Just about two years ago, Chemistry Nobelist, and atmospheric scientist Paul Crutzen opened a huge can of worms by suggesting that, since the world doesn’t seem to be getting its act together to significantly reduce CO2 emissions, it would be prudent to think about emergency measures in which we engineer ourselves out of the crisis by monkeying directly with the Earth’s solar radiation input instead of dealing with the CO2 content of the atmosphere. The specific proposal was to inject chemicals into the stratosphere that would form sulfate aerosols and hence block sunlight. Crude estimates suggest that the aerosol fix (if it is indeed a fix and doesn’t create more problem than it solves) is more technologically feasible than sci-fi dreams of sunshades at the Lagrange point. Not to say technologically feasible, necessarily, but not so far out as the other schemes. Crutzen’s idea, and related geoengineering proposals, have been discussed here on RealClimate. The subject is once more in the news, thanks to this chipper little op-ed by Ken Caldeira, which appeared in the New York Times this week.
Update: I just noticed that our original RealClimate piece was done before Crutzen’s article was published. You’ll find his article here (subscription not required).
The attraction of the proposal is that we are already conducting an uncontrolled experiment on aerosol-based geoengineering, through the sulfate aerosols injected into the troposphere by dirty coal plants. Along with a lot of nasty health and environmental consequences, this has had some inadvertent benefits in restraining some aspects of global warming. As coal plants get cleaned up in the future some of the cooling aspect of the tropospheric aerosols will be lost. Since aerosols last much longer in the stratosphere than they do in the rainy troposphere, the amount of aerosol-forming substance that would need to be injected into the stratosphere annually is far less than what would be needed to give a similar cooling effect in the troposphere, though so far as the stratospheric aerosol burden goes, it would still be a bit like making the Earth a permanently volcanic planet (think of a Pinatubo or two a year, forever). It might make sense to take a small portion of the aerosol that would have been dumped into the troposphere by retired dirty coal plants, and inject that directly into the stratosphere where it will restore the lost cooling effect while (hopefully) doing less harm than the old stuff dumped into the lower atmosphere. To go farther, though, and count on offsetting the entire unrestrained CO2 production of the coming century with engineered aerosols is fraught with peril.
Scientists just love to think about this kind of stuff, and I’m no different.Harvard is hosting a small workshop on aerosol-based geoengineering, and I have to say I’m looking forward to it. It’s like having a shiny new toy, and the chance that you might actually get to use it to play around with the real Earth and see what happens has a certain fatal attraction to it. Then, too, science thrives on a spirit of free inquiry, and it would be anathema to say that there are some things that just shouldn’t be thought about (though there are certainly some things that, once thought about, shouldn’t be built). But, there’s a real danger of jumping the gun and giving the impression that we already know we have a way out if things get too bad. Ken Caldeira’s Op-Ed is a case in point. “Which is the more environmentally sensitive thing to do: let the Greenland ice sheet collapse, or throw a little sulfate in the stratosphere?” is the way he frames the issue. To be sure, Ken only gets 400 words to make his case (which seems to be that the folks who work on this sort of stuff ought to get some more money), but those 400 words leave little room to explain the vast array of problems that need to be resolved before we can even begin to think of this as an out. Caldeira’s Op-Ed makes it seem like a slam-dunk, needing maybe only a diversion of 1% of climate research funds in order to do the trick.
Here are a few of the problems that need to be worked out: There’s the issue of the effect of the aerosols on stratospheric chemistry (think how unanticipated the chemistry of the Ozone Hole was), and the question of just where the aerosols would go once injected. There’s the question of the effect of the aerosols as cloud-condensation nuclei if they work their way into the tropical upper troposphere — an increase in high cirrus clouds could well lead to warming. Then, there’s the full range of possible effects on the atmospheric circulation. Held and collaborators (PNAS 2006) have implicated the joint effect of aerosols and greenhouse gases in the trend towards Sahel drought, and generally there are issues in what inhomogeneous aerosol forcing might do to things like the North Atlantic Oscillation. Also, a planet with a dim Sun and high CO2 is not the same thermodynamically as a planet with brighter Sun and lower CO2, because the reduced sunlight at the surface is not able to sustain as much evaporation, which has consequences for global rainfall. In a recent essay in Le Monde, Edouard Bard has pointed out additional problems with geoengineering.
In my mind, the most serious peril of sulfate geoengineering is one that stems from a problem that is not at all in dispute: the fact that the lifetime of CO2 in the atmosphere is centuries to millennia, whereas the lifetime of aerosols in the stratosphere is at best a few years. That means committing the future generations to continue the aerosol injection basically every year more or less forever. We’re banking a lot on confidence in future stability and prosperity of the world here. A patrician in the glory days of the Roman Empire might well have expected the Pax Romana to go on forever, but really nobody expects a Dark Age.
One also has to wonder whether the international treaties and organizations needed to agree on and execute a geoengineering scheme are significantly easier to realize than the agreements needed to decarbonize the energy future, which would offer safer and more durable climate protection. And once you open the Pandora’s box of geoengineered climate, what do you do if nations disagree about what kind of climate they want, or if some poor nation objects to suffering drought in order to cancel heat waves in Chicago? Great fodder for science fiction novels about climate wars, but I’d prefer not to have to think about it happening for real.
The problem is that geoengineering a sunshade is being sold as insurance long before anybody has any idea whether it would work and what the unintended consequences would be. It’s not really insurance. It’s more like building a lifeboat, but a lifeboat based on a design that has never been used before which has to work more or less perfectly the first time the panicked passengers are loaded into it. The problem is that by the time we know enough to have any confidence at all in this lifeboat, CO2 may have risen to the point where the lifeboat becomes not just a backup, but a necessity. Would diverting 1% of the world’s climate research funds into this problem clarify the issues in time? I doubt it. Would devoting 10% a year to the problem be worth it? I doubt that, too, in comparison to more pressing research needs.
Now, can we please get back to the serious business of trying to figure out how to economically reduce global CO2 emissions?
Raypierre: “A Pinatubo or two a year forever.” That depends on the time frame and the goals. Assuming 1 Pinatubo = 6MT S, the amount that ultimately was converted to aerosol, the quantities required to offset all new forcing from 2000-2100 range from 0.5 Pinatubos by 2030 to 1 Pinatubo by 2070. This also assumes any negative forcing from tropospheric aerosols steadily decreases and is gone by 2050. Otherwise, even less aerosol is needed.
If the goal is to offset all forcing from 1700-2100, then 0.5 Pinatubos are required by 2015, 1 by 2050 and 1.5 by 2100.
