Greenhouse gas (GHG) emissions in the United States interrupted a steady 19-year climb by dipping slightly in the last annual reporting period, the Environmental Protection Agency reports.
While total U.S. emissions increased by 7.3 percent overall from 1990 to 2009, emissions decreased by 6.1 percent from 2008 to 2009, to the lowest levels seen in 1995, EPA reports in the 2011 U.S. Greenhouse Gas Inventory Report
Despite the overall increase, emissions decreased over the 20-year period in the Industrial Processes, Waste, and Solvent and Other Product Use sectors by 10.4 percent, 14.1 percent and less than 0.4 percent, respectively.
But the declines are not all good news. Much is due to decreasing energy consumption across all sectors in the still-struggling economy. However, EPA also credits a decrease “in the carbon intensity of fuels used to generate electricity” due to many end users switching from coal to natural gas, as coal prices climbed and natural gas dropped.
CO2: 9.9% Increase
Overall, U.S. emissions have increased at an average annual rate of 0.4 percent since 1990, reports the inventory, which tracks the six main greenhouse gases: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.
Of these, carbon dioxide from fossil fuel combustion dominates, accounting for some 79 percent of global warming potential (GWP) weighted emissions since 1990, EPA reports.
CO2 emissions “grew by 9.9 percent (470.6 Tg CO2 Eq.) from 1990 to 2009 and were responsible for most of the increase in national emissions during this period,” the inventory says. CO2 emissions decreased by 6.4 percent from 2008 to 2009.
The transportation (33 percent) and industrial (26 percent) sectors account for the majority of CO2 emissions from fossil fuel combustion.
Tracking Industry, Waste
Non-energy-related industrial segments include coatings and other industries that chemically transform raw materials; titanium oxide production; zinc, iron and steel production; and cement and lime production.
Waste management and treatment activities are also sources of greenhouse gas emissions. In 2009, landfills were the third largest source of so-called anthropogenic (caused directly or indirectly by human activities) methane (CH4) emissions, accounting for 17 percent of total U.S. CH4 emissions. Wastewater treatment accounts for 4 percent of U.S. CH4 emissions, and 2 percent of nitrous oxide (N2O) emissions.
The inventory also calculates carbon dioxide emissions that are removed from the atmosphere by so-called “sinks,” which take up a chemical element or compound as part of its natural cycle. These include carbon uptake by forests, vegetation and soils.
This inventory, prepared in collaboration with federal agencies, is the latest submitted by the United States to the Secretariat of the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC sets an overall global framework for nations to address climate change.