Look how much Sulfer Dioxide are we talking about ?
The general guess is a gram of sulfate in the stratosphere* cancels the effect of over 100,000 grams of CO_2. Given emissions of around 30 trillion kilograms of C0_2 one would need to add (net) less than 300 million kilograms of sulfate per year to cancel that much additional CO_2 and pause global warming. Given the half life of sulfate in the upper stratosphere, if it were sent that high, that corresponds to well a lot more. let's multiply by ten so steady state is cancel ten years of global warming times the half life of sulfate (which is over a year). We are up to 3 billion kilograms of sulfate per year and, why by some strange coincidence that is exactly the amount considered by Kravitz et al in the analysis which concludes that the additional acid precipitation will be a minor problem.
This group at Rutgers is, I think, respected in the field. They are the same group which warned that SO_2 based geoengineering is likely to cause severe problems with reduced rain in India and China which are, from the point of view of the average human, about the two most important aspects of climate.
The amounts of additional SO_2 to be spewed according to their assumptions are 3 to 5 billion kilograms. That would not amount to a doubling of US SO_2 emissions. According to data from the Environmental Defense Fund, the US was emitting 10 billion kilograms of SO_2 in 2002. China emits much more.
I don't see how the increase in US emissions by 30 to 50 %, that is, back to the level the USA emitted in 1990 is going to cause World War III.
I don't see any legal difference between 18 mile high tubes and 1000 foot high chimneys.
Now it is true that SO_2 geoengineering carries the risk of imposing large costs on India and China.
I'm no expert on international politics, but it seems to me that the USA could do worse than develop a partial solution for global warming that, unfortunately, would be worse for China and India than emissions control in China and India.
I mean it seems to me "get your house in order before we are forced to pump up SO2 to keep from roasting" is a pretty effective sounding negotiating strategy if it is a plain direct description of facts and things we will do even though we regret the costs they will impose on India and China.
* yes I know I made fun of people for saying the plan was to inject sulfate. Sulfur dioxide rapidly becomes Sulfate in the presence of water and oxygen, so the stuff up there will be sulfate even if the stuff we send up is sulfer dioxide.
update: teeny tiny factor of 1,000 error corrected. A Tg is a Terragram or a billion kilograms. I wrote a billion grams. ooops.