Most people don’t know what it means, and most of those who know what it means have little or no idea how it’s calculated, but the “social cost of carbon” may be one of the most important concepts—and numbers—in the climate-and-energy-policy debate, and particularly in American regulatory activity.

The Obama Administration’s inflated estimate of the SCC has been its primary justification for all the economy-busting regulations it’s trotted out to force reductions in fossil fuel use.

The incoming Trump Administration could turn all that on its head. If, as the empirical (as distinct from modeling) scientific evidence (as opposed to models’ hypotheses) increasingly shows, added atmospheric CO2 causes very little global warming, its costs are very low, too. And if, as empirical scientific evidence has shown unambiguously for generations, adding CO2 to the atmosphere causes plants to grow better and therefore makes more food available for all animals and people, the SCC could be negative—i.e., each ton of CO2 emitted could do more good than harm, which means we should reward rather than punish emitters. The incoming Trump EPA team understands this. Get ready to see some really interesting developments. For more, see:

• How Climate Rules Might Fade Away
• Trump’s Secret Weapon to Reverse Obama on Climate
• Empirically-Constrained Climate Sensitivity and the Social Cost of Carbon (A major academic, peer-reviewed paper supports lowering the SCC by anywhere from 30% to 80%.)
• Experts Debunk Obama’s ‘Social Cost of Carbon’ Estimate—It Might Be Negative!
• The Social Cost of Carbon

Even without addressing the magnitude of CO2’s warming (presumably negative) and fertilizing (presumably positive) effects, the SCC can be hugely changed by changing the discount rate used to compare current costs of regulation with future costs of warming. A 5% discount rate puts the SCC at $12 a ton; 2.5% at $65 a ton; but 7% makes the SCC negative, i.e., turns CO2 emissions into a benefit, not a cost. And EPA has applied a 7% rate to other emissions. So why’d it apply 5% to CO2? Certainly not good science or economics. That leaves politics.