Interview with Ye Duzheng

Dr Taba recounts:

A Chinese poem was presented to Prof. Ye Duzheng, our interviewee of this issue. on the occasion of his 80th birthday. “Ye” means “leaf” in Chinese, “du” means “diligent”, and “zheng” means “sincere”. Prof. Lu Jiaxi, a former President of the Chinese Academy of Sciences, skilfully used these three words in his composition. The direct translation of the poem is:

Cordial greetings on the 80th birthday of Professor Ye Duzheng. Leafy canopy and deep root bring fruitful harvest in the study of the East-Asian atmospheric general circulation. Diligent study and sincere habit blaze a new trail in the field of global change science.

   

Prof. Ye Duzheng

 

Prof. Ye Duzheng

Ye Duzheng was born on 21 February 1916 in Tianjin, China. In 1935 he entered Tsinghua University in Beijing for undergraduate studies and finished his graduate studies in 1943. For the next two years he worked as a research assistant at the Meteorological Institute of the Central Academy, Chongqing, Shichuang Province. In 1945, he went to the University of Chicago, USA, where the world famous meteorologist, Carl-Gustaf Rossby, and his collaborators were carrying out research on the general circulation of the atmosphere, particularly the newly discovered jet streams. In 1947, the Chicago group published a classical paper on the general circulation. Those who participated in this work (in alphabetic order) were: Jule Charney, George Cressman, Dave Fultz, Seymour Hess, Alf Nyberg, Eric Palmén, Carl-Gustaf Rossby, Zdenek Sekera and Victor Starr. Duzheng was indeed lucky to be in the right place at the right time.

Under the close supervision of Rossby, Ye obtained his Ph.D. in 1948 and continued working as a research associate at the University of Chicago until 1950. In 1949, he published his first important paper on the theory of energy dispersion, explaining energy propagation through dispersive waves, for which work he used four atmospheric models. This was indeed a substantial contribution to the long-wave theory proposed by Rossby. Ye was one of the first meteorologists to provide satisfactory explanations for the formation of “blocking highs”, their intensity and geographical occurrence.

In spite of this remarkable scientific success and the fact that he could have stayed in Chicago, he decided, in 1950, to return to his homeland, where he joined the Institute of Geophysics and Meteorology of the Chinese Academy of Sciences (CAS). His main aim was to explore further the intricacies of the atmospheric general circulation in general and over Asia in particular. In the mid-1950s, the network of aerological stations in China developed rapidly and upper-air data from more than 150 radio-sondes and pilot balloon stations were plotted on meteorological maps. This provided the most valuable source of information for Ye’s group to discover many interesting phenomena about the general circulation of the atmosphere over eastern Asia.

Ye was perhaps the first person to set forth the argument that the Tibetan Plateau, the world’s largest highland (> 2.5 million km2 area and > 4.5 km high on average) was a heat source in summer and a cold source in winter. Taking into consideration the ellipsoid shape of the plateau and its extension (major axis from about 75°E to 103°E and minor axis from about 27°N to 38°N), it can immediately be seen that these figures are comparable with those of the atmospheric long waves in the region. It follows that such an enormous topographic feature with a large heating source in the middle troposphere has a profound effect on the atmospheric circulation. Ye showed that the diurnal heating and nocturnal cooling of the plateau create a wind with opposite components from day to night and that this thermodynamic effect of the temperature field was responsible for the dynamic manifestations of the pressure field. Ye and his collaborators continued their research on the atmospheric general circulation over Asia and the characteristics of the Tibetan Plateau for almost half a century. His group’s monograph on the meteorology of the Tibetan Plateau was considered by many meteorologists to be a major work.

During this same period, Ye extended his studies to include the general circulation over the whole northern hemisphere. In the early 1950s, for example, he and his collaborators demonstrated that, not infrequently, there was an abrupt change in the upper-air circulation over the northern hemisphere in June and October, together with a sudden northward shift of the westerlies and easterlies. They showed that these changes were associated with the onset of the south-west monsoon in India and related phenomena in China and Japan. They studied many aspects of the atmospheric general circulation and the factors affecting it, such as the balance of angular momentum, heat and energy transfer, high and low index phenomena, the occurrence of blockings, etc. In 1958, Ye and his assistant, Chu, wrote the book Some Fundamental Problems of the General Circulation of the Atmosphere, which was one of the earliest publications in the dynamics of the general circulation. In another book, The Problems of Adaptation in Atmospheric Motions of 1963 (co-author Li), Ye proposed a few new concepts, such as the spatial-scale effect in geostrophic adjustment, the adjustment between pressure and windfield in mesoscale motion, the hydrostatic adjustment, etc.
   

