On April 15, the Environmental Protection Agency (EPA) published its report, Inventory of U.S. Greenhouse Gas Emissions and Sinks. The study found that greenhouse gas emissions in the U.S. in 2011, which totaled 6.702 billion metric tons, were reduced by 1.6 percent from 2010 levels and by 6.9 percent from 2005 levels. The report pointed to mild winters, reduced coal use, and vehicle efficiency as reasons why emissions declined. However, overall greenhouse gas emissions have risen since 1990 by 8.4 percent. The 18th annual report was submitted to the United Nations Framework Convention on Climate Change Secretariat.