According to a recent report by the U.S. Energy Information Administration, heat-trapping greenhouse gas emissions declined 3.8% last year even though the nation's economy grew 2.8%. The decline is attributed to efficiency gains, an increased use of natural gas verses coal and an unusually warm winter. Increased use of renewables such as solar or wind is also a factor. Unfortunately, CO2 emissions continue to rise worldwide. Get the details and see the 55-year CO2 tracking chart.