The poem composed and presented to Prof. Ye by Prof. Lu Jiaxi

The poem composed and presented to Prof. Ye by Prof. Lu Jiaxi on the occasion of Prof. Ye’s 80th birthday

Already in the early stages of his work, Ye realized that, in order to obtain a complete knowledge of events occurring in the atmosphere, it was necessary to take into consideration the effects of the hydro-sphere, the geosphere and the biosphere. He was, and still is, a strong advocate of the idea that international cooperation was essential for the development of knowledge in the atmospheric sciences. He paid special attention to organizing and improving research activities in China, playing a fundamental role in founding the Institute of Atmospheric Physics (IAP). Today, IAP’s activities cover almost all aspects of the atmospheric sciences. In the international arena, Ye has been extremely active. He was a member of the Joint Scientific Committee of the World Climate Research Programme of ICSU and WMO (1982-1988), a member of the IAMAP Executive Committee (1983-1987), a member of the Scientific Committee of the International Geosphere-Biosphere Programme (IGBP) (1987-1990) and a member of the IUGG Bureau. He initiated China’s studies on the IGBP and assisted in setting up the START Regional Centre for Temperate East Asia.

One of Ye’s most outstanding services to meteorology in China was the restoration of the Chinese Meteorological Society (CMS), which had been suspended for a decade under the “Cultural Revolution”. He was elected President of the CMS in 1978 and remained in that office until 1986. His first step was the convening of a session of the National Congress of CMS members, when the constitution of CMS was redrafted, and members were urged to participate in the drive to meteorological modernization

Ye’s presidency was noteworthy. Some 100 academic meetings were held and many comprehensive and multi-disciplinary conferences and scientific surveys were organized. Meteorology and meteorological services gained public recognition; continued education was provided at various levels; and national institutions engaged in popular meteorology were established, making CMS a major source of meteorological publicity. Acta Meteorologica Sinica was reactivated; a new publication, Meteorological Knowledge, was launched; the Tu Changwang Scientific and Technological Prize for Young Meteorologists was set up; and exchanges and contacts with foreign counterparts were initiated. In brief, the CMS played an important role in upgrading meteorological science.

Ye has also rendered invaluable service to developing the operational aspects of meteorology in China. In the early 1950s, he provided great support to the establishment of the Joint Centre of Weather Analysis and Forecasts and the Joint Office of Climate Data of the Chinese Academy of Science and the Chinese Meteorological Bureau (later the Weather Forecast Centre and the Climate Data Centre of the China Meteorological Administration (CMA). It was Ye who pointed out the necessity of initiating studies of atmospheric chemistry and he was one of the pioneers of global change research. He proposed many new concepts, such as the predictability of global change, the climate and ecology-sensitive zones in response to global change. As the Chairman of the Chinese National Committee for the IGBP, he brought all branches of the relevant sciences together and ensured the smooth coordination of the IGBP in China.

During more than six decades of meteorological investigation, research and training, Ye has rendered invaluable service to meteorology, not only in China but also Asia and even globally. He has published some 100 scientific papers, monographs and books. He has received the following awards and distinctions; First Grade of 1987 National Natural Science Award for the Research on East Asia General Circulation; Second Grade of 1987 National Natural Science Award for the Research on Adaptation Processes in Rotating Atmospheric Motions; the 1995 Tan Keh Kee Prize in Earth Sciences issued by the Tan Kah Foundation and the 1995 Awards of the Ho Leung Ho Lee Foundation in Science and Technology Achievement. He is an Elected Member of the Chinese Academy of Sciences; Elected Foreign Member of the Finnish Academy of Sciences and Letters; Honorary Member of the Royal Meteorological Society of the United Kingdom, Honorary Member of the American Meteorological Society, and Honorary Member of the Chinese Meteorological Society.

Two of Ye’s greatest qualities are his kindness and his immense enthusiasm to help his students.He is regarded with respect and gratitude by former students all over the world.

