Elements of Change 1995: Session IIISummary

The unprecedented increase in humankind's standard of living since the Industrial Revolution can be attributed in large part to two factors: the development of high-input/high-yield agriculture capable of feeding an increasingly urban population, and an urban-industrial infrastructure, heavily dependent upon fossil fuels for the production and transport of manufactured goods. This interdependence between agriculture and fossil-fuel burning is most pronounced in three regions of the northern mid-latitudes (Figure i.1 ): (I) Eastern North America (25-50°N, 105-60°W) ; (ii) Europe (36-70°N, 10°W-90°E); and (iii) eastern China and Japan (25-45°N, 100-146°E). Within each of these regions, urban-industrial and agricultural activities tend to cluster together into a single large network or plexus of human-impacted land-use categories.

Chameides et al. (1994) have proposed the term Metro-Agro-Plex (or MAP) as a shorthand to describe this intermingling of agricultural and urban-industrial activities within a developed or developing geographical area. They have used the term Continental-Scale Metro-Agro-Plexes (or CS-MAPs) to specifically refer to the three large MAPs of the northern mid-latitudes. Collectively, the CS-MAPs represent a major force in the global economy and also in environmental change. Although they comprise only 23% of the Earth's land surface, the three CS-MAPs account for about 75% of the world's consumption of commercial energy and fertilizers and about 60% of the food crop production and food exports. They are also major source regions for atmospheric pollutants such as carbon dioxide, the nitrogen oxides (NO_x) and the sulfur oxides (SO_x), which affect global and regional climate and air quality. It is this interplay between urbanization and high-input/high-output agriculture, the environmental changes that they cause, and the effects these environmental changes have, in turn, upon socially and economically important institutions within a MAP that formed the basis for the discussions of this Aspen Global Change Institute session.

Although the three Continental-Scale Metro-Agro-Plexes comprise only 23% of the Earth's land surface, they account for about 75% of the world's consumption of commercial energy and fertilizers and about 60% of the food crop production and food exports.

In order to provide a focus for our discussions, this AGCI session undertook a regional-scale case study of China as an evolving CS-MAP. The choice of China was based on its status as the most populous and most rapidly developing nation in the world, with a population estimated at 1.1 billion people and a Gross Domestic Product that is growing at an annual rate of about 13%. By the year 2000, China's population is projected to reach 1.25 billion and by the beginning of the 21st century its economy will likely surpass that of the United States in terms of purchasing power. China also plays an important role in the world food economy, accounting for roughly 20% of global production and consumption of the major staple crops wheat, rice, and maize (FAO, 1991).

The unprecedented combination of economic and population growth in China will bring about profound changes in the nation's landscape and demographics. Large tracts of land now in cultivation will be urbanized or converted to other uses (Streets et al., 1995). Enormous shifts in population will occur as well. About 80% of China's people now live in rural/agricultural areas. However, government plans for China's economic development call for a population of only 200 million in the agricultural sector (Zhou, 1995). To meet this goal, approximately 500 million people will be moved out of these rural areas. Rather than have them move to mega-cities, with their attendant infrastructural and cultural problems, however, the government plans to have them relocate to some 5000 different township and village enterprise zones or TVE's (Tao, 1995). Each TVE will be a small city, with a population of about 100,000 and will be interspersed in and among the agricultural areas of the nation. The resulting land use pattern will make China a patchwork of Metro-Agro-Plexes of unprecedented proportion and complexity. All of this contributed to the choice of China as a focus for the AGCI session on Metro-Agro-Plexes.

China's fertilizer use amounts to 20 Tg N per year, the most of any large economy, and this use is growing by 12% per year. Further, the N uptake efficiency is only 40%, resulting in growing N flux burdens on China's fresh water and atmosphere.

Several important issues emerged from the AGCI discussions of China as an evolving Metro-Agro-Plex . These are outlined below:

In terms of CO₂ emissions alone and their impact upon the climate, the global implications of China's impending economic and industrial explosion are serious. The likelihood that this economic explosion will be fueled by China's abundant coal reserves raise the level of concern. From China's point-of-view, however, the issues of sustainable development and food self-sufficiency are probably more pressing than those of global change. Moreover, given the likely impact on world food markets and the global economy if China should find it necessary to import significant quantities of food, these other issues are also significant for the United States and the global community at large. China currently grows and harvests staple foods at a rate equivalent to about 2900 kcal/capita/day (FAO, 1991). While this rate is about a factor of 3 less than that of the United States, it is adequate, according to nutritional requirements set by the United Nations' FAO, to feed and nourish the Chinese peoples (see Figure i.2A ). And, while the exact balance changes slightly from year to year, on the whole, China has been essentially food self-sufficient in the recent past.

