Earth Systems: Processes and Issues is the ideal textbook for introductory courses in earth systems science and environmental science. Integrating the principles of the natural sciences, engineering, and economics as they pertain to the global environment, it explains the complex couplings and feedback mechanisms linking the geosphere, biosphere, hydrosphere, and atmosphere. An impressive group of internationally respected researchers and lecturers have brought together a vast wealth of teaching experience to produce this fully integrated environmental textbook. It has been designed for the wide range of courses at the first-year university level which touch upon environmental issues: in earth and atmospheric science, environmental science, biological science, oceanography, geography, civil engineering, and social science. Each chapter includes a reading list of the most important references, and problem sets will encourage students to explore the subject further. This text will favorably influence the future development of environmental studies and earth system science.

This paper is the result of a project undertaken in the Institute for International Studies, Stanford University, at the invitation of and with support from the Carnegie Commission on Preventing Deadly Conflict. Donald Kennedy (Center for Environmental Science and Policy) and David Holloway (Center for International Security and Arms Control) were codirectors of the project. Erika Weinthal served as research associate. Walter Falcon, Paul Ehrlich, Roz Naylor, Michael May, Steven Schneider, Stephen Fetter, and Jor-San Choi participated in sessions during which the issues were discussed, drafts developed and criticized, and conclusions reached. The report was written by Donald Kennedy and reviewed by the other collaborators. The team acknowledges with thanks the assistance provided by Jason Robinson, Max Edleson, Elissa Hirsch, and Connie Nelson; the advice provided by the Carnegie Commission staff, especially Jane Holl and Tom Leney; the enthusiastic support of David A. Hamburg; and the helpful contributions of several anonymous reviewers.

GIS analysis was made possible by support for the Center for Conservation Biology gis laboratory from Environmental Systems Research Institute, Inc. Gifts from Peter Bing, Robert Haas, and Jacob Voogd have helped support this and other projects of the Center for Environmental Science and Policy.

Although many fisheries stocks have declined precipitously throughout the world, fish farming--and especially shrimp and salmon farming--has boomed. The increasingly large scale of these enterprises is now having unforeseen ecological consequences on ocean resources through habitat destruction, effluent discharge, exotic species introductions, and heightened fish catch for feed use. Ending unsustainable production practices will require reorienting regulatory policies and fiscal incentives in shrimp- and salmon-producing counties, and enhancing restrictions on environmentally unsound practices.

Nitrogen fertilization is a substantial source of nitrogen-containing trace gases that have both regional and global consequences. In the intensive wheat systems of Mexico, typical fertilization practices lead to extremely high fluxes of nitrous oxide (N2O) and nitric oxide (NO). In experiments, lower rates of nitrogen fertilizer, applied later in the crop cycle, reduced the loss of nitrogen without affecting yield and grain quality. Economic analyses projected this alternative practice to save 12 to 17 percent of after-tax profits. A knowledge-intensive approach to fertilizer management can substitute for higher levels of inputs, saving farmers money and reducing environmental costs.

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.

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.