The first time I heard Ye’s name was in the mid- 1950s when I was a student at the International Meteorological Institute, University of Stockholm. Rossby was my Professor at that time and he used to talk about Ye as an example of a brilliant young man from a developing country. I met Ye for the first time when I visited China in February 1982. I was very happy to see him on the occasion of this interview which took place in Beijing in September 2002.

I wish to take this opportunity to thank wholeheartedly Prof. Wu Guoxiong, a former student of Prof. Ye and currently Director of Academic Sciences and the Geophysical Fluid Dynamics Laboratory, for all his efforts in liaising between Prof. Ye and myself, as well as for the excellent hospitality provided during my visit to Beijing.

H.T. — You are one of the pioneers of global change research. How do you define global change?

D.Y. — As defined by the IGBP, global change encompasses any changes from any means in the Earth’s environment, i.e. changes in the solid earth, the oceans, the atmosphere, biosphere, cryosphere, etc., including people, animals and plants. For the last two decades, geologists and environmentalists have been concerned about the evolution of global change and another linked problem, sustainable development.

The Intergovernmental Panel on Climate Change (IPCC) has conducted several studies on this important problem and the results of their findings are published in various reports. In brief, the IPCC has concluded that: (a) during the last 100 years, the global mean surface temperature has on average increased 0.6±0.2°C and recent years have been the warmest since instrumental observations began. According to all possible emission scenarios of greenhouse gases, the climate models projected that the global averaged surface temperature may increase by 1.4-5.8°C in the next 100 years; (b) as a consequence of this warming, sea-level has risen 10-20 cm on average during the last 100 years and is expected to rise 9-88 cm in the next 100 years; (c) there has been a depletion of the ozone layer with an “ozone hole” in the Antarctic and a decrease of total ozone in the Arctic zone and middle latitudes.

These changes have the potential to influence significantly the existence and development of humankind through changes in grassland and cultivable land, the temporal-spatial distribution of water resources, soil moisture, the changes of the frequency and intensity of extreme climate events in some regions with consequences for agriculture, forestry, animal husbandry and human activities. The question arises of how to adapt to these variations.

H.T. — Is there any evidence that some or most of the warming observed is attributable to human activities?

D.Y — There is more and more evidence to this effect. We are almost certain that the Earth’s climate system has changed on both global and regional scales since the pre-industrial era. We are equally sure that some of these changes are attributable to human activities. For example, the atmospheric concentration of greenhouse gases, such as carbon dioxide (CO2), methane (CH4), nitrogen oxide (N2O) and tropospheric ozone (O3) reached the highest recorded levels in the 1990s. The main reason for this increase was the combustion of fossil fuels, as well as changes in agriculture and land use. The net increases of greenhouse gases have impacts such as raising the mean temperature of the lower troposphere. It is therefore not surprising that the 1990s were the warmest decade and 1998 the warmest year on instrumental record. Indeed, the increase in surface temperature during the 20th century in the northern hemisphere was probably greater than in any other century in the last thousand years. Temperature changes have not been uniform globally; they vary from region to region and also in different parts of the lower atmosphere.
 

Prof. Ye at a lecture

 
Prof. Ye at a lecture

A number of recent detection and attribution studies have provided strong evidence for an anthropogenic origin in the climate record of the last 30-50 years. It is likely that there are some uncertainties in these studies due to natural factors, such as volcanoes, solar radiation and others. A more realistic conclusion would be reached if all the effects, be they anthropogenic or natural forcing factors, were combined. One can quite safely say, however, that most of the observed warming over the last 50 years is attributable to human activities. As regards the southern hemisphere, the amount of data available prior to the year 1860 is unfortunately insufficient to compare with the the recent warming of the northern hemisphere .

H.T. — What are the environmental, social and economic consequences of climate changes?

D.Y. — They are numerous. For example, the hydrological cycle could become very active, which would mean heavy precipitation, as well as a shift in precipitation. There could be a widespread retreat of non-polar glaciers, an increase in sea-level and ocean-heat content and a decrease in snow cover and sea-ice extent, as well as ice thickness. Perhaps the sea-level rise observed recently is the consequence of the 20th century warming which caused thermal expansion of sea-water and widespread loss of land ice. In many parts of the world, regional changes in climate, in particular where there has been an increase in temperature, have already affected hydrological systems and terrestrial and marine ecosystems. These changes are consistent in direction and it could not be said that their occurrence has been by chance alone. These regional changes could cause damage with enormous socio-economic losses, suggesting more evidence of increasing vulnerability to climate change. There are indications that some social and economic systems have been affected by recent increases in floods and drought with catastrophic consequences. On the other hand, one cannot point to regional climate change as the sole culprit, since there are socio-economic factors such as demographic shifts and land-use changes, which could be responsible. It is not easy to quantify the relative impact of climate change, whether anthropogenic or natural, or of other socio-economic factors.

