1 Landscape and landscape-scale processes as
the unfilled niche in the global environmental
change debate: an introduction
Olav Slaymaker, Thomas Spencer and Simon Dadson
1.1 The context
Whatever one’s views, it cannot be doubted that there is
a pressing need to respond to the social, economic and
intellectual challenges of global environmental change.
Much of the debate on these issues has been crystallised
around the activities of the IPCC (Intergovernmental Panel
on Climate Change). The IPCC process was set up in 1988,
a joint initiative between the World Meteorological
Organization and the United Nations Environment
Programme. The IPCC’s First Assessment Report was
published in 1990 and thereafter, the Second (1996), the
Third (2001) and the Fourth Assessment Report (2007)
have appeared at regular intervals. Each succeeding assessment
has become more confident in its conclusions.
The conclusions of the Fourth Assessment can be summarised
as follows:
(a) warming of the climate system is unequivocal;
(b) the globally averaged net effect of human activities
since AD 1750 has been one of warming (with high
level of confidence);
(c) palaeoclimate information supports the interpretation
that the warmth of the last half century is unusual in at
least the previous 1300 years;
(d) most of the observed increase in globally averaged
temperature since the mid twentieth century is very
likely due to the observed increase in anthropogenic
greenhouse gas concentrations; and
(e) continued greenhouse gas emissions at or above current
rates will cause further warming and induce many
changes in the global climate system during the twentyfirst
century that would very likely be larger than those
observed in the twentieth century. Details of the methodology
used to reach these conclusions can be found
in Appendix 1.1.
The IPCC assessments have been complemented by a number
of comparable large-scale exercises, such as the UNEP
GEO-4 Assessment (Appendix 1.2) and the Millennium
Ecosystem Assessment (Appendix 1.3) and, for example,
at a more focussed level, the Land Use and Land Cover
Change (LUCC) Project (Appendix 1.4) and the World
Heritage List (Appendix 1.5). There is no doubting the
effort, value and significance of these enormous research
programmes into global environmental change (Millennium
Ecosystem Assessment, 2005; Lambin and Geist, 2006).
1.1.1 Defining landscape and appropriate
temporal and spatial scales for the analysis of
landscape
It is important to establish an appropriate unit of study
against which to assess the impacts of global environmental
change in the twenty-first century and to identify those
scales, both temporal and spatial, over which meaningful,
measurable change takes place within such a unit. The unit
of study chosen here is that of the landscape. There are
strong historical precedents for such a choice. Alexander von
Humboldt’s definition of ‘Landschaft’ is the ‘Totalcharakter
einer Erdgegend’ (Humboldt, 1845–1862). Literally this
means the total character of a region of the Earth which
includes landforms, vegetation, fields and buildings.
Consistent with Humboldt’s discussion, we propose a
definition of landscape as ‘an intermediate scale region,
comprising landforms and landform assemblages, ecosystems
and anthropogenically modified land’.
The preferred range of spatial scales is 1–100 000 km²
(Fig. 1.1). Such a range, of six orders of magnitude, is
valuable in two main ways:
(a) individual landforms are thereby excluded from consideration;
and
Geomorphology and Global Environmental Change, eds. Olav Slaymaker, Thomas Spencer and Christine Embleton-Hamann. Published by
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(b) landscape belts (Landschaftgürtel) and biomes, which
provide an organising framework for this volume, are
nevertheless so large that their response to environmental
disturbance is impossible to characterise at century
or shorter timescales.
The preferred range of timescales is decades–centuries
(Fig. 1.1). These are intermediate temporal scales that are
relevant to human life and livelihoods (and define timescales
required for mitigation and adaptive strategies in response
to environmental change). The determination of the future
trajectory of landscape change is unthinkable for projections
into a more distant future. Nevertheless, as is argued below,
an understanding of changes in landscapes and biomes over
the past 20 000 years (i.e. since the time of maximum
continental ice sheet development over North America
and Eurasia) provides essential context for a proper understanding
of current and near-future landscape dynamics.
1.1.2 The global human footprint and landscape
vulnerability
The human imprint on the landscape has become global
(Turner et al., 1990a; Messerli et al., 2000) and positive
feedbacks between climate, relief, sea level and human
activity are leading in the direction of critical system state
‘tipping points’. This is both the threat and the opportunity
of global environmental change. Some of the implications
of arriving at such a tipping point are that gradual change
may be overtaken by rapid change or there may even be a
reversal of previously ascertained trends. A few examples
of the most vulnerable landscapes, in which small environmental
changes, whether of relief, sea level, climate or land
use, can produce dramatic and even catastrophic response,
are listed here:
(a) Low-lying deltas in subsiding, cyclone-prone coasts
are highly vulnerable to changes in tropical storm magnitude
and/or frequency. It is clear that societal infrastructure
is poorly attuned to disaster response in such
heavily populated landscapes, in both developed
(e.g. Hurricane Katrina, Mississippi Delta, August
2005) and developing (Cyclone Nargis, Irrawaddy
Delta, May 2008) countries;
(b) Shifting sand dunes respond rapidly to changing temperature
and rainfall patterns. Dunes migrate rapidly
when vegetation is absent; the vast areas of central
North America, central Europe and northern China
underlain by loess (a mixture of fine sand and silt) are
highly vulnerable to erosion when poorly managed, but
are also an opportunity for continuing intensive agricultural
activity guided by the priority of the
ecosystem;
(c) Glacier extent and behaviour are highly sensitive to
changing temperatures and rising sea level. In most
parts of the world, glaciers are receding; in tropical
regions, glaciers are disappearing altogether, with serious
implications for late summer water supply; in
Alaska, British Columbia, Iceland, Svalbard and the
Antarctic Peninsula glaciers are surging, leading to
catastrophic drainage of marginal lakes and downstream
flooding. Transportation corridors and settlements
downstream from surging glaciers are highly
vulnerable to such dynamics;
(d) Permafrost is responding to rising temperatures in both
polar and alpine regions. In polar regions, landscape
impacts include collapse of terrain underlain by massive
ice and a general expansion of wetlands. Human
settlements, such as Salluit in northern Quebec,
Canada, are highly vulnerable to such terrain instability
and adaptation strategies are required now to deal with
such changes; and
(e) In earthquake-prone, high-relief landscapes, the damming
of streams in deeply dissected valleys by landslides
has become a matter of intense concern. The 12
May 2008 disaster in Szechwan Province, China saw
the creation of over 30 ‘quake lakes’, one of which
reached a depth of 750 m before being successfully
drained via overspill channels. If one of these dams had
FIGURE 1.1. Spatial and temporal scales in geomorphology. On the
x-axis, the area of the surface of the Earth in km² is expressed as
8.7 logarithmic units; on the y-axis, time since the origin of the
Earth in years is expressed as 9.7 logarithmic units.
O. Slaymaker et al.2
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been catastrophically breached, the lives of 1.5 million
downstream residents would have been endangered.
Although one example does not make a global environmental
concern, the quake lakes phenomenon is representative
of the natural hazards associated with densely
populated, tectonically active, high-relief landscapes.
1.1.3 Multiple drivers of environmental change
There is an imbalance in the contemporary debate on global
environmental change in that the main emphasis is on only
one driver of environmental change, namely climate
(Dowlatabadi, 2002; Adger et al., 2005). In fact, environmental
change necessarily includes climate, relief, sea level
and the effects of land management/anthropogenic factors
and the interactions between them. It is important that a
rebalancing takes place now, to incorporate all these drivers.
Furthermore, the focus needs to be directed towards the
landscape scale, such that global environmental changes
can be assessed more realistically. Human safety and wellbeing
and the maintenance of Earth’s geodiversity will
depend on improved understanding of the reciprocal
relations between landscapes and the drivers of change.
In his book Catastrophe, for example, Diamond (2005)
has described a number of ways in which cultures and
civilisations have disappeared because, at least in part,
those civilisations have not understood their vulnerability
to one or more of the drivers of environmental change.
Montgomery (2007) has developed a similar thesis with a
stronger focus on the mismanagement of soils.
1.1.4 Systemic and cumulative global
environmental change
Global environmental change is here defined as environmental
change that consists of two components, namely systemic
and cumulative change (Turner et al., 1990b). Systemic
change refers to occurrences of global scale, physically
interconnected phenomena, whereas cumulative change
refers to unconnected, local- to intermediate-scale processes
which have a significant net effect on the global system.
In this volume, hydroclimate and sea level change are
viewed as drivers of systemic change (see Sections 1.6 and
1.7 of this chapter below). The atmosphere and ocean
systems are interconnected across the face of the globe
and the modelling of the coupled atmosphere–ocean system
(AOGCM) has become a standard procedure in application
of general circulation models (or GCMs). A GCM is a
mathematical representation of the processes that govern
global climate. At its core is the solution to a set of physical
equations that govern the transfer of mass, energy and
momentum in three spatial dimensions through time. The
horizontal atmospheric resolution of most global models is
between 1°–3° (~100–300 km). Processes operating at spatial
scales finer than this grid (such as cloud microphysics
and convection) are parameterised in the model. In the
vertical direction, global models typically divide the atmosphere
into between 20 and 40 layers.
Topographic relief, and land cover and land use changes,
by contrast, are viewed as drivers of cumulative change (see
Sections 1.8 and 1.9). The patchiness of relief and land use
and difficulties of both definition and spatial resolution
make the incorporation of their effects into GCMs a continuing
challenge. Nevertheless, developments in global
climate modelling over the past decade have seen the
improvement in land-surface modelling schemes in which
an explicit representation of soil moisture, runoff and river
flow routing has been incorporated into the modelling
framework (Milly et al., 2002). This trend, coupled with
the widespread implementation of dynamic vegetation
models (in which vegetation of different plant functional
types is allowed to grow according to prevailing environmental
conditions) has resulted in a generation of models
into which such a range of complex interacting processes
are embedded that they have become termed global environmental
models instead (Johns et al., 2006).
1.1.5 The role of geomorphology
In these contexts, geomorphology (from the Greek geo
Earth and morphos form) has an important role to play; it
involves the description, classification and analysis of the
Earth’s landforms and landscapes and the forces that have
shaped them, over a wide range of time and space scales
(Fairbridge, 1968). In particular, geomorphology has the
obligation to inform society as to what level of disturbance
the Earth’s landforms and landscapes can absorb and over
what time periods the landscape will respond to and recover
from disturbance.
In this book, we have chosen to view geomorphology
(changing landforms, landform systems, landscapes and
landscape systems) as dependent on the four drivers of
environmental change, namely climate, relief, sea level
and human activity, but also as an independent variable
that has a strong effect on each of the drivers at different
time and space scales. The relationship in effect is a reflexive
one and it is important to avoid the implication of
unique deterministic relations.
Two important intellectual strands in geomorphology have
been so-called ‘climatic’ and ‘process’ geomorphology; they
have tended to focus on different spatio-temporal scales of
inquiry.
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1.2 Climatic geomorphology
Climate’s role in landscape change has long been of interest
to geomorphology. Indeed in the continental European
literature this was a theme that was already well developed
by the end of the nineteenth century (Beckinsale and Chorley,
1991). The greatest impetus to climatic geomorphology
came from the global climatic classification scheme of
Köppen (1901). A clear statement of the concept of climatic
geomorphology was made by de Martonne (1913) in which
he expressed the belief that significantly different landscapes
could be developed under at least six present climatic
regimes and drew particular attention to the fact that humidity
and aridity were, in general, more important as differentiators
of landscape than temperature. The identification of
morphoclimatic/morphogenetic regions and attempts to
identify global erosion patterns (Büdel in Germany, Tricart
in France and Strakhov in Russia) were also important
global-scale contributions. Strakhov’s map of global-scale
erosion patterns is reproduced here (Fig. 1.2) to illustrate
the style and scale of this research. He attempted to estimate
world denudation rates by extrapolating from sediment
yields for 60 river basins. His main conclusions were:
(a) arid regions of the world have distinctive landforms
and landscapes;
(b) the humid areas of the tropics and subtropics, which lie
between the +10 ºC mean annual isotherm of each
hemisphere, are characterised by high rates of denudation,
reaching maximum values in southeastern Asia;
(c) the temperate moist belt, lying largely north of the
+10 ºC mean annual isotherm, experiences modest
denudation rates;
(d) the glaciated shield areas of the northern hemisphere,
largely dominated by tundra and taiga on permafrost
and lying north of the 0 ºC mean annual isotherm, have
the lowest recorded rates of denudation; and
(e) mountain regions, which experience the highest rates
of denudation, are sufficiently variable that he was
forced to plot mountain denudation data separately in
graphical form.
The map is an example of climatic geomorphology in so
far as it demonstrates broad climatic controls but perhaps
the most important contribution of twentieth-century climatic
geomorphology was that it maintained a firm focus on the
landscape scale, the scale to which this volume is primarily
directed. The weakness of the approach is that regional and
zonal generalisations were made primarily on the basis of
form (in the case of arid regions) and an inadequate sampling
of river basin data. There was a lack of field measurements
FIGURE 1.2. Climatic geomorphology (modified from Strakhov, 1967).
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of contemporary process and no discussion of the scale
dependency of key rainfall, runoff and sediment relations.
