U.S. greenhouse gas emissions dropped 2.5 percent in 2016 from 2015 levels and 12 percent from 2005 levels, according to EPA’s most recent edition of the “Inventory of U.S. Greenhouse Gas Emissions and Sinks.” The 2016 decline was largely a result of substitution from coal to natural gas consumption in the electric power sector and warmer winter conditions that reduced demand for heating fuel in the residential and commercial sectors. The percentage decline in greenhouse gas emissions from U.S. power plants was even larger than the decline in total greenhouse gas emissions—dropping 24 percent from 2005 to 2016.
According to the Energy Information Administration, the carbon dioxide component—the largest component of greenhouse gases—declined by 1.6 percent in 2016 and an additional 0.7 percent in 2017. The U.S. experience is in sharp contrast to global carbon dioxide emissions, which are expected to increase by 2 percent in 2017 from 2016 levels, reaching 41 billion tons. China, the world’s largest emitter, is the biggest contributor to the increase with an expected growth rate of 3.5 percent, due primarily to its large coal consumption.
In an amazing turnaround, carbon dioxide emissions from the U.S. electric generation sector were not the largest U.S. component. Carbon dioxide emissions from the U.S. transportation sector surpassed those from the U.S. electric generation sector by 3.7 percent in 2016 and 8.6 percent in 2017, according to EIA. And according to EPA’s report, greenhouse gas emissions from the U.S. transportation sector were 0.4 percent higher than those from the U.S. electric generation sector in 2016.
U.S. Greenhouse Gas Emissions
U.S. greenhouse gas emissions totaled 6,511 million metric tons of carbon dioxide equivalents in 2016, or 5,795 million metric tons of carbon dioxide equivalents after accounting for sequestration from the land sector. Carbon dioxide, the largest component of man-made greenhouse gases, made up 81 percent of total U.S. greenhouse gases in 2016, followed by methane with 10 percent, nitrous oxide with 6 percent, and fluorinated gases, 3 percent.
Carbon dioxide emissions result from burning coal, oil, natural gas, solid waste, trees and wood products, and from certain chemical reactions (e.g., manufacture of cement). Carbon dioxide is removed from the atmosphere (or “sequestered”) when it is absorbed by plants as food as part of the biological carbon cycle.
Methane emissions result from livestock and other agricultural practices, by the decay of organic waste in municipal solid waste landfills, and from the production and transport of coal, natural gas, and oil.
Nitrous oxide is emitted during agricultural and industrial activities, and during the combustion of fossil fuels and solid waste.
Fluorinated gases are industrial gases that consist of hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride–emitted by a variety of industrial processes. These gases are typically emitted in smaller quantities, but they have a high global warming potential, because for a given amount of mass, they trap substantially more heat than carbon dioxide—thousands or tens of thousands more.
In 2016, the U.S. transportation sector generated the largest share of greenhouse gas emissions (almost 28.5 percent), followed by the U.S. electricity sector (28.4 percent), while the industrial sector contributed 22 percent, the buildings sector, 11 percent, and agriculture, 9 percent.
Greenhouse gas emissions from transportation primarily come from burning fossil fuels from cars, trucks, ships, trains, and planes. Over 90 percent of the fuel used for transportation is petroleum based. Approximately two-thirds of our electricity comes from burning fossil fuels, mostly coal and natural gas. Greenhouse gas emissions from industry come from burning fossil fuels and from certain chemical reactions resulting from producing goods from raw materials. Greenhouse gas emissions from the buildings sector come primarily from fossil fuels burned for heat, the use of certain products that contain greenhouse gases, and the handling of waste. Greenhouse gas emissions from agriculture come from livestock such as cows, agricultural soils, and rice production.
In 2016, land use and forestry offset 11 percent of the greenhouse gas emissions. Land areas can act as a sink (absorbing carbon dioxide from the atmosphere) or a source of greenhouse gas emissions. In the United States, since 1990, managed forests and other lands have absorbed more carbon dioxide from the atmosphere than they emit.
While the world is increasing its carbon dioxide emissions, led by China, the United States is decreasing its emissions mainly due to the shale gas renaissance. Between 2005 and 2016, U.S. carbon dioxide emissions declined by 12 percent, while China’s carbon dioxide emissions increased by 50 percent, surpassing U.S. carbon dioxide emissions in 2006. In 2017, U.S. carbon dioxide emissions dropped by 0.7 percent from 2016 levels, while China’s emissions are expected to increase by 3.5 percent. The United States is the world leader in achieving President Trump’s “energy dominance” yet it still manages to reduce its greenhouse gas emissions, without having to be a member of the Paris accord.