I think you need to discount possible farther future benefits, because so much change can intervene and make the analysis invalid. That is, when people want to

I think you need to discount possible farther future benefits, because so much change can intervene and make the analysis invalid. That is, when people want to do something-- risks tend to be understated and possible future benefits tend to be overstated. I don't back the precautionary principle, but I do think risk in cost-benefit analysis has to be viewed from a pretty cautious place, in general (not just science).