"Analysis of vulnerability provides a starting point for the determination of effective means of promoting remedial action to limit impacts by supporting coping strategies and facilitating adaptation."⁽¹³⁾

BOX 1: Definitions of key terms (from reference 14)

Most climate change impacts and adaptation studies completed to date have used, as a starting point, scenarios of future climate, from which potential impacts on ecosystems and human activities are identified and adaptation options assessed. For example, several of the studies cited in this report used a scenario of doubled concentration of atmospheric carbon dioxide as the basis for assessing potential impacts. Although such studies have yielded useful insights and contributed significantly to improving our understanding of interactions between climate change, ecosystems and human systems, several limitations of this approach have become apparent, particularly if the goal of such studies is to assist in adaptation decision making.

For instance, studies based primarily on the output of climate models tend to be characterized by results with a high degree of uncertainty and large ranges, making it difficult to estimate levels of risk.⁽¹⁵⁾ In addition, the complexity of the climate, ecological, social and economic systems that researchers are modelling means that the validity of scenario results will inevitably be subject to ongoing criticism. For example, recent papers suggest that the exclusion of land-use change and biological effects of enhanced carbon dioxide,⁽¹⁶⁾ and the poor representation of extreme events,⁽¹⁷⁾ limit the utility of many commonly used scenarios. Such criticisms should not be interpreted as questioning the value of scenarios; indeed, there is no other tool for projecting future conditions. What they do, however, is emphasize the need for a strong foundation upon which scenarios can be applied, a foundation that provides a basis for managing risk despite uncertainties associated with future climate changes.

This foundation lies in the concept of vulnerability. The IPCC defines vulnerability as "the degree to which a system is susceptible to, or unable to cope with, adverse effects of climate change, including climate variability and extremes.⁽¹⁴⁾ Vulnerability is a function of a system's exposure to the impacts of climate, its sensitivity to those impacts, and its ability to adapt.⁽¹⁸⁾ It is important to distinguish vulnerability from sensitivity, which is defined as "the degree to which a system is affected, either adversely or beneficially, by climate-related stimuli.⁽¹⁴⁾ Sensitivity does not account for the moderating effect of adaptation strategies, whereas vulnerability can be viewed as the impacts that remain after adaptations have been taken into account.⁽¹³⁾ Therefore, although a system may be considered highly sensitive to climate change, it is not necessarily vulnerable. Social and economic factors play an important role in defining the vulnerability of a system or region.

Applying a vulnerability approach to climate change impacts and adaptation research involves five major steps, as outlined in Figure 1. In this approach, an understanding of the current state of the system provides an initial assessment of vulnerability that is independent of future changes in climate. This allows researchers to improve their understanding of the entire system and develop more realistic estimates of the feasibility of future adaptation options. Consideration of current conditions also encourages the involvement of stakeholders (see Box 2) and facilitates the implementation of "no-regrets" adaptation strategies. To assess future vulnerabilities, researchers build upon the knowledge achieved through examining current vulnerability by applying projections of future climatic and socio-economic conditions.

FIGURE 1: Steps in the vulnerability approach. Note that research need not follow a linear progression; instead, the process should be iterative, with some steps being undertaken simultaneously.

The primary goal of the vulnerability approach is to promote research that contributes to adaptation decision-making by providing a framework in which priorities can be established in spite of the uncertainties concerning future climate change.

BOX 2: Involving stakeholders

Factors Affecting Current Vulnerabilities

The current vulnerability of a system is influenced by the interrelated factors of adaptive capacity, coping ranges and critical thresholds.

The IPCC defines adaptive capacity as "the ability of a system to adjust to climate change (including climate variability and extremes) to moderate potential damages, to take advantage of opportunities, or to cope with the consequences."⁽¹⁴⁾ More simply, adaptive capacity is a measure of a system's ability to adapt to change. A system with a high adaptive capacity is able to cope with, and perhaps even benefit from, changes in the climate, whereas a system with a low adaptive capacity would be more likely to suffer from the same change. Enhancing adaptive capacity is an often-recommended "no-regrets" adaptation strategy that brings both immediate and long-term benefits.

Considerable research has been dedicated to identifying the factors that influence adaptive capacity (see Table 2). Although this research provides useful indicators, quantitative assessment of adaptive capacity remains challenging. In fact, there is little agreement on the necessary criteria for evaluating these determinants, and what variables should be used.⁽⁸⁾ Characteristics such as per capita income, education level and population density have been used as proxy variables for some of the determinants.⁽²¹⁾

Current vulnerability is often estimated by examining how a system has responded to past climate variability. A system that has a proven ability to adapt to historical climate fluctuations and stress is generally considered less vulnerable. Researchers therefore suggest that there is much to be learned from the natural hazards literature.⁽²²⁾ Studying how communities have responded socially, economically and politically to past disasters provides insight into potential responses to future events. Other researchers caution, however, that observed responses to past events may potentially be "highly misleading predictors of future response."⁽²³⁾ It is important to consider the ability of a region or community to learn from the past and implement strategies to reduce losses from similar events in the future. For example, since the 1998 ice storm, Quebec has taken significant measures to strengthen emergency preparedness and response capacity, and is therefore much better positioned to cope with future extreme events.⁽²⁴⁾

Table 2: Key determinants of adaptive capacity (based on reference 8).

