Hundreds of millions of people worldwide have been switching off lights for an hour at 8.30pm local time today, in what is described as the biggest climate change protest ever attempted.
In Britain the venture was promoted by environmental groups and NGOs like WWF (http://earthhour.wwf.org.uk/ ).
"This is a mobilisation for change everyone can join in at the flick of a switch," a spokesperson told Ekklesia.
The Earth Hour initiative started in Sydney two years ago. It was launched by green campaigners keen to cut energy use and do something about the tipping-point created by the human contribution to global warming.
The aim is to create a huge wave of public pressure to influence the governmental cliamte change meeting in Copenhagen later this year, which will be seeking a new treaty.
The switch-off will take place in over 3,500 towns and cities across 88 countries.
In Britain a number of churches are joining in, though overall faith communities have been slower than others to pick up the challenge.
Some accuse cathedrals and other large civic buildings of contributing to energy waste and light pollution by their desire to be illuminated.
Among high profile Christian backers of the campaign are Archbishop Emeritus Desmond Tutu and Bishop of London Dr Richard Chartres.
In Sweden, church bells will ring out at 8.30pm to mark the moment and encourage people to participate.
Earth Hour was launched in 2007 as a solo event in Sydney, Australia, with more than two million people involved. Last year's event claimed the participation of 370 cities.
This time Sydney was one of the first places to switch off.
Locations taking part this time include Edinburgh Castle in Scotland, Big Ben in London, the Bird's Nest Stadium in Beijing and the Egyptian Pyramids.