John’s suggestion boils down to the idea of geoengineering, i.e. planetary-scale technological ‘quick-fixes’ to help cool the global climate. The most common geoengineering proposal is injection of sulfate aerosols into the lower stratosphere, meant to mimic the effects of large volcanic eruptions (which have a temporary but significant cooling effect on global climate). John’s argument is essentially that (1) geoengineering is absolutely necessary at this point, and (2) airplanes could provide an effective means of dispersal of the cooling agents.

Geoengineering via sulfate injection has actually been proposed by some prominent scientists, e.g. Nobel laureate Paul Crutzen. It’s still a very controversial issue, and I won’t discuss the detailed pros and cons here. Suffice it to say that it’s based purely on theory, and although there could be significant benefits from the cooling effect, there would almost certainly be major negative impacts as well. Perhaps most important of these is the continuing acidification of the ocean, which among other things could cause mass extinction of marine organisms. Ultimately, although geoengineering might mitigate the warming effect of increasing atmospheric CO2, it does nothing to address the root cause, i.e. fossil fuel and land use emissions. These are just the basic facts….

As for my opinion of John’s argument, while part (2) might well have some merit, I don’t entirely agree with part (1), i.e. the premise. There are apparently some climate scientists who would agree with it, but I prefer to take a more optimistic approach. I think it’s entirely plausible that society will start curtailing CO2 emissions in time to avoid the need for drastic geoengineering measures — in fact, Jim Hansen, myself, and our colleagues have outlined such measures in detail in several recent papers (http://arxiv.org/abs/0704.2782, http://arxiv.org/abs/0804.1126).

So, the main thing missing is the will, since the means are already there — although they are obviously not being applied to the necessary scale. The global public already seems to recognize not only the seriousness and urgency of the global warming problem, but it also seems to be willing to take action to resolve it (based on public opinion polls from around the world). So, it seems to me that the onus is really on elected leaders and leaders of industry to obey the public will! The change has to start here in the US and in other developed countries — mainly because they are responsible for the vast majority of the problem to date, but also because their actions would likely have a ripple effect among developing countries.

Releasing climate active agents during flight could make the airplanes CO2 negative at a large rate.

It is not the case that I believe this would be a good solution, it just is less worse.

We have to be able deal with scenarios worse than what the IPCC projects — this means, no matter how you flip it, doping the atmosphere with sun screen. Either water, or other cooling agents like the ones we get from large volcano eruptions. This mechanism is after all proven not to induce irrevocable catastrophe — while if the Tundra melts, or the Amazonas burns, then we are in hell.

There is no other realistic immediate delivery at the moment than airliners — they would spread the agents evenly, and the tech is there and a whole lot simpler than rocket tech.

Further, the costs could be shared between governments(through the quota system, and tax breaks), consumers (that could pay a premium to fly with planes on climate cooling duty), and the aviation industry out of self interest.

A small fact: the current IPCC models factor methane emissions from melting tundra. But they do not factor the emissions from the melting lakes in north russia. Measurements indicate that the methane release from the lakes is equal in size to that from ground. Mind that this is factors working into a feedback loop, and the halflife of methane that escapes to the atmosphere.

It is insane to accept a solution to a problem on this scale with no guarantee of success nor any fast enough mechanism to mitigate failure of either estimates or the implementations of the (too weak?) measures.