I think that the case for longtermism gets stronger if you consider truly irreversible catastrophic risks, for example human extinction. Lets say that there is a chance of 10% for the extinction of humankind. Suppose you suggest some policy that reduces this risk by 2%, but introduces a new extinction risk with a probability of 1%. Then it would be wise to enact this policy.
This kind of reasoning would be probably wrong if you have a chance of 2% for a very good outcome such as unlimited cheap energy, but an additional extinction risk of 1%.
Moreover, you cannot argue that everything will be OK several thousand years in the future if humankind is eradicated instead of “just” reduced to a much smaller population size.
Your forum and your blog post contain many interesting thoughts and I think that the role of high variations in longtermism is indeed underexplored. Nevertheless, I think that even if everything that you have written is correct, it would still be sensible to limit global warming and care for extinction risks.
Thank you very much for sharing your paper. I have heard somewhere that Thorium reactors could be a big deal against climate change. The advantage would be that there are greater Thorium reserves than Uranium reserves and that you cannot use Thorium to build nuclear weapons. Do you have an opinion if the technology can be developed fast enough and deployed worldwide?