Energy sector carbon dioxide emissions fell in 2015, federal officials reported on Monday, pushing emissions 12 percent below the critical benchmark year of 2005.

Emissions from the energy sector have declined primarily due to the decreased use of coal for electricity generation, a trend made possible by low-priced natural gas, the Energy Information Administration reported.

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The emissions decrease in 2015 coincided with an expansion of the American economy, meaning economic growth and electricity generation emissions again weren’t linked last year.

The economy is 15 percent larger than it was in 2015, but the United States used 15 percent less energy per unit of gross domestic product and produces 23 percent fewer emissions by that same measure, the EIA said.

2015 was the first time power sector emissions have declined since 2012, the EIA noted. Beyond a continued shift away from coal, the EIA said milder weather contributed to a lower demand for heating, which meant less energy generation and emissions.

Measuring carbon emissions against 2005 levels is critical for the U.S.’s contribution to international climate change work. The Obama administration has said it will look to cut all American emissions — from electricity generation and elsewhere — by 26 to 28 percent, from 2005 levels, by 2025 as part of the United Nations climate deal reached in Paris last year.

The Clean Power Plan, an Environmental Protection Agency regulation to cut energy sector pollution, aims to reduce electricity generation emissions by 32 percent, from 2005 levels, by 2030. The plan is currently on hold pending litigation.