http://www.EarthHour.org/about

It started with a question: How can we inspire people to take action on climate change?

The answer: Ask the people of Sydney to turn off their lights for one hour.

On 31 March 2007, 2.2 million people and 2100 Sydney businesses turned off their lights for one hour - Earth Hour. If the greenhouse reduction achieved in the Sydney CBD during Earth Hour was sustained for a year, it would be equivalent to taking 48,616 cars off the road for a year.