SAN DIEGO -- San Diego residents are being urged to turn off their lights for one hour Saturday night as part of the second annual worldwide Earth Hour.

Thousands of towns and cities around the world have committed to turning off nonessential lights between 8:30 and 9:30 p.m. tomorrow to draw attention to the issue of global climate change.

"The city of San Diego is happy to join other major cities around our nation and the world in this yearly symbolic demonstration," Mayor Jerry Sanders said.

The mayor said the San Diego region reduced its electricity demand by about 75 megawatts during Earth Hour last year -- enough energy to power about 50,000 homes.

Sanders was joined by Councilwoman Donna Frye at a news conference outside City Hall today to promote participation in the event.

Frye acknowledged that the event is "more of a symbolic action," but an important one.

"We just want to encourage everybody to remember to help extend the life of our earth," she said.

Earth Hour, led by the World Wildlife Fund, began in 2007 in Sydney, Australia, but spread to cities around the world last year when an estimated 50 million people turned off their lights.

Among the world's landmarks that went dark were the Sydney Opera House, the Coliseum in Rome, Stockholm, Sweden's Royal Castle, the Empire State Building and the Golden Gate Bridge.

Sanders said all nonessential lights at city facilities in San Diego will be turned off in recognition of Earth Hour.