menu that is only about reducing emissions or reducing sunshine by reflecting more back out into space. Even if we achieved zero emissions tomorrow, it would take centuries for the excess CO2 to be absorbed by land and ocean—and even after a thousand years, about 20% would still remain up in the air. [4]

Everything changed about 2003 when it became clear that the excess CO2 absorbed by the ocean acidifies the ocean surface, making big changes in the ocean ecology, striking at the bottom of the food chain [5]. So even if we stopped the rise in global mean temperature, we’d still be in big trouble from this second effect of excess CO2.

The obvious solution to both problems is to remove the excess CO2 from the air, stashing it in long-term storage. But there is surprisingly little discussion of such carbon sequestration among the climate docs. In the public discussion, it also becomes confused with two other things.

• Once it is labeled as geoengineering, it becomes confused with mimicking volcanoes by injecting sulfur in the stratosphere. Since that conjures up “pollution,” many people stop listening.
• Second, it becomes confused with another proposal involving carbon sequestration, that of scrubbing smokestack emissions (not the atmosphere) to slow the growth of excess CO2, which its proponents hope will allow the continued use of coal.

The atmospheric CO2 cleanup is analogous to what an artificial kidney does in removing harmful molecules from the blood. What we need is the functional equivalent of the scrubbers used on submarines that remove CO2 from the air. While plantations of giant scrubbers have indeed been proposed [6], they would require many new power plants to run them.

The other way to reduce the air’s excess CO2 is to unbalance the carbon cycle, typically by preventing some of the CO2 captured by photosynthesis from going back into the air when cells decompose. One has to stash dead biomass where the air can’t get to it. While sealed landfills help, it is only the ocean depths that would appear to have the capacity to draw down all of the CO2 that we have added since 1750.

This scale of cleanup also addresses the other potential source of despair among the climate scientists, an abrupt climate shift. Like a fall or a heart attack, it comes as a surprise and, since you don’t know in advance if it will be minor or catastrophic, the imperative is to prevent it.

For example, global drought used to affect 14% of land surface at any one time, counting only the two most extreme categories of drought [7]. Then in 1982, it doubled. It stayed near double until 1997, when it jumped up to triple. (It came back down to double in 2005, also suddenly). These abrupt steps were all surprises to the climate scientists. There was nothing in the models to predict such a fast flip.

Physicians cannot predict heart attacks either—but they can do a good job of preventing many of them. And what might prevent abrupt climate shifts? We have to stop pushing the natural system so hard and so fast [8] and that means getting rid of the excess CO2 before another flip can happen.

That makes it three big reasons for cleaning up the excess CO2:

1. Overheating,
2. Acidification, and
3. Abrupt climate shifts.

While the time scale for the first two is gradual over decades, that for the third is anytime—say, next year. Any framing of climate choices ignoring the second and third threat is a dangerous oversimplification.

William H. Calvin is a professor at the University of Washington in Seattle, the author of Global Fever: How to Treat Climate Change (University of Chicago Press, 2008).

WCalvin@UW.edu

1. Marengo J, et al (2008) The drought of Amazonia in 2005. J Climate 21:495–516. DOI: 10.1175/2007JCLI1600.1

2. Wilson, E. O., personal communication, 2006.
3. Houghton RA (2007) Balancing the global carbon budget. Ann Rev Earth Planet Sci 35:313–347. DOI:10.1146/annurev.earth.35.031306.140057

4. Archer, D., et al, Atmospheric Lifetime of Fossil-Fuel Carbon Dioxide.  Ann. Rev. Earth Planet. Sci. 37 (2009).

5. Caldeira, K. & Wickett, M. E., Anthropogenic carbon and ocean pH. Nature 425, 365 (2003). . DOI:10.1038/425365a

6. Lackner, K. S., A guide to CO2 sequestration. Science 300, 1677–1678 (2003). DOI: 10.1126/science.1079033
Keith D (2009) Why capture CO2 from the atmosphere? Science 325:1654-56. DOI: 10.1126/science.1175680

7. Dai, A., Trenberth, K. E. & Qian, T., A global data set of Palmer Drought Severity Index for 1870–2002: Relationship with soil moisture and effects of surface warming. J. Hydrometeorology 5, 1117-1130 (2004). http://www.cgd.ucar.edu/cas/adai/papers/Dai_pdsi_paper.pdf with an update in 2006.

8. Calvin, W. H., Global Fever: How to Treat Climate Change (University of Chicago Press, London and Chicago, 2008).