Showing papers in "Global Environmental Change-human and Policy Dimensions in 1999"

Climate change and global water resources

Abstract: By 2025, it is estimated that around 5 billion people, out of a total population of around 8 billion, will be living in countries experiencing water stress (using more than 20% of their available resources). Climate change has the potential to impose additional pressures in some regions. This paper describes an assessment of the implications of climate change for global hydrological regimes and water resources. It uses climate change scenarios developed from Hadley Centre climate simulations (HadCM2 and HadCM3), and simulates global river #ows at a spatial resolution of 0.5]0.53 using a macro-scale hydrological model. Changes in national water resources are calculated, including both internally generated runo! and upstream imports, and compared with national water use estimates developed for the United Nations Comprehensive Assessment of the Freshwater Resources of the World. Although there is variation between scenarios, the results suggest that average annual runo! will increase in high latitudes, in equatorial Africa and Asia, and southeast Asia, and will decrease in mid-latitudes and most subtropical regions. The HadCM3 scenario produces changes in runo! which are often similar to those from the HadCM2 scenarios * but there are important regional di!erences. The rise in temperature associated with climate change leads to a general reduction in the proportion of precipitation falling as snow, and a consequent reduction in many areas in the duration of snow cover. This has implications for the timing of stream#ow in such regions, with a shift from spring snow melt to winter runo!. Under the HadCM2 ensemble mean scenario, the number of people living in countries with water stress would increase by 53 million by 2025 (relative to those who would be a!ected in the absence of climate change). Under the HadCM3 scenario, the number of people living in countries with water stress would rise by 113 million. However, by 2050 there would be a net reduction in populations in stressed countries under HadCM2 (of around 69 million), but an increase of 56 million under HadCM3. The study also showed that di!erent indications of the impact of climate change on water resource stresses could be obtained using di!erent projections of future water use. The paper emphasises the large range between estimates of ‘impacta, and also discusses the problems associated with the scale of analysis and the de"nition of indices of water resource impact. ( 1999 Elsevier Science Ltd. All rights reserved.

Increasing flood risk and wetland losses due to global sea-level rise: regional and global analyses

Abstract: To develop improved estimates of (1) #ooding due to storm surges, and (2) wetland losses due to accelerated sea-level rise, the work of Hoozemans et al. (1993) is extended to a dynamic analysis. It considers the e!ects of several simultaneously changing factors, including: (1) global sea-level rise and subsidence; (2) increasing coastal population; and (3) improving standards of #ood defence (using GNP/capita as an ‘ability-to-paya parameter). The global sea-level rise scenarios are derived from two General Circulation Model (GCM) experiments of the Hadley Centre: (1) the HadCM2 greenhouse gas only ensemble experiment and (2) the more recent HadCM3 greenhouse gas only experiment. In all cases there is a global rise in sea level of about 38 cm from 1990 to the 2080s. No other climate change is considered. Relative to an evolving reference scenario without sea-level rise, this analysis suggests that the number of people #ooded by storm surge in a typical year will be more than "ve times higher due to sea-level rise by the 2080s. Many of these people will experience annual or more frequent #ooding, suggesting that the increase in #ood frequency will be more than nuisance level and some response (increased protection, migration, etc.) will be required. In absolute terms, the areas most vulnerable to #ooding are the southern Mediterranean, Africa, and most particularly, South and South-east Asia where there is a concentration of low-lying populated deltas. However, the Caribbean, the Indian Ocean islands and the Paci"c Ocean small islands may experience the largest relative increase in #ood risk. By the 2080s, sea-level rise could cause the loss of up to 22% of the world’s coastal wetlands. When combined with other losses due to direct human action, up to 70% of the world’s coastal wetlands could be lost by the 2080s, although there is considerable uncertainty. Therefore, sea-level rise would reinforce other adverse trends of wetland loss. The largest losses due to sea-level rise will be around the Mediterranean and Baltic and to a lesser extent on the Atlantic coast of Central and North America and the smaller islands of the Caribbean. Collectively, these results show that a relatively small global rise in sea level could have signi"cant adverse impacts if there is no adaptive response. Given the ‘commitment to sea-level risea irrespective of any realistic future emissions policy, there is a need to start strategic planning of appropriate responses now. Given that coastal #ooding and wetland loss are already important problems, such planning could have immediate bene"ts. ( 1999 Elsevier Science Ltd. All rights reserved.

