Some experts believe China has surpassed the United States as the world's top emitter of greenhouse gases, yet it has made strides in enhancing energy efficiency and promoting renewable energy, environmentalists and officials said Friday.

"I think China is taking climate change seriously and that's a good sign that there will be a good outcome here in Bali," said Artur Runge-Metzger, head of the European Commission delegation at the conference on the Indonesian island.

Even hard-to-please environmental groups who relish lambasting industrialized countries for pollution are praising Beijing, though it's clear China - which relies heavily on dirty, outdated coal burning techniques - has a lot more to do.

China's ranking on Germanwatch's 40th annual index, which ranks 56 industrialized and emerging countries, was an improvement of four places over last year, the group said Friday.

The United States and Saudi Arabia were the worst on the list, at 55th and 56th places, respectively.

Environmental watchdog Germanwatch noted the Chinese government has enacted policies promoting renewable energy, including mandates that solar, wind, hydroelectric and other forms of renewable energy provide 10 percent of the nation's power by 2010. It also has ordered key industries to reduce energy consumption by 20 percent.

Politicians and activists said China's defensive posture of the past has given way to constructive discussions at the Bali climate change conference. Beijing has also taken the lead among developing countries in calling for wealthier nations to speed up the transfer of cleaner technologies to emerging economies to help shift away from fossil fuels.

Hans Verolme, director of WWF International's Global Climate Change Program, attributed China's position to concerns over energy security and a recognition that climate change is already having a severe impact on the country, with worsening drought, water shortages and floods.

"China has made up its mind about a year ago that it was going to get serious," Verolme said. "They want to show to the world it understands and it wants to do what is necessary to stop dangerous climate change."Delegates from nearly 190 nations are attending the Dec. 3-14 gathering charged with launching negotiations that will lead to an international accord to succeed the 1997 Kyoto Protocol on global warming.

Kyoto, which was rejected by the United States, commits three dozen industrialized countries to cut their greenhouse gases an average of 5 percent below 1990 levels between next year and 2012, when it expires.

U.N. climate chief Yvo de Boer told reporters discussions over a post-Kyoto agreement were going well and that "the mood is good."

But he acknowledged efforts to persuade developing nations to embrace binding reduction targets were nearly dead. China, along with India, Brazil and other developing countries, have argued that industrialized countries should take the lead cutting emissions since they are responsible for the bulk of them.

"Nothing has been ruled out," de Boer said. "Binding commitments from developing countries is not off the table, but is crawling toward the edge."

On Germanwatch's climate index, Saudi Arabia, the world's largest oil exporter, was the biggest "climate sinner" for the second year in a row, Saudi Arabia, because it has no policies to address its growing emissions.

It has a long history of playing an obstructionist role at climate change conferences, and activists say it has suggested it would not sign onto any future agreement unless it is guaranteed compensation for the loss of revenue it expects when economies shift away from oil to cleaner energies.

A Saudi Arabian official could be immediately reached for comment.

Saudia Arabia was followed by the United States, the only major industrialized country not to have signed Kyoto. The U.S. delegation declined to comment on the report.

Australia's new government did an about-face earlier this week and agreed to ratify the protocol.

Though Canberra ranked third on the list of offenders Friday, it could drop to 20th if Prime Minister Kevin Rudd follows through with promises to reduce emissions. That would put it near Finland.