Interactions Among Driving Forces, Proximate Sources, and the Impacts of Land Use/Land Cover Change--Background Information

Introduction to Global Change 


The earth is constantly changing. Every environmental domain, that of water (hydrosphere), of the air (atmosphere), of rocks (lithosphere) and soils (pedosphere), of ice (cryosphere) and of vegetation and living organisms (biosphere) -- all of these domains are in constant flux. The changes that occur may happen in matters of seconds or over millions of years; they may occur in one place only, or on the entire globe; and changes in one environmental sphere affect changes in others. So the earth can be thought of as a system of interacting evolving, environmental spheres.

Human-induced changes in the environment have always been profound and common in almost all parts of the world, but the scope (both spatially and qualitatively) of human-driven alterations of the environment has immensely enlarged as population numbers and technological capacities increased (e.g., Mathews 1983; Turner & Butzer 1992). With mounting evidence of environmental transformations on a global scale and especially serious concerns about changes in the earth's atmosphere with yet-unknown consequences for global and regional climates, scientists have become interested in these global environmental and especially global climatic changes.

The Human Dimensions of Global Change

vested interest in a healthy and productive environment. Questions that concern global change scientists include what such an environment looks like, how to keep a healthy and productive environment, what forces drive its degradation, and how to manage societal activities on a global scale such that we maintain and/or repair the earth's capacity to sustain the lives and livelihoods of all of its inhabitants. Basically, scientists attempt to understand the causes, consequences, and areas of intervention for the management of global change.

These issues concerned scientists in the early 1970s, when the environmental movement began to flourish in the Western world (e.g., Commoner 1970, 1977; Ehrlich 1968; updated and revised in 1990; Meadows et al. 1972). This flurry of interest in the understanding and modeling of global environmental and socio-economic futures was followed by a decade or so of relative neglect, until the early 1980s, when global change research revived. It was mostly physical scientists who dealt with these questions until, in the late 1980s and early 1990s, people recognized that recent global changes are largely human-induced, that they do and will affect human societies, and thus that they could only be understood with the input from the social sciences. Since then it has become common to speak of the human dimensions of global change, i.e., of human driving forces, mitigating forces, proximate sources, impacts, and responses to global change.

Human driving forces or macro-forces are those fundamental societal forces that in a causal sense link humans to nature and bring about global environmental changes. In this sense, the study of global changes through the lens of nature-society relationships is a profoundly geographical theme. Human driving forces comprise the sum of individual and group actions, but they are more manageably described as collective categories of these actions (Turner 1989: 93). An oft-cited typology of these macro-forces is presented below (Table 1); it should be noted, however, that many versions of this typology and alternatives to it exist in the social science research literature on global change.
 

In the absence of empirical studies that might document the workings of these forces, social scientists try to extract relevant knowledge from studies undertaken for purposes other than understanding global change. Thus, our understanding of these global human driving and mitigating forces is still in the early stages. What we do know is that "the rich traditions of social-science research into [nature-society] relationships have demonstrated their great complexity and the variability that they can display by period, site, and situation. Any nature-society relationship ..., even if stimulated by a "global force," ... cannot be adequately understood independent of the contingencies of its local and historical occurrence. Prescriptions divorced from the specificities of context are not only inadequate but dangerous" (Meyer, Turner, and Young 1990: 1).

It is therefore necessary to determine the intermediate mechanisms that translate the multi-tiered, complex global driving forces into local human action. In describing these mechanisms, global change researchers speak of proximate sources of change. The list of such proximate sources is virtually endless, but some examples given below illustrate their role in nature-society interactions. Figure 2 below shows how human driving forces, mitigating forces and human behavior interact to bring about the proximate sources of change which in turn cause different types of land use/cover changes mediated by the characteristics of the physical environment.

Figure 2: The Human Causes of Global Environmental Change
(Click on thumbnail to enlarge)

Source: Turner, B.L. 1989. The human causes of global environmental change.
His Figure 11.1, p.91; reprinted with per-mission from the National Academy of Sciences.

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Proximate driving forces are the aggregate final activities that result from the interplay of human driving and mitigating forces to directly cause environmental transformations, either through the use of natural resources (e.g., as input into agriculture, mining activities, or as raw material for industrial production), through the use of space, through the output of waste (solid waste, emissions, pollution, etc.), or through the output of products that in themselves affect the environment (e.g., cars, plastic bags). This causality is again highly complicated when we consider issues of geographic scale, time, magnitude, and clustering of proximate sources of change:

• How does geographic scale affect our understanding of these forces?
• How do we incorporate time lags between past action and current or future impacts?
• Of what magnitude does an activity have to be in order for us to recognize its causal workings?
• Where are the thresholds beyond which impacts become visible?
• How do the workings and impacts of proximate sources differ when they occur in a clustered manner rather than singly?

Types of Global Environmental Change

In the second, cumulative, sense, global refers to "the areal or substantive accumulation of localized change. ... Changes of the cumulative type include those that 'are local in domain, but which are widely replicated and which in sum constitute change in the whole human environment'" (Turner et al. 1990: 17, citing H.

Brookfield 1989). Examples of this type of global change include soil degradation (e.g., Blaikie 1985; Blaikie and Brookfield 1987; Grainger 1982; Tolba 1984), or the loss of biodiversity (e.g., Swanson 1995). Soil erosion or soil fertility losses resulting from local agricultural practices occur almost everywhere on earth, constituting in their totality a global change of the soils of the world. Species and habitats are lost locally, yet the phenomenon of biodiversity loss is experienced almost everywhere on earth, cumulatively causing an alteration of the biosphere.

