United Airlines, Mesa Air Group to buy 200 electric planes

Other investors include Breakthrough Energy Ventures and Lowercarbon Capital.

Why it matters: Air travel is a significant source of carbon dioxide emissions, and electric, hydrogen and other clean fuel technologies offer the potential to address the problem — if they can be successfully commercialized.

The big picture: "Tuesday’s deal is the latest in a series of bets on new aircraft concepts yet to be tested but that United said could help it reduce carbon emissions," the Wall Street Journal reports.

• The airline industry is increasingly staking — and announcing preliminary orders — for various kinds of electrified flight.
• United is backing the vertical takeoff and landing startup Archer, and American Airlines and Virgin Atlantic recently invested in the U.K.-based Vertical Aerospace.

Reality check: These investments and preliminary purchase orders are the early stages of plans to electrify flight, hardly a guarantee the models will be built or incorporated into the airlines' routes.