 Reunited group The Police played hits such as Message in a Bottle |
It attracted an average audience of 2.7 million viewers and was beaten by a re-run of animated film Monsters Inc.
However, 19 million people in the US saw some coverage of Live Earth during the day, Nielsen Media Research said.
And MSN said the online broadcast of the gigs set a new record for an entertainment event.
More than nine million "streams" were generated during the day, surpassing the previous peak for the Live 8 concerts to fight global poverty in 2005, the company added.
'Solve the crisis'
The global day of concerts, staged at nine locations including Tokyo, Hamburg and Rio de Janeiro, concluded with the event at Giants Stadium in New Jersey.
Acts including The Police, Bon Jovi, Kanye West and KT Tunstall took to the stage. 
Former US Vice-President Al Gore, who inspired the Live Earth project, also made an appearance, telling concert-goers: "Put all of this energy in your heart and help us solve the climate crisis."
Mr Gore and his fellow activists have attracted criticism from high-profile figures such as Live Aid and Live 8 organiser Bob Geldof, who accused Live Earth of lacking achievable goals.
And the musicians taking part - such as Madonna, who played at London's Wembley Stadium - were accused of setting bad examples with celebrity lifestyles that included world tours and excessive spending.
Grammy-winning guitarist John Mayer acknowledged after his set at Giants Stadium that rock stars were not necessarily good environmental role-models.
"If you want to peg me as not being entirely eco-friendly, you'll win," he said. 
"I also think it's very difficult to judge the success of a movement. You can't find out by nine o'clock this evening how much awareness was raised."
He added: "What you're really talking about is the placement of an idea at a rock show."
In the UK, TV coverage of Live Earth was watched by an average audience of 3.1 million viewers between 2000 and 2200 BST, less than a third of the figure for the previous weekend's Concert for Diana.