... the EPA's estimated net global benefits of climate regulations ($67 billion), this march would, on expectation, yield an expected $201 million in benefits - enough to save 60,000 lives.
Careful. An important fact is that money goes differently far in different contexts, and the figure that you are using for "enough to save 60,000 lives" represents an extremely good use of money. The benefits under discussion will not be distributed so as to all go on such cases. In fact many of them are health benefits which have been converted into a dollar value (I couldn't find the conversion rate on a skim read, but I can guarantee that it will be a lot more expensive than $3,500 per life -- probably between 1 and 3 orders of magnitude more, depending on the country they benchmark from).My estimate of the impact of the global effect of the Climate March on humans should be significantly lower using the government's impact estimate, though it's difficult to say how much because the estimate is global, so it involves both American lives and African lives, and there's a good argument that a loss from an African economy is likely to be much more damaging to that country's economy than a comparable to the U.S. This is perhaps the crux of the issue with climate change. But I think this should revise the estimated human impact downward by about two orders of magnitudes.
This led me to realize that I neglected the lion's share of the impact of climate change - the impact on wild animals. The impact in this case is again highly uncertain but seems most likely to increase the impact of climate change by several orders of magnitude (see here for an analysis).
So I'm led to conclude that there is even more uncertainty than that which I pointed out in my original post, and I'm inclined to move participation in that particular march from "toss-up" to "ineffective," but I don't think this bleeds over much to other causes and to smaller- and medium-sized marches more in need of support. Moreover, I'm inclined to repeat the cliché that more research is needed in this area.