Whilst one may be critical of these earlier attempts to deal
with landscape-scale geomorphology, now is a good time to
revisit the landscape scale, with a firmer grasp of the relief, sea
level and human activity drivers, for the following reasons:
(a) the development of plate tectonic theory and its geomorphological
ramifications has given the study of
earth surface processes and landforms a firmer geological
and topographic context;
(b) a better understanding of the magnitudes and rates of
geomorphological processes has been achieved not
only from contemporary process measurements but
also from the determination of more precise and
detailed records of global environmental change over
the last 20 000 years utilising improved chronologies
(largely ocean rather than terrestrially based) and benefiting
from the development of whole suites of radiometric
dating techniques, covering a wide range of
half-lives and thus timescales; and
(c) the ability to provide, at a range of scales, quantitative
measurements of land surface topography and vegetation
characteristics from satellite and airborne remote sensing.
1.3 Process geomorphology
From the 1950s onwards an Anglo-American geomorphology
came to be reorientated towards quantitative research on
the functional relations between form, materials and earth
surface processes. These ‘process studies’, generally at the
scale of the small drainage basin or below, began to determine
local and regional rates of surface lowering, or denudation,
material transport and deposition and their spatial
differentiation. The rates at which these processes take
place are dependent upon local relief and topography, the
materials (bedrock and soils) involved and, of course, climate,
both directly and indirectly through the relations
between climate, vegetation characteristics and surface processes.
The emphasis on rates of operation of processes led
to a greater interest in the role of hydroclimate, runoff and
sediment transport both in fluvial and in coastal systems. The
role of vegetation in landscape change also assumed a new
importance for its role in protecting the soil surface, in
moderating the soil moisture and climate and in transforming
weathered bedrock into soil (Kennedy, 1991).
1.3.1 Process–response systems
One of the most influential papers in modern geomorphology
concerned the introduction of general systems thinking
into geomorphology (Chorley, 1962). General systems
thinking provided the tool for geomorphologists to analyse
the critical impacts of changes in the environmental system
on the land surface, impacts of great importance for human
society and security. One kind of general system that has
proved to be most fruitful in providing explanations of
the land surface–environment interaction is the so-called
process–response system (Fig. 1.3). Such systems are
defined as comparatively small-scale geomorphic systems
in which deterministic relations between ‘process’ (mass
and energy flows) and ‘response’ (changes in elements of
landscape form) are analysed with mathematical precision
and attempted accuracy. There is a mutual co-adjustment of
form and process which is mediated through sediment
transport, a set of relations which has been termed ‘morphodynamics’
and which has been found to be particularly
useful in coastal studies (e.g. Woodroffe, 2002).
Morphodynamics explains why, on the one hand, physically
based models perform well at small spatial scales and
over a limited number of time steps but, on the other hand,
why model predictions often break down at ‘event’ and
particularly ‘engineering’ space-timescales. Unfortunately,
these are exactly the scales that are of greatest significance
in the context of predicting landscape responses to global
environmental change and the policy and management
decisions that flow from such responses.
1.3.2 The scale linkage problem
The issue of transferring knowledge between systems of
different magnitude is one of the most intransigent problems
in geomorphology, both in terms of temporal scale and
spatial scale (Church, 1996).The problem of scale linkage
can be summarised by the observation that landscapes are
characterised by different properties at different scales of
investigation. Each level of the hierarchy includes the
cumulative effects of lower levels in addition to some
new considerations (called emergent properties in the technical
literature) (Fig. 1.4).
FIGURE 1.3. A simplified conceptual model of a process–response
system.
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At the landscape scale, here taken to be larger than the
large basin scale in Fig. 1.4, there are further emergent
properties which have to be considered such as regional
land use and hydrology.
Figure 1.5 combines a consideration of both temporal
and spatial scales. At one extreme of very small spatial
scale, such as the movement of individual sand grains
over very short timescales, the process–response model
works well. At the other extreme, large landscapes that
have evolved over millions of years owe their configuration
almost exclusively to past processes. Discontinuous sediment
disturbances have a history of variable magnitude and
frequency of occurrence. The practical implication is that,
in general, the larger the landscape we wish to consider the
more we have to take into account past processes and the
slower will be the response of that landscape in its entirety
to sediment disturbance regimes. Coastal morphology and
drainage networks, which occupy the central part of
Fig. 1.5, exemplify the scales of interest in this volume.
1.4 Identification of disturbance regimes
Global environmental change has become a major concern
in geomorphology because it poses questions about the
magnitude, frequency and kinds of disturbance to which
geomorphic systems are exposed. What then are the major
drivers of that change? Discussions about the rhythm and
periodicity of geological change have spilled over into
geomorphology. In his discussion of rhythmicity in terrestrial
landforms and deposits, Starkel (1985) directed attention to
the fact that the largest disturbance in the geologically
recent past is that of continental-scale glaciation (see
Plates 1 and 2). Periods of glaciation alternating with
warmer episodes define a disturbance regime characterised
by varying rates of soil formation and erosional and
depositional geomorphological processes during interglacial
and glacial stades (Fig. 1.6).
Some of the excitement in the current debate over global
environmental change concerns precisely the question of
the rate at which whole landscapes have responded to
past climate changes and disturbances introduced by tectonism
(e.g. volcanism, earthquakes and tsunamis) or human
activity.
1.4.1 Landscape response to disturbance
The periodicity of landscape response to disturbance in
Fig. 1.6 is controlled by the alternation of glacial and
interglacial stades. The magnitude and duration of this
response is a measure of the sensitivity and resilience of
the landscape. In the ecological and geomorphic literature,
this response is commonly called the system vulnerability.
Conventionally, human activity has been analysed outside
FIGURE 1.4. The scale linkage problem (modified from Phillips,
1999) illustrated in terms of a spatial hierarchy which contains new
and emergent properties at each successive spatial scale.
FIGURE 1.5. The relative importance of historical vs. modern
explanation as a function of size and age of landforms and
landscapes (modified from Schumm, 1985). Note the assumption
that size and age are directly correlated, an assumption that is most
appropriate for coastal, fluvial and aeolian landscapes, but does not
easily fit volcanic and tectonic landscapes.
FIGURE 1.6. Periodicity of erosion and sedimentation (modified
from Starkel, 1985). IGS is interglacial stade; GS is glacial stade; and
IG is the present interglacial.
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the geosystem (and Fig. 1.6 contains no human imprint) but
the weakness of this approach is that it fails to recognise the
accelerating interdependence of humankind and the geosystem.
The IPCC usage of the term ‘vulnerability’, by
contrast, addresses the ability of society to adjust to disturbances
caused by environmental change. We therefore
follow, broadly, the IPCC approach in defining sensitivity,
adaptive capacity and vulnerability as follows. ‘Sensitivity’
is the degree to which a system is affected, either adversely
or beneficially, by environment-related stimuli; ‘adaptive
capacity’ is the ability of a system to adjust to environmental
change, to moderate potential damages, to take
advantage of new opportunities or to cope with the consequences;
and ‘vulnerability’ is the degree to which a
system is susceptible to, or unable to cope with, adverse
effects of environmental change. In sum, ‘vulnerability’ is a
function of the character, magnitude and rate of environmental
change and variation to which a system is exposed,
its sensitivity and its adaptive capacity (Box SPM-1 in
IPCC, 2001b, p. 6.).
In general, those systems that have the least capacity to
adapt are the most vulnerable. Geomorphology delivers a
serious and often unrecognised constraint to the feasible
ways of dealing with the environment in so far as it controls
vulnerability both in the ecological sense (in the absence of
direct human agency) and in the IPCC sense. A number of
unique landscapes and elements of landscapes are thought
to be more likely to experience harm than others following
a perturbation. There are seven criteria that have been used
to identify key vulnerabilities:
(a) magnitude of impacts;
(b) timing of impacts;
(c) persistence and reversibility of impacts;
(d) estimates of uncertainty of impacts;
(e) potential for adaptation;
(f) distributional aspects of impacts; and
(g) importance of the system at risk.
In the present context, such landscapes are recognised as
hotspots with respect to their vulnerability to changes in
climate, relief, sea level and human activities. We think
immediately for example of glaciers, permafrost, coral
reefs and atolls, boreal and tropical forests, wetlands, desert
margins and agricultural lands as being highly vulnerable.
Some landscapes will be especially sensitive because they
are located in zones where it is forecast that climate will
change to an above average degree. This is the case for
instance in the high arctic where the degree of warming
may be three to four times greater than the global mean. It
may also be the case with respect to some critical areas
where particularly substantial changes in precipitation may
occur. For example, the High Plains of the USA may
become markedly drier. Other landscapes will be especially
sensitive because certain landscape forming processes are
particularly closely controlled by thresholds, whether
climatic, hydrologic, relief, sea level or land use related. In
such cases, modest amounts of environmental change can
switch systems from one state to another (Goudie, 1996).
1.4.2 Azonal and zonal landscape change
The overarching problem of assessing probable landscape
change in the twenty-first century is approached here in two
main ways. A group of chapters which are ‘azonal’ in
character concern themselves with ways in which geomorphic
processes are influenced by variations in mass, energy
and information flows, and this self-evidently includes
human activity. These azonal chapters deal with land systems
that are larger than individual slopes, stream reaches and
pocket beaches, but generally smaller than continentalscale
regions. By comparison, the zonal chapters use whole
biomes as their organising principle, similar to those used in
the Millennium Ecosystem Assessment (2003) (Plate 3). In
these chapters also, environmental change is driven, not
only by hydroclimate, relief and sea level but also by
human activity.
In addition to understanding the terrestrial distribution of
biomes, it is also important to recognise the broad limits to
coral reef and associated shallow water ecosystems, such
that the upper ocean’s vulnerability to global environmental
change can also be assessed (Fig. 1.7).
FIGURE 1.7. Global distribution of coral reefs, mangroves and
seagrass. Scale of diversity ranges from 0–10 genera (low); 10–25
genera (medium); and >50 (high) (modified from Veron, 1995).
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The decision to structure the book chapters using a
bottom–up (azonal) and a top–down (zonal) approach
reflects the fact that both approaches have complementary
strengths.
1.5 Landscape change
Geomorphology emphasises landscape change under the
influence of climate, relief, sea level change and human
activity (Chorley et al., 1984) and does so at a range of space
and timescales. With respect to temporal scales, attention is
confined in this volume to the last complete glacial–
interglacial cycle and forward towards the end of the
twenty-first century (Fig. 1.8). The reasons for the selection
of these end points are that they include one complete
glacial–interglacial cycle (see Chapter 14), and thus the
widest range of climates and sea levels in recent Earth
history. This period includes the rise of Homo sapiens sapiens;
and extends forward to a time when future landscapes
can be modelled with some confidence and for which credible
scenarios of landscape change can be constructed.
Included in this timescale are the closing stages of the
Pleistocene Epoch (150 000 to 10 000 years ago); the
Holocene Epoch (10 000 years BP until the present) and a
recent, more informally defined, Anthropocene, extending
from about 300 years ago when human impact on the
landscape became more evident, and into the near future.
The comprehensive ice core records from Greenland (GISP
and GRIP) and from Antarctica (Vostok and EPICA) (Petit
et al., 1999; EPICA, 2004) (Fig. 1.8); lake sediments from
southern Germany (Ammersee) (Burroughs, 2005) (Fig. 1.9)
and elsewhere; and a number of major reconstructions of
the climate of the last 20 000 years using past scenarios
(Plates 1 and 2) provide a well-authenticated record of the
Earth’s recent climatic history.
The record of changing ice cover and biomes since the
Last Glacial Maximum (LGM) has been reconstructed by
an international team of scientists working under the
general direction of the Commission for the Geological
Map of the World (Petit-Maire and Bouysse, 1999; Plates 1
and 2). The authors stress that the maps are tentative but
contain the best information that was available in 1999. The
maps depict the state of the globe during the two most
FIGURE 1.8. Climate records from East Antarctica (Vostok ice
core) covering the last glacial–interglacial cycle (modified from
Petit et al., 1999). Note the rapid warming followed by a gentler,
stepped cooling process and also the close correlation of
temperature and CO2.
FIGURE 1.9. A comparison of the
record from Ammersee, in
southern Germany, and the GRIP
ice core from Greenland showing
the close correlation between the
Younger Dryas cold event from
12.9 to 11.6 ka BP at the two sites
(from von Grafenstein et al., 1999).
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contrasted periods of the last 20 ka. The LGM was the
coldest (c. 18 ka ± 2 ka BP) and the Holocene Optimum
(HOP) was the warmest (c. 8 ka ± 1 ka BP) period. These
periods were only 10 ka apart and yet there was a dramatic
reorganisation of the shorelines, ice cover, permafrost, arid
zones, surface hydrology and vegetation at the Earth’s surface
over that interval. Thus within a 10-ka time-span (in
many places less) the two vast ice sheets of Canada and
Eurasia, which reached a height of 4 km and covered about
25 million km², disappeared; 20 million km² of continental
platform were submerged by the sea; biomes of continental
scale were transformed and replaced by new ones; and
humans could no longer walk from Asia to America nor
from New Guinea to Australia nor from France to England.
It is also interesting to compare these shifts in the terrestrial
landscape with change in sea surface temperatures over
the same period of time. In particular, in the tropical oceans,
these changes were relatively small – as illustrated by the
change in the 20 ºC isotherm (which provides a broad limit
to coral growth) – with the greatest changes being in the
variable strength of the equatorial upwelling systems on the
eastern margins of the ocean basins (Fig. 1.10).
