Hybrid-electric aircraft will soon kick off a new era of cleaner air travel, just as the pioneering Toyota Prius heralded the start of the electric car movement 20 years ago.

Why it matters: Replacing small regional planes that run on fossil fuels with hybrid or electric aircraft would help reduce climate-damaging CO2 emissions. It could also make air travel easier and cheaper for people living in smaller cities not served by major airlines.

The big picture: CO2 emissions from aviation have risen rapidly over the past two decades, reaching about 2.8% of global CO2 emissions from fossil fuel combustion, according to the International Energy Agency.

• And with passenger air travel growing at about 5% a year — except during the pandemic — airlines have been scrambling to lower their carbon footprint.

State of play: Fully electric planes, while promising, are limited by available battery technology.

• Batteries cost less and pack more energy into a smaller package than they did a decade ago, but they're still too heavy to allow planes to fly long distances or carry heavy loads.
• They do work, however, in low-flying air taxis for short runs across a city or to the airport.
• These new electric vertical takeoff and landing (eVTOL) aircraft are getting a lot of attention on Wall Street, but they won't be widely available until around 2035, according to a Deloitte analysis.

Yes, but: For medium distances of 50 to 500 miles — the city-hopping routes ignored by hub-and-spoke airlines — hybrids offer a practical solution that can be ready in just a few years.

• UBS, the Swiss investment bank, forecasts a $178 billion market for hybrid-electric aircraft.

Driving the news: Surf Air Mobility, a regional air travel service, said this week it would acquire Ampaire, a developer of hybrid electric powertrains for aviation.

• Surf Air co-founder and CEO Sudhin Shahani called Ampaire's technology a step toward "the next great shift in air travel: sustainable aviation that's accessible to everyone."
• For now, the company's plan is to upgrade existing turboprop aircraft with Ampaire's hybrid technology on short, regional routes while the industry works toward fully electric aviation for all trips.

How it works: Upgrading today’s aircraft for electric power is a relatively low-cost, low-risk path to aircraft certification, says Ampaire CEO Kevin Noertker.

• Its "Electric EEL," for example, is a retrofitted Cessna plane, with an electric motor in the nose and a traditional combustion engine in the rear.
• Both systems provide thrust, but in the air, the engine is mostly used to recharge the 50 kWh battery stored under the fuselage.
• In October, the EEL completed a 341-mile test flight between Los Angeles and San Francisco.
• Ampaire also partnered with Hawaii-based Mokulele Airlines on a series of test runs between the islands’ small airports with mock payloads.

What they're saying: "It is a very long time — well over a decade, maybe two — before your large trans-continental planes are electric," says veteran aviation executive Fred Reid, now president of Surf Air Mobility.

• "The beauty of a hybrid is that they're already flying. You can save 25 to 30 percent on operating costs and it makes a dent on the environmental problem."
• "We could upgrade 20-30,000 planes, and give them a shelf life for another 20 years."