To get a 75% reduction from 2000 to 2050, a target to prevent the 2 degree C rise, requires 0.5 Pinatubos by 2050.
Of course, we still don’t know what the threshold is for reducing incoming sunlight that would prevent harmful climate change. That’s why the modeling work and field trials are required. It may be much less than the above.
A point of technical clarification since this gets messed up everywhere and by everybody. You can’t inject sulfuric acid aerosols. They have to be created. They don’t come in 5-gal buckets either, although Ken’s analogy was a good one for the general audience he was trying to reach.
I covered the problems, perceived and real with this in the Tierney blog response. With regard to ozone, it has been estimated that mid latitude ozone depletion reached 3-7% or thereabouts with Pinatubo. However, there were no reports of surface damage from increased UV from this.
Given that we wouldn’t have to get much farther than 0.5 Pinatubos before 2050, this gives plenty of time to see if there are any ozone depletion effects. Plus, the ozone destroying chemicals are decreasing at the same time, so by 2050, there may be no issue here at all.
There is also no evidence that Pinatubo led to significant increases in cirrus clouds. Remember, the troposphere cooled during the Pinatubo aerosol period, not warmed. Also, note that aerosol droplets from volcanic eruptions are much more dispersed than those from say aircraft exhaust plumes that do produce a form of cirrus clouds under certain conditions.
The concern that reduced sunlight may impact photosynthesis also seems without merit. Again, there is no evidence of Pinatubo causing problems with this, either due to a reduction in total radiation or a decrease in beam vs. diffuse, beam being around 40% normally (that’s the disk of the sun).
The main concern and rightly so, is a decrease in global precipitation due to less evaporation due to less sunlight reaching the surface. The threshold has to be determined at which this would become a problem and as I said in the Tierney blog, varying the aerosol distribution latitudinally and vertically might be able to counter this. Again, the modeling must be done.
It should also be said that modeling studies need to examine not only the potential downsides of the aerosol approach, but also the benefits as well as ways to do it in a beneficial way.
I am growing tired of the BUT YOU SEE THIS MIGHT GO WRONG response that is automatically generated when we haven’t done much more than make rather rudimentary engineering concept proposals. Let’s find out if it can work before we decide it won’t.
The argument that going the aerosol route will result in a committment of hundreds of years discounts unnecessarily further technological advances. For example, air capture of CO2 is not possible on a climatologically significant scale in 2007, but may be in 2057.
The argument about international agreements seems a little specious also. Isn’t that the same argument that said we shouldn’t try Kyoto? Granted, Kyoto has not lived up to expectations, but it didn’t take 50 years to negotiate.
One thing that was correct in Raypierre’s analysis. If we wait too long to investigate this and the other geoengineering technologies, we may have to use them, but at a time not of our choosing and under conditions resembling a global triage.
Re: #41
“In most areas of science, uncertainty weakens evidence and makes it harder to prove a hypothesis.
But two US experts argue that climate change is different, because of the way its uncertainty is a reflection of sensitivity.”
Am I the only one that bristles when things like this are said? Specifically the “but this is different” part. Typically, when people stand up and say “but this is different”, they’re deluding themselves. Remember the “new economy” where profits don’t matter? What idiocy! Remember “cold fusion”? Remember all the perpetual motion devices that have been “invented”?
And it’s doubly troubling for scientists to claim that uncertainty in relationships evokes certainty in conclusions. It doesn’t. It actually evokes uncertainty in conclusions and to claim otherwise is not supportable.
I’m sure that some out there will say that using the best information we have as inputs gives the corresponding range of outputs (from major impact to catastrophic impact) and that those results demand that action be taken. But it still comes down to models that contain significant uncertainties with respect to our fundamental understanding of systemic interactions and therefore MUST be viewed as lacking in accuracy.
re: #41
“. . . but we need carbon taxes urgently . . .”
Can anyone tell me the reduction in CO2 emissions per unit of carbon tax? From that we can calculate the the amount of tax required to reduce emissions to an ‘ineffective’ level and additionally the total tax costs for such a program. What is the time constant for the effects of a carbon tax to be detected in the atmosphere?
BTW, what is the emissions level required to significantly abate future Global Warming?
The penultimate paragraph in this piece is interesting.
Thanks.
Martin Vermeer (46). I like that idea. The Chinese would only need to build a couple and with their recent interest in high altitude engineering (Qinghai–Tibet railway) they may be up to the task of a 20km+ tall smokestack…
Actually the Nature article includes a diagram (I have no idea how serious it is) that shows some kind of facility (It does not appear to be a power plant) with a ~35km flexible hose teathered to a “high altitude blimp” injecting SO2 into the stratosphere. The article also includes a diagram of the outer space Frizbee like sunshades (16 trillion!) Raypierre mentioned in the first paragraph. These diagrams give the article a certain “Popular Science” like feel. I half expected to turn the page and read about the latest advances in the field of flying cars.
Lou Miller (29), a somewhat similar plot was presented in the ‘60’s sci-fi movie “A Crack in the World” In this case the bomb down the volcano stopped the world from splitting in half. It ends with the attractive blond scientist admiring our new second moon…
Doesn’t anybody in here comprehend the lunacy of ‘engineering the atmosphere’?
The more we study the atmosphere, the more there is to learn. We know so little about it that we cannot safely predict the outcome from changing a single input.
And we somehow propose the notion that we can engineer a ‘solution’ to a problem whose parameters are not yet nailed down?
Solving an unknown with an unknown is somehow a comforting thought?
It scares the daylights out of me…
Is nuclear fusion was to be cracked by 2080 would it be too late or in time to resolve our energy needs? People would like a technology fix as it shows us that progress is all around and that we can still use technology to resolve our issues whilst progressing into the future.
Re #55:
I sure do! It’s the ultimate in human arrogance to believe that we know enough about the system to understand all of the side-effects that would be created.
Tracking back on Alvia Gaskill, I found many articles already dealing with this subject. One example:
http://www.smh.com.au/news/world/weird-science-to-the-rescue/2006/09/25/1159036472330.html?page=fullpage
“Inadvertent geoengineering of the climate is already under way,” says Alan Robock, a professor of meteorology at Rutgers University. “Trying to counter that with advertent geoengineering when we have no idea of the consequences is a very bad and dangerous idea.”
Focusing on the idea of injecting sulfates into the stratosphere, he identified a series of risks with the scheme after studying the impact of the eruption of Mount Pinatubo in 1991. These included a decrease in ozone, enhanced ultraviolet radiation and acid rain caused by sulfates turning to sulfuric acid.
“And we wouldn’t have blue skies any more. Skies would turn grey across the globe and psychologically that could have a very negative impact.”
