Now they say nations have a mandate to tackle climate change.

“The world said yes to climate action, now governments must follow,” said the World Wildlife Fund (WWF) a day after hundreds of millions of people worldwide followed its call to turn off lights for a full hour.

From an Antarctic research base and the Great Pyramids of Egypt, from the Colosseum in Rome to the Empire State building in New York, illuminated patches of the globe went dark on Saturday night to highlight the threat of climate change. Time zone by time zone, nearly 4,000 cities and towns in 88 countries dimmed nonessential lights from 8:30 p.m. to 9:30 p.m.

WWF called the event, which began in Australia in 2007 and grew last year to 400 cities worldwide, “the world’s first-ever global vote about the future of our planet”.

“Last night’s message from the masses was loud and clear: Delay no more, real action now!” said Kim Carstensen, leader of WWF’s Global Climate Initiative, in a statement.

Negotiators from 175 countries gathered on Sunday in Bonn for the latest round to craft a deal to control emissions of the heat-trapping gases responsible for global warming.

German boy and girl scouts on Sunday presented the top U.N. climate official, Yvo de Boer, with a blue “ballot box” symbolically representing the world’s vote the night before to save the earth.

“If the world keeps polluting ... we will lose our future,” a young Girl Scout told Mr. de Boer.

The climate chief thanked the young people as well as the WWF for mobilising the massive show of support. “I wouldn’t be surprised if that was actually the largest public demonstration that there has ever been on an issue like this,” he said.

“Earth Hour has always been a positive campaign,” said Earth Hour executive director Andy Ridley.