1.5.1 The Last Glacial Maximum
First of all, there needs to be a caveat with respect to the
timing of the LGM (Plate 1). There is strong evidence that
the maximum extent of ice was reached in different places
at different times. The ice distribution that is mapped
corresponds to the maximum extent during the time interval
22 ka to 14 ka years BP, which covers the global range within
which the maximum is believed to have occurred. During
the LGM, mean global temperature was at least 4.5 °C colder
than present. Permafrost extended southwards to latitudes of
40–44º N in the northern hemisphere (although in the south,
only Patagonia and the South Island of New Zealand experienced
permafrost). Mean sea level was approximately
125 m lower than at present. Large areas of continental
shelf were above sea level and colonised by terrestrial vegetation,
particularly off eastern Siberia and Alaska, Argentina,
and eastern and southern Asia. New Guinea was connected
to Australia, the Persian Gulf dried up and the Black Sea,
cut off from the Mediterranean Sea, became a lake.
There was a general decrease in rainfall near the tropics.
Loess was widespread in periglacial areas and dunes in
semi-arid and arid regions. All desert areas were larger
than today but in the Sahara there was the greatest southward
extension of about 300–400 km. Surface hydrology
reflected this global aridity except in areas that received
meltwaters from major ice caps, such as the Caspian and
Aral seas. Grasslands, steppes and savannas expanded at
the expense of forests.
1.5.2 The record from the ice caps and lake
sediments
The transition between the LGM and the Holocene was
marked by a partial collapse of the Laurentide/Eurasian ice
FIGURE 1.10. Changing tropical ocean temperatures, LGM to present (modified from CLIMAP, 1976 and Spencer, 1990).
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sheets. This led to a surge of icebergs, recorded in the
sediments of the North Atlantic by the last of the so-called
Heinrich events (thick accumulations of ice-rafted sediments)
around 16.5ka. There followed a profound warming around
14.5 ka (Fig. 1.9) which coincided with a rapid rise in sea
level (see Section 1.7), presumably associated with the
break-up of part of the Antarctic ice sheet (Burroughs, 2005).
Between 14.5 and 12 ka BP the mean annual temperature
oscillated violently and between 12.9 and 11.6 ka the last
great cooling of the ice age (known as the Younger Dryas
stade) occurred. Rapid warming continued until around
10 ka but thereafter, the climate seems to have settled into
what looks like an extraordinarily quiet phase when compared
with the earlier upheavals. The Holocene Epoch is
conventionally said to start around 10 ka because the bulk
of the ice sheet melt had occurred by that time, but the
Laurentide ice sheet, for example, did not disappear until
6 ka BP.
Although climatic fluctuations during the Holocene have
been much more modest than those which occurred during
the previous 10 ka, there have been fluctuations which have
affected glacier distribution in the mountains, treeline limits
in the mountains and in the polar regions, and desiccation of
the Sahara. The CASTINE project (Climatic Assessment of
Transient Instabilities in the Natural Environment) has
identified at least four periods of rapid climate change
during the Holocene, namely 9–8 ka; 6–5 ka; 3.5–2.5 ka
and since 0.6 ka. In terms of landscape history, it is also
important to recognise that the mean global temperature
may not be the most significant factor in landscape change.
Precipitation amounts and soil moisture availability and
their variability of occurrence and intensity over space
and through time have had a strong influence on regional
and local landscape evolution.
1.5.3 The Holocene Optimum
A caveat also needs to be applied with respect to the timing
of the HOP (Plate 2). The maximum values of the signals
for each of the various indicators of environmental change
are far from being coeval. During the HOP, the mean global
temperature was about 2 °C warmer than today. By 6 ka BP,
mean relative land and sea level was close to that of the
present day except in two kinds of environments:
(a) the Canadian Arctic and the Baltic Sea where isostatic
(land level rebound after ice sheet load removal) adjustments
were at a maximum;
(b) deltas of large rivers, such as the Mississippi, Amazon,
Euphrates–Tigris and Yangtze, had not reached their
present extent.
The glacier and ice sheet cover cannot be distinguished
from that of today at this global scale. Permafrost, both
continuous and discontinuous, was within the present
boundary of continuous permafrost in the northern hemisphere.
Significantly wetter conditions were experienced in
the Sahara, the Arabian Peninsula, Rajasthan, Natal, China
and Australia, where many lakes that have subsequently
disappeared were formed. In Canada the Great Lakes were
formed following the melting of the ice sheet and the
isostatic readjustment of the land. Rainforest had recolonised
extensive areas and the taiga and boreal forest had
replaced a large part of the tundra and areas previously
covered by ice sheets (Petit-Maire, 1999).
This time-span of 20 000 years has been selected in order
to encapsulate the extremes of mean global cold and
warmth experienced between the LGM and the HOP, a
range that one might expect to contain most of the reasonable
scenarios of environmental change over the next 100
years. Certainly, this range defines the ‘natural’ variability
of Earth’s landscapes but, notably, little distinctive human
impact was discernible at this global scale of analysis.
Recently, however, Ruddiman (2005) has claimed to
recognise the effects of human activity in reversing the
trends of CO2 and methane concentrations around 8–5 ka
BP. His hypothesis is that clearing of the land for agriculture
and intensification of land use during the Holocene has
so altered the climate as to delay the arrival of the next
glacial episode. This is a controversial hypothesis which
requires further testing. If the hypothesis is supported, it
emphasises the importance of the warning issued by Steffen
et al. (2004) against the use of Pleistocene and Holocene
analogues to interpret the Anthropocene, the contemporary
epoch which is increasingly dominated by human activity
and is therefore a ‘no analogue’ situation.
1.6 Systemic drivers of global
environmental change (I): hydroclimate
and runoff
1.6.1 Introduction
Water plays a key role in the transfer of mass and energy
within the Earth system. Incoming solar radiation drives the
evaporation of approximately 425 × 103
km3
a− 1
of water
from the ocean surface and approximately 71 × 103
km3
a− 1
from the land surface; precipitation delivers about 385 × 103
km3
a− 1
of water to the ocean and 111 × 103
km3
a− 1
to the
land surface. The balance is redressed through the flow of
40 × 103
km3
a− 1
of water from the land to the oceans in
rivers (Berner and Berner, 1996). Global environmental
change affecting any one of these water transfers will lead
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to changes in runoff and river flows. However, the prediction
of changes may not be simple because the role of hydrological
processes in the land surface system is complex and
involves interactions and feedbacks between the atmosphere,
lithosphere and vegetation.
The hydrological cycle is affected by changes in global
climate, but also by changes that typically occur on a
smaller, regional scale, such as changes in vegetation type
and land use (for example the change from forest to agricultural
pasture land) and changes in land management.
These latter changes may also include reservoir construction,
abstractions of water for human use, and discharges of
water into river courses and the ocean.
Increasing atmospheric carbon dioxide levels and temperature
are intensifying the global hydrological cycle,
leading to a net increase in rainfall, runoff and evapotranspiration
(Huntingdon, 2006). Changes are projected to
occur not only to mean precipitation and runoff, but also
to their spatial patterns. Within the tropics, precipitation rates
increased between 1900 and 1950 but have declined since
1970. In contrast, mid-latitude regions have seen a more
consistent increase in precipitation since 1900 (IPCC, 2007a).
The intensification of the hydrological cycle is likely to
mean an increase in hydrological extremes (IPCC, 2001a).
Changes to the frequency distribution of rainfalls and flows
of different magnitude can have a disproportionately large
effect on environmental systems such as river basins, vegetation
and aquatic habitats. The reason for this disproportionality
is because extreme flows provoke changes when
certain thresholds in magnitude or in the duration of runoff
are exceeded. There are suggestions that interannual variability
will increase, with an intensification of the natural El
Niño and North Atlantic Oscillation (NAO) cycles, leading
to more droughts and large-scale flooding events. Key
questions that this section will address include:
(a) what changes in precipitation, evaporation and consequent
runoff have been observed over the historical
period; and
(b) what changes are projected under future climate and
land use scenarios.
1.6.2 Observed changes in precipitation,
evaporation, runoff and streamflow
Surface temperatures
Global mean surface temperatures have increased by
0.74 ºC± 0.18 ºC over the period 1906–2005, although the
rate of warming in the last 50 years of that period has been
almost double that over the last 100 years (IPCC, 2007a).
With this change in surface temperature comes the
theoretical projection that warming will stimulate evaporation
and in turn precipitation, leading to an intensified hydrological
cycle. In the earliest known theoretical work on the
subject, Arrhenius (1896) showed that specific humidity
would increase roughly exponentially with air temperature
according to the Clausius–Clapeyron relation. Numerical
modelling studies have since indicated that changes in the
overall intensity of the hydrological cycle are controlled not
only by the availability of moisture but also by the ability of
the troposphere to radiate away latent heat released by
precipitation. An increase in temperature of 1 Kelvin
would lead to an increase in the moisture-holding capacity
of the atmosphere by approximately 3.4% (Allen and
Ingram, 2002). The convergence of increased moisture in
weather systems leads to more intense precipitation; however
the frequency or duration of intense precipitation
events must decrease because the overall amount of water
does not change a great deal (IPCC, 2007a).
Pollutant aerosols
In addition to the effects of temperature increases, the
effects of pollutant aerosols can be significant. Increases
in sulphate, mineral dust and black carbon can suppress
rainfall in polluted areas by increasing the number of cloud
condensation nuclei. This leads to a reduction in the mean
size of cloud droplets and reduces the efficiency of the
process whereby cloud droplets coalesce into raindrops
(Ramanathan et al., 2001). An additional effect of increased
atmospheric aerosol loading is a reduction in the amount of
solar radiation that reaches the land surface; this may affect
the amount of evaporation and therefore precipitation. The
effects of aerosol loading are expected to be highest in
highly polluted areas such as China and India and evidence
is emerging that aerosol loading may explain the recent
tendency towards increased summer flooding in southern
China and increased drought in northern China (Menon
et al., 2002). Recent analyses indicate that aerosol loading
led to a reduction in solar radiation reaching the land surface
of 6–9 W m− 2
(4–6%) between the start of measurements
in 1960 and 1990 (Wild et al., 2005). However,
between 1991 and 2002, the same authors estimate that
the amount of solar radiation reaching the Earth’s surface
increased by approximately 6 W m− 2
. This observed shift
from dimming to brightening, has prompted Andreae et al.
(2005) to suggest that the decline of aerosol forcing relative
to greenhouse forcing may lead to atmospheric warming at
a much higher rate than previously predicted.
Precipitation
Precipitation trends are harder to detect than temperature
trends, because the processes that cause precipitation are
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more highly variable in time and space. Nevertheless,
global mean precipitation rates have increased by about
2% over the twentieth century (Hulme et al., 1998). The
spatial pattern of trends has been uneven, with much of the
increase focussed between 30° N and 85° N. Evidence for a
change in the nature of precipitation is reported by Brown
(2000), who finds a shift in the amount of snowfall in
western North America between 1915 and 1997. Zhang
et al. (2007) used an ensemble of fourteen climate models
to show that the observed changes in the spatial patterns of
precipitation between 1925 and 1999 cannot be explained
by internal climate variability or natural forcing, but instead
are consistent with model projections in which anthropogenic
forcing was included.
Runoff
Rates of surface and subsurface runoff depend not just on
trends in precipitation, because the water balance for any
soil column dictates that runoff is the difference between
precipitation and evaporation. When an unlimited amount
of water is available at the surface, the rate of evaporation is
controlled by the amount of energy available and the water
vapour pressure deficit (i.e. the difference between the
actual vapour pressure and the vapour pressure at saturation)
in the overlying air (Penman, 1948). The amount of
energy available depends on the net solar radiation received
at the surface. The water vapour pressure deficit depends on
the temperature of the air and its specific humidity. The rate
of transport of air across the surface exerts a key control on
the potential evaporation rate because it determines how
readily saturated air is refreshed so that further evaporation
can occur. In practice, an unlimited amount of water is
available only over persistent open water in oceans, lakes
and rivers. Over the land surface, the rate of actual evaporation
depends not only on meteorological variables but
also on the nature of the vegetation and on the amount of
available soil moisture.
Evapotranspiration
Only limited observations of evaporation are available.
Sparse records of potential evaporation from evaporation
pans show a generally decreasing trend in many regions,
including Australia, China, India and the USA (IPCC,
2007a). Roderick and Farquar (2002) demonstrate that the
decreasing trends in pan evaporation are likely to be a result
of a decrease in surface solar radiation that may be related
to increases in atmospheric aerosol pollution. On the other
hand, Brutsaert and Parlange (1998) have pointed out that
pan evaporation does not represent actual evaporation and
that in regions where soil moisture exerts a strong control
on actual evaporation any increase in precipitation which
drives an increase in soil moisture will also lead to higher
rates of actual evaporation.
In any case, at the scale of a river basin, vegetation
controls the amount of evaporation from the land surface
through its effects on interception and transpiration. A
significant fraction of precipitation falling on land can be
intercepted by vegetation and subsequently evaporated.
The rate of evaporation from intercepted water depends
on the vegetation type and structure of the plant canopy; it
is normally higher for forest canopies than for grassland. In
contrast, transpiration occurs through the evaporation of
water through plant stomata. The rate of transpiration
depends on available energy and vapour pressure deficit
but also on stomatal conductance: the ease with which the
stomata of a particular plant species permit evaporation
under given environmental conditions. Stomatal conductance
depends on light intensity, CO2 concentration, the
difference in vapour pressure between leaf and air, leaf
temperature and leaf water content. All of these properties
change over timescales relevant to global change, but the
most significant variant may be CO2 concentration (Arnell,
2002).
