Lawrence Berkeley National Laboratory

A. Introduction 1. The Working Group III contribution to the IPCC Fourth Assessment Report (AR4) focuses on new literature on the scientific, technological, environmental, economic and social aspects of mitigation of climate change, published since the IPCC Third Assessment Report (TAR) and the Special Reports on COB2B Capture and Storage (SRCCS) and on Safeguarding the Ozone Layer and the Global Climate System (SROC). The following summary is organised into six sections after this introduction: - Greenhouse gas (GHG) emission trends, - Mitigation in the short and medium term, across different economic sectors (until 2030), - Mitigation in the long-term (beyond 2030), - Policies, measures and instruments to mitigate climate change, - Sustainable development and climate change mitigation, - Gaps in knowledge. References to the corresponding chapter sections are indicated at each paragraph in square brackets. An explanation of terms, acronyms and chemical symbols used in this SPM can be found in the glossary to the main report.