Published Tuesday, 17 April 2012
The Fight Club star, who is a United Nations Ambassador for Biodiversity, will reward the three campaigns that pull in the most donations for environmental initiatives by 15 May.
He says: "I think it's very clear that figuring out how to live sustainably within the environmental systems that support us is the defining challenge of our era.
"Earth Day is important because it's about waking up more people to that challenge and committing to engage in it ourselves."
The first place winner will receive £15,625, while second and third places will get £9,374 and £6,250 respectively.
Actor Ian Somerhalder's IS Foundation is among the charities which have entered the competition thus far.