Dozens of iconic structures were plunged into darkness as part of an annual climate change awareness campaign. Despite millions of people taking part, critics say the reduction in power consumption is trivial.
Cities around the world switched off the lights illuminating their best-known landmarks for 60 minutes on Saturday evening to mark Earth Hour.
The Brandenburg Gate in Berlin, the Eiffel Tower in Paris, Egypt's Great Pyramid, New York's Empire State Building, the Sydney Opera House, the Shanghai Tower and the Christ the Redeemer monument in Brazil were just some of the more than 100 monuments that were thrown into darkness.
The symbolic gesture was part of the 13th edition of a campaign organized by the green group World Wide Fund for Nature (WWF) to highlight humanity's impact on the environment.
Alongside those iconic structures, tens of thousands of people and businesses in dozens of cities in North and South America, Europe, Asia, Australia and New Zealand turned off their lights at 8:30 p.m. local time to highlight humanity's energy use and the need for conservation.
"Earth Hour is still is the world's largest grassroots movement for people to take action on climate change," WWF Australia CEO Dermot O'Gorman told the Agence France-Presse news agency.
"It's about individuals taking personal action but joining with hundreds of millions of people around the world to show that not only do we need urgent action on climate change, but we need to be protecting our planet," he added.
More than 7,000 towns and cities in 187 countries observed last year's event, according to organizers.
Earth Hour started in 2007 in Sydney and has grown to involve millions of people, businesses and landmarks who set aside an hour to switch off lights and promote the movement.
Critics, however, complain that the energy savings from the hourlong campaign are insignificant. Others say Earth Hour demonizes electricity, when abundant, cheap lighting is one of mankind's greatest 20th-century achievements.
Mass extinction underway
The last 12 months have seen some of the direst warnings on the impact of climate change on our natural habitat and species.
A WWF report in October said that 60 percent of all animals with a backbone — fish, birds, amphibians, reptiles and mammals — had been wiped out by human activity since 1970.
Another report confirmed the extent of the mass extinction event, only the sixth in the last half-billion years.
Millions of schoolchildren, meanwhile, took part in global protests earlier this month urging greater action on climate change. The Youth Strike 4 Climate Change movement was led by Swedish teen activist Greta Thunberg, who has been nominated for the Nobel Peace Prize.