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Precipitation falling onto the land surface in terrestrial ecosystems is transformed into either “green water” or “blue water.” Green water is the portion stored in soil and potentially available for uptake by plants, whereas blue water either runs off into streams and rivers or percolates below the rooting zone into a groundwater aquifer. The principal flow of green water is by evapotranspiration from soil into the atmosphere, whereas blue water moves through the channel system at the land surface or through the pore space of an aquifer. Globally, the flow of green water accounts for about two-thirds of the global flow of all water, green or blue; thus the global flow of green water, most of which is by transpiration, dominates that of blue water. In fact, the global flow of green water by transpiration equals the flow of all the rivers on Earth into the oceans.
At the global scale, evapotranspiration is measured using a combination of ground-, satellite-, and model-based methods implemented over annual or monthly time-periods. Data are examined for self-consistency and compliance with water- and energy-balance constraints. At the catchment scale, average annual evapotranspiration data also must conform to water and energy balance. Application of these two constraints, plus the assumption that evapotranspiration is a homogeneous function of average annual precipitation and the average annual net radiative heat flux from the atmosphere to the land surface, leads to the Budyko model of catchment evapotranspiration. The functional form of this model strongly influences the interrelationship among climate, soil, and vegetation as represented in parametric catchment modeling, a very active area of current research in ecohydrology.
Green water flow leading to transpiration is a complex process, firstly because of the small spatial scale involved, which requires indirect visualization techniques, and secondly because the near-root soil environment, the rhizosphere, is habitat for the soil microbiome, an extraordinarily diverse collection of microbial organisms that influence water uptake through their symbiotic relationship with plant roots. In particular, microbial polysaccharides endow rhizosphere soil with properties that enhance water uptake by plants under drying stress. These properties differ substantially from those of non-rhizosphere soil and are difficult to quantify in soil water flow models. Nonetheless, current modeling efforts based on the Richards equation for water flow in an unsaturated soil can successfully capture the essential features of green water flow in the rhizosphere, as observed using visualization techniques.
There is also the yet-unsolved problem of upscaling rhizosphere properties from the small scale typically observed using visualization techniques to that of the rooting zone, where the Richards equation applies; then upscaling from the rooting zone to the catchment scale, where the Budyko model, based only on water- and energy-balance laws, applies, but still lacks a clear connection to current soil evaporation models; and finally, upscaling from the catchment to the global scale. This transitioning across a very broad range of spatial scales, millimeters to kilometers, remains as one of the outstanding grand challenges in green water ecohydrology.
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.
There are three important linkages to explore between climate change and health in terms of potential policy responses. The first of these linkages relates to the impacts on health resulting from climate change. In 2009, The Lancet described climate change as “the greatest global health threat of the 21st century,” referencing the direct and indirect effects it is having on public health. While a number of impacts are directly observable (i.e., an increased frequency and severity of many extreme weather events), others are more indirect, being mediated through environmental and social systems (i.e., the health complications associated with mass migration or violent conflict). Further, it is well understood that resilience and adaptive capacity play an important role in reducing these impacts—often leaving low-income communities worse off than most.
The second important linkage between climate change and health relates to the co-benefits of mitigation and adaptation. Policy responses to climate change will inevitably come with both intended and unforseen externalities and “side-effects” (both positive and negative). Traditional public health tools, such as health impact assessment, can be valuable in identifying and understanding these co-benefits to better guide policy. Indeed, many of the mitigation solutions yield substantial benefits for public health: switching away from coal-fired power plants as an energy choice improves cardiovascular and respiratory health; designing cities which are cycle- and pedestrian-friendly increases rates of physical activity (helping to tackle obesity, diabetes, many cancers, and heart disease) while also reducing greenhouse gas emissions from vehicles.
