A candle mural is lit on the forecourt of the Opera House representing WWF and 60+ as the lights are switched off for Earth Hour on March 31, 2012, in Sydney, Australia.
- [Mark Metcalfe/Getty Images]

The sails of the Opera House and the Sydney Harbor Bridge in darkness as the lights are switched off for Earth Hour on March 31, 2012, in Sydney, Australia.
- [Marianna Massey/Getty Images]

Volunteers help light a candle mural on the forecourt of the Opera House representing WWF and 60+ before the lights are switched off for Earth Hour on March 31, 2012, in Sydney, Australia.
- [Mark Metcalfe/Getty Images]

Volunteers help light a candle mural on the forecourt of the Opera House representing WWF and 60+ as the lights are switched off for Earth Hour on March 31, 2012, in Sydney, Australia.
- [Marianna Massey/Getty Images]

In this composite image the Luna Park entrance is seen before on March 30, 2012 (top), and after the lights are switched off for Earth Hour on March 31, 2012, in Sydney, Australia.
- [Lisa Maree Williams/Getty Images]

In this composite image the Sydney city skyline is seen before on March 30, 2012 (top), and after the lights are switched off for Earth Hour on March 31, 2012, in Sydney, Australia.
- [Lisa Maree Williams/Getty Images]

In this composite image the Sydney Harbor Bridge and the city skyline are seen before on March 30, 2012 (top), and after the lights are switched off for Earth Hour on March 31, 2012, in Sydney, Australia.
- [Lisa Maree Williams/Getty Images]

5000 blue and green candles in an eight-meter shape of Planet Earth burn in front of the Brandenburg Gate during Earth Hour 2012 on March 31, 2012, in Berlin, Germany.
- [Adam Berry/Getty Images]

A volunteer lights one of 5000 blue and green candles in an eight-meter shape of Planet Earth in front of the Brandenburg Gate during Earth Hour 2012 on March 31, 2012, in Berlin, Germany.
- [Adam Berry/Getty Images]

A volunteer lights one of 5000 blue and green candles in an eight-meter shape of Planet Earth in front of the Brandenburg Gate during Earth Hour 2012 on March 31, 2012, in Berlin, Germany.
- [Adam Berry/Getty Images]

People hold candles during the sixth annual Earth Hour in Moscow, Russia, on March 31, 2012.
- [KIRILL KUDRYAVTSEV/AFP/Getty Images]

A girl lays a candle during the sixth annual Earth Hour in Moscow, Russia, on March 31, 2012.
- [KIRILL KUDRYAVTSEV/AFP/Getty Images]

People launch a Chinese paper wish lantern during the sixth annual Earth Hour in Moscow, Russia, on March 31, 2012.
- [KIRILL KUDRYAVTSEV/AFP/Getty Images]

Sri Lankan President Mahinda Rajapakse holds a candle during the Earth Hour ceremony at the presidential official residence in Kandy on March 31, 2012.
- [Ishara S.KODIKARA/AFP/Getty Images]

A man holds a candle during an Earth Hour ceremony at the Sri Lankan presidential official residence in Kandy on March 31, 2012.
- [Ishara S.KODIKARA/AFP/Getty Images]

Pakistani children hold lit candles to mark the sixth global Earth Hour, in Karachi on March 31, 2012.
- [RIZWAN TABASSUM/AFP/Getty Images]

A Pakistani girl lights candles in front of parliament house to mark the sixth global Earth Hour, in Islamabad on March 31, 2012.
- [FAROOQ NAEEM/AFP/Getty Images]

Badaling Great Wall is illuminated during the Earth Hour 2012 power switch off on March 31, 2012, in Beijing, China.
- [Lintao Zhang/Getty Images]

This combination of pictures shows the ION Orchard shopping mall illuminated (below) before and darkened (top) after the start of the sixth annual Earth Hour on March 31, 2012, in Singapore.
- [ROSLAN RAHMAN/AFP/Getty Images]

People gather in front of Malaysia's iconic Patronas Twin Towers as they stand unlit during Earth Hour in Kuala Lumpur on March 31, 2012.
- [SAEED KHAN/AFP/Getty Images]