BEIJING - The United States and China are working in a closer and more cooperative basis than ever before in tackling climate change and the "common but differentiated responsibility" principle has played a positive role, the US special envoy for climate change Todd D. Stern said here Friday during a press meeting.

Stern said that in the Lima Climate Change Conference when the negotiations were stalled, the CBDR (Common But Differentiated Responsibilities) principle helped break the deadlock and bridge the gap between countries.

Stern expressed optimism for the Paris Climate Change Conference, which will be held at the end of this year, saying that "there is a greater level of convergence on some very important structural issues" and "greater measure of realism among parties with respect to what need to happen in order to get a Paris deal".

China and the US issued a joint statement on climate change in November last year, in which the "common but differentiated responsibility" principle was reiterated, and both countries announced their goals and efforts to tackle climate change in the next 15 years.

China intends to achieve the peaking of carbon dioxide emissions around 2030 and increase the share of non-fossil fuels in primary energy consumption to around 20 percent by 2030.

"The two targets are quite significant", Stern said, particularly the non-fossil fuel. "By our estimate, China actually would need to develop something around 800 gigawatts of renewable or nuclear energy between now and 2030, that's more than all the coal that is used in China now."

China and the US have been engaged in various fields of clean technology cooperation, including clean fuels for vehicles and smart city initiatives. "These all sorts of active technology cooperation are ongoing and increasing." Stern said.

Stern, currently on a visit to Beijing, has met with senior Chinese officials on strengthening further cooperation on climate change between the two countries.