Finally, the health system itself has an important role in responding directly to climate change. This is frequently understood in terms of a health facility’s ability to withstand and respond to the impacts of climate change, and to the adaptive capacity of the health system itself. But there is also a role for the health system to play in reducing its own emissions. In countries like the United Kingdom and the United States, the formal health system is responsible for as much as 3–8% of national emissions, and has subsequently made commitments to reduce its environmental impact. A 2013 review of the UK National Health Service’s carbon footprint indicated that as much as 60% of this came from procurement, 17% from building energy, and 13% from health system–related transport. A number of the solutions available are often designed in a way that improves patient outcomes and satisfaction, while reducing the costs of healthcare. In low- and middle-income countries, the focus is placed on ensuring access to reliable electricity, a task well suited to decentralized micro-grids with sustainable power generation.
Academic literature on the topic of health and climate change has expanded rapidly in recent years and includes the 2009 and 2015 Lancet Commissions on health and climate change, the 2010 series on the health co-benefits of mitigation, and the 2014 Intergovernmental Panel on Climate Change’s 5th Assessment Report.
Richard G. Lawford and Sushel Unninayar
The global water cycle concept has its roots in the ancient understanding of nature. Indeed, the Greeks and Hebrews documented some of the most some important hydrological processes. Furthermore, Africa, Sri Lanka, and China all have archaeological evidence to show the sophisticated nature of water management that took place thousands of years ago. During the 20th century, a broader perspective was taken and the hydrological cycle was used to describe the terrestrial and freshwater component of the global water cycle. Data analysis systems and modeling protocols were developed to provide the information needed to efficiently manage water resources. These advances were helpful in defining the water in the soil and the movement of water between stores of water over land surfaces. Atmospheric inputs to these balances were also monitored, but the measurements were much more reliable over countries with dense networks of precipitation gauges and radiosonde observations.
By the 1960s, early satellites began to provide images that gave a new perception of Earth processes, including a more complete realization that water cycle components and processes were continuous in space and could not be fully understood through analyses partitioned by geopolitical or topographical boundaries. In the 1970s, satellites delivered quantitative radiometric measurements that allowed for the estimation of a number of variables such as precipitation and soil moisture. In the United States, by the late 1970s, plans were made to launch the Earth System Science program, led by the National Aeronautics and Space Agency (NASA). The water component of this program integrated terrestrial and atmospheric components and provided linkages with the oceanic component so that a truly global perspective of the water cycle could be developed. At the same time, the role of regional and local hydrological processes within the integrated “global water cycle” began to be understood.
Benefits of this approach were immediate. The connections between the water and energy cycles gave rise to the Global Energy and Water Cycle Experiment (GEWEX)1 as part of the World Climate Research Programme (WCRP). This integrated approach has improved our understanding of the coupled global water/energy system, leading to improved prediction models and more accurate assessments of climate variability and change. The global water cycle has also provided incentives and a framework for further improvements in the measurement of variables such as soil moisture, evapotranspiration, and precipitation. In the past two decades, groundwater has been added to the suite of water cycle variables that can be measured from space. New studies are testing innovative space-based technologies for high-resolution surface water level measurements. While many benefits have followed from the application of the global water cycle concept, its potential is still being developed. Increasingly, the global water cycle is assisting in understanding broad linkages with other global biogeochemical cycles, such as the nitrogen and carbon cycles. Applications of this concept to emerging program priorities, including the Sustainable Development Goals (SDGs) and the Water-Energy-Food (W-E-F) Nexus, are also yielding societal benefits.
Erin N. Haynes, Lisa McKenzie, Stephanie A. Malin, and John W. Cherrie
Technological advances in directional well drilling and hydraulic fracturing have enabled extraction of oil and gas from once unobtainable geological formations. These unconventional oil and gas extraction (UOGE) techniques have positioned the United States as the fastest-growing oil and gas producer in the world. The onset of UOGE as a viable subsurface energy abstraction technology has also led to the rise of public concern about its potential health impacts on workers and communities, both in the United States and other countries where the technology is being developed. Herein we review in the national and global impact of UOGE from a historical perspective of occupational and public health. Also discussed are the sociological interactions between scientific knowledge, social media, and citizen action groups, which have brought wider attention to the potential public health implications of UOGE.
Céline Granjou and Isabelle Arpin
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.
