For one hour on Saturday starting at 8:30 p.m, local time, cities around the world will send a collective message about conservation and climate change.
Called Earth Hour, the event encourages participants to turn off all non-essential lights for 60 minutes. This year, 7,000 cities in 162 countries are participating.
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Organized by the World Wide Fund for Nature, Earth Hour began in Australia in 2007, and has grown exponentially ever since.
We've compiled photos from Earth Hour events worldwide, below:
Paris, France
Image: AP/Remy de la Mauviniere
Moscow, Russia
Image: AP/Denis Tyrin
Athens, Greece
Image: AP/Petros Giannakouris