Annual Review of Environment and Resources - Volume 34, 2009

This article describes the field of the detection and attribution of climate change and highlights recent progress, major issues, and future directions. The attribution of global temperature variations over the past century to a combination of anthropogenic and natural influences is now well established, with the anthropogenic factors dominating. Other aspects of the climate system, including regional quantities, are increasingly being found to also show a detectable signal of human influence. Of particular interest, though, is the attribution of changes in nonmeteorological quantities, such as hydrological and ecological measures, and of changes in the risk of extreme weather events to anthropogenic emissions. Methods are being developed for tackling these two problems but are still in the early stages. As the field gradually includes a service focus, the biggest challenges will become the integration of various approaches into an overall framework and the communication of the capabilities and limitations of that framework to the outside community.

This review focuses on the increasing vulnerability of the world ocean to multiple anthropogenic stresses in the latter half of the twentieth century and the first decade of the twenty-first century. The multiple stresses, which affected the world ocean in the latter half of the twentieth century, could have been controlled on a timescale of decades, had governments and their subjects chosen to do so. In the twenty-first century, the timescale of remediability has been observed to shift from decades to centuries and even to millennia. The major additions to the suite of multiple stresses consist of the combined impacts of changing ocean thermal structure and increasing acidification, both of which are the results of increased anthropogenic CO2 emissions. The consequences of these recent changes are assessed. The assessment makes clear collectively what is known and unknown and what responses are available to human social systems to adapt to these accelerating changes.

Mercury pollution poses global human health and environmental risks. Although mercury is naturally present in the environment, human activities, such as coal burning, have increased the amount of mercury cycling among the land, atmosphere, and ocean by a factor of three to five. Emitted to the atmosphere in its elemental form, mercury travels worldwide before oxidizing to a form that deposits to ecosystems. In aquatic systems, mercury can convert into methylmercury, a potent neurotoxin. People and wildlife are exposed to methylmercury as it bioaccumulates up the food chain. Mercury continues to circulate in the atmosphere, oceans, and terrestrial system for centuries to millennia before it returns to deep-ocean sediments. Areas of uncertainty in the global biogeochemical cycle of mercury include oxidation processes in the atmosphere, land-atmosphere and ocean-atmosphere cycling, and methylation processes in the ocean. National and international policies have addressed direct mercury emissions, but further efforts to reduce risks face numerous political and technical challenges.

Here we review the fundamental interactions between hydrology and the cycling of carbon (C) and nitrogen (N) in terrestrial and stream ecosystems. We organize this review around five commonly studied environments: land-atmosphere interface, soil, groundwater, streams, and headwater catchments. Common among all environments is that hydrological transitions, either episodic changes in water availability or hydrologic transport of reactants, result in disproportionately high rates of C and N cycling. Two major research challenges in coupling hydrological and biogeochemical research are (a) effectively scaling reactions at these spatiotemporal transitions and (b) combining the progress made within each of the five environments listed above into an integrated understanding of hydrobiogeochemical cycles. Changes in local-to-regional hydrological cycling are likely to result in unexpected surprises at the landscape scale until progress in these research areas is made.

Nitrogen (N) is central to living systems, and its addition to agricultural cropping systems is an essential facet of modern crop management and one of the major reasons that crop production has kept pace with human population growth. The benefits of N added to cropping systems come, however, at well-documented environmental costs: Increased coastal hypoxia, atmospheric nitrous oxide (N2O), reactive N gases in the troposphere, and N deposition onto forests and other natural areas are some of the consequences of our inability to keep fertilizer N from leaving cropped ecosystems via unmanaged pathways. The N cycle is complex, and solutions require a thorough understanding of both the biogeochemical pathways of N in agricultural systems and the consequences of different management practices. Despite the complexity of this challenge, however, a number of technologies are available today to reduce N loss. These include adding rotational complexity to cropping systems to improve N capture by crops, providing farmers with decision support tools for better predicting crop fertilizer N requirements, improving methods for optimizing fertilizer timing and placement, and developing watershed-level strategies to recapture N lost from fields. Solutions to the problem of agricultural N loss will require a portfolio approach in which different technologies are used in different combinations to address site-specific challenges. Solutions will also require incentives that promote their adoption.

