Almost as soon as modern mass-market electric vehicles became available, skeptics began asking if they actually delivered an environmental benefit. After all, they argued, charging batteries from a generating plant that burns fossil fuels simply relocates the greenhouse gas emissions to someone else’s neighborhood.

There was some basis for this position: An April 2012 report titled “State of Charge: Electric Vehicles’ Global Warming Emissions and Fuel Cost Savings Across the United States,” by the Union of Concerned Scientists concluded that electric vehicles were cleaner than hybrids in only 45 percent of the country. That was because in many areas, the majority of grid electricity used to charge the vehicles was generated at coal-fired power plants.

The situation has changed.

The UCS has announced an updated analysis showing that today, 60 percent of Americans live in regions where EVs charged with grid electricity are responsible for fewer heat-trapping global warming emissions per mile than even the most efficient hybrids.

When the 2012 report was released, proponents of electric vehicles were not pleased, and automakers with deep commitments to EV development were even less pleased. Just before the release of that report, the chief executive of Nissan and Renault, Carlos Ghosn, declared that electrics were cleaner than any car that burned gasoline, even in areas where all the electricity was generated by burning coal.

The data indicated otherwise. The UCS determined that in an area where electric power was generated using a high proportion of coal — as it is in much of the nation’s midsection — an electric vehicle was no cleaner than a high-mpg subcompact fueled only by gasoline.

In the two years since that report, utilities have added clean sources of electricity to their mix, and electric vehicles have become more efficient.

“Electric vehicles are doing more and more to fulfill their technological promise,” Don Anair, research and deputy director of the scientist group’s Clean Vehicles Program, said.

The group says the average battery-powered EV sold over the past year used 0.33 kilowatt-hours per mile, a 5 percent improvement over the 2011 data that was the basis for the original report. Some are cleaner than the average.

In other words, the average electric vehicle operating within the Midwest electric power grid, which blankets several states, is now as clean as a gasoline-engine car achieving 43 mpg. In 2012, that number was 39 mpg. At .27 kwh per mile, the BMW i3 charged with power from the Midwest grid would be as clean as a car achieving slightly more than 50 mpg.

States that don’t depend heavily on coal for power generation fare much better. An average purely electric vehicle in New York achieves the equivalent of 112 mpg, according to the group’s data, while in California the number is 95 mpg. Other states lag: Colorado, which relies heavily on coal, is again at the bottom of the list, with an EV achieving the same emissions as a 34-mpg gasoline-engine car.

The calculations by the UCS are based on utility emissions data from a 2010 EPA report. Because many utilities have adopted renewable electricity sources, actual efficiency is better. In a phone interview, Anair said he calculated the percentage of coal use nationwide to have declined by about 5 percent from 2010 to 2014, based on data from the U.S. Energy Information Administration.

Furthermore, when an EV owner charges from rooftop solar panels, the EV’s environmental effect is far lower because the charging electricity was produced without the direct use of fossil fuels. A Ford Motor Co. spokesman, Aaron Miller, wrote in an email that a 2013 survey found that 37 percent of EV customers either had solar panels on their home or planned to purchase them in the next 12 months.

The updated UCS report suggests that given the current state of the electric utility network, electric vehicles are not a cure-all that could greatly reduce fleet emissions overnight, in part because EVs are concentrated in states with clean power.

“In order to deliver the full benefits in oil savings and emissions, EVs need to be deployed throughout the country,” Anair said.

“Still, a big part of the answer is to be like Bob Dylan and go electric,” he said. “With increasing renewable electricity, carbon standards for power plants under development and continued improvement in vehicle technologies, the benefits of EVs will continue to grow.”