If you're planning this holiday season (perhaps even today) to become one of the tens of millions of people in the U.S. to buy a video game system, you  may want to consider how the purchase of a Nintendo Wii, Sony PlayStation or Microsoft Xbox will impact your carbon footprint (or, at very least, your electric bill).

The Natural Resources Defense Council (NRDC), a New York-based environmental organization, in a new report says that video game systems are huge energy wasters, mostly because people (read: kids) tend to leave them on even when they're not using them.

The study, conducted with Portland, Ore., environmental research and consulting firm Ecos Consulting, found that game consoles (40 percent of U.S. homes have at least one) consume an estimated 16 billion kilowatt hours per year—roughly equal to the annual electricity use of the city of San Diego. This energy usage isn't going to drop anytime soon: Between 2002 and 2007 more than 62 million video game consoles were sold in the  U.S. (Wii was the No. 1 seller, followed by PlayStation and the Xbox). The Washington Post reports that the National Institute on Media and the Family found that 92 percent of kids, ages two to 17, play video games regularly.

Sony PlayStation 3 (which uses 150 Watts of energy) and Microsoft Xbox 360 (which uses 119 Watts) are the biggest offenders, while the Nintendo Wii draws less than 20 Watts, according to the NRDC report. The PlayStation 3 and Xbox 360 each if left on all the time, consume more than 1,000 kilowatt-hours each year—equal to the annual energy use of two new refrigerators. The PlayStation 3, which can also be used as a high-definition video player, uses five times the power of a stand-alone Sony Blu-ray player to  show the same movie.

Ecos and the NRDC offer some solutions, calling for video game console makers to develop more energy-efficient devices that use many of the same power-saving features found on PCs (such as the automatic powering down of a system if it is left idle for a certain period of time). After a period of one to three hours of inactivity, for example, the video game console could automatically save the status of the game to memory and initiate auto power-down. Or, the consoles could come with a "sleep" button that could be used to save power when the players are away from their games. The Xbox 360 and PlayStation 3 have power-saving features, but they are turned off by default when the consoles are shipped and most people don't even know  they exist.

Such power-saving features could save approximately 11 billion kilowatt-hours of electricity per year, cut the nation's electricity bill by more than $1 billion per year, and avoid emissions of more than 7 million tons of carbon dioxide each year—an amount equal to the global warming pollution from all the cars on the road in San Jose, Calif., according to the report.

(Image courtesy of iStockphoto; Copyright: Skip ODonnell)