Landmark buildings around the world switched their lights off for one hour on Saturday 23 March to mark Earth Hour, a campaign to highlight the problem of climate change.

Earth Hour started in Sydney in 2007, when 2.2 million people turned off all non-essential lights for an hour. The next year was an even bigger event as major cities around the world followed Sydney's lead and turned off their lights for an hour to raise awareness about the need to take action on climate change.

Earth Hour, organised by the World Wide Fund for Nature (WWF), has since snowballed into a global event.

This year, key landmarks around the world such as the Sydney Opera House and Harbour Bridge, the Petronas towers in Malaysia, the UK parliament and Buckingham Palace and the Empire State Building all took part.

(Courtesy: DanaeYiakkoupi, YouTube)

In the UK, Earth Hour ambassador, pop group McFly gave a live acoustic performance in panda onesies to kickstart the event. Celebrity chefs Gordon Ramsay and Raymond Blanc came out with special recipes for families to prepare and eat by the candlelight. WWF roped in Kevin McCloud, Miranda Richardson and Alistair McGowan to record Rudyard Kipling's famous Just So stories.

Besides the Empire State Building in New York, the US will mark the occasion by switching off the glitzy lights of the Las Vegas strip, Los Angeles Airport and Niagara Falls.

Earth Hour 2013
The lights on Lions Gate Bridge are turned off during Earth Hour in Vancouver, British Columbia 23 March, 2013. The World Wildlife Fund crowned Vancouver the title of Global Earth Hour Capital for 2013. Reuters
Earth Hour 2013
A combination picture shows a general view of the Parilament Building and the Sukhbaatar statue before (top) and during the Earth Hour at Sukhbaatar Square in Ulan Bator Reuters
Earth Hour 2013
People sit near candles during Earth Hour, after lights were turned off in the city of Cali Reuters
Earth Hour 2013
Leifeng Pagoda is seen behind the West Lake before (L) and during the Earth Hour in Hangzhou, Zhejiang province Reuters
Earth Hour 2013
The Angel Independence Monument is seen during Earth Hour in Mexico City Reuters
Earth Hour 2013
A photo of the Chicago skyline during Earth Hour in Chicago, Illinois Reuters
Earth Hour 2013
A combination photograph shows the skyline with the Empire State Building on the right before (top) and during (bottom) Earth Hour in New York Reuters
Earth Hour 2013
The city centre of Frankfurt is seen during Earth Hour Reuters
Climate Change New York Los Angeles