This is what London during Earth Hour last year...
Lights across the capital will be switched off at 8.30pm tonight in aid of the World Wildlife Fund's "Earth Hour."
Organised by the World Wildlife Fund, last year it saw 7000 towns and cities across 154 countries take part to show support for the environment.
It comes as the Intergovernmental Panel on Climate Change prepares to launch its latest report in Japan on how global warming will affect wildlife, food supplies and the weather.
London singer Sophie Ellis-Bextor will lead the switch-off in London with a candle-lit performance at Southbank Centre.
Celebrations for Earth Hour have already begun in Samoa, New Zealand, Fiji and Australia.