=====
I repeat that the danger of floating concepts such as this, is that CO2-emitters will use it as an opportunity to argue that it would be “less expensive and less disruptive” to allow them to avoid serious reductions in output. After all, if we are going to “need” this sort of geo-engineering anyway, why go through the expense of grafting carbon reduction technology onto their processes, (can you here it now?) “unnecessarily increasing the cost of energy so that it is out of reach of poor and underdeveloped countries (not to mention, poor people in developed countries).
In only a year of following this issue, I am still completely certain that this argument will gain traction as the concept of geo-engineering our way out of global warming becomes more popular.
End result: an increase in white noise and FURTHER DELAY.
Off Topic: GEO4 is out
The new Global Environment Outlook 4. 550 pages.
A quote from a short story on it in the Guardian Unlimited below followed by a link to the multimedia report itself…
GEO-4 Report
United Nations Environment Programme
environment for development
http://www.unep.org/geo/geo4/media/
You don’t have to recapture it and do it over again the next year — assuming the sequestration isn’t leaky. –raypierre]
Considering the number of people who could be killed due to a leaky bit of fizzy CO2 sequestering, I’m not real sanguine about the technology.
If I am following the evidence correctly, increase in man made Co2 will cause a greater heating during warming trends, even though apparently the initial warming periods seem to be naturally caused. Which makes sense.
Currently the natural forces are in a warming trend and increasing the warming trend through manmade emmissions may cause a more rapid warming.
My question concerns policy.
Assuming global warming is true, it could then be argued that curtailing manmade emmissions could help moderate the current rise in temperatures.
But what happens if the natural causes reverse and start a cooling period? Would not a rise in level of manmade emmissions then help moderate the cooling earth? Wouldn’t that be a very good thing?
Should we begin a policy to reduce emmissions if by time the effects are felt in the environment the natural causes have reversed the warming trend? Wouldn’t we then be contributing to global cooling? Wouldn’t that be a very bad thing?
This seems as good a place as any to ask this question…
Several months ago, the Economist ran an article about a proposal made by Alfred Wong of UCLA at the AGU to directly expunge CO2 from the atmosphere. Some details are given in the article, but briefly, the idea was to ionize CO2 over the arctic with giant lasers. The CO2 ions would circle around the Earth’s magnetic field lines at a precise frequency. A huge RF transmitter tuned to that frequency could give them more energy, which would cause them to follow the field lines… straight up into space.
He claimed to have done calculations showing that the CO2 expunged this way would dwarf the CO2 produced by whatever powered the laser/RF transmitter.
This would not seem to suffer from any of the problems with geongineering mentioned in this article. Directly removing CO2 from the atmosphere is a very clean solution- carbon expulsion trumps CCS any day of the week.
But I haven’t heard anything about it since. Why not? Is there some obvious flaw that has escaped me? Did someone discover an error in his calculations? Or can he just not get funding?
> a nuclear weapon was exploded on or under the ocean surface,
> then water vapour would be ejected into the stratosphere.
Alastair, please. THINK. You can look this stuff up.
http://www.metacafe.com/watch/34566/imax_underwater_nuclear_test/
If there’s a more truly evil way to use a nuclear weapon than other use, setting it off underwater is that.
“In case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area. The particles contain mostly sea salts with some water; these can have a cloud seeding effect causing local rainout and areas of high local fallout. Fallout from a seawater burst is difficult to remove once it has soaked into porous surfaces because the fission products are present as metallic ions which become chemically bonded to many surfaces…..”
http://en.wikipedia.org/wiki/Nuclear_fallout
Fermi suggested there may be no intelligent life in the universe, outside of brief episodes confined to planetary surfaces before they develop science and end themselves. How can people be so smart and so incredibly stupid?
Paul M: Have no fear, there will be traces of our civilization millions of years hence. About 1980, some forward thinking people erected a granite monument near here with some advice for survivors or whoever cares to read these words of advice:
(In 8 modern languages and 4 ancient ones:
Maintain humanity under 500,000,000 in perpetual balance with nature.
Guide reproduction wisely – improving fitness and diversity.
Unite humanity with a living new language.
Rule passion – faith – tradition – and all things with tempered reason.
Protect people and nations with fair laws and just courts.
Let all nations rule internally resolving external disputes in a world court.
Avoid petty laws and useless officials.
Balance personal rights with social duties.
Prize truth – beauty – love – seeking harmony with the infinite.
Be not a cancer on the earth – Leave room for nature – Leave room for nature.
http://en.wikipedia.org/wiki/Georgia_Guidestones
“…What do you do if nations disagree about what kind of climate they want…” is no more an issue for geoengineering than it is for truly effective Kyoto-like agreements. Both require some agreed cost-benefit about optimal global climate.
Walt Bennett re:55,
I think that most people probably share your reservations. The problem is that any time we cary out some grand scheme to resolve a big problem, the law of unintended consequences tends to bite us on our collective posteriors. I’m sure the internal combustion engine seemed like an excellent idea at the time, too.
We should also remember that many of the economic remedies being bandied about will be perceived similarly by economy and business types. In reality, our understanding of economics is much cruder than our understanding of atmospheric dynamics, so understanding the unintended consequences and risks posed by a carbon tax or cap and trade scheme is even more difficult. At least with greenhouse gas molecules, they aren’t saying, “Hmm, how can I scam the system and get rich off of this development.”
So, I suppose we will bandy solutions back and forth for awhile, each camp suggesting changes in the other’s bailiwick that they don’t fully understand. Scientists may want a change in the economics, while economists would like to see a change in the physics. Neither is likely to be realized.
re #53:
Can anyone tell me the reduction in CO2 emissions per unit of carbon tax? From that we can calculate the the amount of tax required to reduce emissions to an ‘ineffective’ level and additionally the total tax costs for such a program. What is the time constant for the effects of a carbon tax to be detected in the atmosphere?
A good place to start is:
http://www.carbontax.org
with some numbers at:
http://www.carbontax.org/wp-content/uploads/2007/09/carbon-tax-_-4-sector-model-_-25-sept-2007.xls
and elsewhere.
Iron fertilization of the oceans is a cheap and low tech method to sequester CO2 faster than normal.
It is also far safer than injecting sulfate aerosols into the atmosphere
and is much longer acting.
http://en.wikipedia.org/wiki/Iron_fertilization
As a side benefit, sea life will flourish.
Pretty much a win-win!
Re. #53, Dan Hughes:
See #59.
IMO it’s misleading, because the US administration is still insisting (a) on only discussing emissions intensity targets (for reducing, not total emissions, but only the rate of growth of US emissions), and US emissions intensity will reduce even under business as usual; and (b) the US administration is still insisting on only considering voluntary targets, despite the fact that even many major US corporations are calling for mandatory caps and despite the fact that there is no evidence that their existing voluntary targets have made any difference.
