Adaptation refers both to the process of adapting and to the condition of being adapted. The term has specific interpretations in particular disciplines. In ecology, for example, adaptation refers to changes by which an organism or species becomes fitted to its environment (Lawrence, 1995; Abercrombie et al., 1997); whereas in the social sciences, adaptation refers to adjustments by individuals and the collective behavior of socioeconomic systems (Denevan, 1983; Hardesty, 1983). This chapter follows Carter et al. (1994), IPCC (1996), UNEP (1998), and Smit et al. (2000) in a broad interpretation of adaptation to include adjustment in natural or human systems in response to experienced or future climatic conditions or their effects or impacts—which may be beneficial or adverse.

As both a process and a condition, adaptation is a relative term: It involves an alteration in something (the system of interest, activity, sector, community, or region) to something (the climate-related stress or stimulus). Description of an adaptation requires specification of who or what adapts, the stimulus for which the adaptation is undertaken, and the process and form it takes (Downing et al., 1997; Krankina et al., 1997; UNEP, 1998; Pittock et al., 1999; Risbey et al., 1999; Reilly and Schimmelpfennig, 2000). These elements are summarized in Figure 18-2 and addressed in turn in subsequent subsections.

Furthermore, for most systems and communities, changes in the mean condition commonly fall within the coping range (see Figure 18-3), whereas many systems are particularly vulnerable to changes in the frequency and magnitude of extreme events or conditions outside the coping range (Baethgen, 1997; Schneider, 1997; Rayner and Malone, 1998; Kelly and Adger, 1999). Interannual variations are key stimuli in many sectors (Rosenzweig, 1994; Adams et al., 1995; Mearns et al., 1997; Bryant et al., 2000).

Natural and human systems have adapted to spatial differences in climate. There also are examples of adaptation (with varying degrees of success) to temporal variations—notably, deviations from the annual average conditions on which climate change scenarios focus. Many social and economic systems—including agriculture, forestry, settlements, industry, transportation, human health, and water resource management—have evolved to accommodate some deviations from "normal" conditions, but rarely the extremes. This capacity of systems to accommodate variations in climatic conditions from year to year is captured in Figure 18-3 in the shaded "coping range." This capacity also is referred to as the vulnerability or damage threshold (Pittock and Jones, 2000). The coping range, which varies among systems and regions, need not remain static, as depicted in Figure 18-3. The coping range itself may change (move up or down, expand or contract), reflecting new adaptations in the system (De Vries, 1985; de Freitas, 1989; Smit et al., 2000). The coping range indicated in Figure 18-3 can be regarded as the adaptive capacity of a system to deal with current variability. Adaptive capacity to climate change would refer to both the ability inherent in the coping range and the ability to move or expand the coping range with new or modified adaptations. Initiatives to enhance adaptive capacity (Section 18.6) would expand the coping range.

Adaptations come in a huge variety of forms. Adaptation types (i.e., how adaptation occurs) have been differentiated according to numerous attributes (Carter et al., 1994; Stakhiv, 1994; Bijlsma et al., 1996; Smithers and Smit, 1997; UNEP, 1998; Leary, 1999; Bryant et al., 2000; Reilly and Schimmelpfennig, 2000). Commonly used distinctions are purposefulness and timing. Autonomous or spontaneous adaptations are considered to be those that take place—invariably in reactive response (after initial impacts are manifest) to climatic stimuli—as a matter of course, without the directed intervention of a public agency. Estimates of these autonomous adaptations are now used in impact and vulnerability assessment. Planned adaptations can be either reactive or anticipatory (undertaken before impacts are apparent). In addition, adaptations can be short or long term, localized or widespread, and they can serve various functions and take numerous forms (see Table 18-1).

Table 18-1: Bases for characterizing and differentiating adaptation to climate change (Smit et al., 1999).
General Differentiating Concept or Attribute	Examples of Terms Used
Purposefulness	Autonomous		Planned
	Spontaneous		Purposeful
	Automatic		Intentional
	Natural		Policy
	Passive		Active
	Strategic
Timing	Anticipatory		Responsive
	Proactive		Reactive
	Ex ante		Ex post
Temporal Scope	Short term		Long term
	Tactical		Strategic
	Instantaneous		Cumulative
	Contingency
	Routine
Spatial Scope	Localized		Widespread
Function/Effects	Retreat - Accommodate - Protect Prevent - Tolerate - Spread - Change - Restore
Form	Structural - Legal - Institutional - Regulatory - Financial - Technological
Performance	Cost - Effectiveness - Efficiency - Implementability - Equity

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