When you look out the window this evening and see a darkened skyline, don’t panic. The blackout will be intentional and for a cause dear to many hearts. From the Empire State Building to the Golden Gate Bridge, to the Sydney Opera House, the world’s most iconic landmarks will go dark for one hour beginning at 8:30 p.m. for this year’s Earth Hour. Now in its 10th year, Earth Hour is an annual event where more than 170 nations across the globe unite to bring visibility to climate change. Event participants are urged to refrain from using non-essential electricity for one hour.

Earth Hour has become one of the world’s largest movements devoted to sustainability. Millions are expected to participate in this year’s event, which was first introduced by the World Wide Fund for Nature (WWF) in Sydney, Australia. As USA Today notes, the event is a way of bringing visibility to efforts underway to reduce greenhouse gas emissions.

We're all in for #EarthHour. This year, Earth Hour lands on March 25 at 8:30PM local time. Will you join us? https://t.co/UIlm63YeSJ pic.twitter.com/fdetTn90d5 — Maroon 5 (@maroon5) March 22, 2017

Earth Hour is growing in popularity in the U.S. with many organizations and communities planning observations of the event. In California, spectators can expect the famous Pacific Ferris Wheel at Santa Monica Pier to go dark. The L.A. Public Library will be participating in the event as well.

On the east coast, Philadelphia has several public events planned to coincide with Earth Hour festivities. The Philadelphia Zoo plans to observe the event and the city’s electrical supplier, PECO, will shutter the LED lights system that displays news and graphics 24/7 atop its Center City building.

In New York City, the third annual Earth (angel) Hour will be held in West Chelsea featuring candle-lit live entertainment. Also in New York City, the United Nations is expected to support Earth Hour. U.N. Secretary-General António Guterres released a video through the Global Goals for Sustainable Development Facebook page to urge participation in this year’s event.

The U.N. support aligns with efforts underway since the Paris Agreement went into effect on November 4, 2016, to curtail greenhouse gas emissions.

Elsewhere, more businesses are urging citizens to unplug and save energy during Earth Hour. The technology company Nokia tweeted a message of sustainability to its 2.22 million followers.

Small actions can make a big difference. Here are some ways to save energy – share your own sustainability tip with us! #EarthHour pic.twitter.com/MXFDfieBpX — Nokia (@nokia) March 24, 2017

The principles of Earth Hour have also been adopted in the classroom as a way to promote environmental protection to young students. Event organizers have created lesson plans, activity sheets, and classroom activities tied to creating awareness. For instance, the Awesome Science Lab in Scarborough, Ontario, had students create lists of things they could do on a Saturday night that didn’t involve electricity.

The grade 5 students brainstormed some great ideas for celebrating #earthhour2017 at home and school. @EcoSchoolsTDSB , @WardenAvePS pic.twitter.com/OorNzIEIN0 — Awesome Lab (@awesomelab644) March 22, 2017

Though Earth Hour generally receives positive press for its efforts, this year the event and WWF have come under fire by environmentalists, such as the president of Environmental Progress, Mike Shellenberger, and the Director of the Copenhagen Consensus Center, Bjorn Lomborg, who criticized Earth Hour in a USA Today op-ed for being an empty political gesture that does little to aid the 1.3 billion worldwide who live every waking hour of their lives without a dependable electricity source.

“What the planet needs isn’t a futile, brief-lived, feel-good political gesture like Earth Hour, but sustained, greater investment in research and development of green energy. Only when solar and wind power are effective and competitive will the entire world be able to afford to make the switch away from fossil fuels.”

To counter criticism, WWF pointed to the tremendous impact that Earth Hour has had, including generating nearly 7,000 related events, billions of Twitter impressions, and thousands of donations to change climate change. Though one hour alone can’t significantly change the effects of global warming, supporters no doubt hope that the visibility that the event generates will lead to increased visibility for environmental issues.

[Featured Image by Kamil Zihnioglu/AP Images]