Global Warming is a serious issue that has been given much attention in the last few years. In recognition of this growing concern, the World Wide Fund for Nature Australia promoted an international movement called Earth Hour.

Earth Hour basically asks cities from all over the globe to turn off their lights for an hour on March 29, at 8 p.m. on their local times. The first major city to participate was Sydney. Check out the pictures above to see city in its darkest hour (in a literal sense).

Some critics have dismissed this event as a gimmick, but the WWF begs to disagree. Andy Ridley, who heads the initiative, says that interest has been immense. Even Google turned off the lights on their web page (with a black background) in the US.

The event has a strong backing from Australia. The country's new Prime Minister, Kevin Rudd, made the environment one of his top priorities after taking office. His first official act as Prime Minister was to sign up for the Kyoto Protocol on tackling climate change.

A lot of other cities will be participating in Earth Hour. Check out this offsite link to see if yours is one of them.