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Greenhouse gas emissions from commercial air travel are growing at a faster clip than predicted in previous, already dire, projections , according to new research — putting pressure on airline regulators to take stronger action as they prepare for a summit next week.

The United Nations aviation body forecasts that airplane emissions of carbon dioxide, a major greenhouse gas, will reach just over 900 million metric tons in 2018, and then triple by 2050.

But the new research, from the International Council on Clean Transportation , found that emissions from global air travel may be increasing more than 1.5 times as fast as the U.N. estimate. The researchers analyzed nearly 40 million flights around the world last year.

“Airlines, for all intents and purposes, are becoming more fuel efficient. But we’re seeing demand outstrip any of that,” said Brandon Graver , who led the new study. “The climate challenge for aviation is worse than anyone expected.”