Executive summary

This chapter describes the significant developments in methods and approaches for climate change impact, adaptation and vulnerability (CCIAV) assessment since the Third Assessment Report (TAR). It also introduces some of the scenarios and approaches to scenario construction that are used to characterise future conditions in the studies reported in this volume.

The growth of different approaches to assessing CCIAV has been driven by the need for improved decision analysis.

The recognition that a changing climate must be adapted to has increased the demand for policy-relevant information. The standard climate scenario-driven approach is used in a large proportion of assessments described in this report, but the use of other approaches is increasing. They include assessments of current and future adaptations to climate, adaptive capacity, social vulnerability, multiple stresses, and adaptation in the context of sustainable development. [2.2.1]

Risk management is a useful framework for decisionmaking and its use is expanding rapidly.

The advantages of risk-management methods include the use of formalised methods to manage uncertainty, stakeholder involvement, use of methods for evaluating policy options without being policy prescriptive, integration of different disciplinary approaches, and mainstreaming of climate change concerns into the broader decision-making context. [2.2.6]

Stakeholders bring vital inputs into CCIAV assessments about a range of risks and their management.

In particular, how a group or system can cope with current climate risks provides a solid basis for assessments of future risks. An increasing number of assessments involve, or are conducted by, stakeholders. This establishes credibility and helps to confer 'ownership' of the results, which is a prerequisite for effective risk management. [2.3.2]

The impacts of climate change can be strongly modified by non-climate factors.

Many new studies have applied socio-economic, land-use and technology scenarios at a regional scale derived from the global scenarios developed in the IPCC Special Report on Emissions Scenarios (SRES). Large differences in regional population, income and technological development implied under alternative SRES storylines can produce sharp contrasts in exposure to climate change and in adaptive capacity and vulnerability. Therefore, it is best not to rely on a single characterisation of future conditions. [2.4.6.4,2.4.6.5]

Scenario information is increasingly being developed at a finer geographical resolution for use in CCIAV studies.

A range of downscaling methods have been applied to the SRES storylines, producing new regional scenarios of socio-economic conditions, land use and land cover, atmospheric composition, climate and sea level. Regionalisation methods are increasingly being used to develop high spatial-resolution climate scenarios based on coupled atmosphere-ocean general circulation model (AOGCM) projections. [2.4.6.1 to 2.4.6.5]

Characterisations of the future used in CCIAV studies are evolving to include mitigation scenarios, large-scale singularities, and probabilistic futures.

CCIAV studies assuming mitigated or stabilised futures are beginning to assess the benefits (through impacts ameliorated or avoided) of climate policy decisions. Characterisations of large-scale singularities have been used to assess their potentially severe biophysical and socio-economic consequences. Probabilistic characterisations of future socioeconomic and climate conditions are increasingly becoming available, and probabilities of exceeding predefined thresholds of impact have been more widely estimated. [2.4.6.8, 2.4.7, 2.4.8]

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