China should halve CO2 emissions by 2050-U.S

* China current plans put on track to halving- Pershing

* U.S. cannot rule out border tariffs on carbon goods



(Adds quotes, details, background)

By Gerard Wynn and Alister Doyle

BARCELONA, Spain, Nov 5 (Reuters) - China should roughly halve its greenhouse gas emissions by 2050 as part of a strong assault on global warming, the head of the U.S. delegation at U.N. climate talks in Barcelona said on Thursday.

Jonathan Pershing urged China, which has overtaken the United States as the top emitter, to clarify its goals for curbing its greenhouse gases as part of a new U.N. pact due to be agreed in December in Copenhagen.

Leading industrialised countries agreed at a summit in Italy in July that the world must halve greenhouse gas emissions by 2050 to avoid the worst effects of climate change, and promised to cut their own emissions by 80 percent.

China should cut by about 50 percent, which would allow for somewhat lower targets for poorer countries and give them room to grow their economies, Pershing told Reuters on the sidelines of the 175-nation talks in Barcelona from Nov. 2-6.

"If you put China in there at a 50 percent reduction. If they are in that middle band, plus or minus some percentage, that seems about right."

China would be on course to halve emissions if it repeated its present energy efficiency five-year plan into the future, he said, but had to commit such plans to international review.

"They're doing pretty well. But they haven't yet made the formal statement to have those reviewed by an international process. For us that's a huge part of this discussion."

Beijing has not set a 2050 goal for its emissions, saying that it needs to put priority on ending poverty. The United States has not made a formal demand of China.

The Group of Eight failed at a summit in Italy in July to persuade developing nations such as China and India to sign up to a global goal of halving world emissions by 2050 as part of a drive to slow more droughts, storms, floods and rising seas.



BARCELONA

The U.N. talks in Barcelona have struggled to overcome a rich-poor divide. Developing nations say rich countries have to do far more before they sign up to a halving of emissions, and note that the United States has not set a carbon law for itself.

Pershing said that there was "a lot of work still to be done" on domestic U.S. legislation. The Senate Environment and Public Works Committee is debating a bill to cut emissions by 20 percent below 2005 levels by 2020.

"We are still treating Copenhagen as a significant milestone where we can be part of a deal. What exactly that means clearly does depend on what Congress can deliver," he said.

He said the United States was "not opposed" to a legally binding climate treaty under the U.N. process. Many environmental groups say a legally binding outcome is in doubt.

Many nations at the U.N. talks say that Washington, the only developed country outside the existing U.N. Kyoto Protocol for curbing emissions until 2012, has to come up with a number for cuts in Copenhagen or others will simply sit on the fence.

Pershing said that China should more clearly define its goals, including a promise by President Hu Jintao in September to make a "notable" reduction in the amount of carbon emitted per dollar of economic output by 2020.

"They've talked about their renewables numbers -- pretty good numbers. They're talked about their forestry numbers, pretty good numbers. But they have an undefined carbon intensity number. They need to define that," he said.

Pershing said that the United States had not ruled out use of border tariffs if Washington feels that foreign exporters are getting an unfair advantage if carbon curbs push up U.S. costs.

"We cannot rule them out," he said. "The answer is that there is no decision."