From Sydney to Seoul, London to Lima, and Dubai to Davis Station in frozen Antarctica, hundreds of millions of people are expected to switch off their lights on Saturday to mark "Earth Hour".
The movement that began in Sydney in 2007 to raise awareness about climate change now brings together people from around the world to turn the lights off for 60 minutes to reduce energy consumption.
"It's an hour in one day of the year," Earth Hour co-founder and executive director Andy Ridley told AFP early Saturday.
"The amount of power that's saved during that time is not really what it's about. What it is meant to be about is showing what can happen when people come together."
Ridley said 134 countries or territories were on board for the event, with many groups expected to use the hour to also pay tribute to Japan which this month suffered a 9.0 magnitude quake and tsunami.
In Scotland, there will be a traditional bagpipe lament to remember the thousands killed in the disaster while a minute's silence will be observed by a group climbing the Sydney Harbour Bridge and another in Antarctica.
Ridley said hundreds of millions of people took part in 2010 and he was hopeful of the same response this year when landmarks such as the world's tallest building Burj Khalifa in Dubai, Times Square New York, the London Eye and Brazil's Christ the Redeemer statue go dark to mark the hour.
Designed as a symbolic act to make people aware of everyday energy use, Earth Hour has evolved into a global movement, and this year will take place from 8:30pm local time around the world.
United Nations Secretary General Ban Ki-moon urged people to celebrate the shared quest to "protect the planet and ensure human well-being."
"Let us use 60 minutes of darkness to help the world see the light," he said of the event, which kicks off in the Pacific, takes in Fiji, New Zealand and Australia, before rolling to Asia, Europe, Africa and the Americas.
"The simple and powerful idea of switching off lights for an hour to drive action on climate change began in Sydney and has been embraced around the world," said Australian Prime Minister Julia Gillard from Canberra's Parliament House, a landmark which will go dark from 8:30 pm (0930 GMT).
British Prime Minister David Cameron said sharing responsibility was the key to fighting climate change, describing Earth Hour as "a huge symbol of global solidarity, an inspiring display of international commitment."
Earth Hour this year will focus on connecting people online so they can inspire each other to go beyond the hour and make commitments to help protect the environment, Ridley said.
Organisers are asking people to commit to an action, large or small, that they will carry through the year to help the planet.
Ridley said he never expected the Earth Hour movement to become so large.
"We didn't imagine right at the beginning... it would be on the scale that it is now. And the fact that it is so cross cultural, beyond borders and race and religion," he said earlier this week.
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