"After it is filled, the world’s largest man-made lake will act as the greatest natural air-conditioner on the planet," Three Gorges Project Corp. vice-manager Li Yongan was quoted as saying by China News Service (Zhongguo xinwen she) on Nov. 19. Other Chinese media, including Hubei Daily, Changjiang Daily, Yangcheng Evening News and the Sina.com Web site, later picked up the story.

Mr. Li went on to say that the future Three Gorges reservoir would raise the temperature in the surrounding area by three to four degrees Celsius in winter, and lower it by four to five degrees Celsius in summer. He said Chinese Academy of Sciences researchers had reached these conclusions after a rigorous, five-year study whose results had been officially approved.

The reservoir’s moderating influence on the local climate would be welcome news to the residents of Chongqing. Along with Nanjing and Wuhan, the municipality, located at the upstream end of the future Three Gorges reservoir, is one of China’s notoriously scorching "furnaces" in the summer, when temperatures routinely soar to the mid-30s Celsius and beyond.

Mr. Li also referred to the reservoir, which will inundate 632 square kilometres of land and hold 39.3 billion cubic metres of water, as "the world’s largest man-made lake," resembling an "inland ocean."

Four months before Mr. Li made his recent remarks, the newspaper produced by his own corporation – the Three Gorges Project Daily (Sanxia gongcheng bao) – ran an apology and blasted other Chinese media for carrying a climate-change story that made identical claims.

On July 17, the newspaper retracted a piece it had picked up from the Chongqing Evening News (Chongqing wanbao). That original story (under the headline, Research: Three Gorges Reservoir to Act as ‘Air-Conditioner’) was widely reported by leading media outlets such as Xinhua news agency, People’s Daily, South Daily (Nanfang ribao), the English-language China Daily – and by the Three Gorges Project Daily, the official newspaper produced jointly by the Three Gorges Project Construction Committee and the Three Gorges Project Corp.

According to the Chongqing Evening News story, which ran on June 25, the Three Gorges reservoir, "the largest man-made lake in the world now being built on the Yangtze River, will function as an ‘air-conditioner’ once filled to capacity, lowering the temperature in nearby Chongqing municipality by five degrees Celsius in summer and raising the temperature by three to four degrees Celsius in winter." The author attributed these conclusions to a five-year research project begun in 1997 and led by Yu Xiaogan, senior researcher at the Nanjing Institute for Lake and Geographic Research, a branch of the Chinese Academy of Sciences.

Soon after this story was posted on their Web site, experts at the Three Gorges Project Corp. questioned its conclusions. Guo Tao, who, like Li Yongan, is a vice-manager of the corporation, told the Three Gorges Project Daily that two points required clarification. First, the Three Gorges reservoir will not be "the world’s largest man-made lake." And second, stating that "the huge lake will function as an air-conditioner" is definitely problematic, Prof. Guo said, adding that the reservoir’s impact on the Chongqing climate will be far less dramatic than claimed.

Shi Zhenhuan, director of the corporation’s science and technology department, agreed with Prof. Guo and provided documentary evidence that the Three Gorges reservoir will be only the 24th largest in the world. Its storage capacity of less than 40 billion cubic metres will be dwarfed by the reservoirs of many other dams, including Kariba between Zambia and Zimbabwe (184 billion cubic metres), Bratsk in Russia (169 billion cubic metres) and the Aswan High Dam in Egypt (148 billion cubic metres).

Prof. Shi said the environmental impact study for the Three Gorges dam – conducted by the Chinese Academy of Sciences and the Yangtze Water Resources Conservation and Research Institute, and approved by China’s State Environmental Protection Administration in 1992 – had concluded that building the dam would have a limited effect on temperatures, and only in the immediate area surrounding the reservoir. The researchers concluded that the average temperature in the hottest summer months would probably be lowered by 0.7 to 1 degree Celsius, Prof. Shi said.

The Three Gorges Project Daily then contacted Yu Xiaogan, the senior researcher at the Nanjing institute who was said to have led the study cited by the Chongqing Evening News.

Mr. Yu reacted with surprise to news of the article. He said he had not been involved in any such study, nor had he been contacted by the reporter who wrote the story. He then fired off letters to the Chongqing Evening News and the Three Gorges Project Corp., saying the "air-conditioner" story was untrue and had damaged the reputation of the Chinese Academy of Sciences. His own professional competence had been called into question, he said, as experts across the country read the story with skepticism. He demanded the newspaper publish a retraction.

The Three Gorges Project Daily contacted the author of the original Chonqing Evening News article, Yue Zhiming. The reporter said he got the idea for the "air-conditioner" story after overhearing tourists in the Three Gorges area chatting about the issue. He said he had interviewed a few experts on the subject, but perhaps should have dug deeper before rushing into print. "I reached the conclusion on my own that the world’s largest man-made lake would become a huge air-conditioner, and the figures I cited were just my own rough estimates," Mr. Yue acknowledged.

The Three Gorges Project Daily published an apology, saying it had "learned a lesson: We should not have picked up the story without double-checking the facts, especially given that our newspaper is the official publication dedicated to coverage of the Three Gorges dam."

Now, observers are left wondering whether Three Gorges Corp. vice-manager Li Yongan reads his company’s own newspaper – or whether, in his eagerness to tout the benefits of the dam, he has chosen to overlook the Three Gorges Project Daily’s retraction in order to fan local hopes for some respite from Chongqing’s scorching summers.