More than 100 landmarks across the UK will switch 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 will be switched off between 8.30pm and 9.30pm tonight as part of an international event organised by conservation charity WWF to urge action to save the planet.
Sydney Opera House, Egypt’s Great Pyramids, the Eiffel Tower in Paris, Brazil’s Christ the Redeemer monument and the Empire State Building in New York are among the sites worldwide where the lights will be switched off.
Photographs began flooding social media as it turned 8.30pm in New Zealand and Australia.
The event sees landmarks, businesses and people switching their lights off for an hour of darkness, and aims to highlight the impacts humans are having on the planet through climate change, pollution, plastic and food production.
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.
Options include restoring nature in your neighbourhood, planning a holiday closer to home, washing clothes at 30 degrees or changing the way you eat.
The 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.
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.
WWF warns that people living today are the first generation to experience the effects of climate change, and the last to be able to change it - while the planet is also suffering plastic pollution and deforestation.
This year, as well as switching off for an hour, the environmental charity is asking people to make a pledge to change one thing in their lives that will help protect the planet.
The Metropolitan Police Service will also be taking part again, stopping its iconic revolving sign outside New Scotland Yard and switching off lights "where it is operationally feasible".
A statement from the force said: "The Met is committed to reducing its carbon emissions associated with the running of its estate and its fleet, as well as minimising resource consumption, enhancing biodiversity, minimising waste and promoting a circular economy."
WWF Scotland director Lang Banks said: “Our world is under threat like never before.
“From our forests to our oceans, wildlife and marine populations are being devastated by the impacts of humans and changes to the climate.
“We know many people here in Scotland and globally want to do something but are not sure where to start.
“By coming together with millions of people around the world for Earth Hour, we create a strong, united voice that changes things for the better.”
He added: “We’re the first generation that knows the extent of the damage we’re doing to our planet and we could be the last that can do anything about it.
“That’s why I’m asking everyone to raise their voice for the planet by making a pledge and taking part on Saturday.”