For Orville Schell, a top China hand in the United States, the climate agreement struck by President Xi Jinping and US President Barack Obama in Beijing in November was "historic", but he said enlisting sub-national level support is critical to implement the deal.

Under the agreement, the US intends to reduce its emissions by 26 to 28 percent below its 2005 level by 2025, while China intends to achieve a peak of CO2 emissions and increase the share of non-fossil fuels in primary energy consumption to about 20 percent by 2030.

Schell, director of the Center on US-China Relations at the Asia Society in New York, is a key figure behind a report released on March 4 entitled A Vital Partnership: California and China Collaborating on Clean Energy and Combating Climate Change.

Calling Xi and Obama's climate deal "historic", Schell said the question is how to actually implement the ambitious targets. "Without the cooperation of the states and provinces and the large cities, I don't think they can get there," he said.

California, the most populous US state, is known for its tough air quality standards in reducing emissions in the past decades, and it also leads renewable energy and electric car industries. The state's cap-and-trade program launched three years ago provides an example of how to reduce carbon emissions by imposing extra costs on polluters.

Schell was excited when Xie Zhenhua, then vice-chairman of the National Development and Reform Commission, signed an agreement in September on behalf of China with California Governor Jerry Brown to boost cooperation on climate change. It was regarded as the first agreement by the country with a US state.

"That's why I think this is so interesting that more things are being done now between China and the sub-national level (in the US)," Schell said.

Though a supporter of Obama, Schell described Washington as "hopeless", referring to the many climate change deniers in the Republican-controlled Congress.

"In California, that's not true," said Schell, who has spent much of his life in California. "Here is the place where things can really get done."

Schell believes it's also an important matter for China-US relations, where the two sides disagree on many issues but are finding common ground.

"I think this brings us right to the environment," said Schell. "I think this is an area which really deserves to be explored. We really do need to build more musculature between the two countries because here we can solve something. We can actually do something meaningful together."

Schell said China should pay more attention to agreements with cities and states in the US because Washington has proved to be a very difficult partner, whereas governors and mayors don't have to worry about the South China Sea, Taiwan or nuclear proliferation.

Schell suggests Obama should gather all the US governors and mayors who are dealing with China to have a national conference and enlist them to help the larger relationship between the countries.

"The president should take some credit and should help them."