Jeffrey Sachs, the former head of the UN Millennium Project, said it was "absolutely fundamental" for the two largest emitters of greenhouse gases to make more serious efforts to cut carbon dioxide levels, Al Jazeera reported.
The US has failed to ratify the Kyoto Protocol, an international set of rules on climate change, and China's environmental watchdog said it had failed to reach any of its pollution control goals for 2006.
Sachs said: "It's a mistake to let either China or the US think they are doing a lot."
