The number of electric vehicles on the world’s roads is surging, hitting a record number last year.

That would seem to be good news, as the world tries to wean itself off fossil fuels that are wrecking the global climate. But as electric cars become more popular, some question just how environmentally friendly they are.

The batteries in electric vehicles, for example, charge on power that is coming straight off the electric grid — which is itself often powered by fossil fuels. And there are questions about how energy-intensive it is to build an EV or an EV battery, versus building a comparable traditional vehicle.

Are electric vehicles greener?
The short answer is yes — but their full green potential is still many years away.

Experts broadly agree that electric vehicles create a lower carbon footprint over the course of their lifetime than do cars and trucks that use traditional, internal combustion engines.

Last year, researchers from the universities of Cambridge, Exeter and Nijmegen in The Netherlands found that in 95% of the world, driving an electric car is better for the environment than driving a gasoline-powered car.

Electricity grids in most of the world are still powered by fossil fuels such as coal or oil, and EVs depend on that energy to get charged. Separately, EV battery production remains an energy-intensive process.

A study from the Massachusetts Institute of Technology Energy Initiative found that the battery and fuel production for an EV generates higher emissions than the manufacturing of an automobile. But those higher environmental costs are offset by EVs’ superior energy efficiency over time.

In short, the total emissions per mile for battery-powered cars are lower than comparable cars with internal combustion engines.

“If we are going to take a look at the current situation, in some countries, electric vehicles are better even with the current grid,” Sergey Paltsev, a senior research scientist at the MIT Energy Initiative and one of the study’s authors.

Paltsev explained that the full benefits of EVs will be realized only after the electricity sources become renewable, and it might take several decades for that to happen.

y chain,” George Crabtree, director of the U.S. Department of Energy’s Joint Center for Energy Storage Research, told CNBC, adding that the energy source used in battery production makes a huge difference on the carbon footprint for EVs.

Batteries made in older gigafactories in China are usually powered by fossil fuels, because that was the trend five to 10 years ago, he explained. So, EVs that are built with batteries from existing factories

But that’s changing, he said, as “people have realized that’s a huge carbon footprint.”

Experts pointed to other considerations around battery production.

They include unethical and environmentally unsustainable mining practices, as well as a complex geopolitical nature of the supply chain, where countries do not want to rely on other nations for raw materials like cobalt and lithium, or the finished batteries.

Mining raw materials needed for battery production will likely be the last to get decarbonized, according to Crabtree.

Recycling and decarbonizing the grid
Today, very few of the spent battery cells are recycled.

Experts said that can change over time as raw materials needed for battery production are in limited supply, leaving firms with no choice but to recycle.

McKinsey’s Hannon outlined other reasons for companies to step by their recycling efforts. They include a regulatory environment where producers, by law, would have to deal with spent batteries — and disposing them could be more expensive.

“People who point to a lack of a recycling infrastructure as a problem aren’t recognizing that we don’t need extensive recycling infrastructure yet because the cars are so new, we’re not needing many back,” he said.

Most auto companies are already working to ensure they have significant recycling capacity in place before EVs start reaching the end of life over the next decade, he added.