H.T. — Could you give us an idea of what we should expect as regards climatic and environmental changes during the next 25-100 years?

D.Y. — I can only repeat what has been said by the IPCC, namely that, under all global scenarios, the concentration of CO2, averaged surface temperature and sea-level will all rise during the 21st century—how much it is hard to say. For every scenario, a different socio-economic assumption (demographic, technological, etc.) has to be made, each with a different result, depending on the release levels of greenhouse gases and aerosols. At the same time, one has to take into consideration the effects of removal processes such as carbon sinks.

Taking all the relevant factors into account, one can expect a concentration range of between 490 and 1 260 ppm, which is 75-350 per cent above the year 1750 (pre-industrial concentration). This means an average global temperature of 1.4-5.8°C over the period 1990-2100, which is between two and ten times larger than the value of observed warming over the 20th century. In the IPCC Second Assessment Report, the corresponding values were 1.0-3.5°C . For the periods 1990-2025 and 1990-2050, the projected increases are 0.4-1.1°C and 0.8-2.6°C respectively.

The question arises as to what sort of consequences these temperature changes would have on the precipitation pattern. The IPCC report says it is very likely that precipitation will increase in high latitudes in both summer and winter during the 21st century. There might be increases over the northern mid-latitudes, tropical Africa and the Antarctic in winter and south-eastern and eastern Asia in summer. Australia, Central America and southern Africa may show decreases, mainly in winter. There might be also larger variations in precipitation.

It is is expected that the glaciers will continue to retreat. Because of the thermal expansion of the oceans and the melting of glaciers and ice caps, the projected rises in sea-level around 2050 might be anything between 0.03 m and 0.32 m.

H.T. — If the IPCC scenarios prove to be realistic, what will be the repercussions?

D.Y. — Projected climate changes will have both beneficial and adverse effects on environmental and socio-economic systems but, if the changes are considerable, the adverse effects may increase. This will also depend on the region: in a small area, a slight climate change can be beneficial for a short period. If the situation persists, however, and the changes increase, the adverse effects will appear. As regards the effects of climate change on human health, some of the effects are direct: with increased heat, of course, there will be heat-stress effects; with floods and storms, there will be unavoidable loss of life. The health impacts depend also on local environmental conditions. The indirect effects of climate change on humans will show up in the range of diseases which appear, such as malaria. The climate changes will have stronger adverse effects on human health in lower-income populations, in particular in tropical and sub-tropical countries.

Other important effects of climate change would be the changes taking place in ecological productivity and biodiversity. Incidents such as fires, drought, pest infestation and storms are events which will have catastrophic effects on ecosystems, resulting in the extinction of some endangered species. With an increase of CO2 concentrations, the productivity of plants will increase, but one should not forget the climate changes associated with them and their subsequent effects. The IPCC models for cereal crops show that, in some temperate areas, a small temperature increase may result in increased yields. In tropical and sub-tropical areas, however, the yields will decrease. The question arises as to what sort of effects these changes would have for livestock producers. If the effect of temperature rise is lower productivity and increased prices, then there is a risk of hunger for vulnerable populations. For the inhabitants of small islands and low-lying coastal areas, sea-level rise will mean greater risk of coastal flooding and erosion. People living in deltas and adjacent coastal areas will face the risk of displacement. Beaches, freshwater, fisheries, coral reefs, etc., will be exposed to great risk.

H.T. — How much do we know about the effects of increasing atmospheric concentrations of greenhouse gases and the human-induced change of climate, regionally and globally?