Increased CO2 concentration stimulates photosynthesis
and may encourage plant growth in some plant species that
use the C3 photosynthesis pathway, which includes all trees
and most temperate and high-latitude grasses (Arnell,
2002). Carbon dioxide enrichment has the additional effect
of reducing stomatal conductance by approximately 20–
30% for a doubling of the CO2 concentration. Thus, for a
given set of meteorological conditions, the water use efficiency
of plants increases. Considerable uncertainty exists
over whether this leaf-scale process can be extrapolated to
the catchment scale; in many cases the decreased transpiration
caused by CO2-induced stomatal closure is likely to be
offset by additional plant growth (Arnell, 2002).
Trends in streamflow
Only patchy historical data are available to assess global
patterns of streamflow. Dai and Trenberth (2002) estimate
that only about two-thirds of the land surface has ever been
gauged and the length and availability of observed records
are highly variable. Detecting trends in streamflow is problematic
too, because runoff is a spatially integrated variable
which does not easily permit discrimination between
changes caused by any of its driving factors. Streamflow
and groundwater recharge exhibit a wide range of natural
variability and are open to a host of other human or natural
influences.
In an analysis of world trends in continental runoff,
Probst and Tardy (1987) found an increase of approximately
3% between 1910 and 1975. This trend has been
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confirmed in a reanalysis of data between 1920 and 1995 by
Labat et al. (2004). In areas where precipitation has
increased over the latter half of the twentieth century, runoff
has also increased. This is particularly true over many parts
of the USA (Groisman et al., 2004). Streamflow records
exhibit a wide range of variability on timescales ranging
from inter-annual to multi-decadal and for most rivers,
secular trends are often small. There is evidence that flood
peaks have increased in the USA because increases in surface
air temperature have hastened the onset of snowmelt
(Hodgkins et al., 2003). In many rivers in the Canadian
Arctic, earlier break-up of river ice has been observed
(Zhang et al., 2001).
Caution must be exercised in the interpretation of longterm
hydrological trends. Using flow observations made
during the last 80–150 years, Mudelsee et al. (2003) found
a decrease in winter flooding in the Elbe and Oder rivers in
Eastern Europe, but no trend in summer flooding. They
concluded that the construction of reservoirs and deforestation
may have had minor effects on flood frequency.
Svensson et al. (2006) showed that, in a study of long
time series of annual maximum river flows at 195 gauging
stations worldwide, there is no statistically significant trend
at over 70% of sites. They attributed the lack of a clear
signal to the wide ranging natural variability of river flow
across multiple time and space scales. Hannaford and
Marsh (2006) described a set of benchmark UK catchments
defined to represent flow regimes that are relatively undisturbed
by anthropogenic influences. Over the past 30–40
years they found a significant trend towards more protracted
periods of high flow in the north and west of the
UK, although trends in flood magnitude were weaker.
However, they pointed out that much of the trend is a result
of a shift towards a more positive NAO index since the
1960s. The NAO is a climatic phenomenon in the North
Atlantic Ocean and is measured by the difference in sea
level pressure between the Icelandic Low and the Azores
High. This difference controls the strength and direction of
westerly winds and storm tracks across the North Atlantic.
Some component of many observed runoff trends can be
explained by changes to environmental properties other
than climate. Increases in runoff have resulted from land
use change, particularly from the conversion of forest to
grassland or agricultural land (Vörösmarty and Sahagian,
2000). The most significant effect of removing trees is the
reduction in canopy evaporation; that is, evaporation from
water intercepted by the tree canopy and stored on leaves.
In the Plynlimon experimental catchments in upland Wales,
United Kingdom, Roberts and Crane (1997) found that
clearcutting of ~30% of the coniferous forest cover led to
an increase in runoff of 6–8%. In snow-dominated
catchments, the effects of deforestation are more significant
because a large amount of snow is permitted to accumulate
if forest is cleared (Troendle and Reuss, 1997). Conversely,
abandonment of agricultural land and upland afforestation
can reduce the volume of runoff. In the Plynlimon catchments
experiment, annual evaporation losses (estimated as
the difference between annual precipitation and annual runoff)
in the forested Severn catchment were ~200 mm
greater than in the grassland Wye catchment. This represents
a 15% reduction in the flow (Robinson et al., 2000).
Most studies of the effects of land cover on the water
balance have involved catchment-scale measurements and
it is, at present, uncertain whether these findings can be
extrapolated to regional and planetary scales.
1.6.3 Projections for future changes
An assessment of the potential impacts of future climate
change on precipitation, evaporation, and therefore runoff
is a fundamental influence on the strategies adopted by land
and river managers. It is impossible to make a reliable
prediction of the weather more than about a week in advance,
but projections of the statistical properties of future climate
can be obtained by using general circulation models
(GCMs) to construct climate scenarios (see Section 1.1.4).
Models that encompass an ever-wider range of environmental
processes have led to a shift in the goals of climate
modelling. Instead of simply providing projections of
future average weather, current environmental models provide
a powerful tool to examine numerically the complex
feedbacks that exist within the Earth system. They have
also fuelled studies that fall under the broad title of ‘detection
and attribution’, in which historical observed changes
in measured environmental variables are partly explained
through understanding gained using climate simulations.
For example, Gedney et al. (2006) attempt to show that
statistically significant continent-wide increases in
twentieth-century streamflow can be explained by the effect
of CO2-driven stomatal closure on continental-scale
transpiration.
In contrast to numerical weather prediction, which is an
initial-value problem where governing equations are solved
to find the time-evolution of the system given a set of initial
conditions, a typical GCM experiment corresponds to a
boundary-value problem in mathematics. In a boundaryvalue
problem, boundary conditions for the problem are
used to constrain solutions to the governing equations that
are consistent with the imposed conditions. For example,
the frequency distribution of rainfall magnitudes may be
required under different scenarios of atmospheric CO2 concentration.
The detailed trajectory of changes in CO2 is
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highly dependent on socioeconomic factors which govern
the behaviour of human societies. The IPCC has published
a range of plausible alternatives in its Special Report on
Emissions Scenarios (SRES) in which the scenarios are
defined (Appendix 1.1).
Temperature and precipitation
Globally averaged mean water vapour, evaporation and
precipitation are projected to increase with global environmental
warming (IPCC, 2007a). Current models indicate
that future warming of 1.8–4.0 °C by 2100 (depending on
the scenario chosen) will drive increases in precipitation in
the tropics and at high latitudes; decreases in precipitation
are expected in the subtropics (Plate 4). The intensity of
individual precipitation events is predicted to increase,
especially in areas seeing greatest increases in mean precipitation,
but also in areas where mean precipitation is
projected to fall. Summer drying of continental interiors is
a consistent feature of model projections (IPCC, 2007a).
Hydroclimate and runoff
Despite some consistent patterns, the spatial response of
precipitation to climate change is much more highly variable
than that of temperature. Plate 5 shows the spatial
pattern of precipitation and other hydrologically related
changes projected for the A1B scenario (Appendix 1.1).
Runoff is expected to fall in southern Europe and increase
in Southeast Asia and at high latitudes. The impact of these
changes has been assessed by Nohara et al. (2006), who
find that in high latitudes river discharge is predicted to
increase but in much of Central America, Europe and the
Middle East, decreases in river flow are expected.
1.7 Systemic drivers of global
environmental change (II): sea level
1.7.1 Introduction
Variations in sea level form part of a complex set of relations
between atmosphere–ocean dynamics, ice sheets and
the solid Earth, all of which have different response timescales.
Thus changes in sea level resulting from global
environmental change are, on the one hand, masked by
shorter-term variations in the elevation of the sea surface.
These fluctuations can be considerable: El Niño–Southern
Oscillation (ENSO)-related inter-annual changes in ocean
level in the western Pacific Ocean are ~45 cm (Philander,
1990), of comparable magnitude to many estimates of the
magnitude of sea level rise to 2100. Furthermore, nearfuture
sea level changes will take place against a backdrop
of ongoing geological processes. The geographical variability
in Holocene sea level histories has been well established
(e.g. Pirazzoli, 1991) and geophysical models have identified
large-scale sea level zones, with typical sea level curves, for
the near- (Zone I), intermediate- (Zone II) and far-fields
(Zones III–VI) in relation to former ice sheets (Clark et al.,
1978) (Fig. 1.11).
These differences have implications for future coastal
vulnerabilities. Some coasts (in Zones IV and V for example)
will have adjusted to coastal processes operating at
present, or close to present, sea level for at least 5000 years
whereas other regions (Zone II for example) will only have
experienced present sea level being reached within the last
1000 years.
At the inter-ocean basin scale, coral reef systems in the
Indo-Pacific Reef Province lie in the far-field, with near
present sea level being reached at ~6 ka BP. Thereafter,
hydro-isostatic adjustments and meltwater migration back
to former ice margins, and in some cases local tectonics,
resulted in a mid-Holocene sea level high of ~ +1 m,
followed by a gradual fall to present mean sea level
(Fig. 1.11). In the western Indian Ocean, sea level rose
rapidly (6 mm a− 1
) until 7.5 ka BP then dramatically
slowed (to ~1 mm a− 1
), with near present sea level being
attained at 3.0–2.5 ka BP (Camoin et al., 2004); however, in
the central and eastern Indian Ocean a mid-Holocene high
FIGURE 1.11. Sea level regions and associated sea level curves,
6–0 ka BP, assuming no eustatic component after 5 ka BP. RSL,
relative sea level (modified from Clark et al., 1978).
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stand of ~ +0.5 m has been reported (Woodroffe, 2005;
P. Kench, personal communication, 2007). By contrast,
the reefs of the Atlantic Reef Province lie within the intermediate
field and experienced a decelerating rate of sea
level rise through the Holocene, with present sea level
being reached only within the last 1000 years (Toscano
and Macintyre, 2003) (Fig. 1.11). These different sea
level histories go some way to explaining the gross morphological
differences between reef provinces. Thus IndoPacific
reef margins are generally characterised by wide,
low-tide-emergent reef flats and, in some locations, by
supratidal conglomerates and raised reef deposits. By contrast,
in the Atlantic reef province, emergent reef features
are lacking and relatively narrow reef crests are backed by
shallow backreef environments and lagoons. These differences
are of importance: as sea level rises, near-future reef
responses will take place over these different topographies.
Finally, at the within-region scale, continuing adjustments
to the unloading of ice, reflooding of shallow shelf
seas and sedimentation in coastal lowlands in the British
Isles since the Last Glacial Maximum have resulted in
maximum rates of land uplift of ~1.5 mm a− 1
on coasts in
western Scotland but corresponding maximum subsidence
of –0.85 mm a− 1
on the Essex coast of eastern England
(Shennan and Horton, 2002). In Scotland, therefore, sea
level rise will be partially offset by uplift whereas in southeast
England sea level rise will be additive to existing rates
of relative rise.
Long-term trends in coastal erosion – such as along the
eastern seaboard of the USA where 75% of the shoreline
removed from the influence of spits, tidal inlets, and engineering
structures is eroding (Zhang, 2004) and the eastern
coastline of the UK where 67% of the shoreline length has
retreated landward of the low-water mark (Taylor et al.,
2004) – can be reasonably associated with sea level rise
over the last 100–150 years. The exact linkage, however, is
most probably more event-based. Komar and Allan (2007)
have identified increased ocean wave heights along the
eastern seaboard of the USA and related them to an intensification
of hurricane activity from the late 1990s; they
have also argued that increased erosion along the US west
coast since the 1970s has been associated with increasing
wave heights due to higher water levels and storm intensities
(Allan and Komar, 2006). In addition to sea level
change and its variability, coastal erosion is also driven by
other natural factors, including sediment supply and local
land subsidence. Anthropogenic activities can intensify
these controls on coastal change. Finally, the impact of
such processes depends upon the ability of coastal landforms
to migrate to new locations in the coastal zone and to
occupy the accommodation space that becomes available
(or not) to them (Fitzgerald et al., 2008). These issues, and
many more, are dealt with in Chapters 5, 6 and 7.
1.7.2 Recent sea level rise
Global sea level has been rising at a rate of ~1.7–1.8 mm
a− 1
over the last century, with an acceleration of ~3 mm a− 1
during the last decade (Church et al., 2004; Church and
White, 2006) (Fig. 1.12). The total twentieth-century rise
was 0.17 ± 0.05 m (IPCC, 2007a).
Observations since 1961 indicate that the oceans have
been absorbing 80% of the heat added to the climate
system, causing the expansion of seawater and perhaps
FIGURE 1.12. Annual averages of
global mean sea level (mm), 1870–
2003. Sea level fields have been
reconstructed since 1870; coastal
tide gauge measurements are
available since 1950; and altimetry
estimates date from 1993.
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explaining half the observed global sea level rise since 1993
(Table 1.1), although with considerable decadal variability
(IPCC, 2007a). Smaller component contributions are estimated
to have come from glacier and ice cap shrinkage and,
with less certainty, from the Greenland, and particularly, the
Antarctic ice sheets. There is, however, no consensus on
Antarctica. The balance of opinion appears to be for a
shrinking West Antarctic ice sheet and a growing East
Antarctic ice sheet, leading to a near-neutral effect (possibly
perturbed by ice shelf losses on the Antarctic Peninsula). It
should be noted, however, that the fit between estimated
and actual sea level rise over the much longer period 1961–
2003 is poor (Table 1.1).
This may partly be a function of the change in the
measurement base after 1993, to satellite altimetry and away
from tide gauge records. In the latter case, water level
records are complicated by local vertical land movements,
driven by glacial isostatic adjustments, neotectonics and/or
subsurface fluid withdrawal, which need to be subtracted
from the water level record. An additional uncertainty is
that knowledge of changes in the storage of water on land
(from extraction and increases in dams and reservoirs)
remains poor. However, it is also not clear to what extent
the sea level record reflects secular rise and to what extent it
is a measure of regional inter-annual to inter-decadal climate
variability from phenomena such as ENSO, the NAO
and Pacific Decadal Oscillation (PDO) (Woodworth et al.,
2005) the effects of which are also strongly spatially
variable (Church et al., 2004). Thus, for example, elevated
sea levels and anomalously high sea surface temperatures
in the Pacific Ocean were closely correlated during the
major 1997–1998 El Niño event (Allan and Komar, 2006).
