Acknowledgements. -- Foreword. -- Executive summary. -- List of abbreviations. -- Introduction. -- Observed climate changes and impacts. -- 21st century projections. -- Focus: sea-level rise projections. -- Focus: changes in extreme temperatures. -- Sectoral impacts. -- System interaction and non-linearity - the need for cross-sector risk assessments. -- Appendixes. -- Bibliography. This report provides a snapshot of recent scientific literature and new analyses of likely impacts and risks that would be associated with a 4À Celsius warming within this century. It is a rigorous attempt to outline a range of risks, focusing on developing countries and especially the poor. A 4ÀC world would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on ecosystems and associated services. But with action, a 4ÀC world can be avoided and we can likely hold warming below 2ÀC.