LONDON (AP) ― Sydney’s iconic Harbor Bridge and Opera House went dark for an hour on 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 are 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.

Buckingham Palace, Tower Bridge, and St. Paul’s Cathedral are among the other London landmarks due to go dark later Saturday, as is the Savoy hotel, where managers planned to light the front hall, bars and restaurants with candles.

In Paris, more than 230 monuments and major gathering points will dim lights for an hour ― including Notre Dame Cathedral, the Arc de Triomphe, as well as fountains and bridges over the Seine.

An exception: The Eiffel Tower, which the mayor’s office said would go dark for only five minutes “for security reasons.”

In Germany, activists from the Washington-based WWF plan to light 5,000 blue and green candles in the form of a globe in front of Berlin’s Brandenburg Gate before city officials switch off the monument’s lighting.

Across the Nordic nations, government buildings and municipalities are joining in. Among them are Stockholm’s royal castle and the Swedish capital’s huge globe-shaped sports arena. In Sweden’s second largest city, Goteborg, the main boulevard will bathe in an hour’s darkness.

The WWF, the global environmental group which organizes the event, said the number of countries and territories participating has grown from 135 last year to 147 this year.

Libya, Algeria, Bhutan and French Guinea are among those participating for the first time.