Miranda Kerr has been announced as an Earth Hour global ambassador for the second year running, and is backing the initiative's I Will If You Will challenge, encouraging people to take action on saving the environment, beyond the 60 minutes participants must turn their lights off for.

The model has pledged to conduct a free yoga class if 500 fans upload YouTube videos stating how they'll take on the challenge. Earth Hour takes place at 8.30pm, March 31.