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Environment | Climate change | Ecotrope

A Portrait of U.S. Greenhouse Gas Emissions

The U.S. Environmental Protection Agency has released a new report on greenhouse gas emissions nationwide that ranks the top sources and measures how much they’re offset by carbon sinks like forests.

It found that overall emissions have increased 8 percent since 1990 despite a 14 percent increase in the amount of carbon that is getting absorbed by land and forests and a dip in emissions since the recession.

Electricity production is the biggest contributor of greenhouse gas emissions in the U.S., the EPA concludes. With 70 percent of our electricity coming from fossil fuels such as coal or natural gas, generating electricity makes up 33 percent of all greenhouse gas emissions. And, while coal produces less than half of our electricity (42 percent), it makes up 80 percent of emissions from the electricity sector.

Transportation is the next biggest contributor at 28 percent of all emissions because of fossil fuels burned in cars, trucks,ships, trains and planes. More than 90 percent of transportation fuel in the U.S. is petroleum-based, according to the EPA.

Industry directly contributes 20 percent of all emissions, but it’s actually the biggest contributor if you include industrial electricity use. However, direct emissions from industry have dropped 13 percent since 1990 while electricity production and transportation have grown.

Commercial and residential emissions – mostly from burning fuel for heat and cooking – make up 11 percent of all greenhouse gas emissions. The EPA also counts methane emissions from landfills, wastewater treatment plants and gases used in air conditioning and refrigeration in this category.

Agriculture contributes 8 percent, half of which comes from soils releasing greenhouse gases because of fertilizer, tilling and irrigation. A third of all ag emissions are methane released by livestock – primarily cattle. About 15 percent comes from manure management, and the rest is from smaller sources such as crop burning and rice production.

Meanwhile, land, forests and harvested wood actually offset 14 percent of all U.S. greenhouse gas emissions by sequestering carbon dioxide from the atmosphere. That’s a 14 percent increase from 1990 thanks to changes in land management, as you can see in the chart below.

The report leaves off at 2011, so we’re a year behind in tallying the totals, but the Energy Information Administration has reported more recent data showing a downturn in carbon emissions due to less coal-burning for electricity and less driving in 2012.

Does any of this surprise you? I think maybe the amount of CO2 sequestered by nature is the most interesting part – that and the fact that changing land management has measurable effects on its ability to offset emissions.

Here’s a graph of the Obama administration’s projections for greenhouse gas emissions through 2050.

We’re on track for a gradual increase in emissions, but the administration has set a goal of cutting emissions to 83 percent below 2005 levels by 2050 through energy efficiency, “clean coal” or sequestering emissions from coal-fired power plants, and more renewables. What are your predictions?

greenhouse gases

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