More than 400 cities worldwide, including four major U.S. cities, participated in the second annual Earth Hour by turning off all lights and electricity for one hour to make a statement about climate change. Businesses and people in Atlanta, Phoenix, San Francisco and Chicago participated in turning their lights off, as well as millions of other people worldwide.

The first Earth Hour took place in only Sydney, Australia, but this year the movement went global, said Liz Ceaser, media and marketing specialist for Creaxion, a company that represents the World Wildlife Fund.

From 8 to 9 p.m. CST, cities across the world went dark, said Dan Foreman, spokesman for Earth Hour.

“Earth Hour was spectacular all around the world,” Foreman said. “There are no words that describe the impact we had, creating a large symbol for the world to notice.”

In Chicago, the Sears Tower, John Hancock building and Navy Pier turned off their lights, and about 500 McDonald’s restaurants shut off their golden arches to save energy and send a message, Foreman said.

Although there are no exact figures yet on how many participated, Foreman estimated that millions around the world took part in Earth Hour and several thousand alone in Chicago.

“Earth Hour says that people care about climate change. It sends a message that this is a serious issue that we are all trying to work on,” he added.

The event in Chicago was a collaboration of the Mayor’s Office, Leo Burnett advertising agency and local power company ComEd. Chicago Mayor Richard M. Daley said in a press release that the event was a large part of his environmental program, “Conserve Chicago Together.”

“Turning off the lights for just one hour shows we can adjust the way we lead our lives,” said Carter S. Roberts, president and CEO of the World Wildlife Fund, in a news release. “It is a simple action that can inspire people around the world to make a serious long-term commitment to reducing energy consumption.”

Safety was a major concern for event organizers, said Foreman. However, the event was pulled off successfully and without any issues or problems, he added.

Businesses and individual residents could sign up to participate through the Earth Hour Web site. Planning for the 2009 Earth Hour, which includes plans to expand the movement and increase involvement, will begin soon.

“The Chicago skyline is one of the most iconic around the world,” Foreman said. “For Mayor Daley, the World Wildlife Fund and ComEd to work hard for months to lead the world in climate change is an amazing thing.”