A mother and her daughter protect themselves from the heavy smog in Shenyang, Liaoning province, on Sunday. [Chang Shenggang / For China Daily]

Smog has been engulfing northern China ever since the region began enjoying central heating in winter. Some experts blame cloudy, windless weather for the smog, but research shows the burning of coal to provide central heating is one of the main reasons for the increase of particulate matter in the atmosphere which causes smog.

Fossil fuels account for as high as about 90 percent of all energy sources in China, which is the highest in the world. Worse, coal accounts for 65 percent of China's total energy consumption while the share of natural gas is just 6 percent. In contrast, the percentage of coal and natural gas is about 32 and 24 in the US. Consider this: to produce the same amount of heat, coal lets off double the volume of emission than natural gas.

To further worsen matters, coal is burned in rather less efficient ways in China. For example, to provide central heating, many cities use small and medium-sized boilers to burn coal, which emit more particulate matter compared with large boilers.

That's why China is under great pressure to cut its carbon emission to fulfill its promise of contributing more to the global effort in the fight against climate change. China indeed has promised to seek cleaner ways of using high-carbon fossil fuels, for instance, by replacing small boilers with bigger ones. But its efforts have not yielded the desired results.

In its proposals for the 13th Five-Year Plan (2016-20), the recent Fifth Plenum of the 18th Communist Party of China Central Committee has emphasized the strategy of increasing the percentage of low-carbon energy sources. And the reduction in the percentage of fossil fuel has been included in the strategy. This is a big breakthrough.

China's coal-control program, funded by Natural Resources Defense Council, recently issued a report advising the government to limit its total annual consumption of coal to 2.72 billion tons of standard coal by 2020, and raise the percentage of non-fossil energy to 15.3. Furthermore, it says, the percentage of coal should be lowered by 57.3.