InsideClimate: Aggressive energy efficiency efforts by households, companies and motorists led to the decline in carbon dioxide emissions from energy use in the United States, according to a recent report. The finding contradicts recent studies that say the power sector's shift away from coal to cheap natural gas caused the bulk of reductions. U.S. emissions last year fell by 205 million metric tons, or 4 percent, from 2011 levels. CO2 Scorecard Group, a small environmental research organization, says that nearly...