The Eiffel Tower lights go out in Paris, France.

This composite image shows the Eiffel Tower submerging into darkness during the Earth Hour switch-off in Paris. Photo: Chesnot/Getty Images

Sydney, Australia, was one of the first places in the world to mark Earth Hour.

Sydney Harbour Bridge, the Opera House and the ferris wheel were among the first landmarks in the world to mark Earth Hour. Photo: Peter Parks/AFP/Getty Images

Girls hold light candles in front of the parliament house during a Earth Hour in Islamabad, Pakistan.

Girls hold candles in front of the parliament house during Earth Hour in Islamabad, Pakistan. Photo: Farooq Naeem/AFP/Getty Images

Monumento a la Revolucion is seen before its lights are turned off in Mexico City, Mexico.

Monumento a la Revolucion marks Earth Hour in Mexico City, Mexico. Photo: Daniel Cardenas/Anadolu Agency/Getty Images

The cathedral of Guadalajara is pictured without lights during Earth Hour, in Guadalajara, Jalisco State, Mexico.

The cathedral of Guadalajara goes without lights during Earth Hour, in Guadalajara, Jalisco State, Mexico. Photo: Ulises Ruiz/AFP/Getty Images

Buckingham Palace in London before and after it switches off its lights for an hour to mark WWF's Earth Hour.

Buckingham Palace in London before and after the hour's switch-off. Photo: Jonathan Brady/PA Images via Getty Images

Red Square in Moscow, Russia, marks Earth Hour.

Red Square in Moscow turns its lights off for an hour for the WWF initiative.

The ancient Acropolis with lights on and off during the Earth Hour in Athens, Greece. Photo: STR/AFP/Getty

The dome of St. Peter's basilica before and after being plunged into darkness for the Earth Hour environmental campaign in the Vatican. Photo: Andreas Solaro/AFP/Getty Images

Much of Hong Kong observes Earth Hour. Photo: Dale de la Rey/AFP/Getty Images

Staff member wearing panda costume poses with candles in Yantai, Shandong Province of China.

A person wears a panda costume while posing with candles in Yantai, Shandong Province, China. Photo: VCG via Getty Images

In photos: World's landmarks turn off lights for Earth Hour

What to read next