Methodology

Electric cars are drastically cleaner than conventional gasoline vehicles. Even the burliest models with the biggest batteries account for less carbon emissions over a life’s use than nearly every gasoline-powered vehicle, no matter how small.

The science on this is clear and the gap will only widen as renewable energy increasingly accounts for a bigger share of the grid. And EVs will become more efficient as chemists and software engineers squeeze more miles out of batteries.

Even so, let’s be clear: there is no such thing as a zero-emission vehicle.

Steel body panels don’t grow on trees. Lithium doesn’t flow out of the ground and into battery plants. Electricity—even if it’s generated by solar panels—isn’t captured without a great deal of capital and carbon expense.

Unfortunately, it’s almost impossible to intricately measure the climate cost of any particular vehicle. The range of critical metrics is dizzying: from the fuel source of the utility feeding the factory, to the specific chemical mix of the car’s battery. Once the vehicle is on the road, much of its carbon impact will vary based on where it parks and spends its days. Cold weather, for example, saps EV efficiency, and a car plugged in near a coal-powered plant will be responsible for far more emissions than one drawing electrons from a solar array.

When we set out to create a model for measuring the “greenness” of the current crop of electric vehicles, we focused on simplicity and equity. We wanted an equation that was relatively easy to understand, quick to apply to new vehicles hitting the market and, nevertheless, a fair proxy for climate costs that could be applied evenly from one car to another.

Our scoring system was developed with advice from three of the leading sources for electric vehicle policy and strategy: Atlas Public Policy, BloombergNEF and the Union of Concerned Scientists*. We arrived at a “Green” model based on two metrics: driving economy, which captures just how well a car uses its resources to get down the road, and battery size, which serves as a proxy for the carbon cost of actually making the vehicle. The former accounts for 70% of the score, while the latter makes up 30%. Our model doesn’t directly account for the carbon cost of actually bolting together the parts and panels of a vehicle.

Here’s what the equation looks like…

miles of range ÷ curb weight

economy benchmark

× 0.7

Green rating =

× 100

+

battery size benchmark

battery size

× 0.3

Green rating =

miles of range ÷ curb weight

economy benchmark

× 0.7

+

× 100

battery size benchmark

battery size

× 0.3

Green rating =

miles of range ÷ curb weight

economy benchmark

× 0.7

+

battery size benchmark

battery size

× 0.3

× 100

  • Miles of range as determined by the EPA
  • Curb weight in pounds
  • Economy benchmark of 0.1099, which is 10% more efficient than the most efficient vehicle to allow room for improved new vehicles
  • 0.7 This is the weighting; on average 70% of an EV’s carbon footprint comes from its driving, according to MIT research
  • Battery size benchmark of 29.34, which is 10% smaller than the smallest EV battery on the market to allow room for new vehicles
  • Battery size measured in kWh
  • 0.3 This is the weighting; on average 30% of an EV’s carbon footprint comes from its manufacturing, most critically the construction of the battery
  • 100 establishes the range, from 0–100

And here’s how we arrived at this approach…

EconomyMost measures of EV efficiency simply crunch how far a car will go based on the size of its battery, but that’s not how most people shop for cars. We wanted a metric that would better capture the entirety of the vehicle. This approach rewards battery efficiency (after all, the battery accounts for much of the curb weight), but also tips the scale a bit for other climate-positive strategies such as using lightweight parts and materials. Ultimately, there’s a carbon cost to everything that goes into a car—be it a seat-heater or a suspension spring. Approaching economy via weight, rather than units of energy, more directly reflects those decisions. Generally, lighter vehicles score better on our scale of economy, but not as a rule. Heavy vehicles with uniquely good range also score well; it’s all relative.

Battery sizeWhen it comes to bolting together an electric vehicle, producing the battery pack alone accounts for the lion’s share of all emissions—usually somewhere between one-third and two-thirds, depending on the product and the plant. Assuming all of the other parts and pieces have similar carbon footprints—a wiring harness, for example, takes about as much resources to make for a Mustang Mach-E as it does for a Mini Cooper SE—the battery pack itself represents the largest climate differentiator. Thus, in our model, the size of the power pack for any particular vehicle is the proxy for all emissions prior to the machine arriving at the dealership or driveway.

A couple of important pointsElectric car model prices, specifications and data are as of June 10, 2022.

None of the vehicles on the market achieved the “highest” Green score (100); the best—the de facto greenest—is the Lucid Air Dream Edition Range with a score of 71.1. In the coming months, dozens of new electric vehicles will hit the road and, soon after, this dashboard. With battery technology improving quickly, some will no doubt travel farther on fewer electrons. We wanted to make sure our model left some room at the top for Green bragging rights yet to come. Theoretically, a future car could score more than 100 in our ranking, though to do so it would have to be a drastically superior vehicle to what’s on offer at the moment (nevertheless, we hope it happens!).

We should also reiterate that this is an imperfect approach, for the many reasons detailed above. There are sound arguments to be made for including other data points or weighting the results differently. There are more nuanced and thorough models for measuring the climate cost of contemporary electric vehicles, including that of the American Council for an Energy-Efficient Economy, which updates its rankings annually, and the Carboncounter churned out by the Massachusetts Institute of Technology, which also includes hybrid and gas-powered vehicles.

The Bloomberg Green Ratings dashboard is one approach among many. Within the category of electric vehicles, it compares one species to another. It is also an approach that lends itself to updating quickly when new machines hit the market. We hope you will find it fair, interesting and helpful.

* The opinions expressed herein do not necessarily reflect those of the organizations that funded the work or the individuals who reviewed it. The Union of Concerned Scientists bears sole responsibility for the report’s contents.

Updates/Corrections:Tesla Model 3 “Standard Range Plus” was corrected to “Rear-Wheel Drive”. The prices listed for the Chevy Bolt EV and the Chevy Bolt EUV were originally transposed; the price listings have been updated. Electric car model prices, specifications and data are as of June 10, 2022. On July 7, 2022: Corrected battery range and base price of Lucid Air. The corrected range established a new economy benchmark for the category—so Green scores for each vehicle shifted.

Additional variants/models of the Lucid Air have been added based on additional information provided by Lucid, including: the Dream Edition Range 21” with a green rating of 66.0; the Dream Edition Performance with a green rating of 65.1; the Dream Edition Performance 21” with a green rating of 62.3; the Grand Touring with a green rating of 71; and the Grand Touring 21” with a green rating of 64.9.