Climate Change 2001:
Synthesis Report
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Introduction

  

9.1

The understanding of climate change, its impacts, and the options to mitigate and adapt is developed through multi- and interdisciplinary research and monitoring in an integrated assessment framework. As understanding deepens, some findings become more robust and some uncertainties emerge as critical for informed policy formulation. Some uncertainties arise from a lack of data and a lack of understanding of key processes and from disagreement about what is known or even knowable. Other uncertainties are associated with predicting social and personal behavior in response to information and events. The uncertainties tend to escalate with the complexity of the problem, as additional elements are introduced to include a more comprehensive range of physical, technical, social, and political impacts and policy responses. The climate responds to human influence without deliberation or choice; but human society can respond to climate change deliberately, making choices between different options. An objective of the TAR and other IPCC reports is to explore, assess, quantify, and, if possible, reduce these uncertainties.

  

9.2

In this report, a robust finding for climate change is defined as one that holds under a variety of approaches, methods, models, and assumptions and one that is expected to be relatively unaffected by uncertainties. A robust finding can be expected to fall into the categories of well-established (high level of agreement and high amount of evidence) and established but incomplete (high level of agreement, but incomplete evidence) in the literature. Robustness is different from likelihood: A finding that an outcome is "exceptionally unlikely" may be just as robust as the finding that it is "virtually certain." A major development in the TAR is that of the multiple alternative pathways for emissions and concentrations of greenhouse gases as represented by the SRES. Robust findings are those that are maintained under a wide range of these possible worlds.

  
9.3

Key uncertainties in this context are those which, if reduced, may lead to new and robust findings in relation to the questions of this report. These findings may, in turn, lead to better or more of the information that underpins policy making. The uncertainties can never be fully resolved, but often they can be bounded by more evidence and understanding, particularly in the search for consistent outcomes or robust conclusions.

  
9.4

Robust findings and key uncertainties can be brought together in the context of an integrated assessment framework.

  
9.5 The integrated assessment framework described in this report is used to bring together the robust findings and key uncertainties in the model projections. Such a framework can encompass all the disciplines involved in understanding the climate, the biosphere, and human society. It emphasizes the linkages between the systems described in the different Working Group reports of the TAR as well as considers linkages between climate change and other environmental issues, and helps to identify gaps in knowledge. It suggests how key uncertainties can affect the whole picture. Figure 1-1 shows how adaptation and mitigation can be integrated into the assessment. The human and natural systems will have to adapt to climate change, and development will be affected. The adaptation will be both autonomous and via government initiatives, and adaptation actions will reduce (but cannot entirely avoid) some of the impacts of climate change on these systems and on development. Adaptation actions provide benefits but also entail costs. Mitigation is unlike adaptation in that it reduces emissions at the start of the cycle, it reduces concentrations (compared to what would otherwise occur), and it reduces climate change and the risks and uncertainties associated with climate change. It further reduces the need for adaptation, the impacts of climate change, and effects on socio-economic development. It is also different in that mitigation aims to address the impacts on the climate system, whereas adaptation is primarily oriented to address localized impacts of climate change. The primary benefit of mitigation is avoided climate change, but it also has costs. In addition, mitigation gives rise to ancillary benefits (e.g., reduced air pollution leading to improvements in human health). A fully integrated approach to climate change assessment would consider the whole cycle shown in Figure 1-1 dynamically with all the feedbacks but this could not be accomplished in the TAR.

  
9.6 Many of the robust findings as listed in Table SPM-3 are concerned with the existence of a climate response to human activities and the sign of the response. Many of the key uncertainties are concerned with the quantification of the magnitude and/or the timing of the response and the potential effects of improving methods and relaxing assumptions.  

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