IPCC Summary Statement
One can certainly do better than quote oneself, but hopefully do worse as well.
"... [C]onfronted with the reality of climate change and a human role therein, the central question for deliberation - What is to be done? - is an ethical-political one, not primarily a scientific one (not "primarily" because, while sober scientific judgment undoubtedly must inform deliberation, the answer eludes science's competence). In other words, to suppose that science simply "tells" us how to address [climate change] is a blatant category mistake."
Put another way ... even assuming that we could believe, to a reasonable level of certainty, that a certain course of action would ameliorate climate change significantly, it still doesn't follow that it ought to be undertaken. The costs of so doing may be unjustifiable.