Greenhouse gas emissions in the US totaled 6,501,000 million metric tons of carbon dioxide equivalent in 2012, a 3.3 percent reduction from the previous year, according to an annual draft report by the EPA.
The decrease from 2011 to 2012 was caused by a drop in the carbon intensity of fuels used by power plants to generate electricity due falling natural gas prices, according to the draft report. A decrease in transportation sector emissions caused by small fuel efficiency gains as well as warmer winter conditions that dampened demand for heating fuel also helped push emissions levels down, the EPA says.
Overall, total emissions have increased 4.4 percent from 1990 to 2012.
The Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2012 tracks total annual GHG emissions and removals by source, economic sector and historical data going back to 1990. The inventory, which is submitted each year to the United Nations Framework Convention on Climate Change, also calculates CO2 emissions that are removed from the atmosphere through the uptake of carbon by forests, vegetation, soils and other natural processes called carbon “sinks.”
The primary GHG emitted by human activities in the US was CO2, representing about 82.7 percent of total emissions. Overall, total emissions of CO2 have increased 5.2 percent from 1990 to 2012.
Electricity generation, transportation, industrial, residential and commercial are the five major fuel consuming sectors contributing to CO2 emissions from fossil fuel combustion, according to the report.
The largest source of CO2, and of overall GHG emissions, was fossil fuel combustion. Natural gas system, enteric fermentation from domestic livestock and decomposing waste in landfills were the main sources of CH4 emissions, which have decreased 10.7 percent since 1990.
Agricultural soil management, mobile source fuel combustion and stationary fuel combustion were the major sources of N20 emissions.
Greenhouse gas emissions in the US fell 1.6 percent from 2010 to 2011. GHG emissions in 2011 were 6.9 percent lower than 2005 levels.