The author of an authoritative report on global warming has warned China about the risks it faces from climate change, and of the need to act soon. Benjamin Robertson reports from Beijing.

New roads are constantly being built in Beijing but construction is unable to keep up with the numbers of new cars hitting the city's streets, Aug. 30, 2005

Global warming has been labeled as one of the greatest challenges of the coming century.  Rising emissions of so-called "greenhouse gases" like carbon dioxide threaten to warm the planet, changing weather patterns and melting polar ice caps.

Author and economist Nicholas Stern says China needs to become a "key player" in averting this scenario, or it will suffer, too.

"If global warming was left uncontrolled, there would be very severe droughts in northern China, severe floods in southern China, and great water stress as a result of receding glaciers and snow caps in the Himalayas," he said.

Stern, a former chief economist at the World Bank, was commissioned last year by the British government to put a price on global warming.  He estimated the cost would be as much as 20 percent of global GDP unless early action is taken.  He says developing countries would be worst affected.

His report has particular relevance for China, where a rapidly industrializing economy has already resulted in widespread environmental damage.  Polluting coal-fired power stations provide 80 percent of the country's electricity needs, and China will soon overtake the United States as the leading emitter of carbon dioxide, one of the gases thought to be changing the world's climate.

Glaciers in the Himalayas are already retreating, and high demand for water from factories and agriculture in northern China means the famed Yellow River sometimes dries up before reaching the sea.

Stern, who has met with government officials and economists in Beijing, told reporters Friday that China is starting to move in the right direction, but not rapidly enough.

"There is a sense of urgency in China, but there is a very practical concern with the question of finance and technology," he said.

The country's recent five-year development plan included promoting reforestation and energy efficiency among its commitments.

Stern suggests using economic incentives as a way to encourage efficient energy use by industry, and investment in greener technologies.

But the Chinese government still seems to be of two minds about the climate.  On the one hand, it talks of being environmentally conscious.  On the other, it still subsidizes the cost of gasoline, and encourages car ownership, in a country whose roads are already crammed with vehicles belching out more and more emissions.