It's a logical argument that seems (and is) obvious. It's rather an alternate version of my argument, which is that even if global warming is not true, the actions we would take to combat it are still positive actions.

That is, even if global climate change is not true, it still makes sense to reduce our energy consumption, and it still makes sense to search for alternative fuels. For one thing, it's is an undeniable fact that fossil fuels are a finite resource. So are nuclear fuels, for that matter. The only infinite source of energy we have is the sun. (Yes, it's not infinite, but if it goes away, so do we, without question.) If you only had five dollars to your name, would you choose to spend it like a drunken sailor, or would you try to make it last as long as possible?

The counterargument to him is that he's ignoring the costs in the two positive scenarios. That is, if we do nothing and don't need to, there's no cost. If we do something and do need to, there's still a significant amount of cost. As such, you can't ignore the ramifications of those two scenarios, since they have different outcomes.

However, you still come up with three scenarios that we've dealt with and overcome before, and one cataclysm.