BEIJING - Three little letters could spell big trouble for global climate change negotiations even after China, the world's biggest emitter of greenhouse gases, announced its first firm goals to curb emissions.

MRV, climate treaty negotiators' shorthand for measurable, reportable and verifiable, sums up environmentalists' concern now China has taken up an emissions target. How will the world know if it is telling the truth about any emissions reductions?

China stressed on Thursday that its goal of reducing carbon intensity by 40 to 45 percent by 2020, compared to 2005 levels -- reducing the carbon dioxide released to generate each yuan of economic activity -- is a domestic policy, not to be picked over by foreigners as part of a new international pact.

Negotiators hope to agree on the basics of that pact when they meet in Copenhagen from December 7.

Trust us, was the message of Xie Zhenhua, the Chinese climate policy envoy who gave a news briefing to explain the policy.

Although this is a domestic voluntary action, it is binding, said Xie. As we've made this commitment, well, Chinese people stick to their word.

But garnering enough international trust to fix a new legally binding climate treaty will not be easy when there is so much wider Western unease about Chinese intentions on trade, security and the environment.

Another worry is the quality of data in a country that has ingrained habits of secrecy, with officials tempted to bend statistics that can decide chances of promotion and demotion.

I think that, unfortunately, this is one of those cultural clashes that could be difficult, said Charles McElwee, an environmental and energy lawyer with Squire Sanders in Shanghai, who follows China's climate change policies.

China has this deep-seated desire not to have other countries poking around into what it considers its internal affairs ... Westerners tend to think, 'If this is your commitment, then put your money where your mouth is'.

To get a climate bill passed into law, President Barack Obama must persuade many in the U.S. Senate that China is doing enough to curb emissions, and being held accountable, he added.

China has long rejected calls to open other areas to outside monitoring, such as legal rights and disease outbreaks.

DEAL BREAKER?

So while climate policy experts welcomed China's goal as a boost for the Copenhagen climate talks, they said governments face tough talks over how that goal will be checked and by whom.

It certainly is a potential deal breaker on the mitigation element of the negotiations, Julian Wong, an expert on Chinese climate policy at the Center for American Progress, a think tank in Washington D.C., wrote in emailed comment. Mitigation refers to actions to eradicate or reduce the threat of global warming.

The best way to do that is for the rest of the world to help China with important capacity-building initiatives in greenhouse gas reporting and monitoring, he wrote.

Beijing's reluctance to turn its domestic vow into a treaty obligation also reflects its own fears that rich nations will not live up to any vows to give poor nations more emissions-cutting technology and money to cope with global warming, said Zou Ji, an expert on the issue at Renmin University in Beijing.

But without that help, China will find it difficult to cut carbon intensity by 40 percent within a decade, he said.

The further we go in reducing carbon intensity, the harder it will be, said Zou, until recently a member of China's negotiating team for the U.N. climate talks. This path is not a level plane, it gets steeper and steeper.

Zou said he also worried that China's energy efficiency numbers reflected padding by officials, and carbon efficiency data could also be distorted by local governments and businesses.

We don't want games with numbers on pieces of paper, he said. We want to see real reductions.

MUTUAL MISTRUST

At talks leading up to Copenhagen, negotiators from rich and poor countries have wrangled over how -- and how closely -- to link their respective efforts to combat global warming.

At the core of the dispute are poor nations' worries that rich nations are trying to impose binding emissions goals by stealth that could hinder growth.

Industrialized powers say if they are making costly adjustments to their economies, big developing nations, such as China, should open their emissions books to outside scrutiny, under a deal made two years ago.

But China and other developing countries say that commitment to accept measurement, reporting and verification refers only to checking emissions steps made with technology or cash from rich nations, such as shutting belching power plants or encouraging cleaner vehicles.

The Copenhagen talks are likely to leave efforts to agree on bridging this forbidding MRV gap until after Copenhagen, which instead will seek a broad political agreement, several analysts said.

This is still uncharted territory for the negotiators, said McElwee, the lawyer. I don't think they have much precedent to draw on.

(Editing by Emma Graham-Harrison and David Fogarty)

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