China and the United States face "arduous works ahead" in reducing greenhouse gas emissions, a leading Chinese energy expert said.

But the two countries have great potential to extend energy technology collaboration, said He Jiankun, director of a low carbon energy lab of Tsinghua University.

Both countries have shown enthusiasm in technology cooperation in fields such as carbon capture and storage, electric vehicles and energy-efficient buildings after the two nations decided to jointly invest $150 million for a research partnership in the next five years, he said.

China will mainly focus on emissions reduction in industrial and production sectors, which consume about 70 percent of China's energy, while the US needs to cut emissions in sectors such as transportation and the building sector, he said.

The average energy consumption per capita in the US is about four times that of China's.

China is also the world's largest consumer of coal, with more than 70 percent of its energy consumption dependent on coal. In general, coal accounts for about 20 percent of energy consumption in most developed countries, complementing oil and natural gas.

He said that if China uses more oil and natural gas, imports will soar and the global supplies may be insufficient.

China is striving to reduce its coal use by developing and investing in clean and renewable energies such as solar, wind, nuclear and hydropower.

Such energy sources will bring great changes to the country after 2020, with the changes more obvious after 2030, He said.

China has set targets to boost non-fossil fuel use to 15 percent of energy consumption by 2020.

"It is inevitable that natural energy consumption, including coal, will continue to grow along with China's process of industrialization and urbanization," he said.

That's also why developed countries pledge to achieve absolute emissions reduction while developing countries only set reduction targets for carbon intensity, the amount of carbon dioxide per unit of GDP, according to the common but differentiated requirements.

"Without such a period, a country cannot achieve absolute emission reduction," he said.

China's carbon intensity decreased by 55 percent from 1990 to 2009, compared with about 15 percent average reduction worldwide, and less than 30 percent of developed countries during the same period.

Energy saving and carbon emissions reduction has been the government's top priority and much efforts have been made to cut coal consumption.

Many obsolete and inefficient coal-fired power plants have been closed. From 2006 to July this year, a total of 70 gigawatts of small-scale coal-fired capacity have been closed and advanced supercritical generating units have been built.

Barbara Finamore, China program director of the Natural Resources Defense Council, said: "China's efficiency is going up by shutting down low efficient plants and building the new coal plants."

China's average efficiency for coal-fired generating units has surpassed many developed countries, including the US, due to the newly built high efficient capacity, she said.

"China has huge potential for energy efficiency," Finamore said, adding that China has made solid progress in renewable technologies.

If the US could lift controls on high-tech and transfer more technologies to China as its contributions to mitigate climate change, China can do a better job in cutting emissions, he said.