Clean energy was a vital area for the United States and China to work together in dealing with climate change, a high-level World Wildlife Fund (WWF) official told Xinhua Tuesday.

Both the United States and China realized clean energy was "the next market" after the IT revolution, which had deeply changed the world, said Keya Chatterjee, acting director of WWF's climate change program.

"China has made some investments in solar energy and wind energy just as the U.S.," she said. "You can see both countries moving into this direction."

Both countries were "a little bit neck and neck" in the field of clean energy, but "the seeds for cooperation have already been there," she said, adding the U.S. strongly desired cooperation with China.

As the two countries produced more than 40 percent of the world's CO2 (carbon dioxide) emissions, their cooperation in this area would be critical for the world, especially for the small island countries and high mountain states that faced a real threat from climate change, Chatterjee said.

"The potential and room for the U.S. and China to collaborate in this area are very wide," she said.

Chatterjee said she had found more constructive signals during the UN climate talks in Bonn, which started on Monday, on the issue of fulfilling the promise of last December's Copenhagen climate summit than before.

At the contentious Copenhagen conference, developed countries promised to raise 30 billion U.S. dollars to help developing countries cope with climate change. It's also one of the key issues at the Bonn session, which has attracted 4,500 participants from 182 countries.

Chatterjee said financing was most definitely a precondition for mutual trust between developing countries and developed countries.

"There is much more consensus than the past," she said. "Just this morning, all the parties are saying we need to be more constructive, we need to go forward, we need to work together and that’s really a new tone and it gives me a lot of hope."

Chatterjee also said the "biggest issue" to be solved was to make the finance more transparent, stressing that financing developing countries to fight climate change was also in the interest of developed countries.

"The biggest issue that we have with the fast track finance right now is there is no common accounting methodology, so different countries are accounting in different ways. It's hard to see exactly where the money is coming from, because it’s hard to measure exactly," she said.

Chatterjee said the earthquake in Haiti was an example of why governments of developed countries needed to explain to the public how aiding developing nations was in their own national interest.

"When there is a disaster within our range of our world, for example, the earthquake in Haiti, we spend much more money responding to those disasters," she said. It made better economic sense to help countries prepare for disasters. Likewise, it made sense to help smaller countries prepare for the impact of climate change, she said.

"We should all be prepared in our own countries and we should all do what we can to help other countries prepare. It's all in our interests," she said.