The population of the Earth is around 6 billion, however a large chunk of the world population have little access to television, 600 million people in India alone for instance. It isn't easy to get exact figures on television access, but it seems reasonable to guesstimate that at least 2 billion people have highly limited access to the medium because most African countries have lower television ownership rates than India, as do several other large Asian nations. So therefore in the rest of the world there needs to be around 1 in 2 people watching Love Earth for the figure to be even remotely plausible. Of course the Chinese government isn't too keen on the event either, so it wasn't broadcast on a national terrestrial network there, so that is probably another billion people who didn't see the event.
All this means that Live Earth would need to be seen by around 2 in 3 people in the west so what were the actual viewing figures in countries like the UK and the USA? Well, somewhaty less than 2 in 3:
The main three-hour American TV broadcast on NBC averaged a meagre 2.7 million viewers...
...It was the same story in Britain, where BBC One coverage of the Live Earth climax at London's Wembley Stadium, leading up to Madonna's eagerly awaited finale, averaged 3.1 million viewers, compared with 11.4 million for the Diana tribute.
In Germany, the ProSieben network registered 1 million viewers for its Live Earth telecast, accounting for a relatively healthy 6.3 percent market share.