US energy-related CO2 emissions in 2012 were the lowest since 1994, at 5.3 billion metric tons of CO2, according to the US Energy Information Administration (EIA). With the exception of 2010, emissions have declined every year since 2007.
The largest drop in emissions in 2012 came from coal, which is used almost exclusively for electricity generation. During 2012, particularly in the spring and early summer, low natural gas prices led to competition between natural gas- and coal-fired electric power generators. Lower natural gas prices resulted in reduced levels of coal generation, and increased natural gas generation—a less carbon-intensive fuel for power generation, which shifted power generation from the most carbon-intensive fossil fuel (coal) to the least carbon-intensive fossil fuel (natural gas).
Other factors contributing to the lower emissions include decreased demand for transportation fuels and mild winter temperatures that reduced demand for heating. The warm winter months during 2012 (particularly in the first quarter) more than offset a slight increase in cooling degree days during the summer months.
EIA will publish a full analysis of 2012 energy-related CO2 emissions later this year.
Duke study. Separately, a new study by Duke University researchers published in the ACS journal Environmental Science & Technology concludes that the cost of complying with tougher EPA air-quality standards could spur an increased shift away from coal and toward natural gas for electricity generation.
The stricter regulations on sulfur dioxide, particulate matter, nitrogen oxide and mercury may make nearly two-thirds of the nation’s coal-fired power plants as expensive to run as plants powered by natural gas, the study finds.
Because of the cost of upgrading plants to meet the EPA's pending emissions regulations and its stricter enforcement of current regulations, natural gas plants would become cost-competitive with a majority of coal plants—even if natural gas becomes more than four times as expensive as coal. This is a much higher fraction of economic vulnerability than has previously been reported—Prof. Lincoln F. Pratson
To conduct the study, Pratson and his team assessed the cost of electricity generation at plants producing 95% of the nation’s coal-fired electricity and 70% of its natural gas-powered electricity. The researchers estimated costs for both types of plants over a wide range of fuel prices and under both existing and pending emissions standards.
Under current standards and at current fuel prices, 9% of US coal-fired plants are more costly to run than a median-cost natural gas plant, they found. Even a modest jump in gas prices could erase this advantage.
However, with tougher emissions standards the EPA would enact and enforce, another 56% of US coal plants would become as costly to run as natural gas plants. The regulations would make 65% of coal plants nationwide as expensive as natural gas, even if gas prices rise significantly.
The net effect of the shift to natural gas on global carbon dioxide emissions remains uncertain, Pratson said, since coal that is not consumed in the United States is already finding its way to other countries in Europe and Asia.
Lincoln F. Pratson, Drew Haerer, and Dalia Patiño-Echeverri (2013) Fuel Prices, Emission Standards, and Generation Costs for Coal vs Natural Gas Power Plants. Environmental Science & Technology doi: 10.1021/es4001642