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.

Authors: Terry Barker (UK), Igor Bashmakov (Russia), Lenny Bernstein (USA), Jean E. Bogner (USA), Peter Bosch (The Netherlands), Rutu Dave (The Netherlands), Ogunlade Davidson (Sierra Leone), Brian S. Fisher (Australia), Sujata Gupta (India), Kirsten Halsnæs (Denmark), BertJan Heij (The Netherlands), Suzana Kahn Ribeiro (Brazil), Shigeki Kobayashi (Japan), Mark D. Levine (USA), Daniel L. Martino (Uruguay), Omar Masera (Mexico), Bert Metz (The Netherlands), Leo Meyer (The Netherlands), Gert-Jan Nabuurs (The Netherlands), Adil Najam (Pakistan), Nebojsa Nakicenovic (Austria/Montenegro), Hans-Holger Rogner (Germany), Joyashree Roy (India), Jayant Sathaye (USA), Robert Schock (USA), Priayadarshi Shukla (India), Ralph E. H. Sims (New Zealand), Pete Smith (UK), Dennis A. Tirpak (USA), Diana Urge-Vorsatz (Hungary), Dadi Zhou (PR China)