Washington DC has been added as a venue for the series of Live Earth concerts, organised by former US Vice-President Al Gore to highlight climate change.
Madonna has penned a song especially for the Live Earth concerts
Country couple Garth Brooks and Trisha Yearwood will be among the artists performing on The Mall in the US capital on Saturday.
Nine cities will stage gigs, including Sydney, Tokyo, Johannesburg, Shanghai, Hamburg, New Jersey and Rio de Janeiro.
Acts including Madonna, Duran Duran and the Beastie Boys will play in London.
And other stars lined up to play around the world include The Police, Lenny Kravitz, Kanye West and the Red Hot Chili Peppers.
LIVE EARTH CONCERT TIMES
Sydney - 0110 BST (1110 local)
Tokyo - 0400 BST (1200 local)
Johannesburg - 1100 BST (1200 local)
Shanghai - 1130 BST (1830 local)
Hamburg - 1300 BST (1400 local)
London - 1330 BST
Washington - 1530 BST (1030 local)
New Jersey - 1930 BST (1430 local)
Rio de Janeiro - 2000 BST (1600 local)
Gore described Live Earth as a "global response" to a "global problem".
"By engaging individuals all over the world, Live Earth will drive corporations and governments to tackle the climate crisis," he said.
But there has also been scepticism about the value of the concerts from some quarters.
Critics say that flying rock stars in on aeroplanes and using a great deal of electricity to power several concerts sends out mixed messages about energy conservation.
"What would be great is if these pop stars - now they realise the damage we are all doing to the climate - look very carefully at their own actions and make some changes themselves," said John Buckley, managing director of the organisation Carbon Footprint.
Referring to Madonna, he told Reuters: "If she made a change then it would be picked up."
Preparations are under way in nine cities, including Rio de Janeiro
He calculated that the singer and her entourage emitted 444 tonnes of carbon dioxide on flights during last year's Confessions tour, more than 40 times the annual output of the average Briton.
Bob Geldof, who organised the Live Aid and Live8 charity concerts, has described the event as lacking a "final goal" and claimed most people already knew about the hazards of global warming.
And speaking to a British newspaper recently, The Who's Roger Daltrey said: "The last thing the planet needs is a rock concert."
Organisers have insisted they were keeping the concerts as green as possible.
Proceeds from ticket sales are going to distribute power-efficient light bulbs and other measures which will offset the shows' greenhouse gas emissions.
Doubts had been cast over whether the Rio de Janeiro gig would go ahead because of concerns about safety on Copacabana Beach, but organisers persuaded a judge that adequate measures were in place.
However, the Turkish event - in Istanbul - was shelved, owing to insufficient sponsorship and lack of time.
Rapper Kanye West is among the acts to pledge their support
Live Earth will also broadcast two songs performed in sub-zero conditions in Antarctica by Nunatak, a rock group made up of five members of the British Antarctic Survey.
They have recorded their contribution in front of 17 colleagues against a backdrop of icebergs.