The concept behind the challenge is to get individuals to make a difference by taking small actions in their every day lives. Yahoo! co-founder David Filo said he wanted to tap into the half a billion Yahoo! users to encourage greener lifestyles.

People can participate at the Yahoo! Be a Better Planet site. For each action you take through a Yahoo! green site you'll rack up points for you and your city. The city with the most points by June 8 will receive a small fleet of hybrid taxis. Individual participants with enough points will get a free compact flourescent bulb (CFL). Photo: Green Options

Actor Matt Dillon said, "I'm concerned with many environmental threats facing us and I want to do my part at reducing global warming." He encouraged the use of motion sensored lights, and suggested a few things each person can do such as replacing incandescnet light bulbs with CFLs, turning off the lights in empty rooms, walking or taking public transportation and unplugging chargers from outlets.

Photo: Green Options: Global Green CEO, Matt Petersen (left); Matt Dillon, actor (center); David Filo, co-founder Yahoo! (right)Matt Petersen, President and CEO of Global Green USA, stressed that when people take individual actions at home and at work, it will not only improve the lives of everyone but will send an important message to corporations and governments across the U.S. that Americans support the mayors climate protection agreement. The mayors climate protection agreement was initiated by Seattle Mayor Greg Nickels to get mayors of cities across the nation to come together to reduce municipal green house gas emissions in leiu of federal support.

The Greenest City in America challenge is just the latest effort by Yahoo! as they move toward greening their practices and operations. Earlier this year Yahoo! teamed up with the producers of An Inconvenient Truth to create an eco-info site 18seconds.org, and last month announced plans to take Yahoo! carbon neutral.