It may be darker than usual in your neighborhood tonight, but don't be alarmed. People around the world are participating in a movement called Earth Hour. Every year, people turn their lights off to spread awareness about sustainability and climate change.

This year, Earth Hour takes place on March 30 from 8:30 p.m. to 9:30 p.m. local time. Supporters can sign a pledge to decrease their environmental footprint by taking part in the blackout, and share their experience on social media using the hashtags #Connect2Earth.

Earth Hour was first started by the World Wildlife Fund — the leading organization in wildlife conservation and endangered species — in 2007 in Sydney, Australia. WWF encouraged millions of people to switch their lights off for one hour to support climate change action.

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Since then, the movement has grown globally and is now the world's largest grassroots movement for the environment.

Landmarks including Big Ben in London, Egypt's Great Pyramids, Brazil's Christ the Redeemer statue, the Sydney Opera House, the Colosseum in Rome, the Eiffel Tower in Paris, Burj Khalifa in Dubai and New York City's Empire State Building have all taken part in going dark.

Millions of people are expected to participate this year in more than 180 countries. WWF hopes the event will send a message to government officials that protecting the planet should be their top priority.

"We're the first generation to know we are destroying our planet," WWF said. "And we could be the last that can do anything about it."

This year, climate change is at the forefront of the conversation more than ever, thanks in part to an initiative by teen climate activist Greta Thunberg, who was has been nominated for the Nobel Peace Prize. She started the Youth Climate Strike movement last September, which has since grown to include hundreds of thousands of students around the world who skip school on Fridays to urge world leaders to act on climate change.

The world faces an "existential crisis, the biggest crisis humanity ever has faced, and still it has been ignored for decades by those that have known about it," Thunberg said during a strike on March 15. "And you know who you are, you that have ignored this and are most guilty of this."