Climate change will affect human settlements against a very dynamic background
of other environmental and socioeconomic factors. Human settlements are expected
to be among the sectors that could be most easily adapted to climate change,
given appropriate planning and foresight and appropriate technical, institutional,
and political capacity. This chapter covers the same general topic areas as
Chapters 11 and 12 of the Second Assessment Report (SAR); however, this chapter
analyzes a wider variety of settlement types, provides a specific assessment
of uncertainty and confidence in findings and adaptive capacity in human settlements,
and places much of the discussion in a context of development, sustainability,
and equity (DSE) (see Munasinghe, 2000). Energy and industry are treated as
part of settlements. Figure 7-1 characterizes the conclusions
of this chapter on two dimensions: scientific support (evidence available in
the literature to support the finding) and consensus in that literature. Both
scales are described more fully in Box 1-1 of Chapter 1 and in Moss and Schneider
Major Effects on Human Settlements
Infrastructure would have increased vulnerability to urban flooding and landslides
(established but incomplete). Detailed modeling of rainfall event frequency
and intensity in the context of global warming has been linked to increased
intensity and frequency of urban flooding, with considerable damage to infrastructure
(see Chapters 4, 8, and 10–15).
Although not definitive for any part of the world, the model-based analysis
is plausible and demonstrates that flooding could be an increased threat for
riverine settlements under climate change. More predictable is loss of snow
pack in many regions, combined with more winter flooding. Landslides are a current
threat in many hilly areas and could be more so with more intense rainfall events.
Figure 7-1: Human settlements impacts, categorized by state of scientific
Tropical cyclones would be more destructive under climate
change (established but incomplete). Close behind floods and landslides are
tropical cyclones (hurricanes or typhoons), which could have higher peak intensity
in a warmer world with warmer oceans (see Chapters 3 and
8, and TAR WGI Chapter
10). Tropical cyclones combine the effects of heavy rainfall, high winds,
storm surge, and sea-level rise in coastal areas and can be disruptive far inland
but are not as universally distributed as floods and landslides.
Water supplies for human settlements would be vulnerable to increased warming,
dryness, and flooding (established but incomplete). There is reasonable consensus
among experts that settlements in regions of the world that already are water-deficient
(e.g., much of north Africa, the Middle East, southwest Asia, portions of western
North America, and some Pacific islands) would face still higher demands for
water with a warmer climate, with no obvious low-cost ways in which to obtain
increased physical supplies. Observations on current water supply balances tend
to back up this conclusion (see Chapters 4 and 10–13).
However, theory and model output, though consistent with this view, are too
weak quantitatively to offer much support, especially for urban areas. Repeated
flooding also could create water quality problems in other areas.
Fire danger in settlements could increase with climate change (speculative
for resource-dependent settlements; established but incomplete for infrastructure).
Examples include forested and wildland/urban fringes in boreal regions (e.g.,
Canada, Alaska, Russia) and in Mediterranean climates in both hemispheres (e.g.,
California, southern Spain and France, and Australia) that could be affected
(see Chapters 11, 12, 13,
and 15). Although general circulation model (GCM)-projected
summer climate in many regions looks similar to the hot, dry “fire weather”
in many warm years of recent memory and economic activity in forests sometimes
is restricted to reduce fire danger, impacts on the resource base have not been
demonstrated, research has not shown what future fuel loadings would be, and
it is unclear whether future economic activity and settlement infrastructure
would be more vulnerable to fire.
Hail and windstorm could cause more damage to settlements (speculative). Although
there is potential for more (and more severe) extreme weather episodes in a
warmer atmosphere, modeling and data have not demonstrated a higher incidence
of storms or of more severe storms (see Chapters 3, 8,
12, and 15).
Agroindustry and artisanal fisheries are sensitive to and in many cases vulnerable
to climate change (well-established overall; competing explanations in specific
regions). This conclusion dates back to the First Assessment Report (FAR). Additional
studies and analysis conducted in the past 10 years have modified the details
of the conclusion but have not overturned it. As described in Chapter 5, agriculture
itself is sensitive to climate change. In some cases, yields may be reduced
by as much as several tens of percent as a result of hotter weather, greater
evaporation, and lower precipitation in mid-continental growing regions in particular.
However, other regions may benefit, with higher yields possible. Impacts on
agricultural processors and suppliers would tend to follow the impacts on agriculture
itself. Changes in ocean conditions from El Niño episodes have demonstrated
that changes such as ocean warming have substantial impacts on the locations
and types of species available for fisheries, especially artisanal fisheries,
but other regions could benefit (see Chapters 5, 6,
Heat waves would have more serious effects on human health and productivity
(competing explanations). The impact of heat waves is most severe on the weakest
parts of the populations (old, chronically ill, very young) that are not acclimated,
but effects on future overall death rates are less clear (see Chapters
9, 11, 13, 14,
and 15). Because anthropogenic warming is projected to
be greater at night than during the day, it would deprive sufferers of nighttime
relief. Projections for several temperate climates show increased risk of severe
heat waves (Chapter 3). As the weather becomes very warm,
economic productivity of unprotected and outdoor populations declines.
