DETROIT (AP) — The U.S. government’s most ambitious plan ever to slash planet-warming greenhouse gas emissions from passenger vehicles faces skepticism both about how realistic it is and whether it goes far enough.

The Environmental Protection Agency in April announced new strict emissions limits that the agency says are vital to slowing climate change as people around the globe endure record-high temperatures, raging wildfires and intense storms.

The EPA says the industry could meet the limits if 67% of new-vehicle sales are electric by 2032, a pace the auto industry calls unrealistic. However, the new rule would not require automakers to boost electric vehicle sales directly. Instead, it sets emissions limits and allows automakers to choose how to meet them.

Even if the industry boosts EV sales to the level the EPA recommends, any reduction in pollution could prove more modest than the agency expects. The Associated Press has estimated that nearly 80% of vehicles being driven in the U.S. — more than 200 million — would still run on gasoline or diesel fuel.

Pointing to surging temperatures and smoke from Canadian wildfires that fouled the air over parts of the U.S. this summer, Dan Becker, director of the safe climate transport campaign at the Center for Biological Diversity, said: “We need to do a hell of a lot more.”

He wants the EPA to slash emissions even further.

Carbon dioxide and methane levels in the atmosphere keep rising. Scientists say July will end up being the hottest month on record and likely the warmest human civilization has seen. The Earth is only a few tenths of a degree from the goal set out in the 2015 Paris Agreement on climate change of limiting warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times.

Though a panel of United Nations scientists said in March that there was still time to prevent the worst harm from climate change, the scientists said the world would need to quickly cut nearly two-thirds of carbon emissions by 2035 to avoid weather that is even more extreme.

Peter Slowik, a senior EV researcher with the nonprofit International Council on Clean Transportation, has calculated that to cut emissions enough to reach Paris Agreement goals, the proportion of new electric and plug-in hybrid vehicles sold would have to reach 67% by 2030. The EPA has projected 60% by then.

"The EPA proposal is a really great start to putting us on a Paris-compatible path,” said Slowik, whose group provides research and analysis to environmental regulators. “But no, it isn’t enough to comply with the Paris accord.”

The council has calculated that carbon dioxide pollution from passenger vehicles would have to drop to 57 grams per mile by 2030 to reach the Paris goals. The EPA’s preferred regulation would cut those emissions to 102 grams per mile by 2030 and to 82 by 2032.

In addition, Slowik cautioned, carbon emissions from new gasoline vehicles would have to drop 3.5% each year from 2027 to 2032. The EPA’s preferred regulation doesn’t set reductions for gas vehicles. But fuel economy standards recently proposed by the National Highway Traffic Safety Administration could.

The EPA contends its proposal will significantly reduce pollution. It estimates that passenger-vehicle carbon dioxide emissions would fall 47% by 2055, when the agency expects most gas-powered vehicles to be gone.

As the biggest source of pollution in the United States, transportation generates roughly 29% of heat-trapping greenhouse gas emissions, according to the EPA. Passenger vehicles are by far the worst transportation polluters, spewing 58% of that sector’s greenhouse gas pollution.

The EPA also is proposing big reductions from other sources, including heavy trucks, electric power plants and the oil and gas industry.

Using sales projections from the EPA and industry analysts from 2022 through model year 2032, the AP calculated that Americans will likely buy roughly 60 million EVs. With 284 million passenger vehicles on U.S. roads today, at that pace only about 22% of them would be electric in nine years. Two million are already in use, and vehicles now stay on the road for an average of 12.5 years.

Dave Cooke, a senior vehicles analyst for the Union of Concerned Scientists, said that even with slow vehicle turnover, studies show the EPA’s proposal would be an important step toward a zero-carbon transportation system by 2050. In addition, power plants that fuel EVs, he noted, will be converted to renewable energy such as wind and solar.

“We know that EVs provide a compounding benefit as we dramatically cut (electric power) grid emissions,” Cooke said.

His group is among those pushing the EPA for more stringent standards than the agency is pursuing.

The EPA will consider such comments before adopting a final regulation in March 2024.

The Alliance for Automotive Innovation, a trade group that represents companies such as General Motors, Ford and Toyota that make most new vehicles sold in the United States, argues the EPA standards are “neither reasonable nor achievable in the time frame covered.”

The alliance says the agency is underestimating the cost and difficulty of making EV batteries, including short supplies of critical minerals that also are used in laptops, cellphones and other items. Sizable gaps in the charging network for long-distance travel and for people living in apartments pose another obstacle.

Though automakers continue to downsize engines and produce more efficient transmissions, the alliance says they need to use their limited resources more on producing EVs than on developing more fuel-efficient technology for gas-powered engines.

Studies by the Massachusetts Institute of Technology show that shifting to electric vehicles delivers a 30% to 50% reduction in greenhouse gas emissions over combustion vehicles, depending on how the electricity is derived.

Jessika Trancik, an MIT professor of energy systems, said electric vehicles are cleaner over their lifetimes, even after taking into account the pollution caused by the mining of metals for batteries. The university has a website that lists auto emissions by vehicle.

Trancik believes that once EV sales accelerate, more people will want them, and the percentages could actually exceed EPA predictions. Sales of EVs, she noted, are growing far faster in many other countries.

“You often see exponential growth,” she said.