SPOKANE, Wash. (AP) —  Researchers have found that methane emissions from local natural gas distribution systems across the U.S. have decreased in the past 20 years.

The researchers at Washington State University pointed to upgrades in metering and regulating stations, changes in pipeline materials, better instruments for leaks and regulatory changes for dropping methane emissions from 36 percent to 70 percent.

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The study showed significant variation by region, with some areas showing higher than average emissions because of large differences in the age and type of pipe.

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The study was published Tuesday in Environmental Science & Technology.

With a series of partner studies, it is helping to determine the natural gas industry’s contribution to U.S. greenhouse gas emissions and global warming.

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