The docket for the Clean Air Act documents other problems with sulfates in the air. Acid rain. Health effects.
Have we forgotten? Any culture that forgets so rapidly deserves to fail.
This is off topic, but I was hoping someone could explain the difference (or point me in the right direction) between NASA’s temperature analysis and Hadley’s. I know the primary difference has to do with the poles — NASA uses data that the Hadley (and the satellites) don’t deal with. However, I don’t understand the details. Any pointers?
Thanks!
The best geoengineering that I can think of is the process of pumping CO2 from the air by growing biomass, using pyrolysis to generate bio-oil and biochar from the biomass, then returning the biochar to the soil where it aids in maintaining fertility while sequestering carbon for centuries, AKA terra preta. Here is a good review paper: http://www.css.cornell.edu/faculty/lehmann/publ/FrontiersEcolEnv%205,%20381-387,%202007%20Lehmann.pdf
Carbon dioxide will have climate and ocean chemistry consequences lasting tens of thousands of years or longer. The environmental risks associated with continued CO2 emission loom large.
Therefore, I am in favor of outlawing CO2 emissions as soon as possible (perhaps grandfathering existing CO2-emitting devices). Actions that increase climate (and chemical) risk and destruction of natural habitat clearly need to be curtailed.
We seem to be in relatively near-term risk of losing Arctic ecosystems and being committed to losing at least parts of the Greenland ice sheet. There is a significantly non-zero risk that precipitation patterns will shift in ways that could contribute to widespread hunger.
Obviously, reducing and then eliminating CO2 emissions is the appropriate public policy response — and we should attack this problem with at least the same vigor with which we attack perceived military threats.
That said, it is entirely possible, if not likely, that political and economic forces will respond too slowly and insufficiently to adequately reduce climate and chemical risk associated with CO2 emissions. (Of course, we should do our part to assure that this does not happen.)
If a climate catastrophe should occur, there will be demands upon politicians to do something. Because of the thermal inertia of the oceans and the long atmospheric life-time of CO2, not to mention the inertia associated with transforming energy systems, it will be too late to forestall catastrophe through emissions reduction.
Let’s take the worst case scenario: Let’s say that geoengineering schemes would merely screw things up further. Wouldn’t any good research program demonstrate that clearly? Wouldn’t it be good for politicians to know that there is no viable technical fix?
I did work researching direct injection of CO2 into the ocean interior, and was a coordinating lead author for an IPCC chapter on the topic. The result of that research was basically that directly injecting CO2 into the ocean interior was not a particularly good idea, and now that option is largely off the table. [By the way, I was criticized by some at the time for coming to a conclusion that led to a reduction in research budgets.] Good research can eliminate chimeric options.
On the other hand, let’s say that some geoengineering options would have some effectiveness at eliminating some adverse consequences of climate change (i.e., could prevent ecosystem loss, reduce hunger, etc.). It is still an open question whether we would ever want to deploy such a system, but at least we would be making decisions based on facts.
As I see it, the main danger associated with geoengineering options is its effect on social and political systems. Just as flood insurance leads people to live in the flood plains of rivers, the perception of the existence of geoengineered climate insurance could lead people to take more climate risk, and work less diligently to reduce CO2 emissions.
Of course there are a host of other problems associated with geoengineering schemes: There will some geographic distribution of winners and losers, with consequent political ramifications; there will be near impossibility of getting complete international consensus on deployment of such options, which implies at least some international political strife; the schemes will be imperfect, at best, at reversing climate change damage and will likely introduce new damage of some sort; these schemes will not do anything to help with ocean acidification; these schemes raise large issues associated with intergenerational equity; these schemes introduce climate risk associated with rapid cessation of deployment (perhaps associated with political turmoil or institutional breakdown); such schemes will not reverse direct CO2 effects on land ecosystems; and so on and so on.
That said, and understanding the risks are great, it is at least possible that these schemes in some form may be able to reduce overall environmental risk. I know if I were a polar bear, I would want somebody to be looking into them.
I suggested in my New York Times Op-Ed that 1% of our climate change technology research budget be directed in this direction with 99% directed towards emission reduction. The exact numbers are somewhat arbitrary, but my point was that putting 0% in is too little and putting a large fraction in would be taking too much emphasis away from emissions reduction.
If we can somehow arrange that we never build another CO2-emitting device, I would happily call for the geoengineering research budget to remain at $0 per year. But given that CO2 emissions and atmospheric CO2 concentrations are higher than ever and increasing more rapidly than ever, it does not seem premature to start thinking about what we might do should disaster strike, even if only to make sure that we do not rashly do something that might merely make matters worse.
[Response: If I were a polar bear, I’d worry about people puffing up overconfidence in the geoengineering solution to the point that the last chance at taking steps that might actually have solved the problem are passed over. While going extinct when the crisis hits, I might worry that a premature and ill-considered geo-engineering “cure” might not only fail to save me, but in the process drive ten tropical species extinct through some unanticipated effect on tropical rainfall. If something starts to go wrong, can we even do regional modelling well enough to determine whether the geoengineered aerosols are to blame? I have no objection to people thinking about these things. As I said, I’m going to Dan’s meeting at Harvard, and even looking forward to it. I just think people ought to be a bit more careful about how they talk to the public. –raypierre]
Also, re. #53, Dan Hughes: the article you linked to (and its penultimate paragraph) is misleading in another sense as well; because no-one credible is claiming that emissions reductions at the required scale will be “easy”. Some measures that could be taken now and aren’t being would be fairly easy to implement and almost cost-free, such as introducing regulations to force US car manufacturers to increase fuel efficiency, taxing car use based on fuel efficiency, banning most tungsten and halogen light bulbs, replacing street lights with solar-powered ones (which would cover its costs after a few years); investing properly in geothermal energy research, and so on; but the scale of emissions reductions that are needed requires far more than these sorts of measures, and it certainly won’t be easy – although the refusal of the US administration to consider even the above measures indicates that they are not even slightly sincere about addressing climate change.
However, what many economists and the IPCC are saying is:
(a) that the economic cost of “business as usual” (as a result of the impacts of global warming) is likely to be far greater in the long term than the cost of achieving emissions reductions at the required scale,
(b) that the cost of emissions reductions at the required scale is likely to be manageable (1% of global annual GDP to be invested in mitigation according to some economists), provided that meaningful action is taken immediately; and
(c) that the longer governments wait before taking serious action to cut emissions, the greater the eventual emissions cut will have to be. The IPCC 2007 WGIII SPM states on page 15: “The lower the stabilization level, the more quickly this peak and decline would need to occur. Mitigation efforts over the next two to three decades will have a large impact on opportunities to achieve lower stabilization levels.” And Kallbekken and Rive 2007 states: “a 20-year delay means that we must reduce emissions at an annual rate that is 5 to 11 times greater than with early climate action.”
