This combo shows the lights around Sydney's Harbor and the iconic Opera House (L) taken on March 23, 2011 (top photo) and on March 26, 2011 as the city switches off its lights to mark "Earth Hour". Australia's Opera House was the first of many global landmarks to go dark on March 26 as "Earth Hour" got underway with hundreds of millions of people around the world set to switch off their lights.

This combo of photos shows the Seoul N Tower before (L) and after (R) the lights were turned off for Earth Hour in Seoul on March 26.
Participants form a Korean character, which reads "Night", with candles before Earth Hour in front of N Seoul Tower in Seoul on March 26. Earth Hour, when everyone around the world is asked to turn off lights for an hour from 8.30 p.m. local time, is meant as a show of support for tougher action to confront climate change.
A combination photograph shows the National Stadium (top), also known as the "Bird's Nest", and the National Aquatics Center, also known as the "Water Cube", before and during Earth Hour in Beijing March 26.
In this composite image of two photos lights are out on the iconic face at Luna Park in the top photo in participation of Earth Hour minutes after the bottom was taken with the lights on in Sydney on March 26.
This combo shows the before and after views of the Taipei 101 building as Taipei marks "Earth Hour" on March 26.
These combo photos show a general view of commercial buildings before, top, and after, bottom, turning off lights at Hong Kong's central district on March 26 to mark the annual Earth Hour.
Mark Morgenroth, from Massachusetts, and Katharine Gilmour, from Britain, hold candles during Earth Hour after lights were turned off in part of central Amman on Saturday.
A composite picture shows the Basilica of Superga before and during Earth Hour in Turin, Italy on Saturday.
This combination of images shows Malaysia's iconic land mark Patronas Twin Towers seconds before (L) and after (R) the lights were switched off for Earth Hour in Kuala Lumpur on Saturday.