Save the date: At 8:30 p.m. on Saturday March 31, cities across the globe will voluntarily blackout for Earth Hour 2012. For more details, view the official video below.

The Empire State Building, Sydney Opera House, Eiffel Tower, Christ the Redeemer, Burj Khalifa, and Great Wall of China will all go dark for one hour this Saturday as a symbolic gesture of each nation's commitment to sustainability.

The annual event known as Earth Hour is an open source idea - anyone can run it, and anyone can be a part of it. Perhaps that's why in just six years' time it's become the world's largest voluntary action for the environment, uniting communities around the world to celebrate a commitment to the planet by switching off lights for one hour on the last Saturday of March.

It's not your classic green fear campaign, Earth Hour Executive Director and Co-Founder Andy Ridley told IBTimes. Not that they don't have their place, but we wanted something that would unite the community.

And unite they have. Earth Hour organizers estimate that 5,251 cities and towns in 147 countries and territories will participate in the 2012 event, reaching 1.8 billion people from to Argentina to Zimbabwe.

That's a far cry from its humble inception in Sydney back in 2007.

It started as a bit of a reaction to the situation in Australia in 2005 and 2006, Ridley said, noting that the government at the time was not taking notice of climate issues.

We got to a point where we were talking to those that already agreed with us and fighting with all those that didn't so we tried to come up with a way of showing -- in a very impressive way -- that people did care.

They knew that it was important to get two groups behind them: companies and school kids.

They partnered with the World Wildlife Foundation in Australia and got the mayor on their side. The first company they got on board was a big one: PricewaterhouseCoopers.

We wanted a conservative, if you will, and credible company to back our idea, Ridley said. And with that, things began to spiral exponentially.

Soon the city of Toronto reached out and wanted to join in. By 2008, 379 cities and towns in 35 countries participated. The next year, Earth Hour saw massive growth with 4,000 cities and towns in 88 countries.

What's happened in the past couple of years has been the digital footprint explosion, Ridley said. People are connecting online. Last year we had 91 million connecting on our social media platforms.

He said this year he was even approached by two teens in Libya who are setting up Earth Hour events in Tripoli. They've convinced the minister to switch off the lights in the former King's Castle, now the National Museum. We wanted to do it last year, they told him, but we were in the middle of a war.

In another extreme, Earth Hour will literally go out of this world in 2012 to the International Space Station where astronaut and WWF ambassador Andre Kuipers will experience the event watching over the planet from above. He'll share photos and live commentary of his experience via the European Space Agency.

UN Secretary General Ban Ki-moon said the United Nations will show its support by turning off lights at the headquarters in New York.

Turning off our lights is a symbol of our commitment to sustainable energy for all, he said in a statement. We need to fuel our future with clean, efficient and affordable energy.

The one hour when lights go out in cities across the globe is the symbolic heart of the event. Ridley knew that he had to have the symbolic on the front end of it, but the campaign aims to be so much more.

Earth Hour is bigger than one hour of lights out and organizers are trying to get that message across this year by asking participants to go beyond the hour, using the symbolism of the event as a catalyst to engage in discussions about facilitating a sustainable lifestyle.

Earth Hour is not a blackout in the traditional sense. Only non-essential lights will be turned off by those that choose to partake. It's a voluntary action by its participants to show their commitment to an act of change that benefits the entire planet.

As the organizers put it: From melting sea ice in the Arctic to a looming deforestation disaster in the Amazon, coral bleaching in the Great Barrier Reef to a drought induced famine in the Horn of Africa. It's time to act.

This year, Earth Hour and WWF ask participants to accept and make their own Earth Hour challenges on YouTube at www.youtube.com/earthhour. It's part of the new I Will if You Will campaign that intends to engage a growing global community to go beyond the hour and coordinate their efforts publicly through Facebook, Twitter, Google+, and other platforms. The idea is yet another way Earth Hour has used social media to rapidly unite the globe around its cause.

The aggregate of everyone's actions is more powerful than the individual, Ridley said. So we're encouraging individuals or organizations to be the inspiration - anyone can be the inspiration to make change and they can share it.

Further proof that Earth Hour is broadening its scope and moving beyond the hour came when it announced in February that its global headquarters would move from Sydney to Singapore.

Ridley said they wanted to capitalize on the incredible growth in the region.

Back at the beginning, we had a kind of one-place plan, he said. It was like, if we can do this, we can then take it beyond the hour. Since then, it's had truly amazing growth and the long-term idea is to create an interconnected global community sharing opportunities, challenges, and ideas around the broader goal.

It sounds very naïve, he said. And maybe it is. But it's what we're trying to do.

RELATED:

8 Out Of 10 Americans Now Urbanites: What's Changed In The Last Decade?

World Water Day 2012: Facts & Ideas For A Sustainable Future

The Best (And Worst) Places To Be A Woman in 2012

The Struggle to Save Maho Bay - the World's First Eco-Resort