Scrubbing CO2 from atmosphere could be a long-term commitment

Jul 01, 2010

With carbon dioxide in the atmosphere approaching alarming levels, even halting emissions altogether may not be enough to avert catastrophic climate change. Could scrubbing carbon dioxide from the air be a viable solution? 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 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 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 were reduced to zero and carbon dioxide in the atmosphere was instantaneously restored to pre-industrial levels.

The researchers found that removing all human-emitted carbon dioxide from the atmosphere caused temperatures to drop, but it offset less than half of CO2-induced warming. Why would removing all the extra carbon dioxide have such a small effect? The researchers point to two primary reasons. First, slightly more than half of the carbon dioxide emitted by fossil-fuels over the past two centuries has been absorbed in the oceans, rather than staying in the atmosphere. When carbon dioxide is removed from the atmosphere, it is partially replaced by gas coming out of ocean water. Second, the rapid drop in atmospheric carbon dioxide and the change in surface temperature alters the balance of the land , causing the emission of carbon dioxide from the soil to exceed its uptake by plants. As a result, carbon dioxide is released back into the atmosphere.

According to the simulations, for every 100 billion tons of carbon removed from the atmosphere, average global temperatures would drop 0.16° C (0.28° F).

Further simulations showed that in order to keep carbon dioxide at low levels, the process of extracting carbon dioxide from the air would have to continue for many decades, and perhaps centuries, after emissions were halted.

"If we do someday decide that we need to remove carbon dioxide from the atmosphere to avoid a climate crisis, we might find ourselves committed to carbon dioxide removal for a long, long time. A more prudent plan might involve preventing carbon dioxide emissions now rather than trying to clean up the atmosphere later."

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jsa09
not rated yet Jul 01, 2010
I can see forward to a future of big factories that just extract carbon from the air making carbon bricks and getting paid big bucks to do it.

Then they will be able to sell the carbon bricks and make more money doing that.
omatumr
1 / 5 (1) Jul 06, 2010
The question is whether CO2 in the atmosphere causes global warming.

CO2 and global temperatures were both rising together, but CO2 continued to rise and global temperatures did not.

Natural solar cycles seem to have much greater influence on global temperatures than CO2 ["Earth's heat source - the Sun", Energy & Environment 20 (2009) 131-144].

With kind regards,
Oliver K. Manuel
Choice
not rated yet Jul 07, 2010
Yes it's going to be hard and there are all kinds of complicating factors, but the longer we wait the more difficult things will get.

Secondly, getting the carbon out of the soils and oceans is also a positive effect. As long as carbon is being sequestered we are improving the entire global system.

By the way for those of you who keep talking about global cycles and El Nino and volcanic emissions, please take a look at these charts and understand that all of these things tend to modulate temperature but only rising CO2 levels shift the whole climate system into hotter average temperatures and new normals: http://politicale.../?p=2754