It appears likely that this variability also underpins the
relations between coastal and global sea level rise, with
faster coastal rise typical of the 1990s and around 1970 and
faster ocean rise during the late 1970s and late 1980s
(White et al., 2005).
1.7.3 Future sea level rise
The average rate of sea level rise throughout the twentyfirst
century is likely to exceed the rate of 1.8 mm a− 1
recorded over the period 1961–2003. For the period
2090–2099, the central estimate of the rate of sea level
rise is predicted to be 3.8 mm a− 1
under scenario A1B
(Appendix 1.1) (the scenario spread is in any case small:
Table 1.2), comparable to the observed rate of sea level rise
1993–2003, a period thought to contain strong positive
TABLE 1.1. Observed rate of sea level rise and estimated contributions
from different sources, 1961–2003 and 1993–2003
Rate of sea level rise (mm a− 1
)a
Source of sea level rise 1961–2003 1993–2003
Thermal expansion 0.42 ± 0.12 1.6 ± 0.5
Glaciers and ice caps 0.50 ± 0.18 0.77 ± 0.22
Greenland ice sheet 0.05 ± 0.12 0.21 ± 0.35
Antarctic ice sheet 0.14 ± 0.41 0.21 ± 0.35
Sum of individual climate
contributions to sea
level rise
1.1 ± 0.5 2.8 ± 0.7
Observed total sea level
rise
1.8 ± 0.5 3.1 ± 0.7
Difference (observed
minus sum of estimated
climate contributions)
0.7 ± 0.7 0.3 ± 1.0
a
Data prior to 1993 are from tide gauges and after 1993 are
from satellite altimetry.
Source: From IPCC (2007a).
TABLE 1.2. Projected globally averaged surface warming and sea level
rise at the end of the twenty-first century
Temperature
change (°C at
2090–2099 relative
to 1980–1999)a
Sea level rise
(m at 2090–
2099 relative to
1980–1999)
Case
Best
estimate
Likely
range
Model-based
range excluding
future rapid
dynamical
changes in ice
flow
Constant Year 2000
concentrationsb
0.6 0.3–0.9 NA
B1 scenario 1.8 1.1–2.9 0.18–0.38
A1T scenario 2.4 1.4–3.8 0.20–0.45
B2 scenario 2.4 1.4–3.8 0.20–0.43
A1B scenario 2.8 1.7–4.4 0.21–0.48
A2 scenario 3.4 2.0–5.4 0.23–0.51
A1FI scenario 4.0 2.4–6.4 0.26–0.59
a
These estimates are assessed from a hierarchy of models
that encompass a simple climate model, several Earth Models
of Intermediate Complexity (EMICs) and a large number of
Atmosphere–Ocean General Circulation Models (AOGCMs).
b
Year 2000 constant composition is derived from
AOGCMs only.
Source: From IPCC (2007a).
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residuals within the long-term pattern of sea level variability.
Under the A1B scenario, by the mid-2090s sea level rises
by +0.22 to +0.44 m above 1990 levels, at a rate of 4 mm
a− 1
. The thermal expansion term accounts for 70–75% of
the total rise, being equivalent to a sea level rise of
2.9 ± 1.4 mm a− 1
in the period 2080–2100 (IPCC, 2007a).
In terms of the history of sea level rise projections, the
IPCC Fourth Assessment predictions appear to suggest a
further reduction in the expected rate of sea level rise
(Fig. 1.13). However, these new projections do not allow
for a contribution from ice flow from the Greenland and
Antarctic ice sheets. Conservative estimates suggest that
accelerated ice flow rates might add +0.1 to +0.2 m to the
upper range of sea level rise (i.e. a sea level rise of up to
0.79 m under scenario A1FI: Appendix 1.1).
Non-model-based estimates of future sea level rise,
based upon a semi-empirical relationship connecting temperature
change and sea level rise through a proportionality
constant of 3.4 mm a− 1
per °C, suggest a potential rise at
2100 of 0.5 to 1.4 m (Rahmstorf, 2007), although this
methodology has been highly contested.
1.8 Cumulative drivers of global
environmental change (I): topographic
relief
1.8.1 Introduction
By contrast with hydroclimate and sea level changes, relief
and human activity (Section 1.9) are discontinuous both
over space and through time. The implications of this
simple fact are profound. Spatial discontinuities dictate
that certain parts of the landscape are more sensitive to
the drivers of change than others; temporal discontinuities
mean that very old and very young landscape elements can
exist side by side (Fig. 1.5). Global impact then becomes
the net effect of change at a large number of disparate sites.
A further implication is that the geomorphologist is best
suited to identify those aspects of the landscape which are
particularly sensitive to disturbance.
1.8.2 The sediment cascade
Continental-scale relief defines a pathway from the highest
mountains to the ocean; local-scale relief, with associated
sinks, defines a complex of pathways which can be best
described by the term ‘sediment cascade’. The type and rate
of weathering, erosion and denudation are profoundly
controlled by these pathways, which ultimately owe their
variety to relief at a wide range of scales.
Weathering is the alteration by atmospheric and biological
agents of rocks and minerals. The physical, mineralogical
and chemical characteristics of the materials are
modified so that these weathering products can be
removed by either mechanical or biochemical erosion.
Mechanical and biochemical erosion involves mobilisation,
transport and export of rock and soil materials
(Fig. 1.14a). Surface and subsurface water is critical to
these processes. How much of these so-called ‘clastic’
sediments are broken up into their constituent chemical
elements, the extent to which these elements have become
combined with nutrients and the amount of comparatively
unchanged rocks and minerals depends on the type and
rate of weathering. The sediment which is exported is
engaged to a greater or lesser extent in exchange processes
between minerals, solutes and nutrients.
Primary sediment mobilisation can usefully be divided
into ‘normal regime’ processes that are more or less pervasive
and occur regularly, and episodic or ‘catastrophic’
events which occur less frequently. The former include
soil creep, tree throw, surface disturbance by animals and
surface erosion from exposed soils; the latter include rockfalls,
rockslides, earthflows, landslides, debris avalanches
and debris flows.
Sediment transport requires both a supply of transportable
sediment and runoff competent to entrain the sediment.
Sediments in suspension and bedload have the greatest
influence on river channel form, whereas solutes, nutrients
and pollutants are important indices of biogeochemical
cycling processes.
The sediment cascade involves inputs and outputs with
delays caused by: rates of rock breakdown, intermittent
sediment mobilising events, the limited capacity of the
flows to entrain sediment, and trapping points that occur
downstream, so that sediment is intercepted and
FIGURE 1.13. Changing estimates of the range of potential sea level
rise to 2100 (predictions in the period 1983–2001) or 2099 (data
from IPCC 2007a).
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remobilised at a later time. Sediment in a drainage system
thus moves through a cascade of reservoirs (Fig. 1.14b).
This simple picture is distorted by the fact that sediment
transport is also a sorting process. Mixtures of sedimentary
particles of differing size and density segregate in the
cascade into subpopulations with different transit times
through the landscape. In the case of disturbance, there is
a spatial complication in that the sediments have diffuse
sources. The sedimentary signal originating in the uppermost
part of the basin may move through a reach subject to
similar disturbance and be reinforced. But at downstream
points, if the disturbance is of varying intensity, the reinforcement
will vary spatially. Sediment on its way from
source to sink gets sidetracked in a number of ways, not
only into channel and floodplain storage but also into other
hillslope locations (Fig. 1.14b).
1.8.3 Topographic relief and denudation
In spite of the variety of ways in which sediment is delayed
on its way to the ocean, there are extensive data sets that
demonstrate a close relationship between topographic relief
and rates of fluvial erosion. With the increasing availability
of digital elevation models, it has also become possible to
infer average natural erosion rates, as illustrated in Fig. 1.15
for the conterminous USA. The units used may be unfamiliar
as they are given in metres of denudation per million
years, but the main message of the map is that relief is a
strong driver of landscape change (see Chapter 2 for an
expansion of this theme and discussion of shortcomings of
this generalisation).
1.8.4 The sediment budget
In order to account for the sources, pathways of movement
and rates of delivery of sediments along coasts and through
river basins, a method of budgeting of sediments has been
developed. A river basin sediment budget is ‘an accounting
of the sources and disposition of sediment as it travels from
its point of origin to its eventual exit from a drainage basin’
(Reid and Dunne, 1996).
If the sediment budget is balanced, the residual will be
zero. Thus the sediment budget can be expressed as
I À O ¼ ÁS (1:1)
where I is input, O is output and ΔS is change of storage
over the time period of measurement. This equation will
hold for any landform or landscape as long as the budget
cell can be unambiguously defined. In the case of the river
2
FIGURE 1.14. (a) The sediment cascade system from biochemical
and mechanical weathering sources to export of sediment, solutes
and nutrients. (b) Relations between sediment mobilisation,
production, deposition and yield. Line widths are proportional to the
amount of sediment transferred and values are shown in t km− 2
a− 1
.
An average of 105 t km− 2
a− 1
is mobilised on hillslopes and only 55 t
km− 2
a− 1
is exported from the basin (from Reid and Dunne, 1996).
FIGURE 1.15. Estimates of average natural erosion (denudation)
rates inferred from GTOPO30 area–elevation data and global
fluvial erosion–elevation relations from Summerfield and Hulton
(1994) (from Wilkinson and McElroy, 2007). Units are in metres of
denudation per million years.
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basin, the budget cell defines itself. But Cowell et al.
(2003), for example, in working with the problem of determining
an objective budget cell in coastal studies, have
coined the term ‘coastal tract’. They define the coastal tract
as the morphological composite comprising the lower
shoreface, upper shoreface and back barrier. They use this
framework in defining boundary conditions and internal
dynamics to separate low-order from higher-order coastal
behaviour (see Chapter 6 for further details).
The sediment budget is a mass-balance-based approach,
which necessarily, in principle, includes a consideration
of water, sediments, chemical elements and nutrients.
This accounting of sources, sinks and redistribution pathways
of sediments in a unit region over unit time is a
complex exercise (Dietrich and Dunne, 1978). The primary
application of sediment budgets to landscapes is
in the accounting of clastic sediment transfers because
clastic sediments provide the most direct indication of
changing surface form. The US Corps of Engineers working
on the coasts of southern California and New Jersey
and geomorphologists working in the Swiss Alps and
northern Scandinavia were the first to employ this methodology
in coastal and river basin geomorphology in
the 1950s.
Sediment budget studies have become a fundamental
element of coastal, drainage basin and regional management,
but only when somewhat simplified (Reid and
Dunne, 1996). They can be formulated to aid in the design
of a project, characterise sediment transport patterns and
magnitudes and determine a project’s erosion or accretionary
impacts on adjacent beaches and inlets (Komar, 1998).
Although Trimble (1995) and Inman and Jenkins (1999)
have developed flexible models to discriminate the effects
of climate change and land use activities on sediment
budgets, their application is at an early stage.
In conclusion, the growing interest in global environmental
change has spurred interest in a variety of massbalance
calculations that permit quantitative comparisons
from one region to another and from one time period to
another, with appropriate scaling. The biggest challenge in
the use of sediment budgets is in making the link between
intensively studied smaller-scale systems to the global scale
and in extrapolating from the short term to the longer term
and future changes.
1.8.5 Limitations of the sediment budget
approach in determining the role of relief
1. Summerfield and Hulton (1994) demonstrated that 60%
(but no more) of the spatial variation of global sediment
yield can be explained by relief and runoff.
2. The sediment budget approach often ignores the role
of tectonics. This is unfortunate because the uplift of
mountain ranges involves the input of new mass which
directly influences the mass balance of the geosystem.
When longer term studies of sediment flux are undertaken,
it is essential to incorporate the style and rate of
tectonic processes (see Chapter 15).
3. Global riverine changes such as chemical contamination,
acidification, and eutrophication which are of great
interest in global environmental change are rarely
included in sediment budgets (see Chapter 3).
4. Order of magnitude effects produced by global-scale
river damming (Nilsson et al., 2005) and general
decrease of river flow due to irrigation (Meybeck and
Vörösmarty, 2005) scarcely require sediment budgeting
(see Chapter 4).
5. Recent studies of the Ob and Yenisei rivers in Russia
(Bobrovitskaya et al., 2003) and of the Huanghe River
in China (Wang et al., 2007) suggest that the decline in
sediment load delivered to the sea in recent years is
caused primarily by soil conservation practices and reservoir
construction; relief and runoff have relatively
little influence.
6. These observations lead logically to an analysis of the
critical role of human activity.
1.9 Cumulative drivers of global
environmental change (II): human activity
Global population growth and the attendant land cover and
land use changes pose serious challenges for management
and planning in the face of global environmental change
(Lambin and Geist, 2006). Wasson (1994) has emphasised
the value of mapping past land use and land cover
changes in attempting to interpret contemporary landscape
change and degradation. De Moor et al. (2008)
have demonstrated that in the past 2000 years, the impact
of climate on river systems can be neglected when compared
with the human impact. They link the considerable
changes in hillslope processes induced by humans with
equivalent sediment supply to the river valleys of the
Netherlands. Factors that influence land cover and land
use change can be divided into indirect and direct
factors.