Nuclear power is confronted with a number of challenges in the near term. One major constraint is the economics of nuclear power, driven by both the high capital costs and financial uncertainties. The second is concern about catastrophic accidents; despite the development of newer reactor designs, the possibility of such an accident has not been completely eliminated. A third is to find a way of disposing nuclear waste that is technically feasible and politically acceptable to the public.

Groundwater plays a major, if often unrecognized, role in both hydrologic and human systems. The majority of the world's drinking water probably comes from groundwater, and in the last half century, there has been an amazing, if largely ignored, boom in agricultural groundwater use that has provided improved livelihoods and food security to billions of farmers and consumers. However, increased use of groundwater has also created problems, and there are fears—sometimes challenged—that the boom may soon turn to bust. This article reviews the recent literature on the geographic and temporal dimensions of groundwater use and the range of technological and institutional approaches that have been applied in attempts at its management. It then examines the key reasons the resource has proven so difficult to manage and concludes that, in many cases, the most promising solutions may lie outside the groundwater sector and within a broader approach to resource systems.

Future trajectories of food prices, food security, and cropland expansion are closely linked to future average crop yields in the major agricultural regions of the world. Because the maximum possible yields achieved in farmers' fields might level off or even decline in many regions over the next few decades, reducing the gap between average and potential yields is critical. In most major irrigated wheat, rice, and maize systems, yields appear to be at or near 80% of yield potential, with no evidence for yields having exceeded this threshold to date. A fundamental constraint in these systems appears to be uncertainty in growing season weather; thus tools to address this uncertainty would likely reduce gaps. Otherwise, short-term prospects for yield gains in irrigated agriculture appear grim without increased yield potential. Average yields in rainfed systems are commonly 50% or less of yield potential, suggesting ample room for improvement, though estimation of yield gaps for rainfed regions is subject to more errors than for irrigated regions. Several priorities for future research are identified.

Irrigated agriculture is the main source of water withdrawals, accounting for around 70% of all the world's freshwater withdrawals. The development of irrigated agriculture has boosted agricultural yields and contributed to price stability, making it possible to feed the world's growing population. Rapidly increasing nonagricultural demands for water, changing food preferences, global climate change, and new demands for biofuel production place increasing pressure on scarce water resources. Challenges of growing water scarcity for agriculture are heightened by the increasing costs of developing new water, soil degradation, groundwater depletion, increasing water pollution, the degradation of water-related ecosystems, and wasteful use of already developed water supplies. This article discusses the role of water for agriculture and food security, the challenges facing irrigated agriculture, and the range of policies, institutions, and investments needed to secure adequate access to water for food today and in the future.

Large-scale anthropogenic changes to the natural environment, including land-use change, climate change, and the deterioration of ecosystem services, are all accelerating. These changes are interacting to generate five major emerging public health threats that endanger the health and well-being of hundreds of millions of people. These threats include increasing exposure to infectious disease, water scarcity, food scarcity, natural disasters, and population displacement. Taken together, they may represent the greatest public health challenge humanity has faced. There is an urgent need to improve our understanding of the dynamics of each of these threats: the complex interplay of factors that generate them, the characteristics of populations that make them particularly vulnerable, and the identification of which populations are at greatest risk from each of these threats. Such improved understanding would be the basis for stepped-up efforts at modeling and mapping global vulnerability to each of these threats. It would also help natural resource managers and policy makers to estimate the health impacts associated with their decisions and would allow aid organizations to target their resources more effectively.

We discuss the challenges confronting environmental governance caused by the increasing connectivity of resource-use systems and the growing functional interdependencies of ecological and social systems. We take as a point of departure the case of the Xingu Indigenous Park (PIX) in Brazil and its surrounding agro-industrial region. This case provides a basis for reviewing the literature on resource governance, including both points of consensus and contentious issues. We argue that no fixed spatial or temporal level is appropriate for governing ecosystems and their services sustainably, effectively, and equitably. We point to the need to recognize the multilevel nature of such problems and the role of institutions in facilitating cross-level environmental governance as an important form of social capital that is essential for the long-term protection of ecosystems and the well-being of different populations.

