One of the crucial issues in any assessment of climate change policy is how to handle discounting and risk. The Stern review (Ch 2) goes back to first principles and gets the main issues exactly right. The reason for both discounting and risk premiums, in economic analysis, is that the marginal value of a dollar of income is lower when we are rich than when we are poor. Hence, we’re prepared to pay for insurance when we are well off in order that it will pay out when we are badly off. Similarly, if we expect income to rise over time, a dollar of income now is worth more, at the margin, than a dollar in the future. The same points are relevant in considering income distribution but this isn’t covered in the parts of the report I’ve read so far.
In addition, there’s a justification for “inherent discounting”, reflecting the fact that some future event (most probably bad, but perhaps good) may mean that “all bets are off” in relation to future consumption levels. Individuals should have reasonably high inherent discount rates, since we may not be around next year, but the appopriate rate for a community is much lower, being confined to the risk of catastrophes like nuclear war.
The Stern review also has a good discussion of probabilities, including the recent literature on problems where there do not exist well-defined probabilities.
The quality of the economics here is very high, and sets a new bar for discussion of these issues.
There’s more on Stern from James Wimberley