The purpose of this chapter is to address several overarching methodological
issues that transcend individual sectoral and regional concerns. In so doing,
this chapter focuses on five related questions: How can current effects of climate
change be detected? How can future effects of climate change be anticipated,
estimated, and integrated? How can impacts and adaptations be valued and costed?
How can uncertainties be expressed and characterized? What frameworks are available
for decisionmaking? In addressing these questions, each section of Chapter
2 seeks to identify methodological developments since the Second Assessment
Report (SAR) and to identify gaps and needs for further development of methods
Detection of Response to Climate Change by Using Indicator Species or Systems
Assessment of the impacts on human and natural systems that already have
occurred as a result of recent climate change is an important complement to
model projections of future impacts. Such detection is impeded by multiple,
often inter-correlated, nonclimatic forces that are concurrently affecting those
systems. Attempts to overcome this problem have involved the use of indicator
species to detect responses to climate change and to infer more general impacts
of climate change on natural systems. An important component of the detection
process is the search for systematic patterns of change across many studies
that are consistent with expectations, based on observed or predicted changes
in climate. Confidence in attribution of these observed changes to climate change
increases as studies are replicated across diverse systems and geographic regions.
Since the SAR, approaches to analysing and synthesizing existing data sets
from abiotic and biotic systems have been developed and applied to detection
of present impacts of 20th-century climate change. Even though studies now number
in the hundreds, some regions and systems are underrepresented. However, there
is a substantial amount of existing data that could fill these gaps. Organized
efforts are needed to identify, analyze, and synthesize those data sets.
Anticipating the Effects of Climate Change
A wide range of methods and tools are now used and available for studies
of local, regional, and global impacts. Since the SAR, improvements have included
greater emphasis on the use of process-oriented models and transient climate
change scenarios, refined socioeconomic baselines, and higher resolution assessments.
Country studies and regional assessments in every continent have tested models
and tools in a variety of contexts. First-order impact models have been linked
to global systems models. Adaptation has been included in many assessments,
often for the first time.
Methodological gaps remain concerning scales, data, validation, and integration.
Procedures for assessing regional and local vulnerability and long-term adaptation
strategies require high-resolution assessments, methodologies to link scales,
and dynamic modeling that uses corresponding and new data sets. Validation at
different scales often is lacking. Regional integration across sectors is required
to place vulnerability in the context of local and regional development. Methods
and tools to assess vulnerability to extreme events have improved but are constrained
by low confidence in climate change scenarios and the sensitivity of impact
models to major climatic anomalies. Understanding and integrating higher order
economic effects and other human dimensions of global change are required. Adaptation
models and vulnerability indices to prioritize adaptation options are at early
stages of development in many fields. Methods to enable stakeholder participation
in assessments need improvement.
Integrated assessment is an interdisciplinary process that combines, interprets,
and communicates knowledge from diverse scientific disciplines in an effort
to investigate and understand causal relationships within and between complicated
systems. Methodological approaches employed in such assessments include computer-aided
modeling, scenario analyses, simulation gaming and participatory integrated
assessment, and qualitative assessments that are based on existing experience
Since the SAR, significant progress has been made in developing and applying
these approaches to integrated assessment, globally and regionally. However,
the emphasis in such integrated assessments, particularly in integrated modeling,
has been on mitigation; few existing studies have focused on adaptation and/or
determinants of adaptive capacity. Methods designed to include adaptation and
adaptive capacity explicitly in specific applications need to be developed.
Costing and Valuation
Methods of economic costing and valuation rely on the notion of opportunity
cost of resources used, degraded, or saved. Opportunity cost depends on whether
the market is competitive or monopolistic and whether any externalities are
present. It also depends on the rate at which future costs are discounted, which
can vary across countries, over time, and over generations. The impact of uncertainty
also can be valued if the probabilities of different possible outcomes are known.
Public and nonmarket goods and services can be valued through willingness to
pay for them or willingness to accept compensation for lack of them. Impacts
on different groups, societies, nations, and species need to be assessed. Comparison
of alternative distributions of welfare across individuals and groups within
a country can be justified if they are made according to internally consistent
norms. Comparisons across nations with different societal, ethical, and governmental
structures cannot yet be made meaningfully.
No new fundamental developments in costing and valuation methodology have taken
place since the SAR. Many new applications of existing methods to a widening
range of climate change issues, however, have demonstrated the strengths and
limitations of some of these methods. For example, many contingent valuation
studies have raised questions about the reliability of such evaluations. Similarly,
more attention is now paid to the limitations of methods that underlie efforts
to reduce all impacts to one monetary value and/or to compare welfare across
countries and cultures. Multi-objective assessments are preferred, but means
by which their underlying metrics might more accurately reflect diverse social,
political, economic, and cultural contexts need to be developed. In addition,
methods for integrating across these multiple metrics are still missing from
the methodological repertoire.
Treatment of Uncertainties
The Earth's linked climate and social-natural systems are very complex;
thus, there are many unresolved uncertainties in nearly all aspects of the assessment
of climatic impacts, vulnerabilities, and adaptation. Subjective judgments are
inevitable in most estimates of such complex systems. Since the SAR, more consistent
treatment of uncertainties and assessment of biases in judgments have been attempted.
Progress also has been made in developing methods for expressing confidence
levels for estimates, outcomes, and conclusions, based on more consistent quantitative
scales or consistently defined sets of terms to describe the state of the science.
Notable attempts to provide "traceable accounts" of how disaggregated
information has been incorporated into aggregated estimates have been made,
but more work is needed. Greater attention to eliminating inconsistent use of
confidence terms or including a full range of uncertainty for key results is
still needed in future assessments. Whereas significant progress on issues of
uncertainty has been achieved in the context of impacts and vulnerability, a
major challenge now lies in addressing uncertainties associated with adaptability.
Decision Analytic Frameworks
Policymakers who are responsible for devising and implementing adaptive
policies should be able to rely on results from one or more of a diverse set
of decision analytical frameworks. Commonly used methods include cost-benefit
and -effectiveness analyses, various types of decision analysis (including multi-objective
studies), and participatory techniques such as policy exercises, but there are
many other possible approaches. Among the large number of assessments of climate
change impacts reviewed in this volume, only a small fraction include comprehensive
and quantitative estimates of adaptation options and their costs, benefits,
and uncertainty characteristics. This information is necessary for meaningful
applications of any decision analytical method. Very few cases in which decision
analytic frameworks have been used in evaluating adaptation options have been
reported. Greater use of methods in support of adaptation decisions is needed
to establish their efficacy and identify directions for necessary research in
the context of vulnerability and adaptation to climate change.