Ian Somerhalder has become the latest celebrity environmental activist to accept the United Nations' role of goodwill ambassador. 


The "Vampire Diaries" star has become a leading Hollywood figure in the world of sustainability, actively working through his foundation and various social media networks to make a difference for environmental initiatives around the world. 


After testifying before Congress last year on species conservation, Somerhalder told reporters that the current generation has more power than ever before to make a difference for the planet. 


"There's Generation X. There's Generation Y. This generation is Generation Extinction," he said. "This generation holds that in their hands — the responsibility of it, and the power to change it. They have the ability to make the changes for themselves and for their environment. It's pretty badass, if you think about how much they can do."


The U.N. thinks so too — and has teamed Somerhalder with its other Goodwill ambassadors Gisele Bundchen, Don Cheadle, Rahul Bose and actress Li Bing Bing in promoting World Environment Day on June 5. For last year’s event, Gisele went head to head with Cheadle to see who could collect the most pledge actions from participants. The model took a large lead and will have a forest planted as a result.


This year the challenge is titled "Green Economy: Does It Include You?" and asks participants to "execute an activity in the week of WED [World Environment Day] (June 3-8, 2012) to celebrate the people’s day for the environment." Five lucky winners will drive away with a fuel-efficient car. 


Check out Somerhalder promoting the contest below. To learn more about World Environment Day, jump here


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