Madonna is to release a new song she has written for Live Earth.The singer has penned 'Hey You' with super-producer Pharrell Williams and intends to bring the record out before the July 7 global warming charity concert at London's new Wembley Stadium. Madonna - who is rumored to be headlining the event - will perform the song at the music extravaganza and hopes it will become the anthem of the day.The 'Hung Up' singer has been working with Pharrell on her new album, which is due for release in November.The hotly-anticipated LP will also include tracks Madonna has co-written with Timbaland, the producer who has masterminded hits for some of the world's biggest pop stars, including Justin Timberlake and Nelly Furtado.Other acts expected to play at the concert include the Red Hot Chili Peppers, Keane, the Beastie Boys, Black Eyed Peas, James Blunt and the Foo Fighters.The London show is part of a worldwide network of concerts taking place on the same day in nine cities to raise awareness of environmental issues.Yesterday it was announced that Istanbul, the capital of Turkey,was the latest city to join the line-up.The event will feature both international acts and local Turkish musicians.Live Earth founder Kevin Wall, the Worldwide Executive Producer of 2005's Live 8 charity concerts, said: "We are thrilled to be adding a new leg of the Live Earth concert series in Istanbul. The goal of Live Earth is to engage a worldwide audience to take action against the climate crisis, and this concert in Istanbul will help to ensure that a truly global audience is reached."The other host cities are New York, Sydney, Shanghai, Tokyo, Johannesburg, Rio de Janeiro and Hamburg.