Want more legroom, more direct flights, and less time stuck in holding patterns? It could be coming to airline passengers, but at a price: higher fares.

Regulators are moving along with targets intended to push commercial airlines to slash their emissions of carbon dioxide not by stuffing more of us onto the existing fleet, but by targeting the underlying issue of aircraft fuel efficiency. That will mean new, fuel-efficient airplanes, an upgrade that could come with creature comforts such as more legroom and state-of-the-art inflight entertainment.

But integrating new airplanes into existing fleets and upgrading technology will cost money, which may lead to higher fares, noted Vera Pardee, a San Francisco-based attorney with the Center for Biological Diversity, one of several environmental groups that are pushing the U.S. Environmental Protection Agency to regulate airline greenhouse gas emissions.