The Sydney Opera House’s gleaming white-shelled roof was darkened Saturday night along with much of the rest of Australia’s largest city, which switched off the lights to register concern about global warming. The arch of Sydney’s other iconic structure, the harbor bridge, was also blacked out, along with dozens of skyscrapers and countless homes in the 4 million-strong city, in an hour-long gesture organizers said they hoped would be adopted as an annual event by cities around the world. Full Story