Though the effort to scale up production, sales, and even to some extent the cultural acceptance of electric vehicles (EVs) on US roadways is commendable, we need corresponding attention to how that electricity is generated in the first place. If it comes from a dirty source like coal, you could be creating far more greenhouse gas emissions than you realize as you gaze in admiration at your smokeless EV tailpipe.

Estimates from the Department of Energy (DOE) show that greenhouse gas emissions nearly triple when the same EV is dependent on a relatively dirty electric grid compared to a relatively clean one (with a greater percentage of electricity coming from renewable sources such as wind, solar, and hydropower). For example, a Nissan Leaf in the Denver area spews 330 grams of carbon dioxide per mile (g/mi), but only 120 g/mi emitted by the same car in the San Francisco area.

Granted, the dirty-sourced EV still fares better than the 500 g/mi average for new, gasoline-powered cars. So yes, by all means, let’s make sure the EV momentum we have seen in the last couple of years doesn’t stall out. But let’s also recognize that we need to use this phenomenon as another lever to persuade policymakers and utilities to increase the proportion of renewables in the overall energy portfolio.

Check out this DOE website where you can plug in your zip code and see how your area and car model stack up: Beyond Tailpipe Emissions.