Iowa farmer Jeff Labertew knows the price of carbon dioxide as well as he does the price of corn. A company pays him $1 per acre – about 50 cents per ton of CO2 emissions – not to till his soil. (Plowing releases CO2 trapped under the soil’s crust.) But that’s a voluntary program. The company pays him to offset its own emissions. Now a raft of bills emerging in the US Congress wants to mandate something similar – a system where the market determines the price. One bill envisions an upper limit of $7 per ton; others would let it swing far higher. In Europe, which has wrestled far longer with impending mandatory cuts in emissions, the price has fluctuated from $30 a ton to $1. Of all the issues now facing policymakers worried about climate change, the price of carbon emissions may be the most fiendishly difficult to solve. Set it too low and companies have little incentive to curb their emissions. Set it too high and the economy grinds to a halt. At least a half dozen bills in Congress aim to solve the problem by letting the market decide through ‘cap-and-trade’ systems. But […]