For the 2012 Earth Hour, a number of celebrities including supermodel Miranda Kerr, transformer star Isabel Lucas and cricket legend Sachin Tendulkar have come together to observe the event and inspire people to take much needed action for the environment.

The first Earth Hour event started in the year 2007 when WWF-Australia inspired Sydney-siders to show their support for climate change action. Around 2.2 million people took part in the event and more than 2,000 businesses turned their lights off to show their support for the initiative.

Over the years, the initiative has witnessed the involvement of people across the globe with many celebrities and known faces taking active part in the event.

In 2011, Earth Hour saw hundreds of millions of people across 135 countries switch off for an hour. For the current occasion, Earth Hour has launched "I Will If You Will" on YouTube to showcase how everyone has the power to change the world we live in, bringing together the world's biggest social video platform with the 'world's largest action for the environment'.

Taking part in this is supermodel Miranda Kerr who will reportedly conduct a free yoga class for the public now that 500 of her fans have committed to create their own "I Will If You Will" challenge for Earth Hour.

Transformers star, Australian actress and keen environmentalist Isabel Lucas, has pledged to plant 100 trees if 100 people plant one tree each.

''Earth Hour is an opportunity to come together to support a cause for the greater good of our planet and our whole human family. A moment to feel grateful for the life giving trees, the air we breath, the food and water that nourish us and the beauty of mother nature," said Lucas.

On the other hand, style and entertainment stars, Giuliana and Bill Rancic from the reality series Giuliana & Bill have promised to both go out on the town and wear Chicago Bears jerseys at their next event, if 5,000 people promise to take part in Earth Hour and turn off their lights at 8:30pm on 31 March, 2012.

Other celebrities who are active members and supporters of Earth Hour include cricket legend Sachin Tendulkar, Colombian television presenter Claudia Bahamón, MTV VJ and Asia Pacific Ambassador Nadya Hutagalung, Celebrity Chef Bill Granger and Universal Pictures.

Catch a glimpse of the celebrities involved in the Earth Hour initiative along with images of Earth Hour celebrations throughout the years: