May 28 (Bloomberg) -- China, the biggest producer of greenhouse gases, said it will play a “positive and constructive” role to help the world fight climate change, according to U.S. Senator John Kerry.

Chinese Vice Premier Li Keqiang recognizes the need for his country to address the issue urgently, Kerry said today at the end of his visit to the country. The two governments will start scientific research into clean energy, while the U.S. will transfer technology to China with sufficient protection for intellectual property rights, the U.S. senator said.

“It’s unequivocally the most constructive and productive discussions I’ve ever had with Chinese officials” involved in environmental issues in 20 years, Kerry said at a press conference in Beijing. “I’m very optimistic about the possibility of producing something positive.”

The comments by Kerry, chairman of the Senate Foreign Relations Committee, are a sign that the top two producers of climate-altering greenhouse gases may be closer to resolving differences that otherwise may imperil a treaty the United Nations is trying to broker to stem global warming.

The former U.S. presidential candidate’s remarks tally with those two days ago by U.S. Energy Secretary Steven Chu, who told reporters in London that “China’s leadership does know the consequences of climate change.” Chu said the U.S. was prepared to act before China in order to end the historic “standoff” between the two countries in forging the new international climate agreement by December in Copenhagen.

40% Reduction

Developing countries including China propose that industrialized countries such as the U.S. to cut emissions by at least 40 percent from 1990 levels by 2020.

“China understands that we can’t achieve this 40 percent target under the current economic circumstances,” Kerry said. “If we start with something realistic, we can achieve it and I think China will accept a more realistic goal by the U.S.”

China was the world’s biggest emitter of greenhouse gases from burning oil, coal and natural gas in 2006, followed by the U.S., according to U.S. Department of Energy data on Bloomberg.

U.S. lawmaker James Sensenbrenner, part of a House of Representatives delegation that is also in Beijing to meet with Chinese officials on global warming, struck a sharply critical note in remarks to reporters today.

Sensenbrenner Skeptical

Talks this week have left him “less than optimistic,” said Sensenbrenner, a Wisconsin Republican and the ranking member of the House Select Committee on Global Warming and Energy Independence. “It’s business as usual for China. The message that I received was that China was going to do it their way regardless of what the rest of the world negotiates in Copenhagen.”

Sensenbrenner pointed out that China’s goal of cutting carbon-dioxide emissions per unit of economic output in fact would allow China to increase emissions even as the Asian nation calls on other countries to reduce output below a certain level.

Underscoring Kerry’s optimism, the Chinese president’s special envoy on climate change Xie Zhenhua wrote in a May 27 South China Morning Post editorial that China views global warming as more serious than the world financial crisis.

“The global financial crisis has, no doubt, exacerbated the challenge of climate change,” Xie wrote. “Since climate change is a more far-reaching and serious challenge, the world must not waver in its determination and commitment to address it.”

‘Take the Lead’

Xie told an audience of business leaders and politicians in Copenhagen on May 24 that the U.S. and other industrialized nations will have to “take the lead” in greenhouse gas reductions and cut emissions between 25 percent and 40 percent by 2020. He also demanded money and technology to adapt to climate change, while promising to increase the use of nuclear and renewable power.

Kerry said a key hurdle to an agreement is defining the “common and differentiated responsibility” to cut gases, using the UN phrase adopted to guide treaty talks since 187 nations met in Bali, Indonesia, in 2007. “Everybody has to agree to the common responsibility to cut emissions, at differentiated levels that each can support. These have to be measurable, reportable and verifiable.”

China has the capacity to meet goals to reduce emissions, Kerry said. The country has already tripled the nation’s capacity for wind-generated energy, closed hundreds of dilapidated power plants and enacted vehicle-emission standards far more stringent than the U.S.

“All of these measures that China has already undertaken are measurable, reportable and verifiable,” Kerry said. “So it’s not hard” for China to meet its target, he said.