1.9.1 Indirect factors
Indirect factors include such broadly contextual factors as
demographic change, socioeconomic, cultural and religious
practices and global trade, which enhance the importance of
governance sensu lato. The indirect drivers are of critical
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importance when we come to discuss scenario building
(Appendix 1.1) in the sense that population level and
density, socioeconomic context, societal values and the
institutions available to implement change must all be
incorporated into any forward-looking thinking.
Population growth
The history of humans as geomorphic agents is now
becoming clear. Virtually all of Earth’s biomes have been
significantly transformed by human activity because of the
enormous growth of the world’s population during the
second half of the twentieth century and the even more
rapid growth in energy use (Turner et al., 1990a). Some
80% of humankind lives in developing countries in Asia,
Africa and South and Middle America and those countries
account for more than 90% of the more than 100 million
births each year. These populations are becoming increasingly
urbanised; thus whilst only 3% of the population of
less developed regions lived in cities larger than 100 000
inhabitants in 1920, this figure is set to rise to 56% by 2030.
By 2015, Asia is predicted to have 1.02 billion people in
urban centres of over 500 000 inhabitants. Many of these
populations are being squeezed into narrow coastal and
estuarine margins. Several of the fastest-growing cities,
with rates of increase of up to +4% per year and all projected
to have populations in excess of 15 million by 2015,
have long histories of exposure to coastal hazards; they
include Shanghai, Kolkata, Dhaka and Jakarta (United
Nations Population Fund, 2007).
As a result, the biomes shown in Plate 3 are actually an
abstract depiction of the climax vegetation in the absence
of human intervention. Only in the areas unmodified by
agriculture, forestry and urbanisation do these biomes
correspond to the terrestrial ecosystems of today.
Socioeconomic context of soil degradation
If land loss continues at current rates, an additional 750000–
1.8 million km² will go out of production because of soil
degradation between 2005 and 2020. There are 95 developing
countries, each with less than 100 000 km² of arable
land, for which the loss of their most vulnerable lands will
mean either loss of economic growth potential or famine or
both (Scherr, 1999). The development of long-term programmes
to protect and enhance the quality of soils in these
countries would seem to be a priority. Countries with large
areas of high quality agricultural land (Brazil, China, India,
Indonesia and Nigeria, for example) will probably focus on
the more immediate economic effects of soil degradation.
Because the poor are particularly dependent on agriculture,
on annual crops and on common property lands, the poor
tend to suffer more than the non-poor from soil degradation.
Countries or sub-regions that depend upon agriculture as the
engine of economic growth will probably suffer the most.
Furthermore, as growing populations in the developing
world become increasingly urbanised, the difficulties in
maintaining food supply chains between cities and their
rural hinterlands are likely to increase (Steel, 2008).
1.9.2 Direct factors
Direct factors include deliberate habitat change; physical
modification of rivers, water withdrawal from rivers, pollution,
urban growth and suburban sprawl (Goudie, 1997).
Cultivated systems
The most significant change in the structure of biomes has
been the transformation of approximately one-quarter
(24%) of Earth’s terrestrial surface to cultivated systems.
More land was converted to cropland in the 30 years after
1950 than in the 150 years between 1700 and 1850. There is
a direct connection between soil erosion on the land (net
loss of agriculturally usable soil to reservoirs) and coastal
erosion resulting from a reduction in sediment delivery to
the coast. It is estimated that human activity affects directly
8.7 million km² of land globally; about 3.2 million km² are
potentially arable, of which a little less than a half is used to
grow crops. Soil quality on three-quarters of the world’s
agricultural land has been relatively stable since the middle
of the twentieth century, but the remaining 400 000 km² are
highly degraded and the overall rate of degradation has
been accelerating over the past 50 years. Almost 75% of
Central America’s agricultural land has been seriously
degraded, as has 20% of Africa’s and 11% of Asia’s.
In the United States, cropland is being eroded at 30 times
the rate of natural denudation (Figs. 1.15 and 1.16) and this
is creating two problems in addition to the obvious loss of
usable land in situ. First of all, there are large sediment
sinks being created on land, where the sink consists mostly
of clastic sediments and secondly, nutrient sinks are being
created offshore. Trimble and Crosson (2000) have commented
helpfully on the implications of the build-up of new
sediment stores in low-order basins.
It has become increasingly difficult to assess the future
impact of environmental changes on the sediment flux to the
coastal zone because of the complex impacts of human activities
(Walling, 2006). Globally, soil erosion is accelerating
as a result of deforestation and some agricultural practices;
but at the same time, sediment flux to the coastal zone is
globally decelerating, because of dams and water diversion
schemes. A summary statement by Syvitski et al. (2005)
notes that human activities have simultaneously increased
the sediment transport by global rivers through soil erosion
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by 2.3 ± 0.6 Gt a− 1
, yet reduced the flux of sediment reaching
the world’s coasts by 1.4± Gt a− 1
because of retention within
reservoirs. Over 100 Gt of sediment and 1–3 Gt of carbon
are now sequestered in reservoirs constructed largely within
the last 50 years. Furthermore, the impact of dams on large
rivers is likely to continue to reduce the global sediment
load and will alter the patterns of sediment flux in many
coastal zones (Dearing and Jones, 2003).
Reduced sediment loads delivered to the coastal zone
result in accelerated coastal erosion and a decrease in habitat.
The reduction of the seasonal flood wave also means that the
sediment is dispersed over smaller areas of the continental
margin. Although this is a correct aggregate picture, it should
be borne in mind that tropical deforestation continues unabated
while temperate forests are being enlarged. There are
therefore numerous individual unregulated basins within the
tropical world (e.g. Indonesia and Malaysia) where sedimentation
at the coast continues to be considerable.
Milliman and Syvitski (1992) concluded that mountainous
rivers, particularly in the island nations of Southeast
Asia, contribute the largest proportion of global sediment
flux. These regions have recent histories of severe deforestation
and are dominated by low-order streams. It is
therefore probable that the most rapid increase in future
sediment flux to the ocean may well come from disturbed,
small–medium-size basins feeding directly to the coast.
This sediment is likely to contain enhanced loads of
adsorbed nutrients and surface pollutants, a phenomenon
which has already been documented in some detail from the
west coast of India (Naqvi et al., 2000). The primary factor
responsible for increased nitrous oxide production is the
intensification of agriculture and the increasingly widespread
application of anthropogenic nitrate and its
subsequent denitrification. The western Indian continental
shelf and the Gulf of Mexico immediately to the south and
west of the Mississippi delta are well-documented hypoxic
zones; that is, the concentration of oxygen in the water is
less than 2 ppm. In the case of the Mississippi–Missouri
drainage basin both phosphates (industrial) and nitrates
(agricultural) constitute diffuse sediment sources which
follow both surface and subsurface hydrological pathways
(Fig. 1.17) (Goolsby, 2000; Alexander et al., 2008). The
average extent of the hypoxic zone was 16 700 km²
between 2000 and 2007. The goal of reducing the extent
of the hypoxic zone to an average of 5000 km² by 2015
looks increasingly difficult as there has been no significant
reduction in nutrient loading (Turner et al., 2008).
Desertification
Desertification is defined by the UN Convention to Combat
Desertification as ‘land degradation in arid, semi-arid
and dry sub-humid areas resulting from various factors,
including climatic variation and human activities’. Land
degradation in turn is defined in that context as the reduction
or loss of biological or economic productivity. From
the perspective of the global hydrological cycle the role of
vegetation in land surface response is critically important,
especially through vegetation–albedo–evaporation feedbacks.
Desertification is a global phenomenon in drylands,
which occupy 41% of Earth’s land area and are home to
more than 2 billion people. Some 10–20% of drylands
are already degraded. This estimate from the Desertification
Synthesis of the Millennium Assessment is consistent
with the 15% global estimate of soils permanently
degraded. Excessive loss of soil, change in vegetation
composition, reduction in vegetative cover, deterioration
of water quality, reduction in available water quantity and
changes in the regional climate system are implicated.
Desertified areas are likely to increase and proactive land
and water management policies are needed (Reynolds
et al., 2007).
1.9.3 Conclusion
The fourth driver of global environmental change, namely
human activity, is the most rapidly changing driver. Land
use and land cover change, especially the transformation of
forest and grasslands to logged forests, agricultural lands
and urbanisation, have the most profound effect. The intensification
of human activity in the temperate and tropical
zones is especially effective in landscape change; by contrast,
in polar latitudes, where population densities are low,
climate in particular, but also relief and sea level, continue
to be the more important drivers.
FIGURE 1.16. Rates of cropland erosion derived from estimates by
the Natural Resources Conservation Service using the Universal
Soil Loss Equation, and scaled to a farmland mean of 600 m Ma−1
.
(from Wilkinson and McElroy, 2007).
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1.10 Broader issues for geomorphology
in the global environmental change
debate
1.10.1 Putting the ‘geo’ into the ‘bio’ debates
Geodiversity is defined as a measure of the variety and
uniqueness of landforms, landscapes and geological formations
(Goudie, 1990) in geosystems at all scales; biodiversity
is defined as the variation of life forms within a given
ecosystem, biome or the entire Earth. There are thus strong
parallels between the two concepts. The term natural heritage
is more easily understood by the general public and sums up
the totality of geodiversity and biodiversity. Geodiversity has
its own intrinsic value, independent of any role in sustaining
living things. The World Heritage Convention came into
force in 1972 and after 35 years the World Heritage List
now identifies, as of 2007, 851 sites of ‘outstanding universal
value’ (http://whc.unesco.org/en/list/). Of these, 191 are
FIGURE 1.17. (a) Diffuse sediment sources of phosphates and nitrates from the Mississippi–Missouri drainage basin. (b) The resultant
hypoxia in the Gulf of Mexico (modified from Goolsby, 2000).
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justified in terms of at least one component of geodiversity
(Appendix 1.4). It is useful to note that biodiversity cannot
exist without geodiversity, the natural diversity of our nonliving
environment. There is a tendency to think of biodiversity
as being fragile, with geodiversity having greater
robustness. However, this is not necessarily the case, but in
those sites where geodiversity is relatively robust the loss of
any one element of that diversity becomes doubly serious.
Geomorphology has an important role to play in identifying
physically sensitive landscapes that are highly responsive
to environmental change. Geoconservation aims to preserve
geodiversity (O’Halloran et al., 1994). This means
protecting significant examples of landforms and soils, as
well as a range of distinctive Earth surface processes. It is
proposed that we have an ethical obligation to retain landforms
and landscapes of unique natural beauty and diversity
for future generations. There is a very good reason for
active geoconservation management because, when a landform
is lost, it can only be replaced over geological timescales.
Glen Canyon in Colorado has disappeared and, in a
significant sense, the Three Gorges of the Yangtze (LiJiang)
River have disappeared. Although it is not anticipated
that the Grand Canyon will disappear sometime soon,
it is only through active geoconservation management that
its pristine status can be maintained (Fig. 1.18).
But there are other reasons why biodiversity concerns
cannot be divorced from geodiversity. There are linkages,
for example, between above-sediment and sediment biota
in freshwater ecosystems, which suggest that the monitoring
of the bio- and the geodiversities should be collaborative
(Lake et al., 2000). The standard view in ecology is that
biodiversity confers stability and resilience and, to a more
limited extent, natural floodplains conserve the resilience of
landforms to changing environmental drivers.
Nevertheless, the analogy between biodiversity and geodiversity
should not be overemphasised given the detailed
functional differences between eco- and geosystems.
1.10.2 Geomorphology, natural hazards
and risks
The dynamic nature of landscapes and landforms over
space and through time has generated interest in defining
geomorphological ‘hotspots’. Biodiversity hotspots are
defined as regions that contain at least 1500 species of
vascular plants and which have lost at least 70% of their
original habitat (Myers et al., 2000). In other words they
are regions of special value and at the same time highly
vulnerable to disturbance. By analogy, geomorphological
hotspots are sites or regions of special value in terms of
geodiversity and highly vulnerable to environmental change.
‘Geoindicators’ have been defined as one way of identifying
such hotspots (Berger and Iams, 1996). They are measures
of geomorphological processes and phenomena that vary
significantly over periods of less than 100 years and are
thus high-resolution measures of short-term changes in the
landscape. Geoindicators have been designed as an aid to
state-of-the-environment reporting and long-term ecological
monitoring. They are also useful in the identification of
potential natural hazards, where irreversible damage to
property and loss of life occur. A wide range of slope failure,
river, coastal and wind erosion related problems which
have been exacerbated by human activity are recognised as
natural hazards. Where the geoindicator detects unusual
movement or instability, a geomorphological ‘hotspot’ is
identified. If this instability is located close to human settlements
or transport corridors, a geomorphological hazard
FIGURE 1.18. Bright Angel
Canyon, Grand Canyon National
Park: a landscape of ‘outstanding
universal value’ (from Strahler and
Strahler, 1994).
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is declared and risk studies may be undertaken. It is the
point of intersection of the human use system with the
extreme geomorphological event which defines a geomorphological
hazard (Glade, 2003).
Because of the high population density, the high-relief
volcanic slopes, the intense rainstorms produced by multiple
annual typhoons, the vulnerable coastline and the tendency
to build settlements in the most vulnerable locations, there
is a tragic history of loss of lives and infrastructure in the
Japanese islands (Akagi, 1973). In the example illustrated
(Fig. 1.19) a village, located on a debris flow fan on the
western flanks of Mount Fujiyama, Japan is the human
use system. The village was overwhelmed by debris flows
(an extreme geomorphological event) following intense
rainstorms accompanying Typhoon 26, in 1966. The
unfortunate coincidence of a human use system interacting
with a geomorphological event system (or sediment
cascade) defines a geomorphological (or natural) hazard.
