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Is the price at the pump making you think about ways to reduce your gas consumption? One reader has electric vehicles on the mind, but wants to know: how green are they when you factor in the environmental impact of the battery and the way your local energy is generated?

Read the answer from our scientist below. And don’t forget to send us your questions on any conservation subject for one of the Conservancy's 550 staff scientists. (Note: We regret that we can only answer one or two questions each month and that we cannot answer the others offline.)

C. Smith of Fort Worth, TX, writes:

Jon Hoekstra, director of science for the Conservancy in Washington, replies:

Thanks for your questions.

Since December, I have driven an all-electric car. It's quick, quiet, comfortable and meets 100% of my everyday driving needs—carpooling to and from work, errands around town, etc. And with gas prices around $4.00 per gallon, my electric car is also saving me a lot of gas money—just $30/month in electricity instead of $200/month in gas. But you weren't asking about that kind of "green."

Batteries in most electric and hybrid cars are under warranty for 8 years, so they don't have to be replaced that often. And when they do, they can be repurposed for use in power backup supplies or recycled into new batteries.

Batteries shouldn't end up in a landfill. That said, a recent cradle-to-grave analysis determined that the lithium-ion batteries are responsible for 15% of the total environmental impact of an electric car.

The biggest environmental impacts of both electric and gasoline-powered cars come from driving. Compared to a similarly sized gasoline-powered car, an all-electric car has 30% lower cumulative energy demand—which means less money from your pocket—and 50% lower greenhouse gas emissions—which means less global warming.

However, the associated electricity generation emits 36% more sulfur dioxide and 22% more particulates that pollute the air.

So which is the greener option?

It was an easy choice for me because most of the electricity where I live is generated by hydropower—it doesn't have any of the sulfur or particulate pollution associated with coal-fired power plants. As more local utilities shift to cleaner generation and more renewable sources, the environmental balance will tilt more strongly toward hybrids and all-electric vehicles.

Even in places that still burn coal to make electricity, I would lean toward hybrid/electric cars because they are more energy efficient and there are proven ways to reduce sulfur and particulate pollution.

Of course, don't forget that the greenest option is to drive less! Walk. Ride a bike. Use public transportation. That's good for the environment and good for your health.