Now in its fourth year, the event looks set to be the biggest yet with thousands of cities and towns in 125 countries-37 more than last year-pledging to take part in the aftermath of a failed climate summit last year.

Despite December’s fractious Copenhagen summit and recent controversy over climate science, public opinion still hopes for meaningful action to avert catastrophic global warming, according to Earth Hour founder Andy Ridley.

Now run by the WWF, Earth Hour began in Sydney in 2007 when 2.2 million people switched off the lights in their homes, offices and businesses for 60 minutes to make a point about electricity consumption and carbon pollution.

The campaign went global the following year, and on March 27, more than 1,200 of the world’s best-known sites will kill their lights at 8:30pm local time in what organizers describe as a “24-hour wave of hope and action”.

A raft of multinational companies including Google, Coca-Cola, Hilton, McDonalds, Canon, HSBC and IKEA have endorsed Earth Hour 2010 and pledged to darken their offices worldwide in support.