SYDENY: The white-shelled roof of the Sydney Opera House fell dark tonight, one of the first landmarks to turn out the lights in an hour-long gesture to be repeated by millions of people around the world who are calling for a binding pact to cut greenhouse gas emissions.

Asian cities followed Australia and New Zealand as the fourth annual Earth Hour cranked up. Buildings in some 4,000 cities in more than 120 countries were expected to unplug to reduce energy consumption and draw attention to the dangers of climate change, according to organisers.

The event will roll across the world, with participants turning off the lights when the clock strikes 8:30 pm local time. From a shopping mall in Manila to the Eiffel Tower in Paris and the Empire State Building in New York, landmarks and skylines will dim.

“We have everyone from Casablanca to the safari camps of Namibia and Tanzania taking part,” said Greg Bourne, CEO of World Wildlife Fund in Australia, the environmental group that came up with the idea that started in Sydney in 2007 and has since grown to every continent.

The shutdown is completely voluntary and street lights, traffic lights and other safety measures are unaffected.

Andy Ridley, a WWF worker in Sydney who cooked up the idea of Earth Hour, said he hoped this year’s event would inspire world leaders to strive for a much stronger climate agreement than that struck at December’s Copenhagen summit, which failed to come up with binding rules on reducing pollution. “What we’re still looking for in this coming year is a global deal that encourages all countries to lower their emissions,” Ridley said today.