D.Y. — Various models show that an increasing concentration of greenhouse gases in the atmosphere will result in changes on all scales—daily, seasonal, interannual and decadal. In many areas, there would be a decrease in diurnal temperature change, mainly in winter, and increased daily variability, especially in precipitation in the northern hemisphere summer. Some models predict more El Niño conditions in the tropical Pacific. No clear agreement has been reached concerning changes of atmosphere-ocean circulation patterns, such as that of the North Atlantic Oscillation. Models also predict increased risks of floods and droughts in many areas with adverse impacts on ecological and socio-economic systems and human health. The maximum wind and precipitation intensity of tropical cyclones is likely to increase. As regards the effects on smaller-scale phenomena, such as thunderstorms, tornadoes, hail and lightning, the results are inconclusive. Some of the abrupt changes in physical and biological systems occurring during the 21st century may have lasting effects over the coming decades. Depending on the rate, magnitude and duration of the climate changes, the consequent effects could appear in many ways, such as changes in soil and vegetation, weakening of the thermohaline circulation of the oceans and reduction of heat transport into high latitudes in Europe. The Antarctic ice sheet will likely increase in mass during the 21st century. On the other hand, the Atlantic and Greenland ice sheets are likely to lose mass. The greater the magnitude and rate of change, the greater the risk of adverse impacts.

H.T.     Can the projected rate and magnitude of warming and sea-level rise be brought down by reducing greenhouse emissions and by how much?

D.Y. — The greater the reductions in emissions and the earlier they are implemented, the smaller and slower will be the warming and rise in sea-level. There are three main factors affecting future climate change: (a) what has happened in the past; (b) the current situation and; (c) the action to be taken in the immediate future. Assuming that developed nations reduce their CO2 emissions at the rate of 2 per cent a year over the period 2000-2100 and developing nations do not, then the global concentration of CO2 in the atmosphere will still grow, but at a diminished rate compared to the scenario in which the developed countries do not reduce their emissions. By the year 2030, the projected concentration of CO2 in the atmosphere would be about 35 per cent. The corresponding reduction in sea-level rise would be 20 per cent. Such an action taken now would have a greater effect in the year 2100 than if it were implemented later. Under this scenario, the emissions by developed countries of CH4, N2O and SO2 are assumed to remain constant at their 1990 level. In order to stabilize CO2 concentrations, a substantial reduction below current levels would be necessary to slow down the rate of warming. One should remember that, to estimate any temperature changes, one has to take into account the effects of the emissions of greenhouse gases other than CO2. In view of the inherent complexity of the interactions of CO2 with other greenhouse gases and various assumptions made in models, one should regard the results with circumspection.

H.T. — What about mitigation and adaptation?

D.Y. — Mitigation—reduction of greenhouse gases—would lessen the pressures on natural and human systems from climate change. If the increase of mean temperature is slower than that predicted by models or if the rate of sea-level rise is slowed down, there would be more time for adaptation. Mitigation actions can, therefore, delay or reduce damage caused by climate change. This would undoubtedly have socio-economic benefits. Any action leading to a CO2 concentration below 1 000 ppm by the year 2100, would reduce the risks associated with a warming above 3.5°C. Stabilization at a lower level would therefore further reduce the associated risks. Another important issue is that all the emissions made by the present generations will affect future generations owing to the inertia of the atmosphere-ocean-climate system, as well as the irreversible effects of climate change on the environment. Although future generations will be better educated and technologically more advanced than we are today, the changes set in motion today or in coming decades will accumulate and perhaps reach magnitudes that some nations will not be able to cope with. If some species become extinct or some ecosystems are lost, there will be no way to remedy the situation and compensate for losses. Any mitigation of climate change by the present generation will reduce risks for the future generation.

H.T. — How do you define the terms “adaptation” and “sustainable development”?

D.Y. — Adaptation means adjusting natural or human systems to fit a new or changing environment. As far as climate change is concerned, it refers to adjustment in natural or human systems to respond properly to expected changes or their effects in order to lessen harm or exploit beneficial opportunities. Adaptation can take several forms. It can be anticipatory or reactive. It can be private or public, autonomous or collective. The question arises as to how adaptation assessments can be made. One has to identify options to adapt to climate change and evaluate them in terms of criteria, such as availability, benefits, costs, effectiveness, efficiency and feasibility. Adaptation costs are expenses associated with planning, preparing, facilitating and implementing adaptation measures, including transition costs. Adaptation benefits can be defined as damage avoided or benefits accrued. Finally, adaptation capacity is the ability of a system to adjust to climate change, including climate variability and extremes to reduce potential damages and to take advantage of opportunities or cope with the consequences. Concerning the definition of sustainable development, it simply means development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

H.T. — Are there any other environmental issues you would like to mention?

