Pharrell Williams addressed students at the United Nations headquarters to discuss the importance of tackling climate change on International Day of Happiness this week (beg16Mar15).

The Happy hitmaker is one of the ambassadors for the organisation's official Day of Happiness, which fell on Friday (20Mar15), and he took to the stage at the United Nations General Assembly Hall in New York to warn guests of the dangers of global warming.

He said, "Music brought me happiness. And when you find out what makes you happy - and it can be something as detailed as a long-term goal or it can be something as simple as the way I feel when my son smiles - you should know that happiness is your birthright. It's a reaction to something. We have to move from climate change to climate action. We're in trouble but we can change."

Williams recently combined his newly appointed title of Creative Director for the second series of Live Earth gigs with his UN post and encouraged fans around the world to sign a petition urging global leaders to step up their efforts to tackle climate change.