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7.2. State of Knowledge Regarding Climate Change Impacts on Human Populations
The TAR differs from the two previous assessments in that the literature has
begun to quantify several of the climate-related risks to human settlements
that previously were identified only in qualitative terms. Additional attention
and research has been devoted to adaptation mechanisms that provide resistance
to climate-related impacts and ability to recover from them. Several economic
and social trends that are specific to development and change in human settlements
will interact with the effects of climate change in the future and may exacerbate
or mitigate the effects of climate change alone.
7.2.1. Nonclimate Trends Affecting Vulnerability to Climate
Population growth: Except for parts of Europe and the Russian Federation, most
regions are expected to experience population growth. Although Special Report
on Emission Scenarios (SRES) marker scenarios in Chapter 3 do not span the entire
realm of possibilities and have not been assigned probabilities, they do show
that under plausible conditions, future regional population growth rates will
range from modest (Europe and North America, where projected rates are just
above or below replacement) to 3% or more (portions of Latin America and especially
Africa).
Urbanization (proportion of population living in urban areas) is expected to
continue, especially in the developing world. Close to half of the world’s population
now lives in urban areas, and the likely trend toward a more urban world means
that the impacts of climate change on human settlements, if they occur, increasingly
will affect urban populations. The most rapid urban growth rates are occurring
in the developing world, where urban populations are estimated to be growing
at 2.7% yr-1, compared to 0.5% yr-1 in more developed
regions (UN, 2000). There also is a growing concentration of population in cities
with more than 1 million inhabitants. The number of such cities worldwide grew
from 80 in 1950 to more than 300 by 1990 and is expected to exceed 500 by 2010
(UNCHS, 1996; UN, 2000). Most cities with more than 1 million inhabitants are
now in the developing world, although—as in more developed regions—they are
heavily concentrated in its largest economies (UNCHS, 1996). Cities also are
reaching unprecedented sizes. However, the future world may be less dominated
by “megacities” (cities of more than 10 million population) than previously
predicted. Megacities are likely to be smaller than previously predicted and
still contain a small proportion of the world’s population—less than 4% in 1990,
the last date for which there is census data for most nations (UNCHS, 1996;
UN, 2000). Most of the world’s urban population live in the 40,000–50,000 urban
centers with fewer than 1 million inhabitants (UNCHS, 1996). In 1990, cities
with more than 1 million inhabitants had just more than one-third of the world’s
urban population and just more than one-seventh of its total population (UN,
2000). Urban population increases were particularly sharp in the second half
of the 20th century in some regions where urbanization had been held down by
policy, such as China (Institute of Land Development and Regional Economy, State
Planning Committee, 1998). Trends toward urbanization mean that the impacts
of climate change on human settlements in most countries, if they occur, increasingly
will affect urban populations, not rural or traditional settlements.
| Table 7-1: Impacts of climate change on human settlements,
by impact type and settlement type (impact mechanism). Typeface indicates
source of rating: Bold indicates direct evidence or study; italics indicates
direct inference from similar impacts; and plain text indicates logical
conclusion from settlement type, but cannot be directly corroborated from
a study or inferred from similar impacts. Impacts generally are based on
2xCO2 scenarios or studies describing the impact of
current weather events (analogs) but have been placed in context of the
IPCC transient scenarios for the mid- to late 21st century. |
 |
|
Type of Settlement, Importance Rating, and Reference
|
|
|
| |
Resource-Dependent
(Effects on Resources)
|
Coastal-Riverine-Steeplands
(Effects on Buildings and Infrastructure)
|
Urban 1+ M
(Effects on Populations)
|
Urban <1 M (Effects on Populations)
|
|
| |
|
|
|
|
|
|
Impact
Type
|
Urban,
High
Capacity |
Urban,
Low
Capacity |
Rural,
High
Capacity |
Rural,
Low
Capacity |
Urban,
High
Capacity |
Urban,
Low
Capacity |
Rural,
High
Capacity |
Rural,
Low Capacity |
High
Capacity |
Low
Capacity |
High
Capacity |
Low Capacity |
Confidence |
|
| Flooding, landslides |
L–M1 |
M–H2 |
L–M1 |
M–H2 |
L–M1 |
M–H2 |
M–H1 |
M–H2 |
M1 |
M–H2 |
M1 |
M–H2 |
H |
|
| Tropical cyclone |
L–M3 |
M–H4 |
L–M3 |
M–H4 |
L–M3 |
M–H4 |
M3 |
M–H4 |
L–M3 |
M4 |
L3 |
L–M4 |
M |
|
| Water quality |
L–M |
M |
L–M |
M–H |
L–M5 |
M–H6 |
L–M |
M–H |
L–M |
M–H |
L–M |
M–H |
M |
|
| Sea-level rise |
L–M7 |
M–H6 |
L–M7 |
M–H6 |
M8 |
M–H9 |
M |
M–H6 |
L8 |
L–M6 |
L |
L–M6 |
H (L for resource-dependent) |
|
| Heat/cold waves |
L–M |
M–H |
L–M |
M–H |
L–M10 |
L–M |
L–M10 |
L |
L–M10 |
M–H11 |
L–M10 |
M–H11 |
M (H for urban) |
|
| Water shortage |
L12 |
L–M |
M12 |
M–H13 |
L |
L–M |
L–M |
M–H |
L |
M |
L–M12 |
M |
M (L for urban) |
|
| Fires |
L–M |
L–M |
L–M14 |
M–H |
L–M |
L–M |
L–M |
L–M |
L–M15 |
L–M16 |
L–M |
M |
VL (M for urban) |
|
| Hail, windstorm |
L–M17 |
L–M18 |
L–M17 |
M–H18 |
L–M |
L–M |
L–M |
M |
L–M17 |
L–M18 |
L–M17 |
L–M18 |
L |
|
| Agriculture/ forestry/fisheries productivity |
L–M19 |
L–M20 |
L–M |
M–H |
L |
L |
L |
L |
L |
L–M |
L–M |
M |
L |
|
| Air pollution |
L–M21 |
L–M |
L |
L |
— |
— |
— |
— |
L–M10 |
M–H22 |
L–M10 |
M–H22 |
M |
|
| Permafrost melting |
L |
L |
L–M23 |
L–M |
L |
L |
L23 |
L |
— |
— |
L–M |
L–M |
H |
|
| Heat islands |
L |
L |
— |
— |
L |
L |
— |
— |
M24 |
L–M24 |
L–M25 |
L–M25 |
M |
|
|
Poverty is becoming increasingly urbanized, as a growing proportion of the
population suffering from absolute poverty lives in urban areas. In more developed
regions and in much of Latin America (e.g., 36% in Latin America—ECLAC, 2000),
poverty is concentrated in urban areas. In other regions, the number of rural
poor still exceeds the number of urban poor, although the proportion of absolute
poor living in urban areas is growing. In addition, the scale and depth of urban
poverty frequently is underestimated, in part because official income-based
poverty lines are set too low in relation to the cost of living (or the income
needed to avoid deprivation) in most urban centers and in part because no provision
is made to include housing conditions, access to services, assets, and aspects
of social exclusion within most government poverty definitions (Satterthwaite
1997). Where it occurs, urban poverty reduces the capacity of urban populations
to take action to adapt to climate change; poverty also may exacerbate many
of its effects.
Market systems and privatization increasingly are being used to provide new
infrastructure and maintain older systems (World Bank, 1994), giving government
a smaller direct role in providing infrastructure for energy, environmental
residuals, communications, and other key urban services. Governments that are
trying to adapt settlements to climate change increasingly may have to work
indirectly through markets and regulation of private providers to adapt buildings
and infrastructure to climate change.
Energy systems are changing in some places, helping to determine which mechanisms
are salient in human settlements impacts (Schipper and Meyers, 1992; Hall et
al., 1993; World Energy Council, 1993a):
- Use of biomass fuels for cooking and space heating in many developing countries
remains significant, which has added to deforestation and environmental destruction
in some places but not others (Leach and Mearns, 1989; Tiffen and Mortimore,
1992). Biomass growth may be stimulated by warming, if precipitation remains
adequate, but may fall otherwise.
- The increase in natural gas use in Europe and North America (and nuclear
power in France) over the past 2 decades has held down the rate of use of
coal and oil and has reduced coal use by 20% in western Europe. Accelerated
coal use is expected in developing Asia (EIA, 1998). Much of the increase
is related to increasing electricity demand, which would be compounded by
climate warming.
- An increasing market share for electricity is occurring in new homes in
all regions. Between 1995 and 2020, the world’s annual consumption of electricity
is projected to rise from 12 trillion to 23 trillion kWh. The greatest increases
are expected in developing Asia and in Central and South America (EIA, 1998).
Climate warming in these regions would increase the demand for space cooling,
which is primarily fueled by electricity, at the same time that rapid electrification
already is stretching capacity.
- Air conditioning in the commercial sector already accounts for a greater
proportion of final energy demand than in the residential sector in developed
countries. Commercial sector energy use also is increasing as a percentage
of the total in developing countries. Some of this is a result of computerization
of commerce.
Transportation activity and associated energy consumption are growing very
rapidly in nearly every region. Except for economies in transition, the amount
of goods traveling by road increased between 1990 and 1996. The increases were
50% or more, and total paved roadways worldwide rose from 39 to 46% of the total
(World Bank, 1999). In all Organisation for Economic Cooperation and Development
(OECD) countries, car ownership continues to rise steadily, but much of the
growth in vehicle ownership is expected in developing countries and transition
economies—especially in east Asia and the Pacific, and especially in urban areas
(World Resources Institute, 1996). This trend contributes to local air pollution
(which can be exacerbated by warm weather episodes) and to greenhouse gas (GHG)
emissions.
A poleward intensification of agricultural, forestry, and mining activities
is occurring, resulting in increased population and intensified settlement patterns
in Canada’s mid-north, for example, and even in arctic areas. Climate change
could profoundly affect settlements in these regions, if climate change is greater
toward the poles (Cohen, 1997). For example, some arctic and subarctic activities
such as mining depend on snow roads, which would have to be replaced with more
conventional transport.
Impact of urban wealth: Many of the worst city-level problems—such as sanitation
and water supply—have been addressed in high-income cities such as those in
Europe and North America, but not in many developing world cities (WHO, 1992;
Hardoy et al., 2000; McGranahan and Satterthwaite, 2000). A wealthy city can
more easily afford the public finance and administration required to regulate
more perceptible forms of pollution than a poor one. However, although the ambient
environment of high-income cities may be more benign in terms of health impacts
of pollution, these cities exert a far greater toll on the regional and global
environment (UNCHS, 1996).
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