The latter example demonstrates one difficulty with this typology: cumulative and systemic global change may not always be clearly distinguishable. We do not know with any certainty whether or not cumulative change will -- in crossing some unknown threshold -- turn into systemic global change. For example, by changing not only the number of species living on earth but also the composition of species, do we not really bring about a systemic rather than a cumulative change? The answer to this question rests on our ability to recognize global-scale impacts and our ability to trace these impacts back to biodiversity loss (see the definition of systemic change above).
 

The second typology (Table 3), more common in the physical than in the social sciences, distinguishes changes by the locales in the earth system in which they occur. Changes in material and energy flows may be geographical or temporal changes, qualitative changes (the kinds of materials or energies flowing through the earth system or its spheres), or quantitative changes (the amounts of materials or energy flowing through the system). Changes in biota have been discussed above. They include changes at the genetic, species, habitat and ecosystemic, and quantitative (amount of biomass) levels. Providing space for biotic changes as one of three fundamental types of global change points to the central role the biosphere plays in the creation and maintenance of a habitable human environment. Finally, changes in the physical structure of the biosphere refer to the structural interlinking of the earth's spheres.

Again, these three types of changes are highly interconnected and overlapping as were systemic and cumulative changes in the previous typology. It should be remembered as well that the focus in the study of the human dimensions of global change is the interaction between these types of global environmental change and humans. This interaction is highly specific to the local conditions both of the environment and of society. Human actions are grounded in place, and because the differences between places are immense, we must expect that this human-environment relationship will vary widely from place to place.

Land Use and Land Cover Change

The study of land use and land cover is central in this respect (see Figure 3). Land use is the observed immediate reason and/or manifestation of environmental change. Consider the following examples: Agricultural and forestry practices have changed entire landscapes; land-management practices more generally alter plant and animal communities both at the species and habitat level, or they affect nutrient cycling and distribution in the soil; creation or changes of transportation routes dissect habitats, and alter water and energy flows; industrial emissions affect environmental and human health and built structures (as for example through acid deposition, or the destruction of the ozone layer). Similarly, we must be interested in how humans adjust to a variable and changing environment, which factors facilitate or impede such adjustments and adaptations, and which factors augment or diminish societal vulnerability to, say, climatic variability, and thus what might be the most effective avenues to take in response to global environmental changes.

Scientists dealing with land use and land cover changes ask:

• "How are land-use changes contributing to global environmental changes?,
• "What social-economic factors determine land use, and how will they change?", and
• "How does land use modify processes that influence global change?" (Ojima, Galvin, and Turner 1994: 300).

Source: Ojima, Galvin, and Turner 1994; their Figure 1, p.301; reprinted with permission from the American Inst. of Biol. Sciences.

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Let us begin by defining and distinguishing land use and land cover. Land use "is the way in which, and the purposes for which, human beings employ the land and its resources" (Meyer 1995: 25). Examples include farming, mining, and lumbering. Land cover, by contrast, "describes the physical state of the land surface: as in cropland, mountains, or forests" (Meyer 1995: 25). The term originally referred to the type of vegetation that covered the land surface, but has broadened subsequently to include human structures, such as buildings or pavement, and other aspects of the physical environment, such as soils, biodiversity, and surface and groundwater.

As Meyer correctly pointed out, changes in land use that lead to changes in land cover do not necessarily imply a degradation of the land (Meyer 1995: 25). That is, these changes do not necessarily mean a decline in productivity or in other desired characteristics of the land. Presumably most land use changes are motivated by the desire to improve the land for human use or pleasure (for example, in the use of fertilizers, pesticides, powerful machinery, increases of total cultivated land area to feed an increasing population, or the setting aside of primary forests in national parks for aesthetic and leisurely enjoyment only) (Ruttan 1971). Degradation -- a state profoundly determined by our perception of the environment -- may occur nevertheless. It may be unintentional and unperceived; it may result from carelessness or from unavoidable necessity if it occurs in the course of working for personal (economic) survival (Blaikie 1985; Blaikie and Brookfield 1987; Watts 1983).

As Figure 3 above depicted, land use/land cover and changes therein are linked to the proximate and driving forces of global change. In the activities accompanying this first unit, we will begin to examine these complex linkages and how they play out in our own local environment. Later exercises will take us to the regional and global scales and allow us to quantitatively analyze the relationships between human driving forces and land use/cover change.

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Key Terms / Phrases

Environmental spheres

Earth as a system

Interplay of natural and human driving forces in environmental change

Global environmental change

Global climate change

Human driving forces/ macro forces

Human dimensions of global change

Typology of human driving forces

Human mitigating forces

Proximate sources of change

Human causes of global environmental change

Causal linkages between proximate sources and environmental change

Complications:

• Geographic scale
• Time lags
• Perception
• Thresholds
• Clustering vs. single impacts

Genetic typology of global environmental change

Systemic change

Cumulative change

Occurrence-oriented typology of global environmental change

Material and energy flows

Biota

Structure of the biosphere

Land use and land cover change

Land use and global environmental change

Linkages among human causes of change and land use/cover

Land use

Land cover