General Motors announced Tuesday that its long-awaited Chevrolet Volt hybrid, a battery- and gas-powered electric vehicle, can get 230 miles per gallon in city driving, dwarfing every other car on the market in fuel efficiency.

Paul Solman: The third in this week’s series of conversations with economist Simon Johnson has to do with the cap and trade debate — whether cap and trade is a good idea, the feasibility of a carbon tax, and…