Carbon dioxide emissions from electric power plants have fallen to their lowest level in decades, and that trend could help states meet their emissions goals under the Obama administration’s Clean Power Plan if it survives court challenges, according to new U.S. Energy Information Administration data and a New York University analysis.

Carbon dioxide emissions from generating electricity in 2015 were 21 percent below 2005 levels in the U.S. The goal of the Clean Power Plan is to cut emissions by 32 percent below 2005 levels by 2030, mainly from coal-fired power plants.

In raw numbers, generating electricity in the U.S. was the source of 1.9 billion metric tons of carbon dioxide emissions in 2015 — roughly the same as in 1993. Emissions peaked in 2007, when the country’s power plants emitted 2.4 billion metric tons of carbon dioxide. By 2014, power plant emissions had dropped to about 2.05 billion metric tons.

Coal use is the largest single contributor to emissions causing climate change. The Clean Power Plan, which the U.S. Supreme Court has put on hold while legal challenges have their day in court, was critical to establishing U.S. credibility during the Paris climate talks last year. States have until September 2018 to decide how to cut emissions under the plan.  

The electric power sector’s carbon emissions are falling for several reasons. Warmer winters in the U.S., influenced by global warming, have reduced the need for people to heat their homes, driving down electric power demand in the winter months, according to the EIA.

There is also a basic shift in how electricity is generated — from coal to natural gas and renewables, EIA analyst Channele Wirman said.

Low natural gas prices have encouraged utilities to shutter coal-fired power plants and build new ones that run on natural gas, which emit roughly half the carbon dioxide as those that use coal. Wind, solar and other renewables helped to cut emissions even more. A decade ago, 8 percent of U.S. electricity came from renewables. Last year, they were the source of 13 percent of the country’s electricity.