The recent implementation of the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) is a major cornerstone of the transformation of international environmental governance in the early 21st century. Often presented as “the Intergovernmental Panel on Climate Change (IPCC) for biodiversity,” the IPBES aims to produce regular expert assessments of the state and evolution of biodiversity and ecosystems at the local, regional, and global levels. Its creation was promoted in the 1990s by biodiversity scientists and nongovernmental organizations (NGOs), that increasingly came to view the failure of achieving effective conservation of biodiversity and ecosystems as the consequence of the gap between science and policy rather than lack of knowledge. Articulating and building new proximities between nature conservation and social development was thus viewed from the beginning as critical to creating the new platform. The IPBES creation process was also rooted in the idea that biodiversity conservation required the implementation of a science-policy interface in which governments would be truly involved, in a similar way as in the IPCC. From 2008 onward, the project was called IPBES, a name that referred to the notion of ecosystem services, defined and popularized by the Millennium Ecosystem Assessment as the services that ecosystems render to people. Its creation was entrusted to the United Nations Environment Programme (UNEP).
The relevance, organization, and missions of the new institution were strongly discussed and debated in a series of multistakeholder meetings convened by the UNEP from 2008 up to the official creation of the IPBES in 2012. Social science scholarship highlighted two main tensions in the genesis and further implementation of the IPBES. The first opposed various views of what counts as legitimate knowledge on biodiversity and ecosystems: while promoters of a “purified science” standard aimed to achieve a science-based institution drawing on peer-reviewed expert opinions (following the model of academic science), promoters of a more open and inclusive definition of biodiversity knowledge promoted a broader recognition of the relevance of types of knowledge beyond academia, such as that of “traditional ecological knowledge.” The second tension concerned two contrasted conceptions of nature and human/nature relations, opposing the ecosystem services framework promoted by Western countries and inspired by the Millennium Ecosystem Assessment and the Mother Earth notion promoted by a number of South-American countries. While some of the research scrutinizing how the IPBES addressed these tensions insisted on the supremacy of Western utilitarian approaches to nature embodied in the notion of ecosystem services, other social scientists emphasized that the IPBES endeavored to encompass the various approaches to nature and to handle them through the experimentation of new inclusive organizations and notions. They also emphasized that bridging science and policy is a collective, ongoing, and fragile achievement that requires diplomatic skills of the institutional leaders so that they can handle the shifting tensions between the participants and build a truly inclusive platform. The IPBES may thus be considered a new, emergent institutional model for organizing science/policy interfaces in the early 21st century, focusing on the production of assessments both scientifically robust and socially inclusive in order to address the unprecedented threats to biodiversity and ecosystems in a time of global change.
Edward B. Barbier
Globally, around 1.5 billion people in developing countries, or approximately 35% of the rural population, can be found on less-favored agricultural land (LFAL), which is susceptible to low productivity and degradation because the agricultural potential is constrained biophysically by terrain, poor soil quality, or limited rainfall. Around 323 million people in such areas also live in locations that are highly remote, and thus have limited access to infrastructure and markets. The households in such locations often face a vicious cycle of declining livelihoods, increased ecological degradation and loss of resource commons, and declining ecosystem services on which they depend. In short, these poor households are prone to a poverty-environment trap. Policies to eradicate poverty, therefore, need to be targeted to improve the economic livelihood, productivity, and income of the households located on remote LFAL. The specific elements of such a strategy include involving the poor in paying for ecosystem service schemes and other measures that enhance the environments on which the poor depend; targeting investments directly to improving the livelihoods of the rural poor, thus reducing their dependence on exploiting environmental resources; and tackling the lack of access by the rural poor in less-favored areas to well-functioning and affordable markets for credit, insurance, and land, as well as the high transportation and transaction costs that prohibit the poorest households in remote areas to engage in off-farm employment and limit smallholder participation in national and global markets.
