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Berlin's Brandenburg Gate, Paris' Eiffel Tower, Rome's Vatican and Barcelona's Sagrada Família have joined the WWF's Earth Hour in switching off their lights for an hour to raise awareness of climate change and energy use.
St Petersburg marked earth hour by turning out the lights of Palace Square. Climate change protesters held a candle lit vigil at 8.30pm local time.
Pakistan marked Earth Hour 2012 by lighting candles for sixty minutes.
In 2007 Sydney started the first ever Earth Hour event, by persuading as many businesses and individuals as possible to switch off their lights.
This year the city was almost completely engulfed in darkness; over two million individuals and more than two thousand businesses took part.
Earth Hour is a global action against climate change.
It started in Australia in 2007 and it has grown to a global day of action. Last year 135 countries across every continent took part.
Organisers hope this year will be even more successful.
The Great Wall of China took part in this year's Earth Hour. Everyone around the world is asked to turn off lights for an hour from 8.30pm local time as a show of support for tougher action to confront climate change.