Global warming may prove to be another problem for designers and builders of the Qinghai-Tibet Railway under construction in northwest China.

Already racking their brains for a solution to building the world's highest railway on the permafrost earth, scientists are finding it much harder than expected to find solutions to construction problems exacerbated by the warming climate.

Many scientists and research institutions were working hard to minimize the impact of global warming on the Qinghai-Tibet Railway,said Lu Chunfang, leader of the construction project.

The frozen earth of the Qinghai-Tibet Plateau was degenerating because of global warming and the increase in human activities in the region, according to recent research.

Research produced by the Chinese Academy of Sciences indicated that the perennial frozen earth on the plateau is now five to seven meters thinner than 20 years ago, while about 10 percent of the plateau's frozen earth had vanished.

Meteorological statistics show the annual average temperature on the Qinghai-Tibet plateau has gone up 0.2 - 0.4 degrees Celsiusfrom the 1970s to the 1990s.

Scientists said the climate changes had impacted on the ground temperature to a depth of 40 meters, with greater changes in layers to a depth of 20 meters.

Global warming had accelerated the erosion of the frozen earth, exerting great pressure on the construction of the Qinghai-Tibet Railway and its future operation.

Scientists said the success of the construction, and maintenance of the railway, would be dependent on finding ways to stabilize the gradually thawing earth.

The permafrost layer thickens as the temperature drops and thins when temperatures increase, reducing the stability of the railway foundation.

Scientists warned that fluctuations in stability caused by changes in the thickness of the permafrost layer could create future hazards if the problem was not resolved.

"We have taken the impact of global warming into consideration when plotting the route of the railway," said Lu Chunfang.

When scientists began designing the railway, they predicted the temperature on the Qinghai-Tibet Railway would rise only 1 degree Celsius in the next 50 years.

But other scientists have estimated that the plateau temperature may rise by 2.2 - 2.6 degrees Celsius in the next 50 years, bringing greater pressure to bear on the design and construction of the railway.

Construction bosses have adopted three special measures to ensure the stability of the roadbed in the permafrost areas, including changing routes, building railway bridges along sections of complex geological conditions, and building soil layers that can insulate the ground from heat created by the railway.

About 550-km section of the railway will traverse perennially frozen areas, the longest stretch of its kind in the world.

The 1,956-km Qinghai-Tibet railway will run from Xining,the capital of northwest China's Qinghai Province, to Lhasa, the capital of Tibet Autonomous Region.

The section linking Xining and Golmud City in Qinghai was completed in 1984. Construction of the 1,118-km section connecting Golmud with Lhasa began in June 2001 and is expected to be completed by 2007.

The construction plan calls for a total investment of 16 billion yuan (US$1.9 billion) for the 554-km permafrost section of the railway.

(Xinhua News Agnecy April 30, 2003)