LONDON — Sydney’s iconic Harbor Bridge and Opera House went dark for an hour Saturday, part of a global effort to shine a spotlight on climate change.

Hundreds of landmarks around the world, including Washington’s National Cathedral, Big Ben in London, the Great Wall of China and Tokyo Tower were being dimmed at 8:30 p.m. local time.

The central Sydney icons have been taking part in the annual event since Earth Hour began as a Sydney-only event in 2007. Australia was among the first countries to hit the light switches each year; in New Zealand, Sky Tower in Auckland and the parliament buildings in Wellington switched off two hours earlier.

In Hong Kong, buildings along Victoria Harbour also went dark.