They said governments should take action to fight global warming by conserving energy, using more renewable energy and reducing dependence on oil and fossil fuels.
The PM was speaking, via satellite link up, at a conference hosted by the Californian Governor.
Mr Cameron said countries like Britain and states like California should take the lead to show environmental protection need not be at the expense of economic recovery.
But he said the forthcoming UN Climate Conference would probably not lead to a legally-binding deal.
Mr Cameron said:
We’re not going to get a global legally-binding deal at Cancun… eventually when you’ve got countries like Britain and maybe states in America that are leading the way on electric cars, on solar panels, on heat pumps… when other countries see the success of green growth and the green economy, even the laggards are going to say ‘hold on, I want a piece of this’.
Representatives of 194 countries are to meet in the Mexican resort city of Cancun from November 29 to December 10 for a second go at striking a deal to curb greenhouse gases after 2012, after last year’s Copenhagen summit.
Addressing the conference in California, the PM stressed that getting a “proper international deal, we need the Chinese to really agree to proper monitoring and evaluation and recording of their emissions”.
We also need to persuade the American administration that it is worthwhile to have a deal that they enter into, as part of the rest of the world all making offers.