Simon Holdaway and Rebecca Phillipps
Northeast Africa forms an interesting case study for investigating the relationship between changes in environment and agriculture. Major climatic changes in the early Holocene led to dramatic changes in the environment of the eastern Sahara and to the habitation of previously uninhabitable regions. Research programs in the eastern Sahara have uncovered a wealth of archaeological evidence for sustained occupation during the African Humid Period, from about 11,000 years ago. Initial studies of faunal remains seemed to indicate early shifts in economic practice toward cattle pastoralism. Although this interpretation was much debated when it was first proposed, the possibility of early pastoralism stimulated discussion concerning the relationships between people and animals in particular environmental contexts, and ultimately led to questions concerning the role of agriculture imported from elsewhere in contrast to local developments. Did agriculture, or indeed cultivation and domestication more generally (sensu Fuller & Hildebrand, 2013), develop in North Africa, or were the concepts and species imported from Southwest Asia? And if agriculture did spread from elsewhere, were just the plants and animals involved, or was the shift part of a full socioeconomic suite that included new subsistence strategies, settlement patterns, technologies, and an agricultural “culture”? And finally, was this shift, wherever and however it originated, related to changes in the environment during the early to mid-Holocene?
These questions refer to the “big ideas” that archaeologists explore, but before answers can be formed it is important to consider the nature of the material evidence on which they are based. Archaeologists must consider not only what they discover but also what might be missing. Materials from the past are preserved only in certain places, and of course some materials can be preserved better than others. In addition, people left behind the material remains of their activities, but in doing so they did not intend these remains to be an accurate historical record of their actions. Archaeologists need to consider how the remains found in one place may inform us about a range of activities that occurred elsewhere for which the evidence may be less abundant or missing. This is particularly true for Northeast Africa where environmental shifts and consequent changes in resource abundance often resulted in considerable mobility. This article considers the origins of agriculture in the region covering modern-day Egypt and Sudan, paying particular attention to the nature of the evidence from which inferences about past socioeconomies may be drawn.
Christopher Morgan, Shannon Tushingham, Raven Garvey, Loukas Barton, and Robert Bettinger
At the global scale, conceptions of hunter-gatherer economies have changed considerably over time and these changes were strongly affected by larger trends in Western history, philosophy, science, and culture. Seen as either “savage” or “noble” at the dawn of the Enlightenment, hunter-gatherers have been regarded as everything from holdovers from a basal level of human development, to affluent, ecologically-informed foragers, and ultimately to this: an extremely diverse economic orientation entailing the fullest scope of human behavioral diversity. The only thing linking studies of hunter-gatherers over time is consequently simply the definition of the term: people whose economic mode of production centers on wild resources. When hunter-gatherers are considered outside the general realm of their shared subsistence economies, it is clear that their behavioral diversity rivals or exceeds that of other economic orientations. Hunter-gatherer behaviors range in a multivariate continuum from: a focus on mainly large fauna to broad, wild plant-based diets similar to those of agriculturalists; from extremely mobile to sedentary; from relying on simple, generalized technologies to very specialized ones; from egalitarian sharing economies to privatized competitive ones; and from nuclear family or band-level to centralized and hierarchical decision-making. It is clear, however, that hunting and gathering modes of production had to have preceded and thus given rise to agricultural ones. What research into the development of human economies shows is that transitions from one type of hunting and gathering to another, or alternatively to agricultural modes of production, can take many different evolutionary pathways. The important thing to recognize is that behaviors which were essential to the development of agriculture—landscape modification, intensive labor practices, the division of labor and the production, storage, and redistribution of surplus—were present in a range of hunter-gatherer societies beginning at least as early as the Late Pleistocene in Africa, Europe, Asia, and the Americas. Whether these behaviors eventually led to the development of agriculture depended in part on the development of a less variable and CO2-rich climatic regime and atmosphere during the Holocene, but also a change in the social relations of production to allow for hoarding privatized resources. In the 20th and 21st centuries, ethnographic and archaeological research shows that modern and ancient peoples adopt or even revert to hunting and gathering after having engaged in agricultural or industrial pursuits when conditions allow and that macroeconomic perspectives often mask considerable intragroup diversity in economic decision making: the pursuits and goals of women versus men and young versus old within groups are often quite different or even at odds with one another, but often articulate to form cohesive and adaptive economic wholes. The future of hunter-gatherer research will be tested by the continued decline in traditional hunting and gathering but will also benefit from observation of people who revert to or supplement their income with wild resources. It will also draw heavily from archaeology, which holds considerable potential to document and explain the full range of human behavioral diversity, hunter-gatherer or otherwise, over the longest of timeframes and the broadest geographic scope.
