Many parts of the world will go dark for an hour Saturday night in more than 170 countries and territories in a show of support for protecting the planet.
Millions of people will participate as homes, cities, hotels, universities and businesses turn off their lights at 8:30 p.m. local time for Earth Hour a demonstration of commitment to fight climate change now in its 11th year.
Among the places going dark this year: the Empire State Building, the Space Needle, the Golden Gate Bridge, the Colosseum in Rome, the Pyramids of Egypt, the Sydney Opera House and the Eiffel Tower.
"There's never been a more critical moment in the fight," said Terry Macko, senior vice president of marketing and communications at World Wildlife Fund.
"Earth Hour is the opportunity to send a message that we remain steadfast in delivering on the goals of the Paris Agreement," he added, referring to the United Nations climate pact signed last year that aims to reduce greenhouse gas emission and strengthen efforts to respond to climate change.
Aside from turning off all lights for the hour, the organization urges people to show support for the global movement by changing their Facebook profile picture, donating their Facebook feed, providing donations and tuning into Earth Hour live performances streamed on Facebook Live featuring artists like Bridgit Mendler, Valerie June and others.
Turning off lights for an hour does not affect emissions of greenhouse gases, but is a symbolic gesture, said Aiguo Dai, a professor in the department of atmospheric and environmental sciences at the University at Albany.
If all of us can find ways to save energy and reduce consumption of fossil fuel, then it will significantly reduce our emissions of greenhouse gases, and that could slow down global warming," he said. "If that still won't be enough, we need to develop new sources of green energy and move away from fossil fuel."
Some hotels across the globe are also participating in their own way. Hilton is hosting a #Travelwithpurposecontest where winners receive a free five-night stay in Canopy by Hilton Reykjavik City Centre in Iceland. Marriott International wants its properties to share images of Earth Hour activities on social media. And Fairmont Washington, D.C. will sell a special "Going Green Martini," donating 100% of sales to the World Wildlife Fund.
Celebrities like Maroon 5 also are supporting the campaign.
Here are some tips from the World Wildlife Fund on how to spend your hour in the dark:
Burn calories by doing a candlelight workout with friends.
Spot the landmarks around you that participate in Earth Hour.
Make art in the dark with your friends and share a good laugh when the lights turn back on revealing the masterpiece.
Host a candlelight dinner party with family and friends.
Look at the stars.
Commit to reducing your carbon footprint.