But this is very different from claiming that it will be easy, as the article you linked to states that people are claiming (quite apart from the difficulties of overcoming the disinformation campaign that has so far successfully reduced support among the less well informed members of the public for the necessary measures to be taken – that also won’t be easy).
Slightly off-topic, but a reminder regarding urgency: Wednesday’s TNYT (2007 Oct 24), has an article entitled China’s Green Energy Gap by Keith Bradsher starting on page C1 (Business Day section) and continued on page C4.
The subtitle is Coal Stays King as Cleaner Fuels Can’t Keep Pace With Demand.
Quoting two sentences: “The country built 114,000 megawatts of fossil-fuel-based generating capacity last year alone, almost all coal-fired, and is on course to complete 95,000 megawatts more this year.
For comparison, Britian has 75,000 megawatts in operation, built over a span of decades.”
Re #62:
“Several months ago, the Economist ran an article about a proposal made by Alfred Wong of UCLA at the AGU to directly expunge CO2 from the atmosphere. Some details are given in the article, but briefly, the idea was to ionize CO2 over the arctic with giant lasers. The CO2 ions would circle around the Earth’s magnetic field lines at a precise frequency. A huge RF transmitter tuned to that frequency could give them more energy, which would cause them to follow the field lines… straight up into space.”
It’s patently bogus. Accelerating a CO2 molecule to escape velocity (15 km/s), even with 100% efficiency, requires far energy more than the energy released burning one carbon atom and even the associated hydrogen atoms.
Matter requires 112 MJ/kg to reach escape velocity. Oil has about 120 MJ/kg (heat) or 60 MJ/kg (electric, assuming 50% efficient). Oil releases about 3 kg of CO2 per kg of oil burned, so you would be releasing roughly 5 kg of CO2 for each kg raised to escape velocity, assuming 100% efficiency from electricity to kinetic energy.
PS: This ignores many other issues that make this idea dead on arrival.
Re: 29, the bomb down the volcano movie:
Ever see the 1965 flick “Crack in the World”, starring Dana Andrews?
I was thinking of a remake: drop a nuke into Erta Ale. Get some REAL rifting action in the Great Rift Valley.
Now we just need to cast the part of the beautiful blonde plate tectonicist and her impossibly handsome geo-engineer boyfriend. Well, OK, just the blonde plate tectonicist — I can play the boyfriend. I wonder if Heather Locklear is looking for work…
Re. #73, Ken Caldeira, a thoughtful and thought-provoking post; but I wish your NYT article had been more similar in tone to your post. I can imagine denialists using your op-ed as an excuse to delay taking action on emissions, whereas the tone of your post, and its qualifications, make it much less easy to abuse in that way.
Re. #56, Pete Best:
See #59, and #74, especially point (c).
Re #68 on iron fertilization. Upwelling cold water and nutrients (#36) brings up iron from the deep ocean.
RE: 54 The blimp with the hose. This is Lowell Wood’s idea to simplify the delivery system for the sulfate aerosol precursor. He mentioned in an article in Rolling Stone that a Kevlar hose and a blimp at 85,000 ft could be used to carry sulfur dioxide.
Several problems with this. If you have ever flown a kite and who hasn’t, you know that the longer the string the harder it is to control. The highest altitude that a tethered blimp (called an aerostat) has ever reached for an extended period of time is around 15,000 ft. Thus, it would be considered a major technological advance to tether a blimp floating in the Overworld stratosphere.
There is presently interest in developing high altitude aerostats for the space and defense departments and to serve as a platform to generate electricity (windmills in the sky). To date, however, these remain concepts with little progress in the hardware department.
From a lift standpoint, it could be done as the blimp would be able to support the hose and tether. The effect of high altitude winds on the aerostat and the hose and tether could cause catastrophic failure.
The low temperatures could also cause the sulfur dioxide to liquify. SO2 has a boiling point of -10C at sea level and the temperatures at 20-35Km range from -33 to -53C. If the SO2 was generated from burning elemental S in air, the moisture in the air could be carried up the hose and freeze, adding weight to the hose as well as potentially blocking it. If dry SO2 were used from an existing source of the gas, liquification is likely unless it is very hot.
Since I am assuming the pressure in the hose will still be 1 atm, I did not consider any decrease in boiling point with altitude. Hydrogen sulfide has a boiling point of -60C and would be a better candidate.
The pressure required to pump the SO2 or H2S 85,000 ft may also be problematic as these gases are heavier than air. In my opinion, F-15s and MIG 31’s along with stratospheric balloons containing a mixture of hydrogen and H2S are the most practical delivery systems in 2007.
Re #76: “It’s patently bogus. Accelerating a CO2 molecule to escape velocity (15 km/s), even with 100% efficiency, requires far energy more than the energy released burning one carbon atom and even the associated hydrogen atoms.”
Not sure if you read the article, but the idea had nothing to do with accelerating ions to escape velocity. (Also, I don’t think that the concept of escape velocity is meaningful for a single molecule, given that it tends to collide with other molecules rather frequently.) I’m not going to try again to summarize, so please consult the article if you have questions.
Not sure what the other problems you allude to are, but I’ be interested to hear them.
Re #63
Hank,
You wrote: “Fermi suggested there may be no intelligent life in the universe, outside of brief episodes confined to planetary surfaces before they develop science and end themselves.” I think he was probably correct :-(
You also wrote that he continued “How can people be so smart and so incredibly stupid?”
I just cannot believe that he had ME in mind when he said that!
However, I am smart enough to see that mankind is stupid enough to cause its own destruction. And I am now coming to terms with the fact that I am too stupid to prevent it. So, reluctantly, I have to agree with you and Fermi that I too, like the rest of humanity, am stupid.
Fermi is also famous for his paradox which is the apparent contradiction between the high probability of extraterrestrial civilizations’ existence and the lack of contact with such civilizations.
It is solved easily if one accepts that any evolving civilisation which develops will inevitably burn up its fossil fuels before it has time to realise that they are the only means of escape from their planet. In other words they will exhaust their resources before they discover their importance. Just like the Easter Islanders!
As Private Frazer said “Waur doomed!”
A littledimensionalanalysis is a dangerous thing, but Crutzen has been on the aerosol case since 1980or so.