Climate change and world food security: a new assessment

Abstract: Building on previous work quantitative estimates of climate change impacts on global food production have been made for the UK Hadley Centre's HadCM2 greenhouse gas only ensemble experiment and the more recent HadCM3 experiment (Hulme et al., 1999). The consequences for world food prices and the number of people at risk of hunger as defined by the Food and Agriculture Organisation (FAO, 1988) have also been assessed. Climate change is expected to increase yields at high and mid-latitudes, and lead to decreases at lower latitudes. This pattern becomes more pronounced as time progresses. The food system may be expected to accommodate such regional variations at the global level, with production, prices and the risk of hunger being relatively unaffected by the additional stress of climate change. By the 2080s the additional number of people at risk of hunger due to climate change is about 80 million people (±10 million depending on which of the four HadCM2 ensemble members is selected). However, some regions (particularly the arid and sub-humid tropics) will be adversely affected. A particular example is Africa, which is expected to experience marked reductions in yield, decreases in production, and increases in the risk of hunger as a result of climate change. The continent can expect to have between 55 and 65 million extra people at risk of hunger by the 2080s under the HadCM2 climate scenario. Under the HadCM3 climate scenario the effect is even more severe, producing an estimated additional 70+ million people at risk of hunger in Africa.

The effect of climate change on hydrological regimes in Europe: a continental perspective

Abstract: This paper outlines the effects of climate change by the 2050s on hydrological regimes at the continental scale in Europe, at a spatial resolution of 0.5×0.5°. Hydrological regimes are simulated using a macro-scale hydrological model, operating at a daily time step, and four climate change scenarios are used. There are differences between the four scenarios, but each indicates a general reduction in annual runoff in southern Europe (south of around 50°N), and an increase in the north. In maritime areas there is little difference in the timing of flows, but the range through the year tends to increase with lower flows during summer. The most significant changes in flow regime, however, occur where snowfall becomes less important due to higher temperatures, and therefore both winter runoff increases and spring flow decreases: these changes occur across a large part of eastern Europe. In western maritime Europe low flows reduce, but further east minimum flows will increase as flows during the present low flow season – winter – rise. “Drought” was indexed as the maximum total deficit volume below the flow exceeded 95% of the time: this was found to increase in intensity across most of western Europe, but decrease in the east and north. The study attempted to quantify several sources of uncertainty, and showed that the effects of model uncertainty on the estimated change in runoff were generally small compared to the differences between scenarios and the assumed change in global temperature by 2050.

Climate change and future populations at risk of malaria

Abstract: Global estimates of the potential impact of climate change on malaria transmission were calculated based on future climate scenarios produced by the HadCM2 and the more recent HadCM3 global climate models developed by the UK Hadley Centre. This assessment uses an improved version of the MIASMA malaria model, which incorporates knowledge about the current distributions and characteristics of the main mosquito species of malaria. The greatest proportional changes in potential transmission are forecast to occur in temperate zones, in areas where vectors are present but it is currently too cold for transmission. Within the current vector distribution limits, only a limited expansion of areas suitable for malaria transmission is forecast, such areas include: central Asia, North America and northern Europe. On a global level, the numbers of additional people at risk of malaria in 2080 due to climate change is estimated to be 300 and 150 million for P. falciparum and P. vivax types of malaria, respectively, under the HadCM3 climate change scenario. Under the HadCM2 ensemble projections, estimates of additional people at risk in 2080 range from 260 to 320 million for P. falciparum and from 100 to 200 million for P. vivax. Climate change will have an important impact on the length of the transmission season in many areas, and this has implications for the burden of disease. Possible decreases in rainfall indicate some areas that currently experience year-round transmission may experience only seasonal transmission in the future. Estimates of future populations at risk of malaria differ significantly between regions and between climate scenarios.

Institutions, climate change and cultural theory: towards a common analytical framework

Abstract: Institutions are the multitude of means for holding society together, for giving it a sense of purpose and for enabling it to adapt. Institutions help to define climate change both as a problem and a context, through such socialised devices as the use of scientific knowledge, culturally defined interpretation of scientific findings, and politically tolerable adaptation strategies. This paper briefly reviews the origins and current status of the ‘new’ institutional theories that have recently developed within the social sciences. The conclusion is that they are based on such contradictory interpretations of human behaviour that, although appealing, a complete synthesis will never be possible. In effect, there is a fundamental institutional ‘failure’ over the interpretation and resolution of climate change. Cultural theory helps to explain why this is the case by throwing light on the inherent contradictions that beset us all when confronted with global warming.

