IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability

7.4.1 General effects

Certain kinds of effects follow from particular manifestations of climate change, wherever those phenomena occur. For example, increased precipitation in already well-watered areas can increase concerns about drainage and water-logging (Parkinson and Mark, 2005), while reduced precipitation in areas already subject to water shortages could lead to infrastructure crises. Sea-level rise will affect land uses and physical infrastructures in coastal areas. Changes in conditions can affect requirements for public health services (Chapter 8), water supplies (Chapter 3) and energy services (such as space heating and cooling). Effects can either be cumulative (additive), as in losses of property, or systematic (affecting underlying processes), as in damages to institutions or systems of production (Turner et al., 1990). Even very gradual changes can be associated with thresholds at which the resilience of human systems switches from adequate to inadequate, such as water-supply infrastructures faced with shrinking water availability. Parry et al. (2001), for instance, estimate that many tens of millions of the world’s population are at risk of hunger due to climate change, and billions are at risk of water shortages.

Besides gradual changes in climate, human systems are affected by a change in the magnitude, frequency and/or intensity of storms and other extreme weather events, as well as changes in their location. In fact, some assessments suggest that many impact issues are more directly associated with climatic extremes than with averages (NACC, 2000). Of some concern is the possibility of abrupt climate changes (Chapter 19), which could be associated with locally or regionally catastrophic impacts if they were to occur.

Although localities differ, interactions between climate change and human systems are often substantively different for relatively developed, industrialised countries versus less developed countries and regions. In many cases, it appears that possible negative impacts of climate change pose risks of higher total monetary damages in industrialised areas (i.e., currency valuations of property damages) but higher total human damages in less-developed areas (i.e., losses of life and dislocations of population) – although such events as Hurricane Katrina show that there are exceptions (Section for developed countries, and monetary damages in developing countries may represent a larger share of their GDP.

Not all implications of possible climate change are negative. For instance, along with possible carbon fertilisation effects and a longer growing season (Chapter 5), many mid- and upper-latitude areas see quality-of-life benefits from winter warming, and some areas welcome changes in precipitation patterns, although such changes could have other social consequences. The greater proportion of the research literature, however, is related to possible adverse impacts. Climate impact concerns include environmental quality (e.g., more ozone, water-logging or salinisation), linkage systems (e.g., threats to water and power supplies), societal infrastructures (e.g., changed energy/water/health requirements, disruptive severe weather events, reductions in resources for other social needs and maintaining sustainable livelihoods, environmental migration (Box 7.2), placing blame for adverse effects, changes in local ecologies that undermine a sense of place), physical infrastructures (e.g., flooding, storm damage, changes in the rate of deterioration of materials, changed requirements for water or energy supply), and economic infrastructures and comparative advantages (e.g., costs and/or risks increased, markets or competitors affected).

Box 7.2. Environmental migration

Migration, usually temporary and often from rural to urban areas, is a common response to calamities such as floods and famines (Mortimore, 1989), and large numbers of displaced people are a likely consequence of extreme events. Their numbers could increase, and so could the likelihood of their migration becoming permanent, if such events increase in frequency. Yet, disaggregating the causes of migration is highly problematic, not least since individual migrants may have multiple motivations and be displaced by multiple factors (Black, 2001). For example, studies of displacement within Bangladesh and to neighbouring India have drawn obvious links to increased flood hazard as a result of climate change. But such migration also needs to be placed in the context of changing economic opportunities in the two countries and in the emerging mega-city of Dhaka, rising aspirations of the rural poor in Bangladesh, and rules on land inheritance and an ongoing process of land alienation in Bangladesh (Abrar and Azad, 2004).

Estimates of the number of people who may become environmental migrants are, at best, guesswork since (a) migrations in areas impacted by climate change are not one-way and permanent, but multi-directional and often temporary or episodic; (b) the reasons for migration are often multiple and complex, and do not relate straightforwardly to climate variability and change; (c) in many cases migration is a longstanding response to seasonal variability in environmental conditions, it also represents a strategy to accumulate wealth or to seek a route out of poverty, a strategy with benefits for both the receiving and original country or region; (d) there are few reliable censuses or surveys in many key parts of the world on which to base such estimates (e.g., Africa); and (e) there is a lack of agreement on what an environmental migrant is anyway (Unruh et al., 2004; Eakin, 2006).

An argument can also be made that rising ethnic conflicts can be linked to competition over natural resources that are increasingly scarce as a result of climate change, but many other intervening and contributing causes of inter- and intra-group conflict need to be taken into account. For example, major environmentally-influenced conflicts in Africa have more to do with relative abundance of resources, e.g., oil, diamonds, cobalt, and gold, than with scarcity (Fairhead, 2004). This suggests caution in the prediction of such conflicts as a result of climate change.

Economic sectors, settlements and social groups can also be affected by climate change response policies. For instance, certain greenhouse-gas stabilisation strategies can affect economies whose development paths are dependent on abundant local fossil-fuel resources, including economic sectors involved in mining and fuel supply as well as fuel use. In this sense, relationships between climate-change impacts and sustainable development (IPCC Working Group II) are linked with discussions of climate-change mitigation approaches (IPCC Working Group III).

In many cases, the importance of climate-change effects on human systems seems to depend on the geographic (or sectoral) scale of attention (Abler, 2003; Wilbanks, 2003a). At the scale of a large nation or region, at least in most industrialised nations, the economic value of sectors and locations with low levels of vulnerability to climate change greatly exceeds the economic value of sectors and locations with high levels of vulnerability, and the capacity of a complex large economy to absorb climate-related impacts is often considerable. In many cases, therefore, estimates of aggregate damages of climate change (other than major abrupt changes) are often rather small as a percentage of economic production (e.g., Mendelsohn, 2001). On the other hand, at a more detailed scale, from a small region to a small country, many specific localities, sectors and societies can be highly vulnerable, at least to possible low-probability/high-consequence impacts; and potential impacts can amount to very severe damages. It appears that large-regional or national estimates of possible impacts may give a different picture of vulnerabilities than an aggregation of vulnerabilities defined at a small-regional or local scale.