The New York Times:

As the United States moves toward taking action on global warming, practical experience with carbon markets in the European Union raises a critical question: Will such systems ever work?

Backers of these markets, which involve setting limits on greenhouse gases and then allowing companies to buy and sell emission permits, see the approach as one of the cheapest and most effective ways to control the gases in advanced economies. The presidential candidates Barack Obama and John McCain have both endorsed the idea.

Yet in Europe, which created the world’s largest greenhouse gas market three years ago, early evidence suggests the whole approach could fail. Carbon dioxide emissions are still rising in many industries, not falling.