Land use change under conditions of high population pressure : the case of Java

Abstract: A long history of increases in population pressure in Java has caused agricultural land use to expand and intensify. More recent land use changes caused the conversion of prime agricultural land into residential and industrial area. Results of a dynamic, regional-scale, land use change model are presented, defining the spatial distribution of these land use changes. The model is based on multi-scale modelling of the relations between land use and socio-economic and biophysical determinants. Historical validation showed that the model can adequately simulate the pattern of land use change. Future patterns of land use change between 1994 and 2010 are simulated assuming further urbanization. The results suggest that most intensive land use changes will occur in Java's lowland areas.

Climate change impacts on ecosystems and the terrestrial carbon sink: a new assessment

Abstract: Climate output from the UK Hadley Centre’s HadCM2 and HadCM3 experiments for the period 1860 to 2100, with IS92a greenhouse gas forcing, together with predicted patterns of N deposition and increasing CO 2 , were input (o%ine) to the dynamic vegetation model, Hybrid v4.1 (Friend et al., 1997; Friend and White, 1999). This model represents biogeochemical, biophysical and biogeographical processes, coupling the carbon, nitrogen and water cycles on a sub-daily timestep, simulating potential vegetation and transient changes in annual growth and competition between eight generalized plant types in response to climate. Global vegetation carbon was predicted to rise from about 600 to 800 PgC (or to 650 PgC for HadCM3) while the soil carbon pool of about 1100 PgC decreased by about 8%. By the 2080s, climate change caused a partial loss of Amazonian rainforest, C 4 grasslands and temperate forest in areas of southern Europe and eastern USA, but an expansion in the boreal forest area. These changes were accompanied by a decrease in net primary productivity (NPP) of vegetation in many tropical areas, southern Europe and eastern USA (in response to warming and a decrease in rainfall), but an increase in NPP of boreal forests. Global NPP increased from 45 to 50 PgC y~1 in the 1990s to about 65 PgC y~1 in the 2080s (about 58 PgC y~1 for HadCM3). Global net ecosystem productivity (NEP) increased from about 1.3 PgC y~1 in the 1990s to about 3.6 PgC y~1 in the 2030s and then declined to zero by 2100 owing to a loss of carbon from declining forests in the tropics and at warm temperate latitudes * despite strengthening of the carbon sink at northern high latitudes. HadCM3 gave a more erratic temporal evolution of NEP than HadCM2, with a dramatic collapse in NEP in the 2050s. ( 1999 Elsevier Science Ltd. All rights reserved.

Climate change scenarios for global impacts studies

Abstract: We describe a set of global climate change scenarios that have been used in a series of studies investigating the global impacts of climate change on several environmental systems and resources — ecosystems, food security, water resources, malaria and coastal flooding. These scenarios derive from modelling experiments completed by the Hadley Centre over the last four years using successive versions of their coupled ocean–atmosphere global climate model. The scenarios benefit from ensemble simulations (made using HadCM2) and from an un-flux-corrected experiment (made using HadCM3), but consider only the effects of increasing greenhouse gas concentrations. The effects of associated changes in sulphate aerosol concentrations are not considered. The scenarios are presented for three future time periods — 30-year means centred on the 2020s, the 2050s and the 2080s — and are expressed with respect to the mean 1961–1990 climate. A global land observed climatology at 0.5° latitude/longitude resolution is used to describe current climate. Other scenario variables — atmospheric CO2 concentrations, global-mean sea-level rise and non-climatic assumptions relating to population and economy — are also provided. We discuss the limitations of the created scenarios and in particular draw attention to sources of uncertainty that we have not fully sampled.

Agrodiversity: definition, description and design

Abstract: ‘Agrodiversity’, a term of the 1990s, refers to interactions between agricultural management practices, farmers’ resource endowments, bio-physical resources, and species. If it is to have practical use, it must be codified as a basis for analysis. A division into overlapping and interrelated components is proposed, which distinguish spatial and temporal variations as well as related developmental issues such as livelihoods and food security.

