Elements of Change 1995: Session III Roz Naylor

This AGCI session on "The Metro-Agro-Plex" grew out of a paper published in Science 264 : 74+, 1994 by Bill Chameides and colleagues, as well as previous AGCI sessions. The focus of this work is on three regions of the northern mid-latitudes that dominate global industrial and agricultural productivity; although the regions cover only 23% of the Earth's continents, they account for most of the world's commercial energy consumption, fertilizer use, food crop production, and food exports. These regions also account for more than one-half of global atmospheric nitrogen oxide emissions and are thus prone to high levels of tropospheric ozone pollution during certain periods of the year. Chameides et al. used global simulation models of atmospheric reactive nitrogen compounds to show that between 9 and 35% of the world's cereal crops are presently exposed over the growing season to average ozone concentrations above a damage threshold of 50-70 ppbv which could significantly lower crop productivity. They estimate that by the year 2020, as much as 30 to 75% of global cereal production will be exposed to potentially damaging thresholds of ozone concentrations.

By the year 2020, as much as 30 to 75% of global cereal production will be exposed to potentially damaging thresholds of ozone concentrations.

The major goals of this AGCI session are to look more closely at nitrogen, carbon, and sulfur cycles in the context of urban/industrial and agricultural development; to expand the use of the Metro-Agro-Plex (MAP) to investigate competition for land and water resources between urban/industrial and agricultural sectors; and to explore how the growth in MAPs in developing regions of the world are affecting the global food economy. Developing countries are of particular interest in this context because a significant decline in agricultural productivity resulting from high concentrations of tropospheric ozone, other air pollutants, or resource constraints could have important impacts on food prices, rural incomes, and the incidence of hunger. In addition, urbanization rates in the developing world are much higher than in the currently industrialized world. By 2025, an estimated 5.2 billion people will be living in cities; 4 billion of these people will be in developing countries (Table 14.1 ). Of the 21 cities projected to have populations of over 10 million in the year 2000, 17 will be in the developing world and more than one-half will be in Asia (Table 14.2 ).

During the past 35 years, over 90% of global production growth in cereals has been attributed to yield increases and less than 10% to area expansion.

China was chosen as a special case study for this AGCI session because of its overwhelming importance in the world food economy, its extremely rapid rate of agricultural, urban and industrial growth, and its high level of dependence on soft coal for economic development. The combination of these factors serves as an excellent model for studying the dynamics of the MAP.

Three questions are particularly interesting in considering the relation between China's MAPs and the world food economy:

Both the socio-economic and the physical dimensions of these issues are of interest in this AGCI session.

China plays a major role in the world food economy in terms of production as well as consumption. For example, it accounts for about 1/5 of the global output of rice, wheat, corn, soybeans, and peanuts, and it has substantially higher yields particularly in the case of cereals than the global average (Table 14.3 ). China also has an extremely limited arable land base per capita compared with the global average. Its per capita arable land base is small even compared with the average for Asia, which, as a region, is very densely populated. As a result, China has intensified its agricultural production by growing more crops per year per hectare and achieving higher yields per hectare for individual crops. This intensification process is characteristic of agricultural development for the world as a whole; during the past 35 years, over 90% of global production growth in cereals has been attributed to yield increases and less than 10% to area expansion.

A main tenant of the agricultural intensification process during this period has been the introduction and dissemination of Green Revolution seed technologies for staple crops, such as rice and wheat, in the developing world. The modern plant varieties have been designed with a new architecture that is capable of taking up more nitrogen inputs and allocating a higher share of nutrients to grain production as opposed to plant biomass production. Global nitrogen fertilizer applications have increased substantially as a result (Table 14.4 ). Despite research efforts to improve nitrogen uptake efficiency, only 40-60% of the applied nitrogen is actually taken up by the plant in most rice and wheat systems. The rest is lost to the environment through various pathways such as nitrification, denitrification, and ammonia volatilization. Nitrogen loss from fertilization has important implications for ground water quality, tropospheric ozone concentrations, the accumulation of nitrous oxide in the stratosphere, and the destruction of the stratospheric ozone layer. Its potential effects on ecosystem processes and atmospheric chemistry are significant at local, regional, and global scales.

One of the most important dietary changes in the region is the increase in meat consumption. About 2 to 5 times more grain is required to produce the same amount of calories through livestock as through direct grain consumption (and as much as 10 times in the case of grain-fed beef in the U. S.).

Given the large and growing use of nitrogen fertilizers in China shown in Table 14.4, it is clear that China has the potential to substantially alter regional and global nitrogen balances. It is also likely that the agricultural sector in China will increasingly contribute to tropospheric ozone concentrations in the region which, in turn, could lower agricultural productivity itself. Whether or not ozone originating from agricultural and industrial processes will significantly alter Chinese agricultural yields is not yet known. Other factors that could lower agricultural productivity include water constraints, soil erosion, climate change, and pest outbreaks. A decline in investments and producer incentives in the farm sector could also reduce productivity. Indeed, a major debate concerning future agricultural output is whether biotic and abiotic constraints are more or less important than policy changes in terms of their impact on future productivity growth.

In order to understand the role of food and agriculture as a driving force of biogeochemical and atmospheric change in China, it is necessary to study the dynamics of consumption as well as production. One of the most important dietary changes in the region is the increase in meat consumption. This switch from direct to indirect (livestock-based) grain consumption is common in most countries (with the exception, for instance, of India) as per capita incomes rise. Although China consumes much less meat per capita than industrialized countries, it consumes measurably more than some of its southeast Asian neighbors. For example, per capita meat consumption in China is currently about 25 kilograms per person per year and rising rapidly, whereas in Indonesia, per capita meat consumption is only 5 to 6 kg/person/year.

What happens in China in terms of grain production, consumption, and trade is important for the world food economy as a whole.

The emergence of China as a livestock economy has implications for nitrogen fertilizer use, nitrate leaching and ammonia loss from animals, and grain balances in the country. About 2 to 5 times more grain is required to produce the same amount of calories through livestock as through direct grain consumption (and as much as 10 times in the case of grain-fed beef in the U.S.). As meat consumption increases, therefore, China's grain requirements will also increase. This trend will place pressure on the country to produce more grain (with more fertilizer) or to import more grain. China's feed grain imports are already rising; in 1994/95, it purchased most of the U.S. surplus corn production. The rising demand for feed grains in Asia more generally has caused the region to become a major cereal importer (Table 14.5 ).

Given the increasing population- and income-driven demand for grains in China, any significant decline in the level or rate of growth in domestic productivity of cereals could dramatically affect prices both within China and in world markets. If environmental or resource constraints were to force the country to purchase an increasing share of its grain needs in world markets, for example, international grain prices would probably increase, and poor countries like those in Sub-Saharan Africa might not be able to afford grain imports in the short run. A more likely scenario one which is already being played out to some extent is that changes in agricultural policy and a decline in economic incentives to agricultural producers in China will cause the country to enter more predominantly into world grain markets. In either case, it is clear that what happens in China in terms of grain production, consumption, and trade is important for the world food economy as a whole. Similarly, what happens in China in terms of alterations in biogeochemical cycles and atmospheric chemistry is important for regional and global environmental change.