Iconic New York City skyscrapers the Empire State and the Chrysler Building, along with landmarks from the Eiffel Tower to Sydney harbor went dark for an hour Saturday to raise awareness over the fight against climate change.
The symbolic one-hour switch-off, first held in Sydney in 2007, has become an annual global event and organisers World Wide Fund for Nature said they expected this year's to be the biggest so far.
The remote Chatham Islands was the first of more than 100 nations and territories to turn off the power at 8:30 p.m. local time, in a rolling event around the globe that ends just across the International Dateline in Samoa 24 hours later.
Tiny Tuvalu, which fears being wiped off the map from rising sea levels, tried to go carbon-neutral for the event, pledging to cut power to its nine low-lying Pacific atolls and asking car and motorcycle owners to stay off the roads, WWF said.
In the Middle East, the world's tallest building, the Burj Khalifa in Dubai, had its lights switched off for Earth Hour.
Egypt participated as well, with lights shut off at the Giza plateau, plunging the three Great Pyramids, the Sphinx and the surrounding desert area into total darkness.
In Europe, some of the world's most recognizable sites faded into darkness.
More than 240 buildings and monuments in Paris participated, including the Eiffel Tower -- which only went dark for five minutes as opposed to the full hour. Some 1,600 candles were lit at its base in recognition of the event.
London's Big Ben took part, and the advertising signs at Piccadilly Circus in the city were also turned off. It is thought to be only the fourth time since World War II that the huge Coca-Cola sign there has been dimmed.
Far to the south in Antarctica, Australia's Davis research station pledged to dim the lights.
"As we watch the lights go out from continent to continent, let us reflect on the fragility and importance of our natural heritage and pledge to protect it for a sustainable future for all," United Nations Secretary-General Ban Ki-moon said in a statement.
The number of participants went significantly up on 2009, when 88 countries and territories and more than 4,000 towns and cities took part. Organizers have estimated between 500 million and 700 million people were involved last year.
This year, even users of ubiquitous Twitter and Facebook could show their support with special applications that turn their displays dark.
Ridley, WWF's executive director of Earth Hour, said he believed the perceived failure of last year's Copenhagen conference on climate change had stimulated interest this time.
"There is real frustration with the politics around climate change," Ridley told Reuters.
Business had shown strong support, he said, including the world's major hotel chains, which he said are responsible for a significant chunk of global emissions.
Some, though, criticized the event.
"To hold a candles-and-champagne party indoors, on the mildest night of the year, for just one hour, shows that the whole thing is green tokenism," said Viv Forbes, chairman of climate change skeptic group the Carbon Sense Coalition.