Citizen 2000: development of a model of environmental citizenship

Abstract: Evironmental citizenship is a nationally-and-internationally stated objective. The interacting components which comprise the environmental citizen are generally not in dispute; it is the relationships between them and their relative importance that are poorly understood. A model of environmental citizenship was developed and tested via a public questionnaire-based survey. Multiple regression-and-correlation analyses indicate that participation in environmental education and training is the most important predictor of environmental behaviour followed by emotionality. However, the complexity of interactions which determine behaviour illustrates that environmental citizens are not produced merely by programmes of education, but by a whole range of factors with which education may interact. The model also demonstrates that the combination of the solutions subscale of sense of personal responsibility and the others subscale of locus of control exert a strong influence on behaviour, indicating the importance of a philosophy that recognizes the value of the individual in solving environmental problems. An internal locus of control is an important pre-requisite of environmental citizenship, as is a combination of both abstract and concrete knowledge. These results are generally comparable with other, largely US-based studies. It is therefore possible to conclude that the inter-relationships between environmental citizenship components are usually constant and that the model of environmental citizenship developed here is transferable.

The role of methane in global warming: where might mitigation strategies be focused?

Abstract: Anthropogenic sources of methane emissions are thought to be nearly twice as high as emissions from natural sources. As the second most important anthropogenic greenhouse gas after carbon dioxide, methane ought to be addressed by policy makers when they consider reductions of national greenhouse-gas inventories. This article first comprehensively reviews source and sink estimates of methane by natural and anthropogenic sectors (wetlands, wet-paddy rice farming, livestock farming, biomass burning, landfills, coal mining, and venting of natural gas or natural-gas pipeline leaks), then proceeds to suggest where different mitigation strategies might be applied. The final section considers how the scenario of a warmer planet may affect the methane biogeochemical cycle.

Climate change research and analysis in India: An integrated assessment of a South-North divide.

Abstract: For more than a decade climate change has been the focus of much research and analysis. Despite the global implications of the problem, the overwhelming majority of the researchers involved worldwide in studying the problem and its possible solutions are from industrialized countries, and participation of lesser-industrialized countries has been limited. While the wide-ranging implications of this South–North divide are sometimes recognized, there is little analysis on the reasons for this divide, why it continues to exist, and what steps might be required to narrow it. Towards this end, this paper analyzes how climate change research and analysis is performed in India, a major lesser-industrialized country. Based on detailed interviews, it explores the factors that play a role in shaping the capability of India to perform, and respond to, climate-change analyses. Drawing on the Indian case study, the paper examines developing-country participation in the international climate science and assessment enterprise. This allows some reflection on the potential pitfalls for international discussions on climate change and what the international community and countries of the South can do to overcome them in order to address this conspicuous South–North divide.

Safe policies in an uncertain climate: an application of FUND

Abstract: Various aspects of the role of uncertainty in greenhouse gas emission reduction policy are analyzed with the integrated assessment model FUND. FUND couples simple models of economy, climate, climate impacts, and emission abatement. Probability distribution functions are assumed for all major parameters in the model. Monte Carlo analyses are used to study the effects of parametric uncertainties. Uncertainties are found to be large and grow over time. Uncertainties about climate change impacts are more serious than uncertainties about emission reduction costs, so that welfare-maximizing policies are stricter under uncertainty than under certainty. This is more pronounced without than with international cooperation. Whether or not countries cooperate with one another is more important than whether or not uncertainty is considered. Meeting exogenously defined emission targets may be more or less difficult under uncertainty than under certainty, depending on the asymmetry in the uncertainty and the central estimate of interest. The major uncertainty in meeting emissions targets in each of a range of possible future is the timing of starting (serious) reduction policies. In a scenario aiming at a stable CO2 concentration of 550 ppm, the start date varies 20 years for Annex I countries, and much longer for non-Annex countries. Atmospheric stabilization at 550 ppm does not avoid serious risks with regard to climate change impacts. At the long term, it is possible to avoid such risks but only through very strict emission control at high economic costs.

Early science–policy interactions in climate change: lessons from the Advisory Group on Greenhouse Gases

Abstract: The consensus-based science advisory apparatus of the global climate regime is frequently faulted for achieving legitimacy at the cost of compromising the policy specificity of its assessments. The merits of an alternate corporatist model with closed-door interaction between a few experts and stakeholders are examined here by exhuming the legacy of the Advisory Group on Greenhouse Gases (AGGG). The study concludes that while such a model engendered policy innovation in the short term, it caused the erosion of scientific and political support over the longer term, leading to the marginalization of the AGGG.

