IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Synthesis Report


This Synthesis Report with its Summary for Policymakers is the fourth and final part of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) – “Climate Change 2007”. It draws together and integrates for the benefit of policy makers and those from others professions, up to date policy-relevant scientific, technical and socio-economic information on climate change. This report is intended to assist governments and other decision-makers in the public and private sector in formulating and implementing appropriate responses to the threat of human-induced climate change. 

The scope of the Synthesis Report includes the information contained in the three Working Group contributions to the IPCC AR4, the Working Group I report on “The Physical Science Basis”, the Working Group II report on “Impacts, Adaptation and Vulnerability” and the Working Group III report on “Mitigation of Climate Change”. It also draws on other IPCC reports, in particular recently published IPCC Special Reports. The Synthesis Report was written by a team dedicated to this task drawn from the authors of each Working Group report of the AR4 led by the Chair of the IPCC. As instructed by the Panel, the authors prepared the draft in a non-technical style while ensuring that scientific and technical facts are recorded correctly. 

The Synthesis Report addresses a range of broad policy-relevant questions, structured around 6 topic headings agreed by the Panel, and it gives careful attention to cross-cutting themes. It consists of two parts, a Summary for Policymakers (SPM) and a longer report. The sections of the SPM follow largely the topic structure of the longer report, but for brevity and clarity, certain issues covered in more than one topic are summarised in one section of the SPM. 

Topic 1 brings together information from Working Groups I and II on observed changes in climate and the effects of past climate change on natural systems and human society. 

Topic 2 addresses causes of change, considering both natural and anthropogenic drivers of climate change. It analyses the chain including greenhouse gas emissions and concentrations, to radiative forcing and resultant climate change, and evaluates whether observed changes in climate and in physical and biological systems can be attributed to natural or anthropogenic causes. In providing that information it draws on information contained in all three Working Group contributions to the AR4. 

Topic 3 presents information from the three Working Group reports on projected future climate change and its impacts. It provides updated information on emissions scenarios and projected future changes in climate in the 21st century and beyond, and describes the projected impacts of future climate change on systems, sectors and regions. Special attention is given to issues of human well-being and development. 

Topic 4 describes adaptation and mitigation options and responses as assessed in the reports of Working Groups II and III, and the inter-relationship of climate change and response measures with sustainable development. The focus of this topic is on response measures that can be implemented by 2030. Technologies, policies, measures and instruments as well as barriers to implementation are addressed along with synergies and trade-offs. 

Topic 5 covers the long-term perspective and analyses scientific, technical and socio-economic aspects relevant to adaptation and mitigation, consistent with the objectives and provisions of the United Nations Framework Convention on Climate Change (UNFCCC). It places decision-making about climate change in a risk management perspective, paying attention to broader environmental and integration issues. The topic describes emissions trajectories for stabilisation of greenhouse gas concentrations at various levels and associated temperature increases, along with information about the costs of mitigation, required technology development and deployment, and avoided climate impacts. It also explores in detail five main reasons for concern regarding climate change, which it finds have become stronger due to new knowledge since the TAR. 

Topic 6 highlights robust findings and key uncertainties.

While the Synthesis Report is a largely self-contained document, it needs to be viewed in the context of the other volumes of “Climate Change 2007” and it is recommended that for further details the contributions of the three Working Groups be consulted. Each of the Working Group reports consists of a series of chapters which contain a detailed scientific technical assessment, a Technical Summary, and a Summary for Policymakers that has been approved by the IPCC line by line.

The longer Synthesis Report contains extensive references to the relevant chapters in the Working Group contributions to the AR4 and other relevant IPCC reports. For easy reading, references in the Summary for Policymakers only lead to the relevant sections of the longer Synthesis Report. The CD RoM included in this report contains the full text of the three Working Group contributions to the AR4 in English, as well as the Summaries for Policymakers and Technical Summaries and the Synthesis Report in all official UN languages. References in these electronic versions are provided as hyperlinks to enable the reader to easily find further scientific, technical and socio-economic information. A user guide, glossary of terms, and lists of acronyms, authors, Review Editors and Expert Reviewers are provided in the Annexes to this report.

The preparation of the Synthesis Report was carried out in accordance with the Procedures for the Preparation, Review, Acceptance, Adoption, Approval and Publication of IPCC Reports, and it was adopted and approved by the IPCC at its Twenty Seventh Session (Valencia, Spain, 12-17 November 2007). 

We take this opportunity to thank: 

  • the Core Writing Team who drafted this report and, with their meticulous and painstaking attention to detail, finalised it 

  • the Review Editors who made sure that all comments were taken into consideration and that consistency with the underlying reports was maintained

  • the members of the Working Groups’ teams of Coordinating Lead Authors and Lead Authors who helped with the drafting 

  • the Head and staff of the SYR Technical Support Unit, particularly Dr Andy Reisinger, and the Technical Support Units of the three Working Groups, for logistical and editorial support 

  • the staff of the IPCC Secretariat for innumerable tasks performed in support of the preparation, release and publication of the report

  • WMO and UNEP for supporting the IPCC Secretariat and for financial contributions to the IPCC Trust Fund 

  • all member governments and the UNFCCC for their contributions to the IPCC Trust Fund 

  • and all member governments and participating organisations for invaluable in-kind contributions, including through supporting experts involved in the IPCC process and hosting meetings and sessions of the IPCC. 

Dr. R.K Pachauri 

Chairman of the IPCC 

Dr. Renate Christ

Secretary of the IPCC