Sydney will be one of 4000 cities plunged into darkness on Saturday night as hundreds of millions of people around the world turn off their lights for Earth Hour.
At 8.30pm (AEDT), lights on the Sydney Opera House, Harbour Bridge and in homes and businesses across the city will be switched off in an effort to lower the earth's carbon footprint and raise awareness.
"From Brazil to America, to Canada, all the way down to Australia, Japan and India - it's a really diverse set of countries taking part this year," Earth Hour executive director Andy Ridley said in Sydney on Saturday.
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"Here in Sydney, the Harbour Bridge lights will go out, the Opera House lights will go out and lights will go out across the city."
This year, a record-breaking 126 countries are taking part in the World Wildlife Find (WWF) initiative, which started in 2007 in Sydney.
International icons such as the Eiffel Tower in Paris, the Empire State Building in New York and the pyramids of Egypt will go dark for the great switch-off, which comes just months after disappointing UN climate talks in Copenhagen.
For the first time this year, the Forbidden city in Beijing will also be taking part, along with 20 cities across China, despite the country's resistance at Copenhagen.
"What we're still looking for in this coming year is a global deal that encourages all countries to lower their emissions and China is going to have to be a big part of that but so is every other major economy," Mr Ridley said.
Earth Hour will kick off in the Chatham Islands, New Zealand, at 5.45pm (AEDT) on Saturday and spread across the globe, finishing in Apia, Samoa, at 6.30pm (AEDT) on Sunday.
"We will have everyone from Casablanca to the safari camps of Namibia and Tanzania taking part," CEO of Australia's WWF Greg Bourne said.
It's amazing how far this has spread," he said.
"The key thing is you turn off the lights to turn on the lights in your mind as to how you reduce your footprint on the planet.
"This is about optimism, it's about innovation, it's about achievement. It's about how do we find a way to make a better world with a lower footprint."