Surrounding the question of natural hazards is the question
of natural risk (Hufschmidt et al., 2005). Natural risk is a
measure of the probability of adverse effects on health,
property and society, resulting from the exposure to a natural
hazard of a given type and magnitude within a certain time
and area. If risk studies had been undertaken before the
event shown in Fig. 1.19, it might have been possible to
develop a plan for mitigation of the disaster and to save
many lives and much property as a result.
1.10.3 Geomorphology and unsustainable
development
The concept of sustainable development has infused the
policy world since the publication of Gro Harlem
Brundtland’s Our Common Future (WCED, 1987). The
concept of sustainability is highly contested in a field like
geomorphology because the drivers of change are themselves
constantly changing and landscapes and their soils
are, over century timescales, frequently collapsing, due to
overexploitation. While the value of sustainability has
achieved wide currency in principle, the implementation
has proved difficult. A distinction should be made between
‘strong sustainability’ in the case of a landscape and a
‘weak sustainability’ in the case of a society. Strong sustainability
concerns preserving the structure and function of
an ecosystem and its supporting geophysical substrate.
Weak sustainability admits that landscapes may be changed
by deliberate human agency so long as the total resource
value is not devalued.
It would perhaps be more realistic in geomorphology, and
in related sciences, to seek evidence of ‘unsustainability’
such that adaptation and/or mitigation can be planned well
in advance of the system collapse. Four key concerns have
been identified by the policy community and two promising
approaches have emerged. Concerns are: the need to integrate
natural and physical science with social science, health
science and humanities research; a focus on the future; the
need to involve stakeholders; and a sensitivity to the appropriate
temporal and spatial scale of analysis required. The
term ‘back-casting’ was coined by Robinson (2004) for an
approach that involves working backward from a desired
future end point to the present and finding the appropriate
policy measures required to reach that point. Scenario
building, discussed in Chapter 3, is one specific application
of the back-casting approach. ‘Integrated assessment’ is
another interdisciplinary process of ‘combining, interpreting
and communicating knowledge from diverse scientific
FIGURE 1.19. Debris flows as geomorphological hazard, illustrated
from the results of an intense rainstorm in 1966 at Ashiwada in
Yamanashi Prefecture, Japan. (a) Pre-1966; (b) post-typhoon 26,
1966 (from Akagi, 1973).
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disciplines in such a way that the whole set of cause–effect
interactions of a problem can be evaluated from a synoptic
perspective’ (Rotmans and Dowlatabadi, 1998).
Whilst it must be admitted that these are promising
policy approaches, especially with respect to their holistic
emphasis, geomorphologists have to ask the question ‘in
what sense can landscapes be sustained over century or
millennial timescales in the face of constantly changing
human activities, sea level changes and climate change?’
Not only is there a problem of constant change and the
possibility of achieving sustainability in the future, but
many would claim that we have already exceeded the
Earth’s capacity to support our consuming lifestyle. Rapid
increase in interest in the ecological footprint idea (Rees,
1992) confirms a move of public opinion towards greater
concern about our degrading environment.
Ecological footprint analysis attempts to measure the
human demand on nature and compares human consumption
of natural resources with the Earth’s ecological
capacity to regenerate them (Plate 6). Ecological footprinting
is now widely used as an indicator of environmental
sustainability. The only prudent policy would seem to be
the absolute minimisation of land cover change especially
where urban sprawl impacts landforms of exceptional interest
or soils whose optimal use is an agricultural one.
1.10.4 Geomorphology and the land ethic
Aldo Leopold’s land ethic (Leopold, 1949) offered this
general principle of land management: ‘A thing is right
when it tends to preserve the integrity, stability and
beauty of the biotic community. It is wrong when it tends
otherwise.’ Land to Leopold had a broad meaning. It
included soils, waters, plants and animals. The boundaries
included people as members of nature. Leopold’s lifelong
land ethics journey led from a stewardship resource management
mentality to stewardship entwined with ecological
conscience.
Geomorphology provides certain constraints that limit
how people should act towards the land and, at another
level, it challenges the unspoken assumptions of an
unwisely managed neoliberal society, which accepts
uncritically the rule of the market. Only recently has the
neoliberal view been willing to attempt proper valuation of
environmental resources (e.g. Millennium Ecosystem
Assessment (2005) and the Stern Review (2007) on the
economics of climate change).
It is clear that the removal of soil cover will reduce
livelihood options for people and agriculture. The careful
management of land and its biogeochemical and aesthetic
properties enhances long-term human security.
1.11 Landscape change models in
geomorphology
1.11.1 Landscape change over long time periods
Brunsden (1980) has developed the idea of ‘characteristic
form time’ (Fig. 1.20). This is a variant on the ‘punctuated
equilibrium’ idea, but its importance is based on the fact
that it is possible for a landscape to remain sufficiently
unperturbed by environmental change such that it develops
a form that is representative of the balance of resistance and
driving forces, a balance which remains relatively
unchanged over long periods of time. Whereas this was
the prevailing assumption in geomorphology during presystems
thinking, such has been the swing towards emphasis
on change that some have questioned the possibility of a
characteristic form ever being achieved. But Brunsden
(1980) has pointed out that there is a need for the concept
of characteristic form because the geological record gives
evidence of past landscapes that appear to have retained
constant characteristics over millions of years (e.g. much of
the interior landscapes of Australia and the extremely low
relief extensive erosion surfaces exposed in the stratigraphy
of the Grand Canyon; Fig. 1.18).
The idea of the landscape as a palimpsest, with evidence
preserved in layers which have simply to be unpeeled in
FIGURE 1.20. Definitions of geomorphological time, impulse
recurrence, reaction, relaxation and characteristic form (modified
from Brunsden, 1980).
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order to discover the evidence of past landscape forming
processes, is well enshrined in the literature (Wasson, 1994).
Frequency and magnitude of geomorphic events
However, in rapidly changing global environments, it is no
longer possible to maintain the fiction of statistical stationarity
in historical environmental data. Even in a landscape
as quiescent as that of the UK, Higgitt and Lee (2001)
demonstrated the difficulty of the concept of frequency
and magnitude over the past 1000 years and Steffen et al.
(2004), by invoking the ‘no analogue’ argument, have made
it doubly difficult to sustain the traditional hydrological
approach to the topic. It seems probable that the coupling
of temporal and spatial dimensions through the analysis of
lake and marine sediments (Dearing and Jones, 2003) and
ice cores will provide the best estimates of changing
frequencies and magnitudes of geomorphic events.
1.11.2 Thresholds and complex response
Individual slopes and river channels lie at variable distances
from ‘thresholds’ (points at which major changes occur
in response to perturbation) (Schumm, 1973; Brunsden and
Thornes, 1979). A simple example of this effect is that a
perturbation may generate a landslide or debris flow at a
location in the headwaters of basin A; and the same perturbation
may generate a similar slope failure close to the
mouth of basin B. The response at the mouth of basin B
will differ significantly from that at the mouth of basin A. In
effect the communication of threshold exceedance through
the river basin system is far more complex and has given
rise to the complex response theory (Schumm, 1973).
Schumm (1973, 1977, 1985, 1991) has demonstrated the
importance of discriminating between intrinsic and extrinsic
variables in the evolution of landscapes. If we consider a
river basin, we see a system which has its own organisation
of river networks and slopes, adjusted to a greater or lesser
extent to the prevailing internal properties of the basin, such
as lithology, hydrology and biomass. These are intrinsic
variables. At the same time, the system is subject to land use
and land cover change and climate change. These are
extrinsic variables. The point at issue is that the intrinsic
and extrinsic variables operate independently and that systems
with apparently identical intrinsic properties will
respond differently to different extrinsic variables Even
more subtly, side-by-side systems with apparently identical
intrinsic properties may respond quite differently to apparently
identical extrinsic variables. This is a result of the
fact that the internal organisation of a geomorphic system
contains historical elements that have not yet reached ‘characteristic
form’ as defined above.
1.11.3 Landscapes of transition
Hewitt et al. (2002) have developed the idea of landscapes
of transition. Nearly all landscapes bear the imprint of past
conditions. Some of these past conditions no longer apply.
Biomes have expanded and contracted geographically over
large areas over geological timescales. There are at least
two ways in which regional landscapes must be considered
as transitional:
(a) some landforms reflect different past conditions. They
are not merely relict forms; they operate as constraints
upon present-day developments and
(b) there are also parts of landscapes and patterns of sedimentation
that are in incomplete transition from past
conditions.
The notion of temporal transition is intended to cover
ways in which environmental changes are uniquely
expressed. Although processes and landforms are driven
by contemporary heat and moisture conditions, available
relief and lithologies, they are not directly responding to
them. They involve mechanisms or patterns of adjustment
that are not readily obvious in climate change or tectonics.
When geomorphic processes are modifying past landscapes,
the adjustments do not travel directly from one
equilibrium to another. There are combinations of intervening
constraints, self-adjusting mechanisms or ‘epicycles’
peculiar to the earth surface processes affected.
In Canada, Church et al. (1999) have suggested that, at
all scales above the order of 1 km², the landscape is still
adjusting to the perturbation of continental glaciation. The
fact that geomorphic systems have variable relaxation times
following disturbance (i.e. time taken to return to the same
conditions as those which prevailed prior to disturbance)
has been well understood, but few careful quantitative
studies have been available until recently.
The response of the cryosphere to global environmental
change, which demonstrates high sensitivity to temperature
change through the threshold 0 ºC, is a more obvious example
than the response of such an extensive and resistant
landscape as the whole of Canada.
There are radical differences in the role of geomorphology
in global environmental change whether one takes the
characteristic form approach or the transitional landscapes
approach. At one level, it is a question of different punctuated
equilibrium models of the landscape, where one is
dominated by quiescence and the other by change. But it is
not necessary to choose between the two approaches. There
are elements of the landscape that have remained unchanged
for long periods of time and others that are highly sensitive.
The challenge and the opportunity of global environmental
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change is to distinguish those parts of landscapes that are
close to threshold and which, because of their vulnerability,
deserve priority attention. The short-term challenge of global
environmental change makes the transitional landscapes
and complex response models more relevant; but this in
no way invalidates the characteristic form time model for
interpreting longer-timescale changes.
1.11.4 Adaptive systems
The transience of components of the landscape and the idea
of transitional landscapes constantly undergoing change are
interesting concepts that are directly relevant to contemporary
global environmental change. If the IPCC definition of
vulnerability is seriously engaged, then geomorphologists
also have to investigate adaptive systems. Reliance on
reactive, autonomous adaptation to the cumulative effects
of environmental change is ecologically and socioeconomically
costly. Planned and anticipatory adaptation
strategies can provide multiple benefits. But there are limits
on their implementation and effectiveness. Enhancement of
adaptive capacity reduces the vulnerability of landscapes
to environmental change, but adaptive capacity varies
considerably among regions, cultures and socioeconomic
groups.
It is possible to learn from ecology where recent models
have placed environmental change and system collapse as
central to an understanding of contemporary change and
where there are similar complexity problems. Panarchy is a
metaphor designed to describe systems of ecosystems at
varying spatial and temporal scales. The terminology
developed for panarchy (Holling, 2001) is entirely ecological
and needs to be translated for the needs of geomorphology.
Holling suggests that complex systems are driven
through adaptive cycles which exist at a range of spatial
scales. The term adaptive is self-evident in ecological systems;
in geomorphic systems we often speak of self-regulating
systems (Phillips, 2003). Adaptive cycles are defined as
consisting of four phases, namely exploitation (the environmental
disturbance regime), conservation (the response),
collapse (threshold exceedance and unpredictable behaviour
of the system) and reorganisation (recovery) (Fig. 1.21). A
geomorphic analogue would be a glacial–interglacial cycle
characterised by both orderly evolution and system collapse.
The duration of these phases of adaptation in ecological
systems depends on three factors: intrinsic wealth, connectivity
and resilience of the system. A geomorphic analogue
would be the intensity and extent of a glaciation (intrinsic
wealth), the connectivity of the erosion–sedimentation
cycles (connectivity) and the time required for the recovery
of the system during interglacials (resilience).
FIGURE 1.21. The panarchy framework (modified from
Gunderson and Holling, 2002). (a) the adaptive cycle;
(b) components of the adaptive cycle; and (c) panarchy in
time and space.
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The panarchy metaphor has a fascinating flexibility in
dealing with complex systems and geomorphologists are
working with this concept in an effort to introduce more
flexible theory into the discussion of geomorphic complexity
(Cammeraat, 2002). Although there are evident differences
between geophysical systems and ecosystems, there are
many parallels in the behaviour of self-organising systems
which can assist in improving attempts to understand and
manage the environment sensitively. The concepts and
terminology of the panarchy model are consistent with
geomorphic concepts such as complex response (Schumm,
1973), threshold exceedance, landscape sensitivity and
barriers to change. Complex adaptive cycles throw new
light on complex response in landscape systems. Resistances
in the panarchy model of ecosystem behaviour perform a
similar function to that of geomorphic barriers to change in
geosystems.
In the context of rapid and accelerating global environmental
change, geomorphologists are well placed to assess
the potential for collapse and/or reorganisation of many of
our desired landscapes. A scenario is a coherent, internally
consistent and plausible description of a possible future
state of the world (IPCC, 2007b.). Scenarios are not predictions
or forecasts but are alternative images without
ascribed likelihoods of how the future might unfold. The
development of scenarios of landscape trajectories is a
worthy aim. With such an approach, it may be possible to
forestall the most serious negative outcomes and make wise
use of the new opportunities created by global environmental
change.