However, China maintains this approximate level of food self-sufficiency at a significant price. As illustrated in Figure i.2B, China's arable land amounts to only about 0.08 hectares per capita, a factor of 10 less than that of the United States and a factor of three less than the global average (Tao, 1992). To compensate, China uses enormous amounts of fertilizer and irrigation. Its current rate of N fertilizer use amounts to about 20 Tg N/yr, the most of any large economy, and it is growing at an annual rate of ~12% (see Figure i.2C). Moreover, the uptake efficiency of the fertilizer in China is low, only about 40% (Smil, 1995). The resulting fluxes of fixed nitrogen into China's fresh waters, and N-containing gases, especially N₂O and NO_X, into the atmosphere are significant and present growing environmental burdens on regional and global scales (Tao, 1992; Galloway et al. 1995).

The prospects for China maintaining its food self-sufficiency in the future are problematic (Brown, 1995; Smil, 1993, 1995). The projected population increase of 100 million people by the year 2000 will be an additional burden on an agricultural system that is already stretched to meet current demand. At the same time, Chinese agriculture will have to cope with the loss of significant lands for cultivation as China's economic development forces the conversion of farmland to other uses (Streets et al., 1995).

A potentially serious complicating factor in China's equation for urbanization and food self-sufficiency is the environment. Although the impacts of future environmental stresses on Chinese agriculture remain largely unassessed, there is every reason to believe that they will be significant. For example, consider the potential effects of climate change. Observations in China indicate that the past few decades' global warming trend has coincided with a significant falloff in precipitation over some of China's most productive rice and wheat fields in the eastern half of the nation (see Figure i.3 ). Such a trend, if it continues, could have devastating effects on a national agricultural system that is highly dependent upon monsoonal rains for irrigation and where "...aridity is (already) a limiting factor threatening...agricultural production in China." (Tao, 1992).

The prospects for China maintaining its food self-sufficiency in the future are problematic.

Moreover, regional and local pollution may already be taking their toll on China's harvests. Tao (1992) estimates that roughly 6.7 million hectares of Chinese farmlands have been impacted by "diverse sources of pollution," causing the loss of about 5% of the nation's annual production of grains. A more quantitative assessment of pollutant effects can be culled from the results of the recent RAINS-ASIA project. In this project, critical (i. e., harmful) loads from sulfur deposition for 14 distinct Asian ecosystems, including rice, other agricultural crops, forests, etc., were calculated (Hettelingh et al., 1991). These critical loads were then compared to model-estimated S deposition rates under present and a variety of future emissions scenarios. The results reveal vast regions of southern and eastern China with low critical loads and thus a susceptibility to damage from acid deposition. Moreover, estimates of sulfur deposition indicate that these regions are receiving deposition in excess of their critical load values (Arndt and Carmichael, 1995).

The projected rapid economic development of China over the next 20-30 years will likely further exacerbate the problem. For example, Galloway et al. (1995) estimate that China will surpass the United States as an emitter of photochemical smog-forming precursors such as nitrogen oxides in the next one to two decades and a recent global modeling study, Chameides et al. (1994), found that these emissions may result in significant increases in the surface ozone concentrations in China. They found that these increases would occur in regions of China that are currently used for agriculture, and concluded that this regional ozone pollution may significantly limit China's food-crop production in the coming decades.

Vast regions of southern and eastern China are susceptible to damage from acid deposition.

Thus the picture of China one or two decades hence filled with burgeoning TVEs, interspersed among the nation's farmlands and fueled by energy derived from burning cheap, high-sulfur coal is a China with enormous air pollution problems that seem bound to impact agriculture negatively. How large will this impact be and what can be done to avert it? On the other hand, what will the role of agriculture be in driving environmental change? These are complex and difficult questions, but nevertheless questions of critical importance that require the attention of the scientific communities.

Because of the critical role meteorology plays in agriculture, any assessment of the viability of China's agriculture must also address the issue of regional climate change. This in turn requires an ability to simulate with reasonable accuracy China's present climatic conditions, in terms of the magnitude, temporal variability, and spatial distribution of key variables such as temperature and precipitation.

Although numerous assessments of regional climate change and its impact upon agriculture have been addressed using global climate models, simulations indicate that, at least for China, these global models do a poor job of replicating basic climatic features in China. For example, consider Figure i.4 , adopted from a preliminary study by Zhou Xiuji (1995). Comparison of observed and model-calculated temperature isopleths over China clearly indicate a tendency for a global climate model (in this case NCAR's Community Climate Model or CCM) to underpredict temperature. On the other hand, a simulation using a mesoscale model (in this case a version of Mesoscale Meteorological Model or MM4) nested within the CCM shows much better agreement with observations. These results suggest that because topographical features and land use characteristics in China occur at scales which are considerably finer than today's global climate models, a regional-scale focus will be required to understand the sub-continent's climate and long-term response to regional and global-scale perturbations.

Another indication of our lack of a comprehensive understanding of climate trends in China comes from an analysis of surface temperature data spanning the 1980s from 160 meteorological stations situated throughout the country (Figure i.5A ). The analysis indicates a striking north/south asymmetry, with a warming trend in the north and a cooling trend over the southeastern portion of the country.