Could it be that having struggled for a literal generation to achieve a modicum of realism in 3-D GCM’s, modelers are abashed that quasi 2-D albedo modification offers more coolth per buck than manhandling and warehousing hundreds of tons of greenhouse gases per capita. Surfaces happen.
What are we worrying about? Global warming is good for your health! Check it out:
US Press Secretary Dana Perino told journalists that global warming isn’t that bad: after all, “many people die from cold-related deaths every winter. And there are studies that say that climate change in certain areas of the world would help those individuals.”
http://www.blogowogo.com/blog_article.php?aid=1060578&t=11
(sigh) About Kevin’s comment #43 about swallowing a horse. We all swallowed the horse(and all the manure that goes with it) when the Supremes annointed Present Occupant and his merry band of jokers.
Getting back to the topic of global engineering,Ken Caldeira makes a good case for studying the proposal. It deserves that. We shouldn’t want to be Luddites and reject any good faith effort out of hand. It’s a shame that we have to act like this with our backs to the wall. For every watt/m^2 of Sunlight that’s blocked, we ought to require a reduction of a certain amount of Gt/yr of carbon from going into the atmosphere.
Re. #56, Pete Best: [Is nuclear fusion was to be cracked by 2080 would it be too late or in time to resolve our energy needs?]
I don’t see that as at all relevant. Nuclear fission works now. It can do anything that fusion can (unless you’re planning on technical miracles like cold fusion), such as replacing coal-fired generation within a few decades. The only real obstacle is hysteria on the part of some of the public.
If someone came up with a working fusion design this year, it most likely wouldn’t be any cheaper or better, and the people who scream “Omigawd, it’s nuclear! We’re all gonna die!” would scream just as loud at nuclear fusion as they do at nuclear fission.
Knowledge and understanding of the world ocean and its proper use are essential to reinforce our GHG reduction efforts. We can use solar absorber rafts to evaporate seawater to enhance orographic rainfall on the east coast of Australia. We can use arrays of ocean current turbines in the Antilles Island passages to steer some current around the Caribbean and the Gulf of Mexico to lower sea level in the Gulf and provide electric power to the Antilles islands for desalination. #36 provides global cooling and nutrient supply.
Alastair, I was paraphrasing Fermi, not quoting, just to be clear that those aren’t direct quotes of Fermi himself.
The example here, thinking it smart to increase aerosols while continuing to emit CO2, despite the rate of change in the physical chemistry of the oceans — science known far more precisely than the physics of the atmosphere — is a classic.
How can smart people be so utterly stupid about pH change?
If we could point to aliens doing this to our planet we’d recognize an enemy without hesitation. Instead we don’t point at each other, we wave hands instead.
Chapter1, I can only hope there’s some sense to that idea, though the math ought to be published and looked at by someone competent to address it. The idea of building huge lasers pointed up over the North Pole will undoubtedly be very interesting to Mr. Putin and others who are already worried about the USA building an advanced anti-missile system using rockets. The only thing they’d find more threatening would be building them in orbit, I imagine. I’ve wondered if the HAARP system had some way to prime a pump just to get CO2 in the upper atmosphere more likely to radiate in the infrared; the notion of tickling it so it will actually depart the planet seems like a lovely one, if there’s any substance to it. But I’m puzzled why big lasers would be needed, especially ground-based ones — how much brighter than the Sun in the designated wavelength would some such installation have to be, to be doing anything more than sunlight does now?
Here’s an earlier article found by searching for mention of Dr. Wong, UCLA and AGU; closest I’ve come. Anyone else found anything?
[PDF]
Electromagnetic Wave Interaction with the Auroral Plasma
File Format: PDF/Adobe Acrobat – View as HTML
Alfred Wong… Geophysical Union (AGU), San Francisco, California, December 1996. …
http://www.physics.ucla.edu/~pau/thesis.pdf
20> The proposal of Gregory Benford et al. to pump nanoparticles with a size range that would selectively reflect UV radiation seems more seductive.
I believe they also advocate using CaCO3 rather than sulfate. Does anyone know why everyone else seems to prefer sulfate particles? Is it just because there is more sulfate data, since that is what volcanoes produce?
Re. #86, actually your post strikes me as irrational. It is not “hysterical”, for example, to point out that there is still no concensus on a long term plan for the disposal of the nuclear waste that is guaranteed to be both safe and affordable. Or to point out that this waste will be highly radioactive for many centuries. Or to point out that the published costs of nuclear-generated electricity never take into account the total lifetime cost of nuclear plants, including decommissioning, maintenance and waste disposal, so one is never able to compare like with like (it’s the only form of electricity in which overall costs are ignored). Or to point out that when Britain privatised its electricity industry it suddenly found that had to heavily subsidise its nuclear industry because it was so inefficient compared with all other forms of electricity generation that were in use, and its costs had previously been hidden. Or to point out that many accidents and leaks in nuclear plants have happened, although most were covered up at the time, that at least one has been extremely serious (Chernobyl), and at least one another has come very close to being (Three Mile Island). Or to point out that if a terrorist flew a plane into a nuclear reactor it would be far more serious than 09/11.
I’m fairly agnostic, these are difficult issues; but in my view anyone on either side of the nuclear debate who characterises the other side as all being irrational are themselves being irrational.
[Response: Nuclear has its share of problems, but if it comes down to a choice between building nuclear or building coal, nuclear starts to look better. Especially if building coal means you are going to have to bet the bank on geoengineering working. I’m a big believer in wedges, and I imagine we can count on nuclear for one or two of our stabilization without unacceptable risk. As for the economics, the right thing to do would be to get rid of nuclear subsidies, and instead put on a sizeable carbon tax. With that, nuclear may start to outcompete coal +sequestration, or for that matter maybe all the renewables we all love would become the winners. –raypierre ]
re: #92 in which raypierre said,” … and instead put on a sizeable carbon tax.”
I asked above at #53, Can anyone tell me the reduction in CO2 emissions per unit of carbon tax?
Still no answers. If the question doesn’t make sense tell me why.
As someone once said, “Those who refuse to do arithmetic are doomed to talk nonsense.”
chapter 1 posts:
[[But I haven’t heard anything about it since. Why not? Is there some obvious flaw that has escaped me? Did someone discover an error in his calculations? Or can he just not get funding?]]
The idea of making the CO2 in the atmosphere escape to space misses one very obvious point. You need to impart escape velocity to each kilogram of CO2 that leaves. Figure out the kinetic energy of a kilogram of CO2 at escape velocity (Ve = 11,200 m/s), and multiply by the number of kilograms of CO2 you want to remove. That gives you an absolute minimum figure for the amount of energy needed to do it. The proposal of using lasers to ionize CO2 and spin it into the Earth’s magnetic field is interesting, but the highest efficiency lasers I am aware of are CO2 lasers, which convert 25% of the input electricity to beam power — so multiply the energy cost by a factor of four. Do you see the objection?
