Pop star Madonna has written a new track to be performed at London's Live Earth concert in July.
Madonna has played to capacity crowds at Wembley on past tours
Hey You was inspired by the climate change campaign and can be downloaded from Microsoft's Live Earth website.
Nine Live Earth shows will take place around the world on 7 July in an attempt to highlight global warming.
The singer will perform the track at the Wembley Stadium concert. James Blunt, Genesis and the Red Hot Chili Peppers are also set to perform.
MSN is donating 25 cents (13p) for each of the first million downloads to the Alliance for Climate Protection.
"Live Earth is about engaging a global audience with tools to tackle the climate crisis," Live Earth founder Kevin Wall said.
Tickets for the Live Earth gig at Wembley sold out in April
The London show will be broadcast live on BBC television and radio and shown in 120 countries.
The Foo Fighters, Duran Duran, Snow Patrol and Razorlight will also perform at the London gig alongside rap group The Beastie Boys, singer-songwriters David Gray and Damien Rice and R&B pianist John Legend.
The Black Eyed Peas, Bloc Party, Corinne Bailey Rae, Keane and Paolo Nutini complete the Wembley bill so far, with more acts expected to be announced.
The concerts aim to set a "green example" for other music events by using measures such as eco-friendly electricity, sustainable lighting and carbon-neutral travel.