"It's an hour of active, thoughtful darkness, a celebration of our awakening to climate change action," Oscar-winning Australian actress Cate Blanchett told Agence France-Presse (AFP).
Residents and businesses across Sydney flicked off the lights for "Earth Hour" event at 7:30 pm (0930 GMT).
Tourists had to view the famous Sydney Opera House by moonlight, while the Harbour Bridge's steel span and the clown's face of the waterside Luna Park fairground were also blacked out.
The neon on a huge blinking Coca-Cola advertising hoarding in Sydney's Kings Cross nightclub district flickered off for the first time since it was installed in 1974.
Restaurants served diners by candlelight and pupils attended schools for special Earth Hour parties.
Many of Australia's biggest companies had signed up for the event, with local McDonald's restaurants turning off the "golden arches" for the occasion.
"We think that signal, the darkness of Sydney, will flash not only around Australia but right around the world," said Greg Bourne of the World Wildlife Fund (WWF), organizer of the event.
It will "send a very positive signal that we can do something," he added.
WWF Australia spokesman Andy Ridley said the event was aimed at raising awareness about climate change.
"It's only by joining together that you can make a difference," he said.
"The world has moved into a time where we see climate change as a serious risk but we want people to realize that it's not all doom and gloom, individuals can take action to help address the problem."
In its first assessment in six years, the UN Intergovernmental Panel on Climate Change (IPCC) in February issued its starkest warning yet about global warming.
UN scientists said fossil fuel pollution would raise temperatures this century, worsen floods, droughts and hurricanes, melt polar sea ice and damage the climate system for a thousand years to come.
"One of the things about Earth Hour is really to get the issue out of the scientific and specialist areas and into the mainstream," said Ridley.
He said WWF hoped to capitalize on the popularity of the event in the longer term with a campaign to reduce Sydney's greenhouse gas emissions by 5% over the next year.
Earth Hour organizers say there are a number of simple steps people can take to reduce electricity use, including unplugging appliances such as televisions, microwave ovens and stereos that are normally left on standby.
Other suggestions include switching to fluorescent light bulbs -- a move the Australian government committed to earlier this year -- and using "green" power sources such as solar.
Güncelleme Tarihi: 20 Eylül 2018, 18:16