Earth Hour is the 60-minutes duration, during which everyone around the world is asked to turn off lights for an hour starting from 8.30 p.m. local time, as a show of support for tougher action to confront climate change.

What began as a climate change campaign in Sydney in 2007, is now an annual global event in which, hundreds of millions of people have voluntarily taken part. Prominent landmarks, monuments and even official buildings across the world have been going dark for an hour for last three years.

According to World Wide Fund for Nature (WWF), organizers of the Earth Hour, Earth Hour 2011, on Saturday March 26, is going to be no exception with about 128 countries and 4616 cities readying up for lessening the use of electricity tonight.

During Earth Hour 2010, the organizers said they expected last year's to be the biggest so far; and yet the participation is growing year after year.

However, whether switching off the lights for just an hour can really save the Earth is a debatable thought and has been in discussions for quite some time.

While countries around the world wait for clock to strike 8.30 p.m., here's an official Earth Hour 2011 video showing the world during the past years' Earth Hour campaign: