I see a problem with this approach, I think, unless I’m missing something:
1. Are global temperatures warming?
2. Do the negative consequences of the change outweigh the positive consequences?
3. Can we do anything that will reverse the change?
4. Do the positive consequences of the action outweigh the negative consequences of doing nothing?
Notice, the steps have nothing at all whatsoever to do with whether or not global warming is anthropogenic. The climate’s “naturalness” is actually irrelevant. If a 10 kilometer-wide asteroid were hurling toward earth at 100,000 km per hour, it would be a completely natural event. However, just because the meteor wasn’t anthropogenic doesn’t mean that we wouldn’t take actions to deflect it.
Notice also, that we could change question 1 from “warming” to “cooling” and the four-step approach still works. And quite frankly, cooling is probably a more historically problematic situation.
If the answer to any one of the above four questions is “No,” then we should do absolutely nothing about a changing climate. If the answer to all of the questions are “Yes,” then, and only then, should we take any actions.
The first problem is in step 3. It doesn’t seem to account for cost. Suppose there is something that we can do (at least in theory) to reverse the change, but it would result in the loss of (say) a quadrillion dollars in global economic growth over the next century. And that points out the problem with Step 4. Rather than comparing the positive aspects of the action to the negative consequences of doing nothing, we need to compare the positive consequences of the action to their cost. For example, Wikipedia (FWIW) says that the gross world product is about seventy trillion dollars. If we were to get a growth rate of 4 percent over a century, that would mean that in 2113, the GWP would be (1.04)**(100), or about fifty times that amount, or about 3.5 quadrillion dollars. If by arbitrarily making energy more expensive with carbon taxes or caps, we were to reduce that growth rate by a mere half a percent (which is probably a conservative estimate — many of the proposals would do much more economic damage), that would reduce the factor of growth after a hundred years to about thirty, instead of fifty. That is, the world would be 20 times seventy, or 1.4 quadrillion dollars poorer over that period of time. You can buy a lot of mitigation against climate issues with that kind of money.