May 23 - China launched a comprehensive survey of its glaciers on Tuesday to discover the impact global warming has had on them over the past three decades.The first survey in 1978, found that China had 46,298 glaciers covering a total area of 59,406 square kilometers.Li Shiyin, the leading scientist in charge of the survey from Chinese Academy of Sciences (CAS), said the glaciers have undergone great changes over the past 30 years.Although some research on glaciers has been conducted in recent years, scientists lack an overall picture of the health of glaciers, and cannot fully evaluate the impact of their shrinking on water resources in west China, Li said.Some studies show that more than 82 percent of the glaciers in China have shrunk over the past three decades. Some are two percent smaller while the most seriously affected is 18 percent smaller.A new analysis by the Cold and Arid Regions Environmental and Engineering Research Institute under CAS said that glaciers in China have shrunk by 3,248 square kilometers, or 5.5 percent, in the past 40 years. Their volume has declined by 389 cubic kilometers, about 7 percent of the total 40 years ago.The shrinkage of glaciers has brought great changes to the water and climate, and caused many natural disasters in west China, said scientists.They said the melting of glaciers would raise water levels of rivers, lakes and wetlands in the short term, but would lead to severe water shortages over the long term.