The worldwide conservation event is being called the biggest mass campaign ever to demand action on climate change.
The organizers said on their website that famous sites like the Empire State Building, the Great Pyramids of Giza, the Petronas Towers in Kuala Lumpur, the Acropolis in Athens and the Taipei 101 skyscraper in Taiwan will turn off their illuminations for one hour in support of the cause.
The French branch of the World Wildlife Fund (WWF) said over 200 buildings in Paris, including the Louvre, Notre-Dame Cathedral and the Paris Opera House will go dark for an hour.
Paris city hall is even contributing 5 minutes of darkness at the Eiffel Tower, where it will halt a display of flashing lights scheduled for 9:00 p.m.
The WWF launched Earth Hour in 2007.
Some 370 cities in 35 countries took part in the event last year and organizers expect at least 1,189 to join in on Saturday.
Participants who spend an hour in the dark are being asked to update others about their experiences and thoughts on blogs and short video clips to be posted at http://12seconds.tv/earthhour.
Secretary general of the United Nations Ban Ki-moon backed the campaign, calling it "a clear message for action on climate change" in the runup to a crucial meeting in Copenhagen.
The Copenhagen conference will work towards a new global pact on curbing emissions of greenhouse gases and providing help for poor countries bearing the brunt of climate change.
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