Sea-level rise increases the cost/vulnerability of infrastructure and coastal
resource-based industry (well-established for infrastructure; established but
incomplete for resources). Although the amount of sea-level rise to be expected
as a result of global warming by any given date and in any given location is
uncertain, some studies are beginning to discuss likely ranges and probability
distributions (e.g., Titus and Narayanan, 1995). The sensitivity of human infrastructure
in coastal zones to given levels of sea-level rise is backed by theory, model
results, and data on current rates of increase. In addition, several industries—such
as tourism and recreation (the principal industry in many island economies)—are
dependent on coastal resources (see Chapters 6, 8,
and 10–17). Effective types of adaptive
responses also are known in some circumstances, but vulnerability with adaptation
is difficult to assess because the capacity and will to respond are uncertain
or in doubt in many instances.
Energy demand in some locations is sensitive, and parts of the supply system
are vulnerable (well-established). Modeling, theory, data, and expert opinion
all say that warming of 1–5ºC would considerably reduce the amount of energy
that would be needed to heat buildings at mid- and high latitudes and altitudes,
whereas cooling energy use would increase (see Chapters 10–15
and 17). The net overall impact on energy use would depend
on local circumstances. If temperature increases take place primarily at night
and during winter months, heating demand would be smaller and the increase in
demand for energy for cooling and irrigation would be somewhat smaller than
otherwise. Future climate is expected to include more intense rainfall events
(which would require more conservative water storage strategies to prevent flood
damage), greater probability of water deficits (less hydroelectric production),
and less precipitation falling as snow (less water available during warm months)
(see Chapter 4). All three factors point to less (or,
at least, less flexible) hydroelectric capacity at current powerhouses. Reduced
flows in rivers and higher temperatures reduce the capabilities of thermal electric
generation, and high temperatures may reduce transmission capabilities as well.
There will be increased air and water pollution impacts (competing explanations).
Climate change could contribute to water pollution problems in human settlements
through drought or flooding, although not by simple increases in flow (which
offers more dilution for pollutants). If droughts and floods become more frequent
(see Chapter 3), so would instances of poor water quality
(see Chapters 4, 10–15,
and 17). Air pollution could be exacerbated if climate
change alters the stability of air sheds and permits greater buildup of atmospheric
pollutants (see Chapters 10–15).
However, the outcomes remain largely theoretical, unsupported by data or modeling.
Infrastructure in permafrost regions is vulnerable to warming (well-established).
Data from circumpolar regions and model results suggest that permafrost areas
would see some melting of permafrost. Permafrost melting is a threat to infrastructure
in these regions because of increased landslides and loss of foundation stability
for structures, as well as increased damage from freeze-thaw cycles, among other
impacts. In addition, melting permafrost is thought to be a source of methane
(CH4) and carbon dioxide (CO2) gases (see Chapters
15 and 16).
Heat island effects could increase heat stress, increase summer energy demand,
and reduce winter energy demand (competing explanations). As discussed in Chapters
3 and 9, heat waves may increase in frequency and
severity in a warmer world, leading directly to increases in mortality among
sensitive populations that are not acclimated. Heat island effects exacerbate
the oppressive effects of heat waves by increasing temperatures experienced
in the summer by up to several °C; at the same time, increased demand for air
conditioning increases the demand for electricity and the severity of the heat
island itself through thermal electric production. Winter energy use for heating
would be reduced by the same phenomenon (see Chapters 11,
13, 14, and 15).
Effects in specific regions are far less clear.
Local capacity is critical to successful adaptation (well-established). Adaptation
means local tuning of settlements to a changing environment, not just warmer
temperatures. Urban experts are unanimous that successful environmental adaptation
cannot occur without locally based, technically and institutionally competent,
and politically supported leadership. Local adaptive capacity generally is strongly
correlated with the wealth, human capital, and institutional strength of the
settlement. In addition, capacity depends in part on the settlement’s access
to national resources. Attempts to impose environmental solutions on settlements
from the international or national level frequently have been maladapted to
local circumstances. The most effective sustainable solutions are strongly supported
and often developed locally, with technical assistance and institutional support
from higher level bodies (see Chapters 10, 11,
14, 17, and 18).
Nonclimate effects are likely to be more important than climate change (competing
explanations). The effects of climate change would occur against a background
of other socioeconomic and environmental change that is itself very uncertain
and complex (see Chapter 3). Model results, the current
rate of environmental change, and economic theory all suggest that climate would
be a relatively small additional uncertainty for most human settlements. Climate
change in isolation also is unlikely to be as important a factor for DSE effects
as other aspects of development, such as economic and technological change.
In combination with other stresses from other processes such as population growth,
however, climate change is likely to exacerbate total stresses in a multi-stress
context. Particularly important could be effects of climate change on equity
because relatively advantaged parts of global and local societies are likely
to have better coping capacities than less advantaged parts.
Managing growth to ensure that it is sustainable and equitably distributed
currently is a greater problem for most countries than the impacts of climate
change. However, some experts are not in agreement on this point for the future,
pointing out that the economic models do not show climate feedback to the economy
and that climate effects are so uncertain that they could well dominate in some
regions, especially by the end of the 21st century.