Australians switched off their lights for 60 minutes Saturday to mark "Earth Hour," a campaign by environmentalists to raise awareness about global warming.  The event was started a year ago in Sydney by the World Wildlife Fund (WWF).  The campaign has spread to major cities worldwide - from Dublin to Chicago and Bangkok to Manila - making Earth Hour 2008 a global movement.  From Sydney, Phil Mercer reports.

Fireworks explode near the Sydney Opera House at the conclusion of Earth Hour in Sydney, 29 Mar 2008

Sydney's symbolic act of switching off some of its lights has caught on.

Tens of thousands of people have taken part in the event in Australia and across the Tasman Sea in New Zealand.

Environmentalists say more than 370 towns and cities across Asia, Europe and North America will also take part in Earth Hour this year.

Organizers say the purpose of Earth Hour is to show that communities care passionately about climate change and want to keep pressure on governments to act decisively.

Critics though have dismissed the event as simply a gimmick that will not make any difference.

That is a charge rejected by Andy Ridley from the World Wildlife Fund, who says interest has been immense.       

"We're aware of villages in Norfolk in England that are doing Earth Hour and we're aware of the big cities like Chicago and Sydney that are doing it," he noted.  "But I think another amazing thing about Earth Hour that surprised us is that it seems to have transcended across borders.  It seems to be really popular in South America. You know, places like Vietnam, we've got Seoul on board as a supporting city.  You know, that's an amazing side of it, I think, that it does seem to transcend politics and cultures."    

There have been a host of celebrations across Australia to mark Earth Hour, including traditional Aboriginal torchlight performances, environmentally friendly dinner parties and special candlelit evenings for single people.

Some nightclubs have also operated without lights while many Australians have marked the occasion quietly in the darkness at home.

Lights on iconic landmarks like the Sydney Harbor Bridge and Opera House have also been dimmed.

Global warming is a big issue here with good reason. Australia is one of the world's worst per capita emitters of greenhouse gases.  Many believe that recent droughts and floods are the result of man's destabilizing influence on the climate.

Environmentalists say last year more than two million people and two thousand businesses turned off their lights for one hour in Sydney, cutting energy consumption by 10 percent.

Other cities officially involved in "Earth Hour" include Atlanta, Montreal, Odense and Tel Aviv along with communities in the South pacific island states of Tuvalu and Fiji.