Monday, December 8, 2008

Vacuum Cleaner for the Air?

Some people litter. It would be better if they didn’t. We can exhort them to do otherwise. It only helps a bit. So we threaten fines. But actually imposing the fines is just too costly. It is cheaper to hire street sweepers. Cleaning the environment is more practical than trying to change each miscreant’s behavior. As with littering, so with greenhouse gasses, I want to argue. It is not that we should stop trying to limit them at the source. But in the final analysis it may be more practical to concentrate on cleaning up the air after the fact.

When we release carbon dioxide (CO2) into the atmosphere it eventually gets reabsorbed – some by trees and plants, but most by the oceans. In the pre-industrial world, atmospheric CO2 was stable at about 270 parts per million. It is now at 380 parts per million and there is an overwhelming scientific consensus that we need to limit carbon dioxide in the atmosphere to at most 450 parts per million, if only on grounds of prudence. So we have 70 parts per million left to spend. At our current rate of output we will do so within 25 years. After that we will only be able to put out what Nature can absorb if we want CO2 to remain at a steady state in the atmosphere. So once we reach our limit, Nature’s rate of absorption will determine our carbon allowance going forward. The prevailing popular assumption has been that the carbon cycle is about 100 years. That is to say, the CO2 put into the atmosphere prior to 1908 has now been fully reabsorbed. But Nature may not be nearly that forgiving. We may be off by a factor of 100! If it takes 10,000 years for CO2 to be fully reabsorbed, once we spend our budget and reach 450 parts per million that will be it! To remain in a steady state, we will effectively need to be on a zero CO2 diet – unless we can remove anything we put out.

Even if we do just that for coal fired power plants, that won’t solve the problem. They constitute only 25% of our total carbon output. The rest comes from many other sources. Some are large, like manufacturing processes. But much comes from you and me as we conduct our daily lives. That is only going to get worse as developing economies grow. Urbanization, electrification, and transportation will drive such carbon output. And even if we had the resolve to do so, regulating the effects of these kinds of social transformations will be extraordinarily difficult to administer.

Instead, cleaning up this output from the air may in the end be a more practical solution. It is a solution that has three other virtues. First, a 100 year cycle would have the virtue of wiping the historical slate clean in a reasonable amount of time. But in a 10,000 year cycle, the carbon output of the now developed world is still with us, and is going to be with us, as is an historical responsibility to clean up our mess. Second, if 450 part per million turns out to be too liberal a level for our collective well being, we would have a way to remove more CO2 to reach a more desirable level. Third, there is no guarantee that a world-wide consensus on what counts as a prudent level of CO2 will emerge. The tradeoff between economic growth and global warming may look very different depending on how well off you are in the here and now. An option to clean the air would allow those who care the most, and can afford to pay for it, to act on their own behalf even as everyone else might benefit.

But is there any prospect of us actually cleaning the air? The fact of the matter is that if carbon capture and sequestration can be developed for coal power plants, a variant of the same technology ought to be possible for ambient CO2. Research in this area is already underway – with the prospect of ambient CO2 capture units being placed in locations that have sustained winds that can be used to both move air through the units and power them. As always, God is in the details. But as we hopefully move forward with a well thought out program for climate research with a new administration, working out those details deserves to be given a high property.


Fulmar said...

well said. And said warily, I suspect. You must know that this is anathema to activists (from Gore and Hansen to the local environmental group). Those who 'get it' soft-pedal it for fear of giving an excuse for complacency, and to avoid attack. The problem is that the 'emissions reduction only' program has already failed, and this will become more obvious once failure cannot be blamed on the US not trying. We'll cut emissions as much as we can, then try to bridge the enormous gap to the CO2 level we can stand with air capture. But a large chunk of the environmental movement cannot even face the need to use coal and capture its emissions. Maybe once Obama has tried his best to salvage cap-and-trade he can lead the climate movement off of Fantasy Island. Until then, Mr. Bunzl, expect some vitriol directed your way...

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