Can we predict the future food production? A sensitivity analysis

Abstract: An attempt is made to assess the sensitivity of food production to various aspects of global change and environmental degradation during the next few decades. As a tool for this study a spreadsheet accounting system for food demand and supply is used. Taking into account the uncertainties of the various influencing factors, such as new technologies, improved management, increased fertilizer use, climatic change, expansion of irrigation, soil degradation and loss of agricultural land, the study indicates that one cannot say with any certainty whether or not food supply will meet expected demand in 2025, especially in Less Developed Countries. Bringing into use 10% of available potential cropland will make little difference.

Rethinking the ecological leviathan: environmental regulation in an age of risk

Abstract: Little attention has been given to the changing role of the state in the mediation of environmental risk. This review paper examines three interrelated themes: first, the extent to which contemporary environmental risks differ from those of the past; second, the various ways in which the rationality and legitimacy of environmental regulation have been challenged by a combination of political and economic developments; and third, the dilemmas posed by different institutional strategies for risk management. The paper argues that in order to better understand the implications of environmental risk for regulatory institutions it is necessary to develop our conception of risk beyond narrowly conceived technical, technological and micro-political discourses.

Climate change in mountain regions: some possible consequences in the Moroccan High Atlas

Abstract: Mountain areas are particularly sensitive to climate change. Seasonal and annual variations in climate already strongly influence agro-ecosystems, and although there is much speculation about the precise effects in such areas, any response of the communities will emerge from existing coping practices. Using examples from the High Atlas in Morocco, the paper explores the implications for livestock management, arboriculture and tourism. Although the local agro-ecosystem may prove resilient initially, the need to change tenure conditions and other rules of management may lead to conflict which exceeds the capacity of local institutions to resolve. At the same time national considerations may also draw the state more fully into conflict with mountain communities over resource use. However, the paper argues that these issues are just as likely to emerge from the evolution of the national economy as from climate change.

Development, democracy and forest trends

Abstract: Global forest trends are analysed in relation to indicators of economic, social and political development. The richest and most democratic countries are characterised by stable or expanding forests, while poor and despotic countries tend to experience rapid forest loss. The conclusion is that a high level of development is beneficial rather than detrimental to the sustainability of forest area. This conclusion is discussed briefly in relation to the relationship between the human and environmental dimensions of sustainable development.

Human implication of changes in the hydrological regime due to climate change in Northern Greece

Abstract: This paper examines the impacts of climate change on various forms of water resources and on some critical water management issues. The study area is the Aliakmon river basin including three subbasins of hydrological interest located in northern Greece. A monthly conceptual water balance model was calibrated for each subbasin separately, using historical hydrometeorological data. This model was applied to estimate runoff values at the outlet of each subbasin under different climate change scenarios. Two equilibrium scenarios (UKHI, CCC) referring to years 2020, 2050 and 2100 and one transient scenario (UKTR) referring to years 2032 and 2080 were implied. It was found that reduction of the mean annual runoff and mean winter runoff values, as well as serious reduction of the summer runoff values would occur in all cases and basins. However, the runoff values for November, December and January were increased, whereas the spring runoff values were decreased, leading to a shifting of the wet period towards December and severe prolongation of the dry period. Moreover, the results indicate that all subbasins exhibit almost the same behavior under the different climate change scenarios, while the equilibrium scenarios (UKHI, CCC) seem to give more reasonable and consistent results than the transient scenario (UKTR). Finally, the negative effects of the climatically induced changes on the hydroelectric production and the water use for agricultural purposes in the study basin were assessed.

Wetter isn't better: global warming and food security in the Congo Basin

Abstract: Over 20 million forest farmers practice slash and burn agriculture in the forests of the Congo Basin ( Bahuchet and de Maret, 1995 . State of Indigenous Populations Living in Rainforest Areas, European Commission DG XI Environment, Brussels). They rely on the long dry season (December–February north of the equator) to ensure that their new fields, cleared from regrowth forest, burn sufficiently well to deposit nutrients into the soil and to minimize the labor required to prepare the field for planting. Data from the Ituri forest in northeastern Democratic Republic of Congo show that the strength of the annual dry season (a) has a direct positive impact on the size of fields cleared each year by slash and burn farmers, and consequently on food production and the severity of the subsequent year's pre-harvest hunger period; and (b) is inversely related to total annual rainfall. These results suggest that the 1 mm/d increase in rainfall predicted for much of the Congo Basin by the 2050s may cause a basin wide increase in the frequency of heavy rains during the dry season, causing a reduction in the size of slash and burn farmers’ fields, and potentially a substantial increase in the food insecurity of poor rural families across the region.

