A new study by scientists at the Carnegie Institution suggests that while removing excess carbon dioxide would cool the planet, complexities of the carbon cycle would limit the effectiveness of a one-time effort. To keep carbon dioxide at low levels would require a long-term commitment spanning decades or even centuries.

Previous studies have shown that reducing carbon dioxide emissions to zero would not lead to appreciable cooling, because carbon dioxide already within the atmosphere would continue to trap heat. For cooling to occur, greenhouse gas concentrations would need to be reduced. "We wanted to see what the response would be if carbon dioxide were actively removed from the atmosphere," says study coauthor Ken Caldeira of Carnegie's Department of Global Ecology. "Our study is the first to look at how much carbon dioxide you would need to remove and for how long to keep atmospheric carbon dioxide concentrations low. This has obvious implications for the public and for policy makers as we weigh the costs and benefits of different ways of mitigating climate change."

For the study, Caldeira and lead author Long Cao, also at Carnegie, did not focus on any specific method of capturing and storing carbon dioxide from the ambient air. The possibilities include approaches as diverse as industrial-scale chemical technologies and changing land use so more carbon dioxide is naturally absorbed by vegetation. For the study, the researchers used an Earth system model under projected conditions at the middle of this century when global surface temperatures have been raised 2° C (3.6° F). They then simulated the effects of an idealized case in which carbon emissions were reduced to zero and carbon dioxide in the atmosphere was instantaneously restored to pre-industrial levels.

(ScienceDaily)

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