China must press ahead with new ways to cut greenhouse gas emissions for the world to have hope of containing global warming, a U.S. energy official said, urging cooperation to end distrust between the two biggest emitters.

David Sandalow, U.S. Assistant Secretary for Energy, made the remarks in Beijing, where he and Washington's top climate change policy envoy, Todd Stern, have been seeking to narrow differences with China over a new global treaty to fight global warming.

In recent years, China has taken significant steps to improve its energy efficiency and reduce its emissions, Sandalow said in speech on Tuesday issued to reporters through the U.S. embassy.

China deserves significant credit for these actions...Yet China can and will need to do much more if the world is going to have any hope of containing climate change, he said.

Defining what that more should be is a crucial issue for negotiators seeking to settle the new global warming pact in Copenhagen in December. Sandalow's speech gave no suggestion that these latest talks have overcome major differences.

China is the world's biggest emitter of greenhouse gases from vehicles, industry and agriculture, having outpaced the United States, scientists believe. Between them the two nations pump out about 40 percent of the carbon dioxide from fossil fuels that is the main greenhouse gas from human activity.

But Beijing says global warming has become such a threat through the emissions of developed countries, and developing economies must not be distracted from growing and, for some time, should not accept a ceiling on their greenhouse gas output.

Yet if China continues its emissions growth at current business as usual rates, global temperatures are likely to eventually rise an extremely dangerous 2.7 degrees Celsius, even if all other nations somehow cut their emissions by 80 percent by 2050, said Sandalow.

The escape from this impasse lies in new energy-saving policies and technology and sources of clean power, he said.

China has abundant opportunities to cut emissions by improving energy efficiency and promoting low-carbon economic growth, said Sandalow.

The Obama administration has promoted clean energy cooperation with China, and a bill before the Congress aims to reduce U.S. greenhouse gas emissions by 17 percent below 2005 levels by 2020.

But China has demanded rich countries make much bigger cuts, and said they should commit up to one percent of their annual economic worth to helping the developing world fight global warming.

(Editing by Sanjeev Miglani)