Grist: Last week, environmentalists got a rare bit of good news: U.S. CO2 emissions dropped 3.8 percent in 2012, according to the U.S. Energy Information Administration. That brings emissions to their lowest level since 1994, and represents the fifth drop in seven years. And unlike some previous years, the drop was not the silver lining to a shrinking economy: The economy grew by 2.8 percent in 2012. That means carbon intensity, which is CO2 emissions per dollar of gross domestic product, dropped by an...