Miranda Kerr has been named as an Earth Hour global ambassador for the second year running.
The Australian supermodel - who is famed for her views on environmental issues and has her own range of organic beauty products - has joined the 2012 campaign, which encourages the public to switch off their lights for 60 minutes on March 31 to help save energy and highlight sustainability.
Miranda - who has a 14-month-old son, Flynn, with husband Orlando Bloom - also pledged to conduct a free yoga class if 500 of her fans upload their own I Will If You Will challenge to www.youtube.com/earthhour, stating how they plan to save the planet.
She said: ''I hope my first challenge inspires my friends, family and fans to make their own promise for the environment.
''This year I've made the commitment to reduce my footprint by offsetting all of my travel. If we all adopt simple practices like recycling, switching to energy efficient lighting or paperless banking then we can make a difference together.''
The yoga class will take place in Sydney, Australia, and will be conducted by Miranda.