[[Nuclear fission works now. It can do anything that fusion can (unless you’re planning on technical miracles like cold fusion), such as replacing coal-fired generation within a few decades. The only real obstacle is hysteria on the part of some of the public. ]]
There are other obstacles as well, such as the facts that nuclear power plants take a long time and a lot of material to build, release radioactive material into the environment in “unplanned releases,” generate waste which must be kept isolated from the biosphere for as much as 10,000 years, and create more potential bomb material cruising around the economy. Oh, and occasional catastrophic accidents are possible, too.
NEW REACTOR TECHNOLOGY: SAFETY IMPROVEMENTS IN NUCLEAR POWER SYSTEMS.
Health Physics. 93(5):547-559, November 2007. (abstract only)
http://www.health-physics.com/pt/re/healthphys/abstract.00004032-200711000-00022.htm;jsessionid=Hjshk1ZkqPpJfsdfgnTn0cPn0c3Zkprfv3pxNvccCPc7jfgBf7vn!1071114923!181195629!8091!-1
“… research on the next generation of nuclear energy systems that can be made available to the market by 2030 or earlier, and that can offer significant advances toward these challenging goals; in particular, six candidate reactor system designs have been identified. These future nuclear power systems will require advances in materials, reactor physics, as well as thermal-hydraulics to realize their full potential. However, all of these designs must demonstrate enhanced safety above and beyond current light water reactor systems if the next generation of nuclear power plants is to grow in number far beyond the current population. This paper reviews the advanced Generation-IV reactor systems and the key safety phenomena that must be considered to guarantee that enhanced safety can be assured in future nuclear reactor systems.”
Nature perfected many ‘bioengineering’ solutions long before men came on the scene … one could do well by simply noticing the methods it uses that have been proven over aeons to work …
Microscopic phytotplankton species expend substantial parts of their very limited energy budget making dimethyl sulphide which simply escapes from them and passes up into the atmosphere, creating sulphate aerosols as it breaks down with hydroxl radicals and ozone …
Why do they expend energy on this wasteful loss of energy and resources , obviously it is not an intelligent act, they have no brain, but rather it could be seen as a mechanism that evolved as-it-were by chance , a system that endures ad thus has shown that it works , by which they make the storms which interestingly whisk them up from the ocean and spread them worldwide … are they are simply ‘buying’ a transport mechanism then? It appears from paleo-science that there is more to it than that, the clouds that they generate as a control mechanism on the earth’s temperature, this is yet another feedback mechanism for survival of all life on the planet and has been working for aeons of time, right back to the earliest life here… the planet was made more hospitable to life by life itself, geo-engineering on grand scale by the tiniest of plants in the sea… which outstrips the cleverest of plans by humans to geo-engineer and more relevantly does no harm to the planet …
One only has to cite that CO2 from human greed in exploiting buried animals and plants being recycled [oil and coal] -over a criminally short period of time without gaining anything much in sense or future sustainable energy from the massive resource- this which we see as waste could so easily be turned back into living biomass by nature , nature has such massive power to expand and cope with our problem if only we would let it, even help it , rather than standing by and letting it die out and make things worse as the dying seas yield up even more CO2 and methane and much more besides…
Simply put, we NEED the seas that we are currently almost half way to killing [half of coral reefs already dead or severely damaged and dying , phytoplankton unable to make their defensive carbonate ‘shells’ because of CO2 acidification of the oceans … these are the base feed of most life in the oceans, fisheries are failing because their food is being killed by us, and we are of course next in line to starve… it makes little sense since we know all this …]
We still have a tiny window of time in which to expand life in the seas , The very safest place to sequestrate our CO2 that nature is used to handling in recycling … and we can harvest the seas again as they become productive, we CAN farm then responsibly as they expand from being dead … [most of the ocean is dead , but from lack of only micro-nutriment , it takes less to bring it to life than the land , but nature has never found the way for most of the sea .. only patches of it and in dynamic moving fashion with only some more lasting areas [sea upwellings of deep water for instance]
Instead the current dozen projects on ‘the geritol solution’ simply waste their [and our!] very limited time window on dumping 100 times more iron than is needed into the sea with even more acid to get a simple algal bloom , some of which [at worst it seems only 1%] falls to the bottom when the whole lot dies…. it is insanely short-sighted, dangerous, and inefficient, when a hundredth of the same iron, slowly increased in the ocean would cause the existing ecosystem to expand naturally and take up many times the amount of Co2 and store it as increased biomass , all recyclable by nature and a massive carbon sink – with only the minutest help from mankind of supplying a miniscule amount of iron which nature nevertheless never has managed to prevent from precipitating out in sea-water and sinking to the depths … despite many creatures that slow the process down to a crawl , just not quite slowly enough though to let much of the oceans come alive … only man can do that, to save the oceans from mankind and for mankind …
We have such a small time window, and we really are clever enough to put this together and get it right first time as is now seemingly required if we are to be prudent and aim NOT at brinkmanship in pushing the planet to the limits it can bear, but to maximise the chance of survival of most life on which we depend …
There is casual talk of ‘ONLY’ 50% of species dying out with our latest plans to limit our behaviour … if one killed even 10% of species on the planet it would ensure our eventual death and the death of most life here eventually, because essential nutriments , most elements of chemistry, are recycled by various species… the whole only works as a whole,…
One cannot cut out a man’s liver and say he has only lost a small percentage of his body, he will live… he will live for a whole, but he will surely die soon …
the planet is no different, different species do the work of recycling all the elements so the whole works… the whole will die quickly if even a few ‘key’ species are lost ,and their life in turn depends on other species … we just cannot afford to do what we are doing, we know it, yet are not putting it together fast enough, the window of opportunity is closing fast and faster with time, the feedbacks are vicious already against us and getting more so…
nature is the biggest force we have to help us and she needs a little help because she just doesn’t operate as quickly as the problem we have throw against her, it is killing her and thus will kill us , because she feeds us too … we do not live on money or oil, but on food … we cannot afford to kill more species and yet we are talking about our most ambitious plans doing just that … we are going the wrong way with inadequate plans that do not take account of all we know, and we do seriously not have time for this mistake …
We have no moral right not to put right the mess we made of the planet already by being greedy and lazy and complacent … we owe that to nature … she needs our help because the problem is too large without our help to solve one small problem she never mastered which we now understand and can help her with so she can clear up our mess and save us too …
Re #92:
I once heard someone say of the ‘no-nukes’ environmentalists that if they ever found out that the Sun was a run-away nuclear reaction, they’d sue to shut it down. :-)
Now, not being an expert in either fusion or fission (I know just enough to be completely wrong), the issue of long term storage of the spent fuel is THE reason we need to keep pushing for fusion.
