Your gas car works fine. Consider an EV anyway, scientists say.

A new study in the journal Science challenges the idea that keeping your gas car running is the greener choice. Researchers found that swapping even a two-year-old gas car for an electric vehicle (EV) cuts lifetime emissions by roughly 50 percent, once you account for the emissions saved from driving electric versus the emissions created making the new car. The study gave gas cars every advantage in the comparison, and EVs still won.

The break-even point comes fast. A separate analysis found EVs typically make up for their manufacturing emissions after about 18,000 miles, or around 18 months of average driving. The new study puts the number even lower: a car needs to be driven only 4,400 miles a year, or a truck 6,700 miles, to repay that carbon debt, well under the 12,500 miles the average driver logs annually. How big the benefit is depends on where you live and how your electricity is generated. In upstate New York, with its hydropower-heavy grid, driving an EV compares to a gas car getting 219 miles per gallon. Even in the coal- and gas-reliant Rockies, an EV beats anything getting less than 68 mpg.

There are exceptions. Plug-in hybrids, which run partly on gas, don't show the same benefit, and a rarely driven second car may not rack up enough miles to offset its manufacturing footprint. The study didn't weigh cost, which matters since EVs tend to cost more upfront but less to run and fuel over time.