[grifpete]

It seems that the article has a simple thesis. a) climate is hard b) human activity is affecting it but because it's hard it's tough to know how much c) hence it's difficult to know what the correct policies should be.

As an economist might say - without clarity on the positive, it's challenging to resolve the normative.

But I am a little puzzled by the failure to discuss outcomes in terms of mathematical expectation. And of course, the author knows more than I ever will about this.

Hence: If our activity might just trigger a sequence of events leading to human extinction...(in other words such a sequence is conceivable and credible) then even if the risk is low as estimated by our (weak) ability to assess such risk, then the outcome is surely so hideous that if our policies are taking us in a direction that makes such an outcome more likely (even if we are not sure by how much) then there is cause for caution and re-examination of policy. It seems to me that our situation at present is of this form. Despite our poor understanding and the fact that things aren't 'settled' (as if they ever will be) this unsettled 'knowledge' is all we have and we have to take it seriously, most particularly if the possible outcomes are ghastly. We can't just wait for better science.