An hour of darkness will descend on cities from Australia to Denmark on March 29 as homes and business turn out the lights to raise awareness about global warming. The event began last year in Sydney, where 2.2 million people shut off the lights, AFP reports. Two dozen cities around the globe will join this year's "Earth Hour."
Chicago, Atlanta, San Francisco, and Phoenix are the American cities on the Earth Hour roster. Other cities taking part include Tel Aviv, Bangkok, and Copenhagen. Along with the Sydney Opera House, icons like San Francisco's Golden Gate Bridge, Chicago's Sears Tower, and Toronto's CN Tower will plunge into darkness.