World landmarks dimmed for Earth Hour

University students hold papers leaf to celebrate before a mini marathon in conjunction during the Earth Hour at the Great Wall of China in the north of Beijing, China, Saturday, March 31, 2012. Hundreds of landmarks around the world including Washington's National Cathedral, London's Clock Tower, the Great Wall of China and Tokyo Tower will be dimmed at 8:30 p.m. local time, as part of a global effort to shine a spotlight on climate change. (AP Photo/ Vincent Thian)