(AP) -- In a showdown between the world's two largest polluters, China accused the United States and other rich nations Tuesday of backsliding on fighting global warming and the top U.S. envoy said Chinese greenhouse gas emission commitments should be independently verified.
Trying to ease the tension, U.N. Secretary-General Ban Ki-moon said rich and poor countries must "stop pointing fingers" and should increase their pledges to cut emissions to salvage the faltering talks on a climate pact. The European Union also urged both the U.S. and China to increase their commitments on emissions targets, but the U.S. would not change its offer.
New negotiating drafts circulating Tuesday showed key issues, including emissions targets for industrial countries, climate financing for developing countries, and verification of emissions, remained unresolved.
"The texts are getting less precise, seemingly," said Melinda Kimble, senior vice president of the U.N. Foundation and a former U.S. climate negotiator.
German Chancellor Angela Merkel said in Berlin that she was "somewhat nervous" about prospects of success in Copenhagen.
Ban's warning in an interview with The Associated Press came as world leaders began arriving in Copenhagen, kicking the two-week conference into high gear in its quest to deliver a deal to curb emissions that cause global warming.
The conference so far has been marked by sharp disagreements between China and the United States and deep divisions between rich and poor nations.
"You can't even begin to have an environmentally sound agreement without the adequate, significant participation of China," said U.S. special climate envoy Todd Stern.
China and other developing countries are resisting U.S.-led attempts to make their cuts in emissions growth binding and open to international scrutiny rather than voluntary.
China, the world's largest polluter, is grouped with developing nations at the talks, but the U.S. doesn't consider China to be in need of climate-change aid.
In Beijing, China accused developed countries Tuesday of trying to escape their obligations to help poor nations fight climate change.
"We still maintain that developed countries have the obligation to provide financial support," Foreign Ministry spokeswoman Jiang Yu said, adding that was "the key condition for the success of the Copenhagen conference."
President Barack Obama and Chinese Prime Minister Wen Jiabao are among more than 110 world leaders expected in Copenhagen this week.
The U.S. has offered a 17 percent reduction from 2005 emissions levels by 2020. That amounts to a 3 percent to 4 percent cut from 1990 levels - the baseline year used by many other countries. China has pledged to cut "carbon intensity" - a measure of carbon dioxide emissions per unit of production - by 40 percent to 45 percent by 2020, compared with 2005 levels.
Since China's economy is expected to double in size in coming years, that pledge means China's emissions will only increase by nearly 50 percent, instead of doubling.
Scientists have warned that the world's commitments so far fall short of what is needed to keep global temperature increases below 2 degrees C (3.6 degrees F) above pre-industrial levels and head off the worst of global warming. They say global warming will create rising sea levels, increasing drought, more extreme weather and the extinction of some species.
Neither the U.S. nor the Chinese offer impressed the 27-nation EU, which has promised to reduce its emissions by at least 20 percent of 1990 levels by 2020 - and go up to 30 percent if others make comparable commitments. Japan and Russia have already promised 25 percent cuts.
"We expect them both to raise ambition level," EU environment spokesman Andreas Carlgren said of the U.S. and China. "Otherwise we won't be able to reach the 2-degree target."
Stern defended the U.S. emissions-cutting target as "equal to or higher" than most of what the EU is proposing.
"I'm not anticipating any change in the mitigation commitment," he said. "Our commitment is tied to our anticipated legislation."
The House in June passed a bill with the 17 percent target. The Senate is discussing a similar bill, but it is not expected to come for a vote for months.
China believes the U.S. and other rich nations have a heavy historical responsibility to cut emissions, and that any climate deal should take into account a country's development level.
Ban said he remains cautiously optimistic about a successful outcome, but he warned that negotiators must work out their differences and not leave major problems for world leaders to resolve.
"This is a time where they should exercise the leadership," Ban said. "And this is a time to stop pointing fingers, and this is a time to start looking in the mirror and offering what they can do more, both the developed and the developing countries."
He said all nations "must do more" to keep carbon emissions below dangerous levels and rich countries should step up commitments to provide a steady flow of money for poor countries to combat climate-linked economic disruptions such as rising seas, drought and floods.
Speaking to the AP at a hotel in Copenhagen, Ban said if negotiators cannot resolve those problems before the leaders arrive, "the outcome will be either a weak one, or there will be no agreement."
"This will be a serious mistake on the part of the negotiators and the leaders if they go back empty-handed," he said.
Zimbabwe President Robert Mugabe was among the first heads of state to touch down in the Danish capital, avoiding a travel ban imposed by Western nations because he was attending to a U.N. conference. Mugabe was to address the conference Wednesday.
"The meeting may be taking place on Danish soil but we're playing by U.N. rules and these rules mean that all the world leaders can meet," Danish Prime Minister Lars Loekke Rasmussen told reporters.
British Prime Minister Gordon Brown was also expected later Tuesday - a day earlier than planned to help push the talks forward.
The U.N. conference's working groups were finishing up two years of work and drawing up their final recommendations on such issues as deforestation, technology transfers and the registration of plans by developing countries to control their emissions.
Drafts on those issues showed some narrowing of gaps but left many disputes to be decided by environment ministers, which ultimately may go up to the heads of state and leaders.
"Ministers have to be very clear and focused over the next 48 hours if we are to make it," said conference president Connie Hedegaard of Denmark.
Talks on a global climate deal hit a snag Monday when developing countries walked away temporarily from the negotiations, fearing industrial countries were backpedaling in their promises to cut greenhouse gases.
The issues concern the details of a final treaty to be negotiated in the next six to 12 months and may not even be included in the political deal reached in Copenhagen.
Former Vice President Al Gore proposed speeding up a binding climate deal.
Instead of finishing up work with a treaty in Mexico City in a year, Gore proposed a final meeting and treaty agreement in July 2010, saying he was sure that Mexico would go along with the hurried-up schedule.
Gore also urged Congress to come up with its climate legislation by April 22 - the 40th anniversary of Earth Day.
Explore further: Great Barrier Reef stays on UN watch list