The Economist has an interesting article on ideas for cooling the planet directly -- in manners other than CO2 emissions reductions -- and how they are being received:
This gloomy outlook has encouraged new interest in a technological fix. A scientific journal, Climatic Change, published a series of papers on the subject in August, including one by Paul Crutzen, a Nobel-prize-winning atmospheric chemist. Other journals followed up. In November the Carnegie Institution and NASA held a conference.
Many big ideas for global cooling have been suggested over the years. They include seeding the skies with compounds to encourage the formation of low-lying, cooling clouds; building a giant sun-shade in space; and dumping iron in the oceans to encourage the growth of algae that would take in carbon when alive and trap it in on the sea floor when dead.
Ken Caldeira, a scientist at the Carnegie Institution, says the most promising idea may be to spray tiny sulphate particles into the upper atmosphere, where they will reflect incoming sunlight. Nature has already done the proof-of-concept work: volcanic eruptions spew such particles into the air, and the cooling effect is well documented.
Schemes of this kind may sound half-crazy; and, admittedly, they do tend to have some technical and aesthetic complications. Deliberately polluting the stratosphere would make the sky less blue, although sunsets would probably be prettier. Blocking out the sun might keep the planet cool, but it would do little to address other effects of high carbon-dioxide levels, such as the acidification of the oceans.
A more fundamental objection is that the models used in geo-engineering are similar to those used in forecasting climate change. Which is to say, they rely similarly on assumptions and extrapolations.
Still, the basic science seems sound. "I started doing this work in an attempt to show that geo-engineering was a bad idea," says Mr Caldeira. "I still think it's a bad idea, but every simulation we do seems to shows it could be made to work."
Ralph Cicerone, president of America's National Academy of Sciences, has said that geo-engineering inspires opposition for "various and sincere reasons that are not wholly scientific". Others might say the same about its support. One early enthusiast was Edward Teller, an Ã©migrÃ© Hungarian physicist known in America as the "father of the hydrogen bomb", and often cited as an inspiration for Dr Strangelove.
Scientists tend now to see geo-engineering research as a form of insurance policy against the effects of continued global warning, not as an excuse for downplaying the problem, nor for tolerating more carbon emissions in the meantime.
You might expect green groups to applaud this belt-and-braces approach. More often, they resist it in principle, and have little time for the research involved. At worst they seem to see it as a scheme by devious scientists to thwart Nature's just revenge.
For my part, I think most of the resistance to direct fixes falls into two camps:
1) The skeptical camp: Those who doubt we can sufficiently predict what is going to happen in order to pull it off.
2) The Nature (Big N) camp: Those who do not as a matter of principle accept the idea that Nature should be tampered with.
I understand the first objection. Speculating on what we can do about climate change relies on the same conditional assumptions as climate change projection. These assumptions are prone to error; thus, any attempt at a fix needs to be undertaken very, very cautiously.
On the other hand, I don't understand the second objection. All creatures by our very presence modify this planet. Long ago, microbes made oxygen on a planet where there was very little. Organisms modify their environment to suit their needs. Human beings are no different. Furthermore, because resources are scarce, every time I consume resources I am doing violence to others who can't consume them. Our entirely lives are characterized by changing the world.
The suggestion that we shouldn't do anything to change the Earth, that we should let it run its course, just strikes me as very silly. We already changed it a lot. We can either change it back or not, but in either case there is no natural state to change it back to. The state of nature was always something we made up.
I think we can expect more of this debate as global warming progresses.
Not only the Direct Fix approach consequences are impossible to approach, but there is always a problem of _scale_
To avoid solutions costing hundreds of $$ Billions (Kyoto, etc..), they propose solutions that cost also hundred of $$Billions.
In many cases the energy and manufacturing requirements implicit to those solutions often make them net polluters, worsening the problems they purport to fix. Inasmusch the industrial requirements can be evaluated at all.
Take for example the proposition to use "magnesium trees" to fix CO2, already discussed on ScienceBlogs. Although deploying 1 million magnesium trees or devices would indeed capture some CO2, it is not clear there is enough magnesium cureently extracted on the planet for the task. And theres the question what to do with the magnesium trees afterwards. The simplistic solution would be to heat them so they could be re-used, but that would dissipate all the CO2 gathered, which would put us back at the starting point.
My point is that this Earth is a HUGE place. Most solutions do not scale up to the task, or would consume 100% of the industrial output of whole continents...
So I'm wary of all such Direct Fixes would-be solutions.
Actually, the numbers have been crunched for negative forcing via particulates, and it's quite inexpensive, although it doesn't solve problems related directly to excess CO2, which means it's most useful as a plan B. It's fairly well-characterized since the negative forcing from particulates is a major component in climate models, distributions like the one proposed already occur naturally from volcanoes, and particulates don't persist in the atmosphere that long, so it's not that risky either.
Sequestration technologies tend to be more expensive - I've heard 2x the marginal cost of abatement at this point. Whether its better to sequester or burn less is one of the things that would be best sorted out by a market for emission credits where credits are awarded for sequestering and expended by emitting CO2 - as the marginal cost of abatement increases as the simplest reductions are realized, sequestration will look more attractive and may even become a mainstay strategy. Sequestered CO2 will most likely ultimately end up stored as carbonates, which can be made relatively cheaply by combining CO2 with an aqueous hydroxide of any of a number of cations.
The main appeal of sequestration technology is that the benefits from it persist if the regulatory regime collapses. Fossil fuels not burnt due to abatement can simply be burnt at a later date if compliance breaks down, but carbon that's already been sequestered shouldn't be going anywhere.
Actually we have a few different strategies involved, so it might help to classify the different interventions.
(1) as Matt discusses, sequestration schemes. The last I read on Ocean fertilization (a couple of years old study) was that perhaps 10-20% of current emisions could be absorbed that way. So perhaps -if it can be proven to really work, there is some low hanging fruit for a partial solution.
(2) Changes in short wave forcings, here we have two general catagories, those that try to increase ground albedo, and those that
inject something into the atmosphere. The former could possibly include encouraging certain types of vegetation over another -say aspen trees versus evergreens. The later are generally of two types,
(a) low altitude condensation nuclei to affect clouds, and (b) high altitude sulphates.
3) All of the proposed "direct fixes" are expensive and have obvious side effects (like ocean acidification) while saving energy is relatively cheap (and often saves money), is a much more direct fix, and has nice side effects like reducing pollution and dependence on unstable governments.
That's not to say geoengineering shouldn't be part of an eventual resolution, but it's a lousy excuse for delaying action on the things we can do right now.
Another reason for resisting these methods are political. Once we start to deliberately control the climate, for example by emitting sulfur, there will be winners and losers. Who get to decide how much sulfur we want to emit? Where do we emit it given that we can also change climate on a regional level? Those who support solutions like this should realize it demands a world government.
Then there is the matter of timescales involved. The CO2 will be around for centuries, the sulfur has to be continuously added since it has a much shorter lifetime. What about if for some reason the organization that is responsible breaks down? It may be war or just international tension. Then the sulfur levels will suddenly drop and we will get a spike of global warming that might be very unpleasant.