For years, coal power has been the biggest source of electricity in the United States, and the biggest single source of air pollution. But the coal industry is now in decline, because of pressure from environmental groups, increasing regulations, and perhaps most of all because of the plummeting price of natural gas.

Coal provided over half of the U.S. power four years ago, and now provides only a third. A further 100 of the 500 coal power plants in the U.S. will likely be shut down in the next few years, according to a new article in the New York Times. The decline will be steepest in Appalachia, where coal has become increasingly difficult and expensive to mine.

What does this mean for the environment? A typical coal plant burns 1.4 million tons of coal each year, releasing SO2, particulate matter, mercury and other pollutants that researchers have linked to thousands of premature deaths every year. Coal plants are also responsible for nearly 35 percent of the CO2 emissions in the U.S. Environmentalists say that if a third of the country’s coal power plants can be shut down by 2020, it will have the same climate benefits as the failed 2009 Climate Change Bill.

Much of the coal will be replaced by natural gas, which is now much cheaper because of the increase in fracking techniques. Natural gas has its own issues: fracking is linked to water pollution and the increased risk of earthquakes. Though it doesn’t pollute as much as coal, natural gas still contributes to climate change; it’s responsible for over a quarter of greenhouse gas emissions in the U.S. Over the long term, let’s hope the switch from coal means less energy from fossil fuels overall, and more renewables like solar and wind.

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