Who pollutes the most in the U.S.? Here's a scorecard

As leaders from around the globe come together in Paris for climate change talks, here's a list of the largest U.S. emitters of the greenhouse gasses behind global warming, according to the University of Massachusetts' Political Economy Research Institute's Greenhouse 100 Polluters Index.

The data used to compile the index are from 2011 and were released in 2013. However, it is unlikely the information has changed much since, according to John Coequyt, the Sierra Club's director of federal and international climate campaigns.

1. American Electric Power (AEP), which gets about 60 percent of its generating capacity from coal. The utility serves about 5 million customers in 11 states, and accounts for 1.944 percent of U.S. greenhouse gas emissions. AEP, however, said it is moving to cut its greenhouse gas emissions. "By the end of 2016, AEP will have retired or refueled 28 coal-fueled generating units," a company spokesperson emailed. "By 2017, we expect our CO2 emissions from our power plants to be 25 percent lower than in 2005, and we will achieve additional reductions in the years ahead."

2. Duke Energy (DUK). The utility accounts for 1.889 percent of U.S. emissions.

3. Southern Co. (SO). The utility accounts for 1.76 percent of U.S. emissions.

4. The federal government. Owner of the Tennessee Valley Authority, Uncle Sam operates 10 coal plants, along with generators on military bases and other properties, and accounts for 1.16 percent of U.S. emissions.

5. Warren Buffett's Berkshire Hathaway (BRK.A), which owns electric utilities, accounts for 1.06 percent of U.S. emissions.

Data from the Environmental Protection Agency, shows that power companies are spewing less greenhouse gases than they did in recent years, a trend the Edison Electric Institute trade group attributes to the increased use of natural gas and renewable energy sources, such as wind and solar.

AEP echoed the sentiment, saying it is currently adding "utility-scale solar resources to our generation portfolio in Indiana," and is "investing heavily in transmission to support renewable integration." The company said it had 74 percent coal-fueled capacity in 2005, and expects that to be down to 51 percent coal in 2016 and 48 percent in 2026.

"While you have seen reductions in a large number of countries including the U.S. and the EU, globally emissions have been rising until this year," said Coequyt, adding that greenhouse gas emissions need to be near zero between 2050 and 2100. "It looks like for the first time ever global emissions will be flat. That's a very good thing."