Earth Hour is an initiative by WWF which is scheduled for Saturday 28th March 2009 at 8-30pm your local time. Individuals, businesses, governments and organizations around the world are being asked to turn off their lights for one hour - Earth Hour - to make a global statement of concern about climate change and to demonstrate a commitment to finding solutions.
Some 1180 cities from 80 countries across the globe have already signed up and a great number of iconic landmarks will be plunged into darkness, including Nelson's Column in London, the Forth Bridge, the Millennium Stadium in Cardiff, the Eiffel Tower, Christ the Redeemer in Rio de Janeiro, Table Mountain in Cape Town and the Sydney Opera House.
Earth Hour originated in Australia in 2007. This video gives more background to the project: