This week, United Airlines pledged to completely eliminate its greenhouse gas emissions by 2050. To make good on that promise, the company says it will invest in emerging technologies that capture planet-heating carbon dioxide from the air. It also plans to continue powering its flights with sustainable aviation fuel.

United is the latest airline to respond to consumers’ growing concerns about climate change and make ambitious commitments to reduce its effects on the environment. Delta announced in February that it would spend $1 billion over 10 years to become carbon neutral by reducing and canceling out emissions with carbon offsets and carbon removal schemes. JetBlue joined a Climate Pledge initiative last week that commits it to becoming carbon neutral by 2040.

THE NEW STEPS UNITED IS TAKING COULD RAISE THE BAR FOR AIRLINES’ CLIMATE GOALS

The new steps United is taking could raise the bar for airlines’ climate goals. Unlike its competitors, United signaled that it won’t rely on carbon offsets and trees to cancel out emissions. Purchasing offsets have become a standard way for airlines and other businesses to write off their carbon emissions, by investing in renewable energy or conservation projects aimed at bolstering forests’ ability to naturally store carbon. But there’s growing evidence that offsets haven’t succeeded in slowing global warming, and have instead given companies a license to keep polluting.

United is following the lead of tech companies like Microsoft and Stripe that have pumped funding into up-and-coming carbon capture technologies. “These game-changing technologies will significantly reduce our emissions, and measurably reduce the speed of climate change — because buying carbon offsets alone is just not enough,” Scott Kirby, United CEO, said in a December 10th announcement.

United says it will make a “multimillion-dollar investment” that will help an initiative called 1PointFive build the first industrial-size plant in the US that can capture carbon dioxide directly from the atmosphere. The carbon dioxide it captures will be stored underground, according to United.

ONE BIG CATCH

But there’s one big catch. The initiative is co-led by Occidental Petroleum, which has in the past said that carbon dioxide captured by plants would be used for enhanced oil recovery — a process that uses the carbon dioxide to get to hard-to-reach oil. Even though the captured carbon is pushed underground, it’s ultimately contributing to the extraction of more fossil fuels. That’s one of the reasons these kinds of technologies have sparked criticism from more progressive environmentalists like Sen. Bernie Sanders.

Airlines, unlike tech companies that have climbed aboard the carbon capture bandwagon, are a little more limited in what they can do to stop contributing to the climate crisis. The most obvious way to limit greenhouse gas emissions is to cut down on flights, which United hasn’t committed to do. Or they could incentivize the development of hybrid planes and electrically-propelled aircraft. Battery technology isn’t advanced enough to allow commercial planes to run on renewables like solar and wind.

In the meantime, there’s sustainable biojet fuel, which United started regularly adding to its fuel mix in 2016, as a good option. If direct air capture plants — which are still in their infancy — can scale up and work out some of their kinks, it gives airlines another way to shrink their carbon footprint.