Sydney lost a little of its sparkle fleetingly on Saturday as Australians who are worried about climate change turned off lights for an hour.

The voluntary and temporary outage was to register support for Earth Hour and signal solidarity with like-minded people in more than 4,000 cities around the globe.

Earth Hour, organised by the World Wildlife Fund and into its fourth year, is intended to pressure governments to act on slowing global warming.

The Empire State Building in New York, the Forbidden City in Beijing, the Eiffel Tower in Paris, the Petronas Towers in Kuala Lumpur, Table Mountain in Cape Town, the pyramids near Cairo, the Brandenburg Gate in Berlin, Rio de Janeiro’s statue of Christ and hundreds of other landmarks will dim for 60 minutes.

Earth Hour 2010 comes five months after world leaders meeting in Copenhagen failed to agree on concerted action to slow the emission of the greenhouse gases that cause climate change.

Earth Hour executive director Andy Ridley said the Copenhagen fiasco had not dampened desire for multilateral action to reduce emissions.

“After Copenhagen we were really fearful that Earth Hour would die, that people would be fatigued with climate change, but the opposite has happened,” he said. “The uptake has been phenomenal.” Mr. Ridley, who claims 1 billion Earth Hour participants in more than 125 countries, said the importance was not electricity saved but issues raised.

An antidote to Earth Hour 2010 is Human Achievement Hour, an initiative of climate change sceptics like Cory Bernardi, a member of parliament for the opposition Liberal Party.

“While Earth Hour activists will be left in the dark, Human Achievement Hour participants will be going to the cinema, enjoying a hot meal, driving their car or watching television,” Mr. Bernardi said.

In fact, both sides of the climate change debate are likely to be out and about and enjoying the wonder of electric power.

In Melbourne’s Federation Square there will be free screenings of films for Earth Hour. In Sydney, participants are being encouraged to watch television by candlelight.

For the first time this year, Canberra’s Parliament House will dim its lights for an hour.

Climate Change Minister Penny Wong was embarrassed last year when it was reported that her Parliament House office lights were left ablaze while she attended an Earth Hour function in another city.