A new report outlining regional differences in electric cars’ contribution to climate change is drawing a lot of media attention, but a few articles have overlooked some important context about how the electric cars compare to all-gas vehicles.

The Union of Concerned Scientists, a research and advocacy organization, released the results of a nine-month analysis last week, which found that the amount of greenhouse-gas emissions that can be attributed to an electric car varies significantly depending upon where it gets its juice.

Obviously, a Nissan Leaf (which the report uses as the base of comparison) that is charged in a region where the electric grid is powered by coal will “emit” more than one in a place that relies on natural gas or renewables. What interested journalists was the notion that, in locations with the dirtiest electricity, electric vehicles produce more climate pollution than some hybrids, and just as much as some of the more efficient all-gas engines.

The report, written by Don Anair, a senior engineer on the Union of Concerned Scientists’ clean vehicles program, calculated the Leaf’s relative greenhouse-gas emissions based on its power consumption and the energy mix in 26 regional electricity grids the country. Here’s some of what they found:

• Nearly half of Americans (45%) live in the “best” regions where EVs produce lower global warming emissions than even the most fuel-efficient gasoline hybrids on the market today (greater than 50 mpg).
• Another third (37%) live in “better” areas where EVs produce emissions comparable to the best gasoline hybrid vehicles (41 - 50 mpg).
• A minority (18%) reside in “good” regions where emissions from EVs are comparable to the most fuel-efficient non-hybrid gasoline vehicles (31 - 40 mpg).

But in the rush to report that some all-gas engines perform as well as electrics where greenhouse-gases are concerned, some reporters have failed to note that there aren’t many models in that class, and only a few, including the Hyundai Elantra, which gets 33 mpg, that are among the top 20 best selling cars in America.

In fact, the Union of Concerned Scientists stressed that, nationwide, electric vehicles “produce lower global warming emissions than the average compact gasoline-powered vehicle (with a fuel economy of 27 miles per gallon)—even when the electricity is produced primarily from coal in regions with the ‘dirtiest’ electricity grids.”

In other words, electrics are always better than all-gas vehicles on the climate front, except in the few instances when they’re not any worse. A number of articles, such as one in the Los Angeles Times headlined, “Electric cars can be no better for global warming, in some cities,” didn’t make clear that, unless you’re driving one the most efficient compact cars or a hybrid, most of the time, they are in fact better. Worse still was an article from the Detroit Free Press, titled “Charging up electric cars could create more emissions than fueling up.”

Moreover, few articles noted that, according to the report, in each of the 50 cities surveyed, “electric vehicle owners will save money on fueling costs compared with the average compact gasoline vehicle even without changing to the lowest-rate plans.” Average savings would be $650 per year with $1,200 per year on the high end and $50 per year on the low end.

The report, if its figures are correct, therefore presents a strong case against purchasing an all-gas vehicle if climate change or fueling costs are a consideration. By calculating the climate impact of electric vehicles in terms of the easily understood miles-per-gallon metric, the report has made it easier for consumers to make an informed choice. As the The New York Times put it:

With gasoline hovering around $4 a gallon and mass-production E.V.’s like battery-powered versions of the Ford Focus and Honda Fit (as well as plug-in hybrids like the Chevrolet Volt, Toyota Prius PHV and Ford Fusion Energi models) either on sale now or coming soon, the report arrives at an ideal time. Its analysis can help shoppers make informed decisions.

Curtis Brainard is the editor of The Observatory, CJR's online critique of science and environment reporting. Follow him on Twitter @cbrainard.