This is deeply interesting work, and its quite disturbing it should be associated with the defense department. As the authors themselves note, this is a perfect game-theoretic scenario where countries must cooperate to avoid "geoengineering wars", but have little trust that someone else won't jump the gun first. Having this sort of research done in cloistered, non-public forums is only going to exacerbate this threat. If I were the leader of say, China's climate policies, I'd consider such research, if done as part of a military-industrial complex, as opposed to a collaborative, public effort, a real threat - how do I know that the US isn't going to unilaterally start pumping sulfates into the atmosphere to try to end the californian drought? Or even darker - what if the US found an optimal way to inject sulfates that would cause failed crops in China but leave the west unscathed?