Between 1999 and 2001, China experienced consecutive years of high temperatures and its average temperature rose. At the first China Climate Conference held last March, experts predicted that China’s climate would go on warming up over the next 50-100 years. What influences will this warming-up have on the Chinese environment? And what measures should be taken to reduce its destructiveness? A reporter for the Science Times recently interviewed Ding Yihui, special advisor on climate changes of Chinese Meteorological Administration and former co-chair of Intergovernmental Panel on Climate Change (IPCC), who is now engaged in study in this field. On reviewing all statistics at hand, he thinks that the warming climate has a great influence on Chinese environment, some of which are destructive, especially in sensitive and fragile areas. Therefore, China must take measures to prevent and solve the problem.
On Land: Trouble Comes from Water
According to Professor Ding, the rising temperature will worsen drought conditions in the northwest, north and northeast areas of China. Take the northwest as an example, the warm climate will increase the rainfall by 20-30 mm (0.8-1.2 inches) in this area, but the evaporation volume will increase by 10-15 percent. If the present evaporation volume is 1,500-3,000 mm (59-118 inches), the increased evaporation volume is far greater than the increased rainfall. It is estimated that between 2030-2050, the northwest China will be short of 20 billion cubic meters (26 billion cubic yards) of water, 10 times of the water now stored in Miyun Reservoir in Beijing. Also, the drought weather will lead to thickening of sand layers, especially in the transition area from farmland to herding land. The chance for sandstorms is high.
Professor Ding refuted the notion that a warm climate will prevent a cold wave from going southward, thus limiting sandstorms. A sandstorm occurs under two basic conditions: The sand source and corresponding climate such as a big wind, Ding said. The warmer climate will reduce the occurrence of big winds, but cannot prevent gales under special conditions, while the sand source will surely become “optimized.” Therefore, the future for sandstorms is not that bright. For instance, the State Climate Center has confirmed that March 20-24 sandstorm this year was the most severe sandstorm in the past 10 years, which affected not only Republic of Korea (ROK) and Japan, but also the United States far away. Statistics from relevant departments of the ROK also show that the country saw more than 160 sandstorms in the past 50 years, but 100 of these occurred after 1990. Based on these facts, survey results showing that “sandstorms were reduced between 1954 to 2000” are unreliable. On the contrary, the government should adjust the observation stations now in existence and conduct systematic and thorough investigations by time and province to get more convincing data.
What’s more, the warmer climate will accelerate the melting of glaciers in western regions. By 2050, half of the present glacierets will disappear. As a result, the fresh water in storage will decrease. As a resource formed during a long time of history, the disappearing of glacierets is irreversible.
According to Ding, disasters such as mud-rock flow and landslides will also occur frequently in southwest China if the urbanization, land development, vegetation destruction and increasing rainfall brought about by warm climate are not brought under control. Worse still, the karst topography will increase, the dangerousness of which is no less than that of desertification in arid regions.
In areas short of artificial irrigation, Ding said, three major grains -- wheat, rice and corn -- will see their output reduced by 5-10 percent. But food security can be guaranteed before 2050. In the field of forestry, tree species will decrease and bio-diversity will be destroyed. It is estimated that by 2050, coniferous forest in frigid zone of northeast China will basically disappear, and grassland in temperate zone will be reduced on a large scale. Except for some tropical rainforests where areas will be increased, most forest area will be reduced, but the rate will be no more than 10 percent.
On Ocean: Far-reaching Influence
Professor Ding said that compared with land system, the ocean is influenced in a broader sense by warming climate. The period of being affected will last up to 1,000 years.
The influences are mainly as follows: First, the rising of sea level due to heat expansion and glacier thawing. In the past 100 years, the sea level in coastal areas has risen by 20-30 cm (7.8-11.8 inches), while in the following century, the rise will reach 88 cm (34.6 inches). Many areas will be swallowed up by sea water. Second, possible ice age in the warm period of north China because of the weakening or ending of Thermohaline Circulation (Heat-Salt Circulation). The heat-salt circulation refers to the relatively warm south surface sea water bringing heat to the relatively cold sea surface in the north, then sinking down to deeper water and returning. The heat exchanges between sea water is of great help to adjusting temperature gaps in the atmosphere, thereby guaranteeing a temperate climate. However, the warming climate will shorten the temperature gap between north and south sea water. At the same time, the increased rainfall in high and middle latitude will lead to desalinization and density weakening of sea water, neither of which is beneficial to the heat-salt circulation. In history, the weakening of heat-salt circulation in the Atlantic Ocean once resulted in an ice age in northern Europe. Further study is needed to determine whether the affected heat-salt circulation in the Pacific Ocean will lead to low temperature in north China. Third, the accelerated destruction of biological systems in the ocean, especially the death of some marine animals, might break down some chain in the balanced biological system. For example, the death of corals in South China Sea should receive high concern from relevant departments. As for fishery, the catch will be reduced.
Measures to Be Taken
How to deal with the environment problems resulting from rising temperatures? Professor Ding advocates accelerating research in related fields and trying to lower damage to the minimum. He said work must be done in the following four aspects.
First, to improve the weather forecasting ability in China, especially the accuracy in regard to both time and place. The focus should be on the next 100 years. Now it has been available in the world to predict the weather in a place in a certain month of a certain year. China must improve the capability of computers while taking as many factors as possible into consideration, and set up an advanced weather forecasting model. It is reported that the Ministry of Science and Technology has invested 15 million yuan (US$1.8 million) in the research project in relevant fields.
Second, to set up an independent basic-level evaluation system suitable to Chinese conditions on the basis of forecasting. Using this system, China will be able to discern fragile zones in climate exchange, give quantitative estimation of data related to fragile zones in the next 50-100 years and connect it with risk disasters. For example, with estimated data, scientists can decide when a disaster will occur, how intense it will be and how much loss it will inflict.
Third, to do a good job in “adaptation” and “reduction.” Adaptation means we must take measures to adapt ourselves to natural changes. For instance, to cope with the problem of a rising sea level, we must build dams to prevent this problem and plant trees to absorb more carbon dioxide. Under this premise, we can reduce influences of disaster through an alarm system and try to avoid destruction brought on by human activity. Also to cope with the rising sea level, we should reduce underground water pumping, thereby slowing down the subsiding of land. Ding emphasized that the state needs to draw out an overall strategy of adaptation and reduction.
Fourth, to keep up with international pace in the study of “dangerous level.” Now a hot issue in the world is: What level of carbon dioxide density will bring irreversible influence to climate? Britain believes the maximum carbon dioxide density should be 750ppm, while China thinks it be 368ppm. If the 750ppm accepted as an international carbon dioxide emission standard, Chinese economic development will be obstructed. However, we cannot set an emission standard suitable for Chinese conditions at present. What’s more, the insufficiency of the study will also lead to some construction risks. The US-based Nature magazine recently published an article predicting the flood rate at 29 large-scale reservoirs of the world and areas around them (including Three Gorges of China). It proposed that as the carbon dioxide density increases, the flood rate rises. If the emission is four times of the present level, half of the 29 reservoirs will see flood risks eight times more than at present. If we can estimate the “dangerous level” in advance, we will avoid hidden troubles as most as we can in designing reservoirs.
Professor Ding Yihui will report the influences of rising temperature on Chinese environment soon. The state will take measures accordingly to overcome unfavorable effects.
(科学时报 [Science Times] by Yao Weijie, translated by Li Jinhui for China.org.cn, May 30, 2002)