 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.
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." 
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."
Safety fears
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 after concerns about safety were raised.
Despite this, however, organisers persuaded a judge that adequate security measures were in place to ensure the gig, on Copacabana Beach, would go off safely.
But the Turkish event - in Istanbul - was shelved, owing to insufficient sponsorship and lack of time.