The continuing expansion of renewable energy technologies, advances in energy efficiency, and the rapid shift from coal to natural gas for generating electricity combined to bring down U.S. carbon dioxide emissions last year to their lowest levels since 1994, according to a report by Bloomberg New Energy Finance. The report said that CO2 emissions fell 13 percent in the last five years alone, which means that the U.S. is now more than halfway toward reaching President Obama’s goal of cutting emissions 17 percent below 2005 levels by 2020. The Bloomberg report said that while the shift from burning coal to natural gas is a significant factor in the U.S.’s continued emissions reductions, the adoption of renewable energy technologies is also playing an important role. The report said the cumulative installed solar, wind, geothermal, and biomass-based energy sources in the U.S. reached 86 gigawatts last year, compared with 43 gigawatts in 2008. Another growing source of emissions cuts is adoption of hybrid and electric vehicles, with 488,000 people in the U.S. purchasing these energy-efficient cars last year.