This also points out why determining whether CO2 is the cause or a sympton of global warming is so important. Everyone (environmentalists, EPA, power companies) agree that the sulfur and mercury pollutants of coal-fired plants are an environmental problem, but the technologies for scrubbing those pollutants are relatively well known. While expensive, they’re no where near the cost of carbon sequestration.
Assume for a moment that the denialists are correct and that CO2 is not causing global warming, then the obvious solution to the energy crisis in the US is coal (at least in the near term). The coal reserves in the US are sufficient for delivering power for at least a century and potentially much, much longer. That would allow us to wean ourselves off of oil (a fuel that we are quickly running out of) while giving us time to find other options. Green options like solar, wind, geothermal; Advanced nuclear options like fusion.
I am a big proponent of an electrical economy. We need to move off of oil as our fuel-source in the near term (20 years or so) on our own terms or we’ll be confronted with doing it on Oil’s terms (“sorry guys, there ain’t no more… whatcha gonna do now?”).
I see this as more important in the near term than reducing CO2 output to control global warming (mainly because the US contribution to CO2 as a percentage of the overall world production is dwindling). The efficiencies gained by going to an electrically powered transporation system could offset most if not all of the added production. For example, the cost of energy required to move a car using electricity is approximately 1/4th that of using oil. If we allow enough coal fired plants to supply the required electricity for our cars, one source I have read said that we’d only need 20 plants. Our electrical power grid now is designed to supply peak production but runs well under peak for most of the day (especially the overnight hours). A rechargeable electric car would even out the peaks and power plants could be designed to run at higher efficiencies due to a smaller delta between peak and off-peak.
This would also allow for the introduction of green power sources whenever they become available. all we’d have to do is build the new power plant (be it solar, fusion, cold-fusion, etc) and turn off the old power plant. That would have absolutely no effect on the transportation system.
And in the meantime, we could walk away from the morass called the Mideast
RE # 92
Dave, I disagree with your comment that:
[in my view anyone on either side of the nuclear debate who characterizes the other side as all being irrational are themselves being irrational.]
You likely are fairly agnostic about a nuclear power future but you also repeat the same litany of complaints the anti-nuke crowd throws up at every conceivable opportunity. Ironically, most of those voices tell us at every opportunity that civilization has only a decade or two to save the planet’s ecosystem from a global warming free fall that triggers eventual total chaos…meters of sea level rise, perpetual drought…. add your scenario here.
Now, compare that sliver of open window opportunity to the anti-nuke campaigners slogans of disposal challenges, costs and risks for thousands of years. Is that a rational balancing of concerns or are those voices so ignorant of the progress being made by engineers in South Africa, China, France and elsewhere to take the pebble bed nuclear reactor to the commercial deployment stage in this next decade.
Global warming is not an environmental problem. The environment is the victim. It is an engineering and environmental challenge of superhuman dimensions.
That the environmental community and activists are not heavily endowed in the science and engineering side of the issue they are so passionate about (and no more passionate than I) is understandable. It takes time and diverts attention from their campaigning to push back and grapple with the hard facts of the modern world and the rapidly expanding lesser-developed world.
Electricity and petroleum are on a level with food and water to maintain survival of a massive civil population. As US population grows so does its demand of electricity and oil. All the hand waiving and admonitions of less-is-beautiful advocates will not change the direction of the increasing demand for electricity and oil throughout the world.
Until we environmentalists put down the placards and banners and come to grips with the massive challenge of meeting the needs of an expanding world economy our movement will forever be typecast as made up of ludites and dreamers who really believe Americans will bicycle and walk to work even if the weather is ugly.
The world does not work as the anti-nuke campaigners think it does. If there is an analogy to that thinking, I say it is the neo-con belief the US can dictate its terms of democracy-forming of people and nations we have no fundamental understanding who they are and how they operate.
Search the pebble bed literature and see if some of your concerns might be alleviated, if only a bit.
RE: 91 Benford’s idea (as best I understand it) is to use diatomaceous earth milled to 0.1 micron in diameter and release this over the Arctic to selectively scatter (not reflect) UV light back into space and then apply the strategy globally.
See this website for more information on aerosol scattering.
http://newmediastudio.org/DataDiscovery/Aero_Ed_Center/
Selectively scattering UV would be difficult, since the UV wavelength range is between 280-400nm with the largest part that reaches the surface between 320-400nm. Particles 0.1 micron in diameter, 100nm would be small enough that they would tend to accumulate together and soon the particles would become large enough to scatter not only UV, but also visible light.
Solid materials like the diatomaceous earth would also be candidates to absorb water vapor, further increasing their size and reducing their atmospheric lifetime.
I haven’t seen any estimates from him as to the expected residence times for the aerosol particles, except in a presentation where it seemed he was thinking they would last two seasons. In the Arctic, the sunlight is compressed into a six months period, so that would be the only time that a sunlight scattering scheme would be useful. MacCracken suggested a similar approach in his Climate Change paper last year, also to minimize the presence of the surfaces on which ozone depletion reactions occur when the polar spring arrives.
Benford says that the diatomaceous earth, unlike the sulfuric acid aerosol would be less chemically reactive and thus safer to use. However, the sulfuric acid aerosol doesn’t participate in chemical reactions that destroy ozone. It only provides a surface on which the reactions can occur. The diatomaceous earth probably can also.
The reason why sulfate aerosols rather than solid particles are being considered is primarily atmospheric residence time and partly because of the experience with volcanic aerosols.
As a practical matter, I think it highly unlikely that the quantities of particles he envisions can be manufactured. That said, delivery into the lower stratosphere over the poles is possible with current aircraft like the 747 that can fly at 40,000 ft.
Release in the Overworld (>54,000ft) for a global program could be done with fighters, but since the bulk density of such nanomaterials is around one fourth that of liquid H2S or SO2, the number of flights to achieve the same release would be much larger. Unless releases could be done gradually, clumping of the material would likely result in it just falling rapidly to the surface. In either case, the dust could get into the airplane engines and cause them to fail.
Delivery of such particles with artillery guns isn’t practical with available technology. Delivery by stratospheric balloons is possible, although since the release would have to be all at once, most of the material would probably clump together and fall rapidly from the sky.
Designing balloon delivery systems where a port would open and the dust would gradually be released greatly complicates a program that would have to launch more than 1000 balloons per day to achieve its goals.