Expansion and intensification of cultivation are among the predominant global changes of this century. Intensification of agriculture by use of high-yielding crop varieties, fertilization, irrigation, and pesticides has contributed substantially to the tremendous increases in food production over the past 50 years. Land conversion and intensification, however, also alter the biotic interactions and patterns of resource availability in ecosystems and can have serious local, regional, and global environmental consequences. The use of ecologically based management strategies can increase the sustainability of agricultural production while reducing off-site consequences.

The race between population and food is a classic theme, yet the outcome of this contest is of enduring contemporary interest. Interestingly, the two variables that are set opposite one another in the race are fundamentally different in character. Population is primarily a stock concept that rises monotonically (when births exceed deaths), whereas food production is overwhelmingly a flow variable that exhibits substantial year-to-year fluctuations. These latter fluctuations, in turn, cause significant economic and nutritional consequences at the household level. The changes are especially important for the poor, even beyond the consequences caused by trend levels of food consumption per capita. In addition, amplifications of price and production variability often produce compensating changes in national food policies. If countries seek to stabilize domestic grain prices, the unintended effect of these actions is further destabilization of global grain markets.

This review explores the potential energy, soil, and water constraints on highly productive agricultural systems. It focuses on the process of agricultural intensification during the past 50 years, and it shows that multiple constraints-as opposed to a single constraint, such as energy-are needed to assess the future sustainability of intensive agricultural production. Recent studies documenting changes in total factor productivity based on long-term experimental trials and field surveys are discussed in detail. The results of these studies are worrisome; they indicate that degradation in soil quality and in the overall natural resource base may threaten the long-run viability of several of the world's most intensive agricultural systems. Other studies are reviewed that support a more optimistic view of resource availability and the ability of improved technology and management to overcome these physical constraints. However, the combined evidence suggests that the increase in agricultural prices required to induce the necessary changes in technology could be devastating to low-income households. Most of the world's poor consume more agricultural output than they produce, and they spend up to 80% of their incomes on food.

Urbanization is now a dominant demographic phenomenon in low- and middle-income countries. By the year 2000, half of the world's population will live in urban areas; of this half, two thirds will be in developing countries, predominantly in Asia. Whether there will be a corresponding shift of poverty from rural to urban areas is the central question of this analysis. Evidence from cross-sectional, time-series, and case data indicates that the percent of poverty in urban areas is dependent on income levels, income growth, and income distribution. The evidence also indicates that the number of poor in rural areas will exceed those in urban areas well into the 21st century. These poverty and urbanization trends are significant politically, and important also with respect to food policy and required investments in agriculture.

All too often, researchers in the academic world find themselves cut off from their colleagues in other disciplines by the level of specialization required in their own fields. The gap between the social and physical sciences, in particular, seems unbridgeable to many scholars. Yet many of the problems confronting the world today demand an integrated approach.

The vast issue of global change -- encompassing changes in atmospheric carbon dioxide and the possibility of global warming, or the dramatic increases in world population and consequent increased pressures on land use and on political systems -- demands a problem-solving approach that integrates our knowledge about the nature of human interaction and activity with the scientific knowledge we have gained on atmospheric, oceanic, and terrestrial patterns of interaction.

Ecological and Social Dimensions of Global Change, published by the Institute of International Studies as part of its "Insights in International Affairs" series, is a collection of lectures by leading physical and social scientists and international legal experts on the implications of global changes in climate and in population, migration, and land use. (See the Table of Contents.) These lectures also examine the responses of the international legal and political communities to these complex changes.

The volume is composed of thirteen talks from an interdisciplinary graduate seminar conducted at the University of California at Berkeley in the fall of 1992. The evolution of this seminar provides a cogent example of how research from a specific field, brought into an interdisciplinary teaching arena, becomes enriched by the input from researchers in other fields. The seminar as originally conceived focused primarily on the ecological dimensions of global change, but the numerous and fundamental links of any given ecological issue to its surrounding social circumstances persuaded the organizers to expand the focus to include the social dimensions of these problems as well. Both the physical and social scientists involved in the seminar subsequently incorporated knowledge gained from their colleagues into their own fields of study. In addition, seminar participants in the fields of legal and political policy-making were able to integrate each discipline's contributions into the prescriptions that they offered for the problem of global change. During the course of the development of this book from the lecture series, commentaries by scholars from a different academic field were added to a few of the original lectures, further broadening the focus.

Following each of the lectures is a transcription of the discussion from the classes which deepen and elaborate some of the key theoretical, methodological, and policy questions raised by the lecturer. In addition, a short bibliography and further questions for class discussion are suggested, making this an ideal text for coursework on the subject of global change. Each section of the book -- the ecological dimensions, the social dimensions, and policy and legal responses -- is preceded by a short introduction to the central ideas encompassed by the contributors to that section.