For most of the past century, diesel engines have been associated with smoky, smelly trucks and buses. Now there's a surprise: A new generation of diesel-powered passenger cars is delivering punchy performance and emission levels so low they pass muster in all 50 U.S. states. Boasting good fuel efficiency, the new "clean diesels" may well overtake hybrids in the market for eco-cars.

Set aside, for now, the really complex and costly financial implications of climate change. Ignore the tricky abstractions of carbon trading. Forget the worries over flooded cities and the ins and outs of renewable energy.