Humans have changed ecosystems more rapidly and extensively in the last 50 years than in any comparable period of human history. We have done this to meet the growing demands for food, fresh water, timber, fiber, and fuel. While changes to ecosystems have enhanced the well-being of billions of people, they have also caused a substantial and largely irreversible loss in diversity of life on Earth, and have strained the capacity of ecosystems to continue providing critical services.

Richly illustrated with maps and graphs, Current State and Trends presents an assessment of Earth's ability to provide twenty-four distinct services essential to human well-being. These include food, fiber, and other materials; the regulation of the climate and fresh water systems, underlying support systems such as nutrient cycling, and the fulfillment of cultural, spiritual, and aesthetic values. The volume pays particular attention to the current health of key ecosystems, including inland waters, forests, oceans, croplands, and dryland systems, among others. It will be an indispensable reference for scientists, environmentalists, agency professionals, and students.

Wheat yields in Mexico, which represent an important measure of breeding and management progress in developing world wheat production, have increased by 25% over the past two decades. Using a combination of mechanistic and statistical models, we show that much of this increase can be attributed to climatic trends in Northwest states, in particular cooling of growing season nighttime temperatures. This finding suggests that short-term prospects for yield progress are smaller than suggested by recent yield increases, and that future gains will require an intensification of research and extension efforts aimed at raising wheat yields.

Global meat production is becoming increasingly industrialized, spatially concentrated, and geographically detached from the agricultural land base. This Policy Forum reviews the process of livestock industrialization and globalization, and its consequences for water, nitrogen, and species-rich habitats in meat- and feed-producing regions often vastly separated in space. It argues that pricing and other policy mechanisms which reflect social costs of resource use and ecological change are needed to re-couple livestock and land in producer countries, drawing on examples from Europe and the United States. It also argues that consumers can play an important role in setting a sustainable course.

The combined forces of El NinoSouthern Oscillation (ENSO) eventsand global warming are likely to have dramatic effects on future cropproduction and food security in Indonesia and other tropical countries.Indonesia consistently experiences dry climatic conditions and droughtsduring El Nino events, resulting in delayed production of rice—thecountry’s primary food staple—and exacerbated problems of foodinsecurity among the poor. Our preliminary analysis suggests thatglobal climate change could cause Indonesia’s “normal” climate state tobe similar to an El Nino state currently. Unfortunately, globalclimate models (GCMs) link poorly to regional hydrologic conditions in thetropics, and have limited coverage of the Indonesian archipelago, excludingareas representing 75% of the population and 66% of the riceproduction (Figure 1). Therefore results from the GCM need to befurther “downscaled” to understand the effects of global climate changeon Indonesian hydrology and agriculture.

Global society is seriously threatened by the environmental impacts of human activities. Although the Millennium Ecosystem Assessment and the Intergovernmental Panel on Climate Change have been established to analyze biophysical aspects of global change, there is no equivalent effort to assess the role of individual behavior in creating those environmental threats. The authors of this Policy Forum propose the institution of a Millennium Assessment of Human Behavior to establish serious dialogues about what can and should be done. It would draw heavily on social scientists and would engage groups of citizens globally in public forums to explore the moral elements and the consequences of choices about environmental change.

Improved understanding of the factors that limit crop yields in farmers' fields will play an important role in increasing regional food production while minimizing environmental impacts. However, causes of spatial variability in crop yields are poorly known in many regions because of limited data availability and analysis methods. In this study, we assessed sources of between-field wheat (Triticum aestivum L.) yield variability for two growing seasons in the Yaqui Valley, Mexico. Field surveys conducted in 2001 and 2003 provided data on management practices for 68 and 80 wheat fields throughout the Valley, respectively, while yields on these fields were estimated using concurrent Landsat satellite imagery. Management-yield relationships were analyzed with t tests, linear regression, and regression trees, all of which revealed significant but year-dependent impacts of management on yields. In 2001, an unusually cool year that favored high yields, N fertilizer was the most important source of between-field variability. In 2003, a warmer year with reduced irrigation water allocations, the timing of the first postplanting irrigation was found to be the most important control. Management explained at least 50% of spatial yield variability in both years. Regression tree models, which were able to capture important nonlinearities and interactions, were more appropriate for analyzing yield controls than traditional linear models. The results of this study indicate that adjustments in management can significantly improve wheat production in the Yaqui Valley but that the relevant controls change from year to year.

Increased efficiency of nitrogen (N) fertilizer use may be achieved with management practices that account for spatial variability in soil properties and temporal variability in climate. In this study, we develop a N management decision model for an irrigated wheat system that incorporates hypothetical diagnostics of soil N and growing season climate. The model is then used to quantify the potential value of these forecasts with respect to wheat yields, farmer profits, and excess N application. Under the current scenario (i.e. no diagnostics), uncertainty in soil and climate conditions is shown to account for an average overapplication of N by roughly 35%. Both soil diagnostics and climate forecasts are shown to increase profits significantly and decrease over-application of N, with minimal changes in yield. Soil variability is roughly three times as important as climate variations in terms of potential impact on profits in this region. The model was also used to simulate the effect of increases in fertilizer price, which have similar positive effects on excess N application but negative impacts on profits. Finally, the role of forecast uncertainty was evaluated, indicating that even limited information on soil or climate can be a useful input to management decisions. Future work is needed to improve operational diagnostics of soil N and growing season climate, whose cost can then be compared to benefits calculated in this study to determine their net value to N management decisions.