1 Introduction

TThis documentation is the essential guide for the users of the WITCH integrated assessment model. A model overview is available in a dedicated website http://www.witchmodel.org. In particular, the website http://doc.witchmodel.org contains an updated and ongoing documentation of the current WITCH model, on which this paper is based upon.

This documentation is organized into different chapters. The second chapter provides a general presentation of the model. The third chapter describes in detail how the economy in general is modelled in WITCH. Chapter four presents the bottom-up modelling of the energy sector. The extraction and market solution for the fossil fuel resources is outlined in chapter 5 while the land-use part and the soft link to the GLOBIOM model is described in chapter six. How emissions of greenhouse gases are modelled and the link to the global carbon cycle, radiative forcing, and global mean temperature is detailed in chapter 7. Since WITCH can be run in a Cost Benefit Analysis mode including impacts and adaptation, their specification is described in chapter eight. The different climate and other policy options that can be run in the WITCH model are outlines in chapter 9. Finally, the implementation of the Shared Socioeconomic Pathways (SSP) and some results are presented in chapter 10.