D.Y. — Other environmental issues of concern are urban air pollution, regional acid deposition, loss of biological diversity, stratospheric ozone depletion, desertification and land degradation. In order to meet human needs, we frequently cause environmental degradation which, in turn, threatens our ability to meet needs, both present and future. Let us take the case of augmented agricultural production through the increased use of nitrogenous fertilizers or the conversion of natural grasslands and forests. These changes will affect the climate through the release of greenhouse gases and will lead to land degradation through erosion and salinization of soils, contributing to loss of bio-diversity.
   

 
Prof. Ye with Dr Taba, colleagues and students

Climate changes can adversely affect agricultural productivity, in particular in the tropics and subtropics, with loss of biodiversity and changes at the genetic and species level. These changes can affect food production and have a considerable impact on poor people. The main factors responsible for anthropogenic climate changes are economic growth, technological changes, changing life-style patterns and demographic shifts. The consequences are, among others, increased demand for food, natural resources and energy.

H.T. — In the face of such gloomy future perspectives, what can be done to stop further damage or lessen the risks?

D.Y. — Two things: mitigation and adaptation. The understanding of climate and its impacts is prerequisite for choosing options to mitigate and adapt. Now that we are certain that climate changes are occurring and are more and more aware of their impacts, climate-change mitigation becomes more necessary. Reduction of greenhouse gases (mitigation) would lessen the pressure on natural and human systems from climate changes. There are no comprehensive quantitative estimates of benefits from mitigation available. However, in cases of temperature increases of a few degrees Celsius, the net primary benefits of mitigation have been  positive. The question arises as to the relation between mitigation costs and benefits in different sectors, countries and development paths. In sectors such as coal-, oil- and gas-dependent industries, the disadvantages of mitigation are evidently economic losses. These economic losses are more immediate and visible. On the other hand, the sectors which are likely to benefit are those using renewable energy or industries whose products are specifically appreciated for using low-emission fuels. Since the energy structure and costs are different in different countries, their costs and benefits from mitigation are different. Carbon taxes can have negative or positive effects, depending on how the revenues from such taxes are used and in which country or area. The main problem here is that one does not know the future relative prices of carbon-based fuels and the non-fossil-fuel energy alternatives. Nevertheless, considerable progress in energy-saving and low-carbon technologies has been made since 1955, and even faster than anticipated.

H.T. — Can you explain the relations between the adaptation to the impacts of global change and sustainable development?

Y.D. — Global change and sustainable development have long been studied separately, without much attention to their interdependence. To a large extent, this has been because global change studies have focused more on the theoretical aspects and the basic research side of the geosciences, while studies on sustainable development have been directed more towards socio-economic aspects. Because of the increasing importance of adaptation measures to alleviate the adverse effects of climate change, however, the interrelations become more apparent.
   

Prof Ye with his wife and daughter

 
Prof Ye with his wife and daughter

From previous remarks, we can conclude that, to a great extent, global change is induced by mankind’s unsuitable activities such as large-scale deforestation, overcultivation, overgrazing and abundant use of fossil fuel, etc. On the time-scale of decades to a century, the change in climate and the environment due to forcing of human activities is nearly the same as that of naturally driven forces. Imagine a scenario of a sea-level rise of 10-20 cm in the next hundred years due to global warming. Add to this the effects of probable sea-level rise due to land subsidence and the consequences of overuse of groundwater and urban expansion in some developed coastal zones and it is easily seen that we are faced with an enormous problem. In some coastal regions of China, this situation is visible beyond any doubt.

Adaptation measures to global change must therefore take into account measures to ensure halting and altering this unsustainable style of life and economic development. Adaptation measures can have both beneficial and detrimental effects. An adaptation measure taken for a temporary or a local interest may make the environmental system even more vulnerable, and adaptation to global change must be based on the principles of sustainable development. Unavoidably, most of the studies and discussions on sustainable development have been based on past climate events and data or present conditions and do not consider adequately what might happen during the coming decades or centuries. This limits the usefulness of the results obtained. Let us take a specific case, agriculture, as an example. The possible rise of temperature and the variation of climate induced by global change will make the choice of adaptation measures more difficult if we wish to ensure future sustainable development. All plans based on studies carried out on sustainable development under present or past conditions will be of little use. It is therefore essential to consider the adaptation to global change, together with a suitable plan for sustainable development. In other words, in planning sustainable development for the future, we must imagine scenarios relevant to that future period. This is why I wish to underline the importance of the interrelation between global change adaptation and sustainable development.

