Searching for the source of the ethane, an aircraft from the National Oceanic and Atmospheric Administration in 2014 sampled air from directly overhead and downwind of drilling rigs in the Bakken region. Those measurements showed ethane emissions far higher than what was being reported to the government by oil and gas companies.

The findings solve an atmospheric mystery — where that extra ethane was coming from, said Colm Sweeney, a study co-author from the Cooperative Institute for Research in Environmental Sciences at the University of Colorado in Boulder.

The researchers said other U.S. oil and gas fields, especially the Eagle Ford in Texas, are also likely contributing to the global rise in ethane concentrations. Ethane gets into the air through leaks from drilling rigs, gas storage facilities and pipelines, as well as from intentional venting and gas burnoffs from extraction operations.

"We need to take these regions into account because it could really be impacting air quality in a way that might matter across North America," Kort said.