BBC: Australia's biggest city, Sydney, has switched off its lights for an hour as the Earth Day climate change protest gets under way across the globe.
A small crowd cheered and applauded as the skyline went dark. The Opera House was lit in a deep shade of green to symbolise renewable energy.
The annual event is organised by WWF, the global environment campaign.
It encourages cities and individuals to switch off non-essential lights for an hour at 20:30 local time.
Critics have dismissed the...