When the House of Representatives passed the American Clean Energy and Security Act on June 26, it was a landmark moment for environmental politics. If the bill passes the Senate to become law — no sure thing, given the 60 votes needed in the upper chamber — it would establish the first national caps on carbon emissions. It would also create what would almost certainly be the world’s biggest greenhouse-gas market, since companies would have the option to buy and sell carbon credits and offsets.
