U.S. emissions of greenhouse gases, which cause climate change, rose just 0.02 percent last year, the smallest annual increase since the recession year of 1991, according to the Department of Energy. At the same time, the U.S. economy grew by 3.9 percent. DOE economist Arthur Rypinski said it would take several years of similar data to establish that structural changes in the nation’s economy are curbing emissions. U.S. emissions are now 10 percent above 1990 levels; in the Kyoto Protocol on climate change, the U.S. committed to reducing emissions 7 percent from 1990 levels by 2012.