The largest negative temperature anomalies are found over the Sichuan basin ( T ~ -0.4°C) and in the western portion of the Yangtze Delta region (T ~ -0.2°C). Interestingly, the region of cooling in southeastern China closely corresponds to the area in China observed to have the most acidic precipitation (Wang and Wang, 1995). The correspondence of these areas suggests that the cooling has been caused by sulfate aerosols produced as a direct result of S emissions from the area.

Because topographical features and land use characteristics in China occur at scales which are considerably finer than today's global climate models, a regional-scale focus will be required to understand the sub-continent's climate and long-term response to regional and global-scale perturbations.

On the other hand, model simulations give a very different picture. Sulfate loadings over China predicted by both global and regional Chemical Transport Models generally predict maxima running in a north-south direction along the eastern coast of China rather than over southeastern China. (In other words, there is no indication of a north-south asymmetry.) Typical are the sulfate loadings illustrated in Figure i.5B from the simulations of Kasibhatla et al. (1995a). Calculations of the (direct) radiative forcing from sulfate aerosol similarly give no indication of a preponderance of cooling in the southeastern portion of China (see Figure i.5C). Moreover, calculations of the combined radiative forcings from greenhouse gases and sulfate aerosols since the Industrial Revolution yield a positive forcing in southeastern China and only a tiny area in northern China with a negative forcing (see for example Figure i.4.5 in IPCC, 1995). Finally, global climate simulations that calculate the temperature changes caused by the forcing from greenhouse gases and sulfate aerosols generally predict a net warming in southeastern China with a band of cooling in the north, in direct contradiction with the data illustrated in Figure i.5 (see for example, Santeret al., 1995).

Global climate simulations that calculate the temperature changes caused by the forcing from greenhouse gases and sulfate aerosols generally predict a net warming in southeastern China with a band of cooling in the north, in direct contradiction with the data illustrated in Figure i.5.

China is a huge country of diverse physical, chemical, and ecological characteristics. From the point-of-view of evolving Metro-Agro-Plexes, the Yangtze Delta is one of the more interesting regions of this nation. Extending from the mouth of the Yangtze River and the city of Shanghai in the east to the city of Chuzhou in the west, the Yangtze Delta comprises Jiangsu and Zhejiang provinces as well as the eastern half of Anhui Province (see Figure i.6 ). The region contains approximately 85 cities and townships, in addition to its one mega-city, Shanghai. With a population approaching 200 million, the region hosts approximately 530 people per km2, making it the most densely populated area in all of eastern Asia (Leman, 1995). Moreover, its major province, Jiangsu Province, has the distinction of having led China in both grain production and industrial output (Streets et al., 1995). Thus we can think of the Yangtze Delta region as one of the most productive Metro-Agro-Plexes in Asia, if not the world.

The Yangtze Delta is growing economically by leaps and bounds. It has been responsible for fully 25% of China's increased Gross Domestic Product since 1990 and has become a prime target for foreign investment (Leman, 1995). The government plans to create a modern highway system in the region that will link its cities, townships, and rural areas together (and no doubt create the same regional photochemical smog episodes that plague the U.S. ). The projected rapid growth of the Yangtze Delta presents a unique target of opportunity to the scientific community to document, analyze, and better understand the dynamic interactions between economic development, rapid population growth, high-input/high-yield agriculture, and regional and global environmental change.

The participants of the AGCI session agreed that much benefit could be gained from the implementation of an interdisciplinary research project aimed at documenting and analyzing the changes occurring in China in general, and the Yangtze Delta in particular, and assessing the likely impact of these changes on critical ecosystems in the region. It was also recommended that this research be closely aligned with the political and industrial organizations active in the region, in order to maximize the translation of the project findings into new technologies and economic and social policies that foster a sustainable economy and environment.

The Yangtze Delta is very densely populated, leads China in both grain production and industrial output, and is growing economically by leaps and bounds.

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Chameides, W. L., P. S. Kasibhatla, H. Levy. W.J. Moxim, Growth of continental-scale metro-agro-plexes, regional ozone pollution, and world food production, Science, 264:74-77, 1994.

FAO, Agrostat-PC: Production, Computerized Information Series, United Nations, Rome, 1991.

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Kasibhatla, P. S., W. L. Chameides, J. St. John, The seasonal variation in anthropogenic sulfate aerosol from a global chemical transport model and its implications for assessing climate change, to be submitted to J. Geophys. Res., 1995.

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Streets, D., Cung, C., Krummel, J., and Haiping Su, Remote sensing of global change: Growth in China's Jiangsu Province, International Journal of Sustainable Development and World Ecology, 2:1-10, 1995.

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Wang Wenxing and Wang Tao, On the origin and the trend of acid precipitation in China, submitted to J. Water, Air, & Soil, 1995.

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Zhou, Xiuji, Mesoscale modeling of regional climate changes in China, to be submitted for publication, 1995.

Much benefit could be gained from an interdisciplinary research project aimed at documenting and analyzing the changes occurring in China in general, and the Yangtze Delta in particular, and assessing the likely impact of these changes on critical ecosystems in the region.