This year's Earth Hour, the third, was the biggest yet as people in a record 126 countries switched off lights for to show concern about climate change.
As well as being a physical phenomenon, the event captured the imagination of the blogosphere, with over 75 million mentions of the event on the internet over 24 hours and at its peak one in every 50 Tweets mentioned the event, making it the most popular subject on Twitter that day.
The event took place on Saturday night with organisers claiming it sent a powerful message that the public want action on climate change.
Andy Ridley co-founder and executive director of Earth Hour said, "The response from citizens, businesses and government has been truly phenomenal.
"Crossing geographic, economic and cultural boundaries, it has brought together people from all over the planet to celebrate the one thing we all share - the place we live."
"WWF's Earth Hour, at a personal, local and global level has become a rallying point for those who want action on climate change and are prepared to be part of the solution."
WWF-International's director-general Jim Leape who attended the lights out celebrations at the Forbidden City in China said, "Tonight, hundreds of millions of people raised their voices by turning out their lights. It is a simple act, but a powerful call to action."
United Nations Secretary-General, Ban Ki-moon said, "The message of Earth Hour is simple. Climate change is a concern for each of us. Solutions are within our grasp and are ready to be implemented by individuals, communities, businesses and governments around the globe."
The First Earth hour began in Sydney in 2007, when 2 million people switched off their lights. In 2008, more than 50 million people around the globe participated.
In 2009, participation swelled to hundreds of millions as 4159 cities, towns and municipalities in 88 countries and many of the world's best known landmarks participated.
This year in the UK highlights included Big Ben, Buckingham Palace and Number 10 Downing Street going dark, and people gathering to watch Piccadilly Circus darkening for only the fifth time since World War II.
Londoners also joined the WWF team in Trafalgar Square as a giant Hour Glass tracked the hour and reminded all who watched, that while time is ticking, there is still enough time to act.
Ireland also embraced the event with many bars and pubs in downtown Dublin took part.
The Temple Bar district was a buzz. The Irish Minister of the Environment gave a nationally televised speech to 300,000 viewers at 8.30pm from a major hotel where the lights went off.
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