Per the Earth Hour website:
"Join millions of people around the world in making a statement about climate change by turning off your lights for Earth Hour, an event created by the World Wildlife Fund.
Earth Hour was created by WWF in Sydney, Australia in 2007, and in one year has grown from an event in one city to a global movement. In 2008, millions of people, businesses, governments and civic organizations in nearly 200 cities around the globe will turn out for Earth Hour. More than 100 cities across North America will participate, including the US flagships–Atlanta, Austin, Chicago, Phoenix and San Francisco and Ottawa, Montreal, Toronto and Vancouver."