1.12 Organisation of the book
Following this introductory chapter, the volume is divided
into two substantive sections, consisting respectively of six
chapters (2–7) and seven chapters (8–14). The concluding
Chapter 15 contains the highlights of conclusions from the
substantive chapters, focussing on the identification of
geomorphic hotspots, major uncertainties and matters of
special concern that ought to be communicated to policymakers,
environmental managers and the scientifically
literate public.
The two substantive sections of the book concern respectively
azonal and zonal topics. In Chapters 2–7 (azonal
topics) we attempt to follow the energy, mass and information
cascade from mountain tops to the sea and focus
attention on the ways in which environmental change is
governed by a limited number of geophysical processes and
their interactions with human activity. The hydrological
cycle and the sediment budget constitute the central themes
of this section and environmental change is discussed under
the influence of this primarily geophysical framework. The
chapters are sequenced along the topographic gradient:
mountain environments; lake systems; river systems; estuaries,
sedimentary coasts and coastal wetlands; beaches,
cliffs and deltas; and coral reefs.
In Chapters 8–14 (zonal topics) we have attempted to
identify the critical landscapes thought to be the most
sensitive to potential environmental change although it is
accepted that this list may not be exhaustive. The biome is
used as the unit of zonality as vegetation is a good integrator
of average climate conditions. The biomes selected for
treatment in depth are: tropical rainforest; tropical wet and
dry savanna; deserts; Mediterranean landscapes; midlatitude
temperate forest and rangelands (with particular
reference to landslides and other slope processes in this
biome); tundra and permafrost-dominated taiga; and ice
sheets and ice caps. In some cases the whole zone is composed
of critical landscapes (e.g. savanna and permafrostdominated
taiga), but in other cases the hotspots are located
around the boundaries of the zone (zones of transition).
The mid-latitude temperate forest lands of Europe have
been deliberately excluded for two reasons: firstly because
the biome has been so intensively modified by human
activity that climate change will probably produce only
marginal geomorphological change and secondly because
the azonal chapters include good coverage of this biome.
The final Chapter 15 sums up the key conclusions on
landscape change trajectories, both positive and negative;
provides warnings about special concerns; lists opportunities
for landscape enhancement; and, where appropriate, makes
recommendations for action by policy-makers and concerned
citizens. It also considers the relation between this
book and the IPCC Fourth Assessment Reports and recommends
a closer integration of future landscape change
discussions with the anticipated IPCC Fifth Assessment.
APPENDIX 1.1
The IPCC scenarios
Assumptions contained within the IPCC scenarios
(Table 1.3) are as follows:
A1. The A1 storyline and scenario family describes a
future world of very rapid economic growth, global
population that peaks in mid-century and declines
thereafter, and the rapid introduction of new and
more efficient technologies. Major underlying themes
are convergence among regions, capacity building and
increased cultural and social interactions, with a substantial
reduction in regional differences in per capita
income. The A1 scenario family develops into three
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groups that describe alternative directions of technological
change in the energy system. The three A1
groups are distinguished by their technological
emphasis: fossil intensive (A1FI), non-fossil energy
sources (A1T), or a balance across all sources (A1B)
(where balanced is defined as not relying too heavily
on one particular energy source, on the assumption
that similar improvement rates apply to all energy
supply and end use technologies).
A2. The A2 storyline and scenario family describes a very
heterogeneous world. The underlying theme is selfreliance
and preservation of local identities. Fertility
patterns across regions converge very slowly, which
results in continuously increasing population. Economic
development is primarily regionally oriented and per
capita economic growth and technological change
more fragmented and slower than other storylines.
B1. The B1 storyline and scenario family describes a convergent
world with the same global population, that
peaks in mid-century and declines thereafter, as in the
A1 storyline, but with rapid change in economic structures
toward a service and information economy, with
reductions in material intensity and the introduction of
clean and resource-efficient technologies. The emphasis
is on global solutions to economic, social and environmental
sustainability, including improved equity, but
without additional climate initiatives.
B2. The B2 storyline and scenario family describes a
world in which the emphasis is on local solutions to
economic, social and environmental sustainability. It
is a world with continuously increasing global population,
at a rate lower than A2, intermediate levels of
economic development, and less rapid and more
diverse technological change than in the B1 and A1
storylines. While the scenario is also oriented towards
environmental protection and social equity, it focusses
on local and regional levels.
How the IPCC process deals with uncertainty
The question of uncertainty in prediction is discussed
explicitly in each of the IPCC reports (IPCC, 2001b, Box
1–1, p. 79) and is reported in two different ways:
(a) a five-point confidence scale is used to assign confidence
levels to many of the conclusions. The confidence levels
are stated as probabilities, meaning that they represent
the degree of belief among the authors of the report in
the validity of a conclusion, based on their collective
expert judgement of all observational evidence, modelling
results and theory currently available. The confidence
levels are: very high (>95%); high (67–95%);
medium (33–67%); low (5–33%); and very low (<5%).
(b) Qualitative ‘state of knowledge’ descriptors, labelled:
well-established; established but incomplete; competing
explanations; speculative descriptors are used when a
quantitative scale seems inappropriate.
All the following initiatives (Appendices 1.2–1.5) have started
with the same ‘storylines’ by envisaging six different future world
contexts as identified in Appendix 1.1.
APPENDIX 1.2
Global Environmental Outlook scenarios
to 2032 (GEO-3: see UNEP, 2002) and the
fourth Global Environmental Outlook:
environment for development (GEO-4)
The Global Environmental Outlook process has over the
past 10 years (1997–2007) produced a series of global
integrated environmental assessment reports aimed at providing
comprehensive, reliable, scientifically credible and
policy relevant assessments on the interaction between
environment and society. GEO-1 (1997), GEO-2 (1999),
GEO-3 (2002) were UNEP’s three previous global assessments
and GEO-4 appeared in 2007. Special attention is
paid to the role and impact of the environment on human
well-being and vulnerability. There are five themes:
(a) Present global and regional issues in the context of the
development of international environmental governance;
(b) State and trends of the global environment analysing
human drivers and the impact of natural phenomena on
TABLE 1.3. Description of SRES emissions scenarios
Scenario Description
A1 Globally integrated world with rapid economic
growth
A1FI – Continued dependence on fossil fuels
A1B – Balance of fossil and renewable energy
sources
A1T – Shift to renewable energy sources
A2 A world of independently operating self-reliant
nations
B1 Globally integrated but with ecologically
friendly growth
B2 Emphasis on local solutions to environmental
problems
Source: After IPCC (1996b).
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the environment, the consequences of environmental
change for ecosystem services and human well-being;
(c) Interlinkages between major environmental challenges
and their consequences for policy and technology
response options;
(d) Cross-cutting issues on how environment can contribute
to sustainable development goals and how environmental
degradation impedes progress; and
(e) Global and sub-global outlooks, including short-term
(to 2015) and medium-term (up to 2050) scenarios for
the major environmental issues.
APPENDIX 1.3
The Millennium Ecosystem Assessment
scenarios to 2100
The Millennium Ecosystem Assessment (2005) was carried
out between 2002 and 2005 to assess the consequences of
ecosystem change for human well-being and to establish
the scientific basis for actions needed to enhance the conservation
and sustainable use of ecosystems and their contributions
to human well-being. The Assessment responds
to government requests for information received through
four global conventions: the Convention on Biological
Diversity, the UN Convention to Combat Desertification,
the Ramsar Convention on Wetlands and the Convention
on Migratory Species.
The underlying assumption of this Assessment is that
everyone in the world depends completely on Earth’s ecosystems
and the services they provide, such as food, water,
disease management, climate regulation, spiritual fulfilment
and aesthetic enjoyment. Over the past 50 years,
humans have changed these ecosystems more rapidly and
extensively than in any comparable period of time in
human history, largely to meet rapidly growing demands
for food, fresh water, timber, fibre and fuel. This transformation
of the planet has contributed substantial net
gains in human well-being and economic development.
But not all regions have benefited from this process. In
fact, most have been harmed or at least rendered more
vulnerable to further change and to reduction in material
productivity. Moreover, the full costs associated with these
gains are only now becoming apparent.
The Assessment focusses on the linkages between ecosystems
and human well-being and in particular on ‘ecosystem
services’. Ecosystem services are the benefits
people obtain from ecosystems. In sum, these services are
quite similar to those provided by geomorphology as discussed
in the previous section. In showing how ecosystems
influence human well-being, human well-being is defined
to include basic material for a good life, such as: secure and
adequate livelihoods, enough food at all times, shelter,
clothing and access to goods; health, clean air and access
to clean water; good social relations; security, including
secure access to natural and other resources; and freedom
of choice and action, including the opportunity to achieve
what an individual values doing and being.
Five overarching questions guided the issues that were
assessed: What are the current condition and trends of
ecosystems, ecosystem services and human well-being?
What are future plausible changes in ecosystems and their
ecosystem services and the consequent changes in human
well-being? What can be done to enhance well-being and
conserve ecosystems? What are the strengths and weaknesses
of response options that can be considered to realise
or avoid specific futures? What are the key uncertainties that
hinder effective decision-making concerning ecosystems?
What tools and methodologies developed and used in the
Assessment can strengthen capacity to assess ecosystems,
the services they provide, their impacts on human well-being
and the strengths and weaknesses of response options?
APPENDIX 1.4
The Land Use and Land Cover Change
(LUCC )Project
Land use and land cover change is an important component of
global environmental change. The International Geosphere–
Biosphere Programme (IGBP) and the International Human
Dimensions Programme on Global Environmental Change
(IHDP) commissioned a Core Project Planning Committee/
Research Programme Planning Committee for Land Use and
Land Cover Change (CPPC/RPPC/LUCC), working from
2000 to 2005.
The main topics covered areas of deforestation or forest
degradation over the last 20 years (1980–2000); the main
areas of land degradation in the drylands and hyper-arid
zones (1980–2000); the main areas of change in cropland
extent (1980–90); the main areas of change in urban extent
(1990–2000); and the fire events with long-term impact on
land cover. There were three research foci: land use dynamics;
land cover dynamics; and regional and global models.
In response to the question ‘How has land cover been
changed by human use over the last 300 years?’ it was
noted that human activities have transformed Earth’s landscapes
for a long time. The pace and intensity of land cover
change increased rapidly over the last three centuries and
accelerated over the last three decades. Rapid land cover
changes are clustered on forest edges and along transportation
networks, mostly in humid forests. Decreases in croplands
O. Slaymaker et al.30
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in temperate regions and expansion of forest lands display
opposite trends from those seen in the tropics, where croplands
are expanding and deforestation is marked. Land
cover change data sets are inadequate for many parts of
the world, but dryland degradation, soil degradation in
croplands, wetland drainage and urban expansion are
some of the most common changes.
In response to the question ‘What are the major human
causes of land cover change?’ the most important finding
was that the mix of driving forces of land use change varies
in time and space, according to specific human–environment
conditions. A distinction is made between decadal timescales,
influenced by individual and social responses to
changing economic conditions, mediated by institutions and
a centennial timescale, dominated by demographic trends.
In response to the question ‘How will changes in land use
affect land cover in the next 50–100 years?’ a number of
predictive models were developed and tested against past
land use patterns, but on the whole a regional approach was
preferred to global modelling. Urbanisation was seen to be
the dominant factor in future land use patterns.
In response to the question ‘How do human and biophysical
dynamics affect the coupled human–environment
system?’ attention was directed to historical and contemporary
examples of land use transitions associated with
societal and biophysical changes. Finally, in response to
the question ‘How might changes in climate and biogeochemistry
affect both land cover and land use and vice
versa?’ it was noted that slow land cover conversion takes
place against a background of high-frequency regionalscale
fluctuations in land cover conditions caused by
harvest cycles and climatic variability. Abrupt short-term
ecosystem changes are often caused by the interaction of
climatic and land use factors.
APPENDIX 1.5
World Heritage Sites, the World
Conservation Union (IUCN) and UNEP’s
Global Programme of Action
Global Scenarios Group (GSG) Scenarios to 2050 (Raskin
et al., 2002) have incorporated ecological and land use
variables. World Heritage sites have been established
under the Convention concerning natural and cultural
sites (1972). Roughly 20% of the 851 World Heritage
Sites have been selected on the basis of ‘natural’ criteria.
From a world landscapes perspective, the most interesting
part of this process is the identification of ‘natural sites’ that
are threatened or are particularly unique and worthy of
preservation (Fig. 1.18).
The IUCN, operating within the Convention on
Biodiversity, has established a Red List of threatened
species and ecosystems. As always, improved governance
mechanisms, capacity-building and awareness raising and
improved financing are the broad policy recommendations.
But within those broad parameters, basin-wide pollution
treatment and basin management of land use and better
allocation of resources, with particular focus on the effects
on coastal areas are emphasised (in cooperation with
UNEP’s Global Programme of Action). In summary, the
most critical factors that influence land and land use change
can be divided into indirect and direct drivers.
Indirect drivers include such broadly contextual factors as:
(a) demographic change;
(b) economic, sociopolitical, cultural and religious drivers;
(c) science and technology;
(d) global trade which magnifies the importance of governance
and management practices; and
(e) urban growth, and more particularly suburban sprawl.
Direct drivers include:
(a) deliberate habitat change resulting from land use change;
(b) physical modification of rivers;
(c) water withdrawal from rivers;
(d) pollution;
(e) sea level change; and
(f) climate change.
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