As the world's economies become more integrated and the global economy subsequently grows, there is increasing concern regarding how such trends will affect the environment. In fact, the relationship between globalization and the environment has become quite contentious in policy circles. In part in response to these controversies, a burgeoning amount of academic attention has emerged that examines the globalization/environment nexus. Although there have been advances in the thinking about these relationships, significant challenges remain. This article provides a critical taxonomy that will help scholars better understand the overwhelming literature on the subject and also outlines the key challenges that scholars and policy makers will face for a second wave of thinking on the subject.

Voluntary environmental programs (VEPs) seek to improve the environment by encouraging, rather than mandating, businesses and other organizations to adopt environmentally protective measures. Since the 1990s, VEPs established by industry, government, and nongovernmental organizations have proliferated around the globe, raising the question of how effective these programs are in securing environmental protection, both on their own and in comparison to traditional mandatory regulations. This article reviews the emerging research literature on VEPs, describing the variation in their structures, providing a framework for assessing their impacts, and summarizing what is known about why organizations engage in voluntary environmental action and what effects these programs have on environmental quality.

There have been significant improvements over the past four decades in our ability to estimate the economic value of environmental amenities and disamenities. The development of many new techniques has broadened what can be measured to include climate change impacts, damages from hazardous waste sites and air pollution emissions, and the value of many ecosystem services. We review the major economic valuation techniques, as well as numerous applications of these valuation methods. However, there remain challenges ahead. The interface between economics and the natural and physical sciences must be strengthened. Additional well-controlled “natural experiments” are always needed. The application of valuation methods outside of the United States remains a monumental task. Reliable measures of nonuse values remain elusive.

Infrastructure is the foundation on which industrialized economies are built. As global population has grown and as economies of many regions have expanded, the quantity and scale of infrastructure has increased dramatically. Although some infrastructure is used to move people and commodities, much infrastructure is also used to control natural processes or to extract natural resources. Thus, understanding environmental change necessitates understanding the role of infrastructure in the environment. We review available inventories of infrastructure and current understanding of environmental impacts for different types of infrastructure. We also examine the current status of aging infrastructure and the potential environmental impacts and benefits of infrastructure decommissioning. Finally, we briefly review policies that have facilitated or inhibited infrastructure decommissioning or environmentally oriented modifications of infrastructure operation.

We review the development of macroenvironmental indicators, an effort driven by a combination of improved understanding of the functioning of Earth's natural systems at large spatial and temporal scales and of increasing demands by an expanding human population for goods and services provided by ecosystems. To be credible, macroenvironmental indicators need to be based on established scientific concepts and supported by extensive data. To be adopted, they need to serve the interests of diverse stakeholders and be perceived as unbiased. The baselines against which they are evaluated must be clear. A modest number of macroindicators of abiotic natural capital, biotic natural capital, and ecological functioning are currently in use. Some of them are designed to report on trends in legislatively mandated goals and standards. Most environmental indicators, however, report on specific components of the environment at small scales. They are not readily aggregated to form synthetic macroenvironmental indicators.

The article reviews two decades of scholars' claims that exposures to pollution and other environmental risks are unequally distributed by race and class, examines case studies of environmental justice social movements and the history and politics of environmental justice policy making in the United States, and describes the emerging issue of global climate justice. The authors engage the contentious literature on how to quantitatively measure and document environmental injustice, especially the complex problems of having data of very different types and areas (such as zip codes, census tracts, or concentric circles) around polluting facilities or exposed populations. Also considered is the value of perspectives from critical race theory and ethnic studies for making sense of these social phenomena. The article concludes with a discussion of the globalization of the environmental justice movement, discourse, and issues, as well as with some policy implications of finding and understanding environmental justice. One unique feature of this review is its breadth and diversity, given the different approaches taken by the three coauthors.

This review article surveys the role of the media in communicating environmental issues. Media representations—from news to entertainment—provide critical links between formal environmental science and politics and the realities of how people experience and interact with their environments. People abundantly turn to media—such as television, newspapers, magazines, radio, and Internet—to help make sense of the many complexities relating to environmental science and governance that (un)consciously shape our lives. I examine how multiscale factors have shaped media coverage in complex, dynamic, and nonlinear ways. These inquiries are situated in historical context as well as in larger processes of cultural politics and environmental change. Discussions here also touch on how media portrayals influence ongoing public understanding and engagement. Connections between media information and behaviors are not straightforward, as coverage does not determine engagement. Nonetheless, this article explores how media reports influence the spectrum of possibilities for different forms of environmental governance.