Lights dimmed on iconic buildings around the world on March 31, 2012, during the annual Earth Hour. The event, held since 2007, encourages 60 minutes of darkness in a bid to bring attention to climate change. Drag the slider below to see what world landmarks looked like before (left) and after the lights went out at 8:30 p.m. local time. Use the arrows at the bottom of the gallery to navigate to the next photo.