SYDNEY (AFP) - Millions of people across the globe will kill their lights for one hour this Saturday, in what organisers hope will be a resounding call for tough action on climate change. The waters of Sydney Harbour will be plunged into darkness for an hour from 8:30 pm (0930 GMT) as the iconic Opera House and Harbour Bridge dim their lights. The pyramids of Giza, Niagara Falls, the Eiffel Tower, the Empire State Building, the Acropolis and Beijing's "Birds Nest" Olympic stadium are among other major landmarks across 84 countries to celebrate Earth Hour. In Hong Kong, famed for its glittering waterfront, more than 1,500 buildings will dim their lights, including many of the city's iconic skyscrapers such as the Bank of China Tower, HSBC's headquarters and the giant International Finance Centre 2. The city will also suspend its daily light show for the first time on Saturday, organisers said. From its beginnings in Sydney two years ago, when 2.2 million people switched off their lights, the event has exploded to this year include 2,848 cities, villages and towns, said director Andy Ridley. "We always had our eye to 2009 because of the Copenhagen (emissions targets) negotiations at the end of the year," Ridley told AFP. A UN-led conference in the Danish capital in December is meant to approve a new global warming treaty for the period after 2012, when the Kyoto Protocol's obligations to cut carbon emissions expire. "We hope that it will be difficult for leaders to look at the scale of involvement and engagement in a broad spectrum of countries without saying 'OK, there's a mandate there,'" Ridley said. "We have eight months to get to Copenhagen and we sort of see this as a referendum on the issue." Earth Hour was born out of frustration at Australia's then-conservative "climate sceptic" government, and Ridley said organisers were overwhelmed by the response in 2007, when almost half of Sydney's population observed an hour of darkness. Crucially, Ridley said countries leading the initiative in 2009 were emerging, high-emissions economies such as Brazil, India and China. "I remember when we first started this people were saying 'there is no chance you will be able to get China to engage in Earth Hour,'" he said. "But for some reason there's, I think, a general sense that climate change is such a massive problem that it's one of those issues that has to be dealt with globally." Critics said the initiative was little more than empty symbolism, with one Danish professor claiming the use of candles during the hour could actually produce more emissions than electric lights. "Even if a billion people turn off their lights this Saturday the entire event will be equivalent to switching off China's emissions for six short seconds," said Bjorn Lomborg, director of the Copenhagen Consensus Centre think-tank. "Moreover, candles produce indoor air pollution 10 to 100 times the level of pollution caused by all cars, industry and electricity production. If you use one candle for each extinguished globe you're essentially not cutting CO2 at all, and with two candles you'll emit more CO2," Lomborg wrote in The Australian newspaper. Ridley agreed the amount of energy saved from powering down for an hour was negligible but said it was a symbolic, awareness-raising act. "In effect, the leaders of the world have to step over the line together," he said. "There will be different lines for different countries but we have to step over the line together and we have to set targets that will help us achieve very, very significant emissions cuts," Ridley added. "We hope that Earth Hour will be part of providing a mandate for those leaders who will be in Copenhagen in December to do that." Chatham Island, the largest of a tiny group of Pacific islands 800 kilometres (500 miles) southeast of New Zealand, will officially begin Earth Hour by switching off its diesel generators at 0645 GMT, or 8:30 pm local time. Millions are set to mark the day with events such as acoustic concerts and candlelit dinners, with church bells set to ring in Sweden and casinos to black out along the garish Las Vegas strip.