More than 100 landmarks across the UK are switching off their lights to mark this year's Earth Hour, joining others from around the world.
From Buckingham Palace to Edinburgh Castle, lights on famous buildings and structures across the UK went dark for an hour from 8.30pm.
More than 7,000 cities in more than 170 countries and millions of people are expected to take part this year, to send a message to leaders that protecting the Earth should be top of their agenda, WWF said.
In the UK, the Houses of Parliament, the London Eye and the Shard, Cardiff Castle, Liverpool Cathedral, Old Trafford, Brighton Pier and the Eden Project are among the landmarks taking part.
As Europe caught up with Asia and Oceania, the lights on the Eiffel Tower were turned off as Paris joined cities across the world in marking Earth Hour.
French President Emmanuel Macron has campaigned to “Make Our Planet Great Again”, but has faced criticism from those who say his efforts to cut greenhouse gas emissions target the poor.
Earth Hour events have spread to more than 180 countries since the movement started in 2007.
In the Polish capital Warsaw, the landmark Palace of Culture and Science turned off its night illumination, along with some churches and Old Town walls.
Earlier, as night fell in Hong Kong, major buildings along Victoria Harbour turned off their non-essential lights and the city’s popular tourist attraction known as the Symphony of Lights was cancelled.
Last year across the UK, 10 million people took part, along with more than 7,000 schools, 400 landmarks and thousands of businesses and organisations, the charity said.
The WWF charity is encouraging people to pledge personal actions as part of this year’s Earth Hour, such as turning the washing machine down to 30C, avoiding single-use plastics, planning a staycation or holiday nearer to home, changing the way they eat or helping restore nature in their local area.