Europe (France on left and Spain on right) seen at night onboard the ISS. For the first time, Earth Hour will extend to the International Space Station. Photograph: ISS/ESA/NASA
The Dutch astronaut André Kuipers, who this week oversaw the trickier task of receiving supplies from one of Europe's unmanned spacecraft, will share photos of Earth and live commentary as landmarks from the Eiffel Tower to the Sydney Opera House switch off their lights. WWF, the event's organisers, say this year will see record participation, with 5,411 cities and towns, and 147 countries taking part, up from 5,251 and 135 in 2011.
Organisations including the International Trade Union Confederation and World Association of Girl Guides and Girl Scouts have asked their members to take part, and Unesco has asked World Heritage sites to take part – the Acropolis in Athens, churchs and convents of Goa and Angkor in Cambodia are among those going dark. In the UK, Buckingham Palace, Tower Bridge and Big Ben will all switch off their lights. Green MEPs said that for Earth Hour they were pledging to fight for measures to cut energy use in Europe. This year, Libya will take part as Mohammad Nattah, 19, has decided to organised Earth Hour in Tripoli.
Launched in 2007 only in Sydney, initially as an energy-saving measure, the hour has spread internationally and become a symbolic event to encourage environmental action and awareness. It is a rolling hour at 8.30-9.30pm across the world on 31 March. Despite the event's high profile, it has also drawn criticism, including from green campaigners. George Marshall, founder of the Climate Outreach Information Network, has previously written in the Guardian that it sends out the wrong message. "Asking people to sit in the dark plays very well to a widely held prejudice that "the greens" want us all to go back to living in caves," he said.
Andy Ridley, Earth Hour co-founder and executive director, said: "Each and every one us play an important role in making a difference to the world we live in. As the lights go off around globe tomorrow, celebrate your commitment to the planet and inspire those around you to take action."
The Office of National Statistics released data to mark Earth hour this week, showing that while Britons are using less energy they are paying more for it. Energy consumption has fallen in volume terms by 11.3% since the first Earth Hour in 2007, but household spending on it has increased 11.3% in the same period from £28.8bn to £35.6bn.
Over fourth-fifths of the price rises in UK energy bills between 2004 and 2010 was because of the rising cost of gas on international markets, an analysis by the government's climate advisers, the Committee on Climate Change, found last year.