Several countries and companies announced plans Wednesday to stop selling cars that run on gasoline or diesel over the next two decades, as part of efforts to clamp down on a significant source of planet-warming emissions.

But the impact of the measures will likely be limited since several major car markets — notably the United States and China — did not sign on, and the pledges received a mixed response from environmental campaigners. Nations and airlines also pledged to reduce emissions from air travel.

On the sidelines of the U.N. climate conference in Glasgow, Scotland, a group of nations said Wednesday that they would work to sell only zero-emission vehicles by 2040, and no later than 2035 in leading auto markets. While the wording of the agreement is vague, it could essentially mean switching to electric-only fleets of cars, trucks and buses — and backing off popular halfway solutions currently in use, such as hybrid vehicles.

The plan was backed by countries including Canada, Chile, Denmark, India, Poland, Sweden, Turkey and the United Kingdom. Several American states and cities also signed sign on, as did major carmakers Ford, General Motors, Mercedes Benz and Volvo.

Some companies, such as Volvo, had already pledged to even earlier targets to phase out combustion engines.

“This welcome move signals that a growing number of countries, auto makers and transportation providers are joining the global push for 100% zero-emissions electric vehicles,” said Jake Schmidt of the New York-based nonprofit Natural Resources Defense Council

But the Brussel-based think tank Transport and Environment said the announcement needs to be backed by legally binding targets and noted the absence of major car markets such as China, the U.S., Germany and France.

Transportation is one of the biggest sources of greenhouse gas emissions, according to the International Energy Agency.

A recent report by the agency found the sale of new internal combustion engine cars — those that run on gasoline and diesel — needs to be phased out by 2035 to ensure the goals set in Paris in 2015 on capping global warming at 1.5 degrees Celsius (2.7 degrees Fahrenheit) can be met.

Efforts to cut car, plane and ship emissions get small boost. #ClimateChange #COP26

German officials said the country declined to sign the agreement announced Wednesday because it contained a footnote that would prevent the use of synthetic fuels produced with renewable energy — an option that some in the current and likely future government want to keep open.

The country has backed a proposal being considered by the European Union to end sales of gasoline-powered cars and vans by 2035.

The U.S. auto industry, meanwhile, has previously pledged to dramatically increase production of electric cars, and a massive new infrastructure package provides $7.5 billion in federal grants to build a network of charging stations.

Creating the infrastructure so that people can drive as far as they need to without worrying about finding a place to recharge is a major hurdle that companies and governments are facing in persuading consumers to switch to electric.

But Bjorn Annwall, the chief financial officer of Volvo, said this was a “solvable problem.”

The Sweden-based carmaker says its customers are demanding Volvo leads on cutting emissions and the company is aiming for at least half of its sales by 2025 to be fully electric, and all by 2030.

“We as an industry need to send the signal,” Annwall told The Associated Press. “We need to get out of combustion engines before 2035 in order to have some chance to reach our climate neutral planet targets for further down the line.”

Separately, Daimler Truck AG, the world’s largest truck maker, and energy giant TotalEnergies announced they will work together on the rollout of zero-emissions hydrogen-powered trucking across western Europe in coming years.

On aviation, about two dozen countries said they would work together to reduce emissions from plane travel to “net zero” by 2050, including by promoting the use of sustainable fuels. “Net zero” means producing only as many emissions as can be absorbed again through natural or artificial means.

Greenpeace described the declaration — signed by Britain, France, Spain, the United States and others — as “brazen greenwashing.”

“They should be reducing flights and massively investing into rail and greener travel options,” the environmental group said.

Separately, 20 airlines announced plans to use planes powered with electric, hydrogen or hybrid engines on 30% of the fleet used for short-haul flights by 2030.

Among the signatories were Air New Zealand, Alaska Airlines, easyJet and Southern Airways Express, operating more than 800 aircraft with over 177 million passengers a year.

And major maritime industry representatives pushed Wednesday for more funding for research into clean ship propulsion technology.

The flurry of announcements on transport emissions follows a pattern at this year's climate talks, which have seen host Britain present side deals that aren't part of the official negotiations — a practice criticized by some environmental campaigners.

“These types of announcements that countries voluntarily say they’re going to do something is not what we need in a climate emergency,” said Greenpeace's executive director, Jennifer Morgan. “They have not worked in the past.”

Achim Steiner, who heads the U.N. Development Program, said promoting clean modes of transport is essential if the world wants to cut emissions in a way that doesn't leave poor nations behind.

China has already put on the road 250 million electric motorcycles, which are particularly attractive to people in developing nations, he noted.

“With solar power off-grid technology, you can run in a village a charging station for electric motorcycles,” Steiner told The Associated Press.

He also suggested that poor countries should follow the example of Kenya, which has long banned the importing of old vehicles to avoid becoming a dumping ground for rich nations' gas-guzzlers.

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