Overview of Hong Kong Island and Kowloon with lights on and off to mark Earth Hour 2010.   (© Ringo Ma, via WWF)

Overview of Hong Kong Island and Kowloon with lights on and off to mark Earth Hour 2010.   (© Ringo Ma, via WWF)

A before-and-after view of the Las Vegas Strip seen during Earth Hour from Mix at THEhotel at Mandalay Bay March 27, 2010 in Las Vegas, Nevada.   (Ethan Miller/Getty Images)

A before-and-after view of the Las Vegas Strip seen during Earth Hour from Mix at THEhotel at Mandalay Bay March 27, 2010 in Las Vegas, Nevada.   (Ethan Miller/Getty Images)

The Sydney skyline is seen before and after the lights are switched off for Earth Hour on March 27, 2010 in Sydney, Australia. Earth hour this year aims to highlight everyone’s environmental footprint on the earth, encouraging individuals to reduce their impact on the planet and help reduce pollution and climate change. (Lisa Maree Williams/Getty Images)

The Sydney skyline is seen before and after the lights are switched off for Earth Hour on March 27, 2010 in Sydney, Australia. Earth hour this year aims to highlight everyone’s environmental footprint on the earth, encouraging individuals to reduce their impact on the planet and help reduce pollution and climate change. (Lisa Maree Williams/Getty Images)

Before and after views of Seattle's Pacific Science Center on Earth Day, March 27th, 2010. (© Jason Ayres Gift Enevoldsen)

Before and after views of Seattle's Pacific Science Center on Earth Day, March 27th, 2010. (© Jason Ayres Gift Enevoldsen)

The hill of the Acropolis before and during Earth Hour in Athens, Greece on March 27, 2010.   (REUTERS/Yiorgos Karahalis)

The hill of the Acropolis before and during Earth Hour in Athens, Greece on March 27, 2010.   (REUTERS/Yiorgos Karahalis)

A before-and-during view of a square near the Bundaran Hotel in Jakarta, Indonesia.   (© WWF-Indonesia / Alfonso Reno)

A before-and-during view of a square near the Bundaran Hotel in Jakarta, Indonesia.   (© WWF-Indonesia / Alfonso Reno)

The Forbidden City, seen before and during the Earth Hour 2010 power switch off on March 27, 2010 in Beijing, China.  (Feng Li/Getty Images)

The Forbidden City, seen before and during the Earth Hour 2010 power switch off on March 27, 2010 in Beijing, China.  (Feng Li/Getty Images)

Lights switched off in Toronto's financial district, Ontario, Canada.  (© Bill Ivy/WWF-Canada)

Lights switched off in Toronto's financial district, Ontario, Canada.  (© Bill Ivy/WWF-Canada)

Table Mountain, above Capetown, South Africa, seen before and during Earth Hour 2010.   (© WWF/South Africa)

Table Mountain, above Capetown, South Africa, seen before and during Earth Hour 2010.   (© WWF/South Africa)

Buildings in the central business district before and after Earth Hour in Singapore March 27, 2010.   (REUTERS/Nicky Loh)

Buildings in the central business district before and after Earth Hour in Singapore March 27, 2010.   (REUTERS/Nicky Loh)