Nowhere, perhaps, will be more important than Shanghai. One of eight cities hosting Live Earth concerts for Al Gore's crusade against climate change next weekend, it will help deliver a vast audience across China.
And with the world's most populous country on board, organisers believe they can reach 2 billion people and eclipse even Live8 as the biggest global media event of all time.
It will begin at 12.10pm in Sydney, then roll around the globe with concerts in Tokyo, Johannesburg, Shanghai, Hamburg, London, New York and finally, at 8pm, Rio de Janeiro's Copacabana beach. A special performance at the British Antarctic Survey Station in Antarctica will ensure all seven continents are included.
There will be saturation coverage from TV, radio and the internet in 119 countries.
Critics have argued the 24-hour spectacular - featuring more than 150 acts including Madonna, Lily Allen, Genesis, Bon Jovi, Kanye West, Kelly Clarkson, Black Eyed Peas and Jack Johnson - will do more for the stars' careers than raising awareness of climate change.
But Gore will use it to urge people to sign a seven-point pledge calling on Governments to agree, within two years, to an international treaty that cuts global warming pollution by 90 per cent in developed countries and by more than half worldwide. It also asks people to cut their own pollution, make their homes, businesses, schools and transport more energy efficient, and plant trees and preserve forests.
With its rapid economic growth and soaring carbon emissions, China is regarded as a crucial target for this message. Kevin Wall, the executive producer of Live Earth, has succeeded where he did not two years ago as a co-organiser of Live8, the centrepiece of the Make Poverty History campaign.
"We're on Chinese TV with 800 million people," he said. "People often think on a parochial basis, so it's vital to be there. We've got to talk and make the whole world listen."
Live Earth China, on the steps of the Oriental Pearl Tower in Shanghai, will feature popular national singers as well as Britain's Sarah Brightman, and be broadcast across the country by the Shanghai Media Group.
Steve Howard, chief executive of The Climate Group, a London-based campaign organisation supporting Live Earth, said: "The United States and China are responsible for half the world's carbon emissions. Live Earth will get huge attention in both. The biggest issue on the planet ever requires the biggest media event ever."
The seed was planted less than two years ago at the Beverly Hills Hotel in California, when Wall, a veteran concert producer, attended a slide show about global warming presented by Gore, as featured in the Oscar-winning documentary An Inconvenient Truth.
"Over the course of the 90 minutes my wife and I were very emotionally moved by the climate crisis," said Wall, 54, a father of three. "We understood for the first time it was about us, our children and our children's children. This is not just a movie - it's happening.
"After Live8 I said never again, but I got the call from Al Gore, the global rock star on this issue. What I can do on the day is deliver 2 billion pairs of eyeballs."
Gore will be at the Giants Stadium in East Rutherford, New Jersey, near New York City, where the Police, Smashing Pumpkins, Alicia Keys and others will perform. "We don't want him getting on planes burning carbon," Wall acknowledged.
Profits from Live Earth will go to Gore's Alliance for Climate Protection. Answering critics who point to the amount of fuel and power used at such events, Steve Howard of the environmental charity Climate Group said: "Dealing with climate change doesn't mean we have got to stop live performances or call for a moratorium on football matches ... If we get this right, in 10 to 15 years time every product will be a green product."