Selection of appropriate greenhouse gas mitigation options

Abstract: Greenhouse gas mitigation options help in reducing greenhouse gas emissions so as to avoid the adverse environmental impacts due to global warming/climate change. They have different characteristics when evaluated using different criteria. For example, some options may be very cost effective, while some may have an additional advantage of reducing local pollution. Hence, selection of these options, for consideration by a national government or by a funding agency, has to incorporate multiple criteria. In this paper, some important criteria relevant to the selection are discussed, and a multi-criteria methodology is suggested for making appropriate selection. The methodology, called the Analytic Hierarchy Process, is described using two illustrations.

Improving impact assessment methods: climate change and the health of indigenous Australians

Abstract: Climate impact assessment has evolved as a range of tools, critical in evaluating potential impacts of climate change. This field has been driven by global concerns and is dominated by western scientific philosophies. Amid claims that it is failing in its role of informing policy, key issues implicated in application of assessment techniques are considered for the case of indigenous health in northern Australia. An argument is made for local scale studies which foster stakeholder involvement and focus on social, cultural and political landscapes; studies which produce outcomes of relevance to stakeholders and planners, as well as scientists and researchers.

Spanning not-implausible futures to assess relative vulnerability to climate change and climate variability1

Abstract: The global-change research community is beginning to turn its attention to assessing the vulnerability of social, economic, political and/or ecological systems to climate change and climate variability in ways that systematically incorporate their ability to adapt. The Workshop on Adaptation to Climate Variability and Change hosted in Costa Rica (March 29}April 1, 1998) by the Intergovernmental Panel on Climate Change (IPCC) stands as evidence of this increased interest. Indeed, the `Scoping Meetinga hosted by the IPCC in late June con"rmed that vulnerability and adaptation will be unifying themes in the work of Working Groups II and III as they prepare the Third Assessment Report (TAR). It is reasonable, therefore, to expect a #urry of activity in this area over the next several years. As the process begins, though, it must be emphasized that the proceedings of the IPCC Costa Rica Adaptation Workshop reiterated the long held belief that long-term uncertainty and near-term variability are ubiquitous. Participants there agreed that

Property rights on genetic resources: economic issues

Abstract: Biodiversity loss is one of the major international environmental problems. This paper analyses the question of how the use of genetic and biochemical resources in biotechnological industries might affect biodiversity conservation. It is argued that the answer will significantly depend on the concrete regimes of property rights on genetic resources and related biotechnological knowledge. One of the main conclusions derivable from this analysis is that a tightening of intellectual property rights may either aggravate biodiversity loss or strengthen biodiversity conservation, depending on various conditions. This result has interesting parallels to the results of second best theory. Furthermore it sheds new light on the debate regarding the relationship between the WTO Agreement on trade-related aspects of intellectual property rights (TRIPs) and biodiversity loss.

Research and communication in the “invisible college” of the Human Dimensions of Global Change

Abstract: The human dimensions of global change research community includes scholars in the natural and social sciences working in universities and government laboratories who share common interests and who communicate with each other through journals, workshops, and conferences and via the Internet. Information and communication technologies, in particular, e-mail, listservs, and the WWW, where speed and low cost are key features, from the backbone of an “electronic invisible college”. The results of a survey of scientists attending the Laxenburg conference in 1997 illustrates the transdisciplinary and international nature of HDGC research, the local and international scale of research, their commitment to public policy, and their increased use of the Internet for networking, data acquisition and analysis, and publication.

From meta-narratives to flexible frameworks: an actor level analysis of land degradation in Highland Tanzania

Abstract: This paper first highlights some of the problems that exist with studies that try to explain the causes environmental degradation, in particular land degradation. Based on this critique it provides a framework, set in the context of an actor-oriented approach, that helps to attain a clearer understanding of the social causes of the physical changes that are interpreted as degradation. The framework is illustrated with reference to a case study from a mountainous area of central-eastern Tanzania.