The $50 per tonne federal carbon tax would have to double to meet emissions targets without new regulatory curbs on polluters, says an environmental group. The current tax to take effect today nationwide will add an extra 12¢ to the cost of a litre of gasoline by 2022, as well 14¢ more for diesel, 13¢ for aviation fuel, 10¢ per cubic metre of natural gas and 8¢ a litre for propane: “The federal government may change the pricing system.”