nce 1990, U.S. greenhouse gas emissions have increased by about 7 percent. From year to year, emissions can rise and fall due to changes in the economy, the price of fuel, and other factors. In 2014, U.S. greenhouse gas emissions increased compared to 2013 levels. This increase was due to a number of factors, including: cold winter conditions resulting in an increase in fuel demand, especially in residential and commercial sectors; an increase in transportation emissions resulting from an increase in vehicle miles traveled; and an increase in industrial production across multiple sectors that also resulted in increases in industrial sector emissions.