The market price of carbon is €4.90 ($6.70) per tonne of CO2 in the EU, $11.50 in California. Big oil companies charge $34 or more. That is closer to the “social cost of carbon”—the damage from an extra tonne of CO2—than to the market price. America’s administration recently estimated the social cost at $37 a tonne. These prices change behaviour. A huge amount of attention is paid to government action. But the sort of carbon price some companies are using for planning would, if it became a market price, have a much bigger impact than any of the policies that governments are now talking about.

Companies and Emissions: Carbon Copy, Economist, Dec. 14, 2013, at 70