An environmental chief in the industrial city of Zhuzhou in central China's Hunan Province, Wen Tiejun jokingly describes himself as a "chimney demolisher".

As a result of tight environment rules made by Wen's department, a textile mill in the city will soon replace a coal-burning boiler with a cleaner, more efficient gas-driven boiler. So an 80-meter-tall chimney for the old boiler will be demolished.

"Since 2006 we have been pushing factories to dismantle more than 100 chimneys that were highly polluting or had been out of use," says Wen, director of Zhuzhou's Environmental Protection Bureau.

A forest of chimneys was once worshiped as a token of modernization of the world's largest developing and most populous country. But nowadays, these towers pouring noxious dust and greenhouse gases are subject to either treatment or demolishment as China rapidly embraces a new concept of development: low carbon.

China will "step up efforts to develop a green economy, a low-carbon economy and a circular economy," President Hu Jintao told global leaders at the United Nations climate change summit on Tuesday.

He promised that the country, the world's third largest economy, would endeavor to cut carbon dioxide emissions per unit of gross domestic product (GDP) by a "notable margin" by 2020 from the 2005 level, a major move to grapple with climate change issues.

This makes the toppling of many polluting chimneys inevitable. But for 64-year-old Zhuzhou resident Ou Houjin, it is something unexpected.

"In the 1950s and 60s, we were delighted and proud with the sound of roaring machines and stacks of chimneys giving off thick smoke, because these indicated that our socialist construction was in full swing and our motherland was prospering," Ou recalls.

After coming to power in October 1949, the Communist Party of China (CPC) led by Chairman Mao Zedong forged a vision of building a rich and powerful socialist country from the "poor and blank" situation. Heavy industry was the backbone.

Only 60 km away from Chairman Mao's birthplace Shaoshan, Zhuzhou was chosen as one of eight industrial bases to be developed since the early 1950s.

Tens of thousands of workers and engineers were dispatched to this riverside town of just 7,000 residents. Large smelters, chemical works, machinery plants and arrays of chimneys were erected, eventually transforming Zhuzhou into an industrial hub with almost 4 million people.

The changes in Zhuzhou may best illustrate China's path to industrialization in the past six decades.

The steel output of China in the early 1950s was less than one thousandth of the world's total. In 2008, crude steel production accounted for 40 percent of the world output. Meanwhile, the annual output of motor vehicles rose from less than 20,000 to about 9.35 million, making China the world's second largest car producer only after Japan.

HIGH PRICE FOR DEVELOPMENT

"Without chimneys, Zhuzhou may never become a key industrial base," argues Ou, who works as an environmental protection advisor for a chemical plant. "But we pay a high price for it."

"In the 1960s and 70s we almost had no idea of environmental protection. Industrial wastes were discharged into rivers and the sky freely," Ou says.

In 2004, Zhuzhou found itself among the ten worst polluted places, according to an official evaluation of overall environmental quality of 113 cities in China.

"The sky was no longer clear and fewer fishes were seen in the river. There was always a strange, acrid odor in the air around the industrial area, sometimes like the smell of rotten eggs. It was so suffocating," Ou says.

As a result of heavy emissions of sulfur dioxide, Zhuzhou fell a victim to serious acid rain pollution. In 2001, the pH level, a major measurement of the pollution, was 3.2 in the city, compared with 7, the neutral level.

"Even after years of efforts to cut SO2 emission, the average reading remains around 4 today," Wen says.

"More alarmingly, we found that investors didn't want to come because of heavy pollution, which constrained further development of Zhuzhou," he says.

Substantial action to cut industrial pollution started from 2003, prompting local enterprises to treat and recycle waste water, and to install dust removal and desulphurization devices on chimneys.

"Some chimneys have to remain, but the emission must be cleaner," Wen says.

The city is now carrying out an even more ambitious plan for development, eyeing not only pollution treatment but also carbon emission reduction.

In 2007, Zhuzhou and neighboring Changsha and Xiangtan cities were chosen by the central government as a pilot zone for building a "resource efficient and environment-friendly society".

"This indicates a crucial change of China's vision for future development -- industrialization does not necessarily mean unsustainability. Highly efficient use of energy and resources and less emission of wastes should be the solution," says China's Environmental Protection Minister Zhou Shengxian.

"Low carbon development has become a global trend, which China should also follow," he says.