The pan-Himalayan rail project, which began in 1958, eight years after mainland troops invaded Tibet, is expected to be finished by the end of this year.

``By 2050, safe operation of the Qinghai-Tibet railway will be affected if temperatures keep rising steadily as observed over past decades,'' Luo Yong, deputy director of the National Climate Center, was quoted as saying.

Winter and summer temperatures on the Tibetan plateau could jump as much as 3.4 degrees Celsius by 2050, causing normally frozen ground under the rail line to melt, the China Daily said. Many climatologists consider the plateau a ``magnifier'' of global climate change and an indicator of warming trends across East Asia, it said.

The railway will span 2,040 kilometers from Xining in Qinghai province, to the capital of Tibet, Lhasa.

China says the rail link will promote development and help raise living standards in the impoverished region, while Tibet activists say it will speed up the pace of Chinese migration to the area and dilute Tibetan culture.

Luo issued his warning at a symposium on climate change in Beijing, which has been simmering under temperatures as high as 40C in a heat wave that has struck northern China. REUTERS