In this time exposure Saturday, photographer Michael Bosanko, not seen, uses a combination of colored-gel lights to paint the words “Earth Hour,” plants, flowers and the World Wildlife Fund logo with St. Stephens tower of the Houses of Parliament in central London in the background. Nearly 4,000 cities in 88 countries joined in dimming nonessential lights to raise awareness about climate change.

Chicago ? From an Antarctic research base and the Great Pyramids of Egypt to the Empire State Building in New York, illuminated patches of the globe went dark Saturday for Earth Hour, a campaign to highlight the threat of climate change.

Time zone by time zone, nearly 4,000 cities and towns in 88 countries joined the event sponsored by the World Wildlife Fund to dim nonessential lights from 8:30 p.m. to 9:30 p.m. The campaign began in Australia in 2007 and last year grew to 400 cities worldwide.

Organizers initially worried enthusiasm this year would wane with the world focused on the global economic crisis, said Earth Hour executive director Andy Ridley. But he said it apparently had the opposite effect.

“Earth Hour has always been a positive campaign; it’s always around street parties, not street protests, it’s the idea of hope, not despair. And I think that’s something that’s been incredibly important this year because there is so much despair around,” he said.

Crowds in New York’s Time Square watched as many of the massive billboards, including the majestic “Phantom of the Opera” marquee, darkened.