1. I agree it is premature to downselect. 2. I think the effectiveness and possible downside effects of stratospheric aerosols have been in question since the get go. (Not sure what you mean about the "past few weeks".) Of course there are technical as well as environmental uncertainties related to marine cloud brightening. The existence of uncertainties is why you need a research program. If we knew everything, a research program would be unnecessary.
3. People have been proposing schemes semi-continuously over the past years. The idea that there are quiet people out there just waiting for a global solicitation to bring out new ideas seems a bit unrealistic. You cannot really do a rigorous comparison that is particularly meaningful without doing more research first. You can do some preliminary screening based on likely effectiveness, risk/damage, cost, ease of deployment, rapidity of action,etc, but this science and technology is in its infancy. It is like it is 1902 and you are doing a comparison of different forms of air travel. Do you think that transcontinental jets would come out high on the list? 4. The Royal Society, given the limited information available, tried to do a multi-dimensional assessment of different proposals, much as you suggest. After going through that process, I think most of the participants concluded that you would need to know a lot more about each option to really do a multi-dimensional assessment that would produce results that would really stand the test of time. http://royalsociety.org/geoengineeringclimate/ I think there are some things that you can show, from fundamental physical principals, are not easily scalable, require huge masses or areas or amounts of energy, etc. I think you can screen some of these things out as non-starters, but I think it is premature to think we can make a ranking of options that will stand the test of time. For example, do we have any real conception of the potential for innovation in "designer" particles? Is there potential to create particles that could be turned "on" and "off" in desirable temporal and spatial patterns? Is there potential for particles that would maintain position, at least latitudinally? If such particles could be "permanently" emplaced, say in the mesosphere, you might be willing to have a relatively high per-particle capital cost. (On the less optimistic side: Do we really understand long-term effects of increased diffuse radiation on terrestrial ecosystems? Do we really understand the effects of increased stratospheric particle loading on ozone chemistry? Do we really understand the consequences of marine cloud brightening on precipitation patterns? etc.) To evaluate options, the scientific and technical work needs to be done. We may be able to distinguish between plausible options worthy of further research and options that can already be shown to be non-starters, but I think it is premature to think that we can now develop detailed assessments that will stand the test of time. ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [email protected] http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 On Sat, Feb 13, 2010 at 7:14 AM, Mark Massmann <[email protected]>wrote: > All- > I'd like to hear other's opinions on this, but it seems to me that > it's too premature to consider down-selecting all of mankind's > geoengineering options to 1) Stratospheric Aerosols and 2) Marine > Cloud Brightening. > > In just the last few weeks, SA's effectiveness and pollution have come > into question. MCB has a number of technical uncertainties as well. > What if neither scheme actually works due to unforseen issues, or has > technical (many-year) delays, or doesn't work nearly well-enough? > > To help ensure the best chances for success (in one or more schemes), > what I believe is really needed here is an all-out global solicitation > (~2 to 3 months) for potential alternative schemes, and doing a > rigorous comparison next to SA and MCB. > > If all issues could be transparently compared between schemes (maybe > using a fault-analysis tree), I think we could work together to rank > preliminary feasibility (thoroughly identifying potential faults as > well as possible ways to solve them). I would envision another 3-5 > schemes to be selected from this work and be added to SA and MCB, at > least for the initial phase of feasibility research. > > Taking a close look at 5-7 schemes would give me (and I believe > mankind in general) a lot more confidence in the direction we are > going. After all, this may be the biggest problem mankind has ever > had to face- we need to take the best shot(s) at this that we can! > > Please comment- > Mark > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]<geoengineering%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. 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