As the world's second largest economy, it is not so surprising that China has finally overtaken the United States to be the largest energy consumer.

The world's most populous country does not need to apologize for its energy use. To boost its economic growth and raise the living standards of its people, China is entitled to energy consumption per capita around the global average level, which is far below that of developed countries.

China's overall energy consumption in 2011 reached the equivalent of 3.48 billion tons of coal. That means the country's energy consumption per capita was 2.6 tons of coal a year, just about the global average.

China's per capita power consumption is 3,400 kilowatt-hours annually compared to Western countries' average of 8,000 kWh, and the US' whopping 15,000 kWh.

Though the Chinese economy remains only about half the size of the US economy, its ongoing industrialization and urbanization has resulted in a considerable increase in energy consumption. The real challenge for Chinese policymakers is how to advance sustainable growth as the world's largest energy user.

It is simply unthinkable for 1 billion or 2 billion extra consumers from developing countries like China and India to live lifestyles as heavily energy consuming as their Western counterparts.

To both enhance its own energy security and fulfill its commitment as a responsible member of the international community, China must redouble its efforts to raise energy efficiency as quickly as possible.

Having managed to cut energy consumption per unit of gross domestic product by about 20 percent between 2006 and 2010, the Chinese government has pledged to reduce it by a further 16 percent in the following five-year period.

Yet with few low-hanging fruits left to pick, China can no longer reap easy energy efficiency gains from shutting down outdated power plants or energy-guzzlers. Worse, economic slowdown may even make it tempting to backpedal on energy conservation as stimulus projects are rolled out.

Chinese policymakers should be aware it is the country's still-low energy efficiency that demands their full attention.