If China opts to cut air pollution by converting low-quality coal in its western provinces to synthetic natural gas for residential use, it could prevent 20,000 to 41,000 premature deaths per year but undercut its own efforts to reduce greenhouse gas emissions, according to a study published last month in the Proceedings of the National Academy of Sciences and released by Greenpeace.

“If the gas were used for industrial purposes, fewer deaths would be averted and they would carry a steeper price—a dramatic increase in carbon dioxide emissions,” AP reports. While it would address immediate, dire concerns about local air quality, that strategy “would have an effect of increased carbon emissions, which would affect the world,” said co-author Denise Mauzerall of Princeton University.

“Public outrage over smog and a desire to meet climate goals prompted Chinese officials to close down coal power plants around Beijing in recent years and suspend plans to construct new plants across the country,” Bloomberg recalls. Now, “China’s pursuit of synthetic gas reflects in part the inability of its domestic oil and gas reserves to meet its national security and economic needs,” the news agency explains, citing climate specialist Ranping Song of the World Resources Institute.

But “compared to burning coal directly for power, converting it into gas and then using that gas to produce electricity can produce almost twice as much carbon dioxide and other greenhouse emissions blamed in climate change.” Mauzerall calculated the additional output at 143 megatonnes per year; Greenpeace put the figure at 409 Mt per year by 2020.

“With the coal-to-gas plants, China’s goal to stabilize its world-leading carbon emissions of about 10 billion tons (9.1 billion metric tons) annually by 2030 would remain achievable but more difficult,” Bloomberg notes, citing Song. “A driving factor will be whether the country can transform its economy away from energy-intensive manufacturing to more service-based industries.”