In 2012, U.S. greenhouse gas emissions dropped 3.3 percent from the previous year, but overall, the nation’s emissions have risen by 4.4 percent from 1990 to 2012 – an annual average rate of 0.2 percent, according to a draft report released by the Environmental Protection Agency last month.
Last year’s slight decline in emissions resulted from several factors, the EPA reported in “Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012," including:
The U.S. released 6.5 billion metric tons of carbon dioxide equivalent in 2012, the report found. The largest source of the nation’s overall greenhouse gas emissions was, not surprisingly, the burning of fossil fuels like coal, oil and natural gas. Fossil fuel combustion is also the largest source of carbon dioxide emissions – also the primary greenhouse gas emitted by human activities in the country. Carbon dioxide accounted for about 83 percent of the country’s total greenhouse gas emissions in 2012 and increased by 5.2 percent from 1990.
Methane emissions – mainly from natural gas systems, livestock digestion and the breakdown of waste in landfills – decreased by 10.7 percent since 1990, the inventory reported. Nitrous oxide emissions rose by 2.8 percent and came mostly from farming and fuel combustion.
Emissions from hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6s) also went up: Their aggregate weighted emissions increased by 66.6 percent from 1990. Though these pollutants are released in much smaller quantities than the more common greenhouse gases, they are still important gases to target for reduction, the EPA wrote, because of their high global warming potential and, for PFCs and SF6s, their long atmospheric lifetime. HFC is released in the production of hydrochlorofluorocarbons (HCFCs), commonly used as a refrigerant in air conditioning and refrigeration applications, propellant in aerosol cans and blowing agent in foam manufacturing. Aluminum production and semiconductor manufacturing account for the majority of PFC emissions, while electrical transmission and distribution systems are the main source of most SF6 pollution.
However, 15.1 percent of America’s manmade greenhouse gas emissions in 2012 were offset by carbon sequestration in forests, urban trees, agricultural soils, and composted yard trimming and food scraps, the report found.
While the EPA’s annual accounting of the country’s greenhouse gas emissions is an important step towards identifying major pollutant sources and tracking our progress towards reducing our county’s carbon footprint, there is a lot of work on the ground that needs to be done to not only hit the Obama administration’s goal of cutting emissions by 17 percent below 2005 levels by 2020, but also preventing a 3-4 Celsius degree increase in global temperature.
You can read the full draft of "Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2012” here.
Image credit: Environmental Protection Agency
Passionate about both writing and sustainability, Alexis Petru is freelance journalist based in the San Francisco Bay Area whose work has appeared on Earth911, Huffington Post and Patch.com. Prior to working as a writer, she coordinated environmental programs for Bay Area cities and counties. Connect with Alexis on Twitter at @alexispetru
Passionate about both writing and sustainability, Alexis Petru is freelance journalist and communications consultant based in the San Francisco Bay Area whose work has appeared on Earth911, Huffington Post and Patch.com. Prior to working as a writer, she coordinated environmental programs for various Bay Area cities and counties for seven years. She has a degree in cultural anthropology from UC Berkeley.