Ann E. Ferris, Richard Garbaccio, Alex Marten, and Ann Wolverton
Concern regarding the economic impacts of environmental regulations has been part of the public dialogue since the beginning of the U.S. EPA. Even as large improvements in environmental quality occurred, government and academia began to examine the potential consequences of regulation for economic growth and productivity. In general, early studies found measurable but not severe effects on the overall national economy. Although price increases due to regulatory requirements outweighed the stimulative effect of investments in pollution abatement, they nearly offset one another. However, these studies also highlighted potentially substantial effects on local labor markets due to the regional and industry concentration of plant closures.
More recently, a substantial body of work examined industry-specific effects of environmental regulation on the productivity of pollution-intensive firms most likely to face pollution control costs, as well as on plant location and employment decisions within firms. Most econometric-based studies found relatively small or no effect on sector-specific productivity and employment, though firms were less likely to open plants in locations subject to more stringent regulation compared to other U.S. locations. In contrast, studies that used economy-wide models to explicitly account for sectoral linkages and intertemporal effects found substantial sector-specific effects due to environmental regulation, including in sectors that were not directly regulated.
It is also possible to think about the overall impacts of environmental regulation on the economy through the lens of benefit-cost analysis. While this type of approach does not speak to how the costs of regulation are distributed across sectors, it has the advantage of explicitly weighing the benefits of environmental improvements against their costs. If benefits are greater than costs, then overall social welfare is improved. When conducting such exercises, it is important to anticipate the ways in which improvements in environmental quality may either directly improve the productivity of economic factors—such as through the increased productivity of outdoor workers—or change the composition of the economy as firms and households change their behavior. If individuals are healthier, for example, they may choose to reallocate their time between work and leisure. Although introducing a role for pollution in production and household behavior can be challenging, studies that have partially accounted for this interconnection have found substantial impacts of improvements in environmental quality on the overall economy.
Noa Kekuewa Lincoln and Peter Vitousek
Agriculture in Hawaiʻi was developed in response to the high spatial heterogeneity of climate and landscape of the archipelago, resulting in a broad range of agricultural strategies. Over time, highly intensive irrigated and rainfed systems emerged, supplemented by extensive use of more marginal lands that supported considerable populations. Due to the late colonization of the islands, the pathways of development are fairly well reconstructed in Hawaiʻi. The earliest agricultural developments took advantage of highly fertile areas with abundant freshwater, utilizing relatively simple techniques such as gardening and shifting cultivation. Over time, investments into land-based infrastructure led to the emergence of irrigated pondfield agriculture found elsewhere in Polynesia. This agricultural form was confined by climatic and geomorphological parameters, and typically occurred in wetter, older landscapes that had developed deep river valleys and alluvial plains. Once initiated, these wetland systems saw regular, continuous development and redevelopment. As populations expanded into areas unable to support irrigated agriculture, highly diverse rainfed agricultural systems emerged that were adapted to local environmental and climatic variables. Development of simple infrastructure over vast areas created intensive rainfed agricultural systems that were unique in Polynesia. Intensification of rainfed agriculture was confined to areas of naturally occurring soil fertility that typically occurred in drier and younger landscapes in the southern end of the archipelago. Both irrigated and rainfed agricultural areas applied supplementary agricultural strategies in surrounding areas such as agroforestry, home gardens, and built soils. Differences in yield, labor, surplus, and resilience of agricultural forms helped shape differentiated political economies, hierarchies, and motivations that played a key role in the development of sociopolitical complexity in the islands.