Americans are spending less time on the road and in more fuel-efficient cars, helping to drive an annual decrease in the amount of greenhouse gasses. An inventory on the Environmental Protection Agency says emissions were down 3.4 percent in the U.S.

Americans are spending less time in their cars and driving vehicles with greater fuel efficiency, helping to spawn an overall decrease in the U.S. inventory of greenhouse gas emissions of 3.4 percent. The decline experienced from 2011 to 2012 is also attributed by the Environmental Protection Agency to limited "new demands" in passenger transportation and an overall warmer winter across the nation, which drove down consumption of heating fuel. In its 19th year, the national overview of greenhouse gas emissions is presented to the secretariat of the United Nations Framework Convention on Climate Change and includes a look at greenhouse gas emissions that are removed via the uptake of carbon through natural processes. The inventory released Tuesday shows that greenhouse gas emissions overall are down 10 percent from levels in 2005. Electrical power generation remains the primary source of greenhouse gas emissions at 32 percent, followed by transportation at 28 percent and industry at 20 percent. Decreases in the inventory are being credited to the transformation in electricity generation from coal to natural gas. Levels in 2012 were a little more than 6.5 million metric tons, of which the overwhelming majority - 82 percent - is carbon dioxide. EPA officials say greenhouse gases are the primary driver of climate change, leading to increased heat-related illnesses and deaths, and worsening air pollution that can cause asthma attacks and other respiratory problems. Transportation activities accounted for 34.4 percent of the U.S. carbon dioxide emissions, and the overwhelming source was passenger cars. The report notes that overall, from 1990 to 2012, total transportation emissions rose by 18 percent due largely to increased travel but limited gains in fuel efficiency over the same time frame. Under President Barack Obama's Climate Action Plan, the EPA is taking steps to address carbon pollution with an emphasis on increasing fuel efficiency for cars and light trucks for model years 2012-2025. The Corporate Average Fuel Economy program mandates an average fuel economy of 54.5 miles per gallon for the 2025 model year. It is estimated Americans will save more than $1.7 trillion over the lifetime of these new vehicles.%3Cimg%20src%3D%22http%3A//