I thought it was at least 200. According to the Wikipedia article on coal, an estimate from British petroleum is 155 years. I don't know under what assumptions this was made, if we don't just adjust for economic growth but also assume that coal should substitute for oil and gas when those run out, it would become less.

We may even come to see acid rain as an acceptable price to pay to prevent global warming.

Anthropogenic SO2 emissions have recently fallen by several percent per year. Because an SO2 sunscreen would increase SO2 emissions by several percent, it would set back progress in cleanup by several years. For example, if this were to start tomorrow, it would make the rain about as acidic as it was in 2004 (and reverse global warming, of course). We might not get back down to today's emission levels and resume progress until 2008.

If we suggest that delaying progress in SO2 cleanup by a few years might be worse than the effects of ongoing global warming, what would that mean? It seems to me that it would would be equivalent to announcing that global warming is an almost negligible problem.

(BTW, if we got good at making useful stuff, like greenhouses and photovoltaics, why would we be inclined to destroy the biosphere?)

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