For environmental activists¹, the message was clear: Earth Hour was a huge success.

Now they say nations have a mandate² to tackle climate change.

"The world said 'yes' to climate action, now governments must follow," the World Wildlife Fund (WWF) said 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, illuminated³ patches of the globe went dark 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 pm to 9:30 pm.

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!" Kim Carstensen, the leader of WWF's Global Climate Initiative, said in a statement yesterday.

Negotiators from 175 countries gathered yesterday in Bonn for the latest round in an effort to craft a deal to control emissions⁴ of the heat-trapping gases responsible for global warming.

German boy and girl scouts⁶ yesterday presented the top UN climate official, Yvo de Boer, with a blue "ballot⁷ box" symbolically⁸ 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 Scout⁵ told de Boer.

The climate chief thanked the young people as well as the WWF for mobilizing the massive show of support.

"I wouldn't be surprised if that was actually the largest public demonstration⁹ that there has ever been on an issue like this," he said.

Earth Hour officially began when the Chatham Islands, 800 km east of New Zealand, switched off its diesel¹⁰ generators¹¹. At Scott Base in Antarctica, New Zealand's 26-member winter team resorted to minimum safety lighting¹² and switched off appliances and computers.

In Australia, Sydney's glittering harbor was bathed in shadows as lights dimmed on the steel arch of the city's iconic Harbour Bridge and the nearby Opera House.

Landmarks¹³ across China joined in.

Beijing's Olympic icons¹⁴ - the Bird's Nest and Water Cube - went dark for an hour.

More than 1,800 buildings in Hong Kong joined, including the International Finance Center and Tsing Ma Bridge. Tourist attraction Symphony of Lights, a Guinness-record winning daily light show in Victoria Harbor, was suspended to show support.

Zhou Teng, 28, an employee of an education consultancy firm, had a candlelight dinner with her husband at a restaurant along Shanghai's Huangpu River.

"We are here not for romance, but to support the campaign," she said.

As the sun moved west, the Great Pyramids and Sphinx in Egypt darkened. So did the Acropolis in Athens and the Colosseum in Rome.

In Paris, the Eiffel Tower, Louvre and Notre Dame¹⁵ Cathedral were among 200 monuments and buildings that went dark. The Eiffel Tower, however, only extinguished its lights for five minutes for security reasons because visitors were on the tower.

The celebration then crossed the Atlantic, where crowds at New York's Times Square watched as many of the massive billboards¹⁶, including the giant Coca-Cola display, darkened. The Majestic¹⁷ Theater marquee at the home of The Phantom¹⁸ of the Opera went dark, along with the marquees at other Broadway shows.

Mikel Rouse, 52, a composer who lives and works nearby came to watch.

"C'mon, is it really necessary? ... All this ridiculous advertising¹⁹ ... all this corporate²⁰ advertising taking up all that energy seems to be a waste," Rouse said.

Hundreds of other cities also joined in, from Chicago to San Francisco to Rio de Janeiro in Brazil, where the iconic Christ the Redeemer statue that watches over the city was darkened, along with the beachfront of the famed Copacabana.

Questions:

1. How many cities and towns participated in Earth Hour this year?

2. Which Beijing buildings turned off their lights?

3. What did the UN’s top climate change official say about this year’s Earth Hour?

Answers:

1. Almost 4,000.

2. The Bird’s Nest and Water Cube.

3. He said he wouldn’t be surprised if this was the largest public demonstration ever about climate change.