An important audience for this report is the UNFCCC Conference of Parties and Subsidiary Bodies, through which implementation of the provisions of the Convention (United Nations, 1992) and associated protocols will be negotiated. The major issue is contained in Article 2 of the UNFCCC and relates to identifying the level for stabilization of GHG concentrations. As stated in that Article, the level for stabilization is set in terms of impacts of climate change. Hence, the focus of this report is on identifying impacts potentially associated with different rates and levels of climate change. It is important to reiterate that readers will not find any magnitude or rate of climate change defined as �dangerous� by this report. As noted earlier, this is because such a designation is necessarily political for two important reasons. First, the impacts associated with any given concentration target or emissions trajectory will be unevenly distributed across countries, ecosystems, and socioeconomic sectors. Thus, some sectors or regions may receive some benefit from a particular pattern of climate change, whereas others will be harmed. It is not the role of the scientific community to determine whether a particular pattern of impacts constitutes �dangerous� interference; that is a political judgment to be negotiated among participating governments and institutions. Second, there are scientific uncertainties associated with climate change scenarios and our knowledge of impacts that may result. Thus, it is not possible to state in absolute terms that particular impacts will be associated with a given concentration target or stabilization pathway. Instead, information about impacts will be conditional and is best considered in a risk management framework�that is, different stabilization targets or pathways pose different risks to food production, ecosystems, and economic development, and such risks are likely to vary by region and over time. There is no way to determine scientifically what level of risk is acceptable under the UNFCCC. This, too, will be a matter for negotiation by governments. However, information on the state of the science presented in IPCC assessments is widely believed to help put such decisionmaking exercises on a firmer factual basis (see discussion of guidelines for practitioners from an international social science assessment of human choice and climate change in Rayner and Malone, 1998).

The TAR focuses on the vulnerability of different systems and regions to various rates and magnitudes of climate change. Assessment of vulnerability and adaptation is relevant not only to identifying impacts associated with different targets but also to identifying �developing country Parties that are particularly vulnerable to the adverse effects of climate change� (Article 12; United Nations, 1997); these countries are to be compensated from the proceeds of the CDM to help meet the costs of adaptation.

Climate change is not an isolated issue; it is intimately connected to other recognized natural hazards and global environmental problems. Separate international conventions and processes exist to address these issues; in several cases, these include successful scientific assessment mechanisms. This report contains information of relevance to these bodies and processes, although it is not the intention of the report to supercede or contradict information developed in those assessments. The purpose of incorporating information of relevance to these issues is to highlight scientific and policy links among them, so that unnecessary tradeoffs can be avoided and potential multiple benefits can be realized (e.g., Orlando and Smeardon, 1999; Kremen et al., 2000). For example, several international conventions and agreements call for sustainable management and use of land and water resources, with varying goals (such as enhancing GHG sinks and reservoirs, protecting biological diversity, safeguarding aquatic ecosystems, managing forests to meet human needs, and halting desertification). To the extent that these objectives are potentially affected by climate change, and to the extent that options to adapt to changing climate conditions can be structured to help attain additional environmental or socioeconomic objectives associated with these other agreements (i.e., co-benefits), this is highlighted in the relevant sections of the TAR.

Although the primary audiences of this report are involved in negotiating and implementing the UNFCCC (United Nations, 1992) and, to some extent, other international agreements on global environmental problems, the report also contains information that is useful to resource managers in national governments; regional institutions such as regional development or lending agencies; and specialized international agencies such as the World Bank, UNEP, UNDP, or the GEF. In the chapters that focus on sectors or systems of climate change (e.g., Chapters 4�9, which cover advances in our understanding of impacts and adaptation options in water resources, agriculture, health, ecosystems, and so forth), planners and managers in national ministries or regional planning authorities will find information on how their mandates�such as encouraging agriculture, providing freshwater, protecting endangered species, or increasing energy production�could be affected by climate change. To the extent provided in the literature, these chapters also include detailed technical and cost information on adaptation options and factors that will influence their implementation. In chapters that focus on regional analyses, managers and planners at regional and international agencies will find information on baselines and trends (climate, socioeconomic, and other environmental); each chapter also highlights particular vulnerabilities and opportunities for adaptation that may occur in each region. It is hoped that this information will be useful in assessing potential projects and opportunities for investment, so that these can be structured to be more robust to potential negative effects of climate change or to take advantage of emerging opportunities. In addition, this report will be useful in the education of the media and the general public about climate, the environment, and development issues.

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