The lack of certainty over global climate change is actually very similar to the “debate” over evolution.
At this point, the overwhelming consensus of informed opinion is that the global climate is changing, and that human activity is at least part of the causality. Still, our understanding of climate mechanisms (and therefore our predictive ability) is very poor.
The question is (in the corridors of power): Since we don’t understand the climate anyway, is it really prudent to alter our behavior?
The question should be: Even though our understanding of climate matters is poor, is it at least sufficient to describe certain “boundary” issues, in order to steer policy?