A number of people writing in the comments thread asked what would happen under international law if the United States undertook a massive geoengineering project that went horribly awry and wiped out Bangladesh or some other country. The short answer is—nothing. Bangladesh could complain until it is blue in its face but it would have no legal claim against the United States. There is nothing like tort law in international law; tort principles have to be put together from the ground up in treaties. Those treaties are few and far between; Bangladesh and the United States belong to no treaty that would create liability for a geoengineering failure. Domestic remedies would be unavailable because of sovereign immunity.

This is not to say that the United States would not pay compensation of some sort. Americans would have to deal with world opinion and their own consciences. But suppose, as I suggested in my earlier post, that the United States alone engaged in geoengineering while the rest of the world merrily free rode. One can imagine Americans believing that if other countries are not paying for the benefits, then they should not complain if they end up bearing some of the costs of failure.

All of this underscores the point I made in my first post: the potential for geoengineering does not eliminate the need for a climate treaty, and instead just complicates negotiations. Ideally, negotiators would resolve in advance how the costs of geoengineering would be shared, and who would be responsible for harms caused by failure.

A few people asked how I could be so sure that geoengineering doesn't eliminate the need for limits on emissions. The answer is: that is what scientists think. But common sense suggests this as well. The question is like asking why we don't just eliminate all environmental and nuisance law with the expectation that the government will come up with a device that extracts all pollution from the air, rendering regulation of the polluting activities of individuals and businesses unnecessary. Geoengineering will take place at a scale that only governments can afford, and will require close coordination among the different governments that engage in it. It is hard to understand why people think that geoengineering would avoid top-down government regulation, or cooperation among governments, of the sort that they find so distasteful about limits on emissions.