...Climate Cassandras say the facts are clear and the case is closed.
The consensus catechism about global warming has six tenets:
1. Global warming is happening.
2. It is our (humanity's, but especially America's) fault.
3. It will continue unless we mend our ways.
4. If it continues we are in grave danger.
5. We know how to slow or even reverse the warming.
6. The benefits from doing that will far exceed the costs.
Only the first tenet is clearly true, and only in the sense that the Earth warmed about 0.7 degrees Celsius in the 20th century.
We do not know the extent to which human activity caused this. The activity is economic growth, the wealth-creation that makes possible improved well-being—better nutrition, medicine, education, etc. How much reduction of such social goods are we willing to accept by slowing economic activity in order to (try to) regulate the planet's climate?
We do not know how much we must change our economic activity to produce a particular reduction of warming. And we do not know whether warming is necessarily dangerous. Over the millennia, the planet has warmed and cooled for reasons that are unclear but clearly were unrelated to SUVs. Was life better when ice a mile thick covered Chicago? Was it worse when Greenland was so warm that Vikings farmed there? Are we sure the climate at this particular moment is exactly right, and that it must be preserved, no matter the cost?
It could cost tens of trillions (in expenditures and foregone economic growth, here and in less-favored parts of the planet) to try to fine-tune the planet's temperature. We cannot know if these trillions would purchase benefits commensurate with the benefits that would have come from social wealth that was not produced.