How Much Money Are We Spending Per Ton of Carbon?

I can't remember the number of zeros before the one in how much this was going to lower global temperature. I also notice that we do our policies have very little cost benefit analysis. This seems like from an economic point of view of full zero. Now maybe there are tipping points. Maybe perhaps there are environmental consequences that they're just not telling us about that are worth spending all this money on. But that doesn't seem to add up.