By examining response to past climatic variability, it is possible to define the coping range of a given system (see Box 3). The coping range refers to the "range of circumstances within which, by virtue of the underlying resilience of the system, significant consequences are not observed."⁽²¹⁾ Critical thresholds can be viewed as the upper and lower boundaries of coping ranges,⁽²¹⁾ and are usually location specific.⁽²⁵⁾ Significant impacts are expected to occur when critical thresholds are exceeded. Some examples of critical thresholds include the maximum air temperature at which a specific crop can grow, the minimum river water levels required for fish survival, and the maximum intensity of rainfall that can be handled by an urban storm-sewer system. Critical thresholds are not always absolute values, but rather may refer to a rate of change.⁽²⁵⁾ Some systems may be able to respond readily to slow rates of change even for long periods of time, whereas a more rapid rate of change would exceed the ability of the system to adjust and result in significant impacts.

BOX 3: Coping range and critical thresholds

Time series of a climate variable (e.g., temperature) Coping range: "The variation in climatic stimuli that a system can absorb without producing significant impacts."(14) Critical thresholds: The boundaries of coping ranges; significant impacts result when critical thresholds are exceeded.(21)

Understanding the coping range and critical thresholds of a system is an important prerequisite to assessing the likely impacts of climate change and estimating the potential role of adaptation. Coping ranges can, however, be influenced by a range of physical, social and political factors, and therefore may not be easy to define. In some instances, traditional knowledge may be an important complement to other data for improving understanding of coping ranges, as well as overall vulnerability to climate change.^{(26, 27)}

Assessing Future Vulnerabilities

To estimate future vulnerabilities, researchers apply scenarios (projections of future climate and socio-economic conditions) to build upon the knowledge and understanding of the system gained through assessing current vulnerability. Important considerations include the nature and rate of future climate change, including shifts in extreme weather, and the influence of changes in socio-economic conditions.

Once the coping range of a system has been defined, climate scenarios can be used as a starting point for determining the probability of exceeding critical thresholds in the future.⁽²⁵⁾ Consider a simplified example of river flow volume, presented by Yohe and Tol.⁽²¹⁾ The upper and lower critical thresholds can be defined by examining current and historical data for the river. For instance, the upper threshold could correspond to the maximum flow volume before serious flooding occurs, and the lower threshold may represent the minimum flow required to sustain water demand in the region (see Box 4, Graph A). The frequency with which these two thresholds have been exceeded in the historical period can be determined, and water managers and other stakeholders recognize this probability as the risks associated with living in the region. Using data from climate scenarios, researchers can estimate how flow volumes could change in the future, and thereby affect the probability of critical thresholds being exceeded (see Box 4, Graph B). Note that exact predictions of the future are not required with this approach, as the focus is on estimated probabilities.⁽²⁵⁾ Furthermore, since this information builds upon current understanding of the river system and is presented in terms that are currently used by water managers, it can be integrated into existing risk-management frameworks.

BOX 4: River flow example of coping range (modified from reference 21)

Graph A: Historical time series of river flow. Note that, over the time period of record, flooding occurs three times and there is insufficient water to meet demand two times. Graph B: Hypothetical future river flow regime with increased variability (higher maximum flows, lower minimum flows), and trend of increased flow. Note that flooding now occurs five times, and there is insufficient water to meet demand four times.

It is important to recognize that coping ranges can change over time, either deliberately through planned adaptation or unintentionally. In urban areas, for example, communities may be able to reduce heat-related health effects, and therefore increase tolerance to heat waves, by introducing such adaptive measures as issuing heat-health alerts, improving access to air-conditioned areas and increasing the use of "cool roofs", which reduce heat absorption by buildings (see Human Health and Well-Being chapter). In the river flow example discussed above, adaptation options, such as adding a dam, dredging the river or building levees, can increase the upper critical threshold of river flow, allowing riverside communities to tolerate higher flow levels (reference 21; see also Box 3). Similarly, introducing water conservation measures, such as restrictions on outdoor water use and improved water use and storage efficiency, may decrease baseline demand for water.⁽²⁸⁾ Increasing coping ranges represents a fundamental goal of adaptation.

Accounting for Adaptation

"It is meaningless to study the consequences of climate change, without considering the ranges of adaptive responses."⁽²⁹⁾

Although it is well recognized that appropriate adaptation can reduce vulnerability, it is only recently that attention has been dedicated to adaptation research.⁽²⁾ Adaptation research involves studying the processes of adaptation, and requires addressing three key questions:

1. What is being adapted to?
2. Who or what will adapt? and
3. How will adaptation occur?⁽³⁰⁾

Addressing these questions requires effective collaboration with stakeholders, a strong understanding of the system and region being studied, and knowledge of potential adaptation options. Recent Canadian examples of adaptation research include the work of de Löe et al.,⁽²⁸⁾ who investigated criteria for identifying appropriate adaptation options, and Smit and Skinner,⁽³¹⁾ who presented a typology of adaptation options for agriculture. Another study examined factors influencing adaptation decisions at the municipal level (see Box 5).

BOX 5: Understanding barriers to adaptation at the municipal level ⁽³²⁾

The adaptation literature also acknowledges the difficulties involved in effectively accounting for adaptation in vulnerability studies. There are many different and interacting factors that influence the response of humans and ecosystems to stress. Evaluation of adaptation must extend beyond "Is adaptation possible?" to also include "Is adaptation probable?" In other words, are people both able and willing to adapt? Additional research into the factors that affect the feasibility, effectiveness, cost and acceptability of adaptation options is recommended.⁽²³⁾