Following are details of some celebrities and politicians involved in environmental issues.

* SPINAL TAP -- The spoof heavy-metal band immortalised by the mock documentary "This is Spinal Tap" has reunited to join a campaign to save the world from global warming.

Director Rob Reiner, whose 1984 film set the bar for the "mockumentary" genre, has made a new short film called "Spinal Tap" as part of a campaign dubbed SOS/Live Earth. The band will also play in London at one of 7 Live Earth concerts on July 7.

* MADONNA -- Madonna has written a new song for the July 7 Live Earth concerts and the first million downloads will result in a donation to the Alliance for Climate Protection.

* LEONARDO DICAPRIO -- The actor started the Leonardo DiCaprio Foundation in 1998 to promote environmental issues. His film, "The 11th Hour", is an environmental documentary on the impact of humans on the planet. It includes former Soviet leader Mikhail Gorbachev and leading scientist Stephen Hawking.

However, DiCaprio's earlier movie, "The Beach", was controversial because of allegations by environmentalists that production work damaged a Thai beach paradise.

DiCaprio fiercely defended the project. "I don't want a bad reputation as somebody who endorses something hostile to the environment," said the Hollywood star.

* AL GORE -- The former US vice president produced a documentary about a slide show he has given on global warming, "An Inconvenient Truth". The short film was presented in Cannes in 2006 and won an Oscar this year.

* ROBERT REDFORD -- Thirty years on the board of the Natural Resources Defense Council, founder of Sundance Preserve, winner of 1993 Earth Day award, 1987 United Nations Global 500 award. In April 2007, he launched a weekly three-hour slot called "The Green", dedicated entirely to the environment, on his Sundance TV channel.

* DARYL HANNAH -- The actress hopes to become a full time activist, campaigning on the environment and slavery. Hannah lives off the electricity grid in the Rocky Mountains, using solar energy and driving a car run on biodiesel made from recycled cooking oil.

* WILLIE NELSON -- With Hannah and biodiesel producers Bob and Kelly King, the country singer helped set up the Sustainable Biofuels Alliance, bringing together activists and scientists to give consumers better guidance on clean fuels.