H.T. — It appears that a great deal of coordination would be needed to ensure a solid interrelation between global change, adaptation and sustainable development.

Y.D. — The Earth is a system of different components. Adaptation to the impacts of global change should also be considered as a problem of the system. For instance, in cases of water shortage, to share the available resources among various regions and activities requires a great deal of coordination. Take northern China as an example and suppose an event of drought; all eyes will be upon the available water resources of the Yellow River. If the upstream regions draw much more water from the upper reaches of the river, this may result in the aggravation of the situation in lower regions (in fact, this has already happened). We can conclude that sustainable development is a coordinated development. This coordination must be on an interregional and international basis. The present trend of global or regional economic integration confirms this view. In reality, people often make a mistake and look at the existing problem having their immediate and local interest in mind. In the case of aridity, if the domains of agriculture, forestry and animal husbandry each take actions independently, the result will be not only that the individual optimum is not achieved, the whole system is injured. Each of the activities must think of itself as part of the whole and even make sacrifices, if necessary, to protect the whole system.

H.T. — I believe that a strategic plan has been formulated to develop an environmentally vulnerable region of China?

Y.D. — The Chinese Government has adopted a strategy to exploit the north-western region, according high priorities to two major activities: (a) construction and development of basic needs of the region, such as roads, transportation, education, etc.; and (b) correct environmental use of available resources. This approach is of vital importance, since the region is either arid or semi-arid and very vulnerable. The severe scarcity of water resources makes the area specifically sensitive to global change. How to choose suitable options to adapt to the future climate change expected in the region requires careful study and consideration in order to ensure the realization of sustainable development.

Water is one of the critical factors which restrain the exploitation of north-western China. The total amount of annual rainfall is already inadequate and this, combined with high evaporation, makes the water sensitivity even more pronounced. The snow, ice and rainfall in mountain areas are the sources of the water which flows in rivers to oases. There is, of course, a considerable amount of underground water in the region which has been accumulated over thousands of years, but it would be extremely dangerous to exploit great quantities of this water before assessing the possibility of its replacement. This has already happened in North China and it is time that we learnt a lesson. The correct and proper exploitation of north-western areas of China requires, above all, a precise knowledge of the future trend of the water supply during the next decades, taking probable global change into consideration. Shi Yafeng and colleagues have estimated that the total area of glaciers in north-western China will decrease by about 40 per cent at the end of the 21st century, as a result of rising temperature. At the start of this process, the temperature increase will cause more ice to melt and an increased amount of available water. However, 20-30 years later, the adverse effects may be catastrophic.

H.T. — What about the coastal areas of China?

Y.D. — In the coastal areas of China, the effects of global change are more pronounced. The impacts are variations in temperature and precipitation and in the frequency of extreme climate events, such as typhoons, and variation in sea-level. As any one of these events can have serious effects on the socio-economic life of the coastal areas, it is not difficult to imagine what would be their combined or collective effects. Zhao Yifao and colleagues have estimated that, up to the year 2050, the relative sea-level rise will be 70 cm in some regions of the Yangtze Delta. The consequences will be the invasion of saltwater into estuaries, storm surges and water logging in low-lying lands, and further coastal erosion. In the Yangtze Delta and adjacent coastal areas, the impacts of sea-level rise are not the only item we should worry about. We must also take into consideration the effects of the discharge and speed of flow of the Yangtze River. Here we have the problem of the balance of the whole water system: the sea on the one side and the Yangtze River on the other. The gigantic projects on the Yangtze River, namely the Three Gorge Dam Project and the proposed South-North Water Transport Project, will also play major roles in the problem of adapting to the impact of sea-level rise.

H.T. — What would you like to say in conclusion?

Y.D. — I would like to conclude this interview by saying that:

• Global change studies require research on the adaptation to impacts of global change;

• Adaptation to global change and sustainable development must be considered together;

• Sustainable development must be planned on the basis of adaptation options suitably adopted for global change;

• Sustainable development is sustainable only when proper adaptation to global change is planned;

• Adaptation and sustainable development are of a systematic nature.

H.T. — Thank you for an articulate interview. Your thoughts are so well founded and explained that they cannot fail to be convincing. I would like to congratulate you on a long and successful career and for your commitment to your scientific principles.

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