News
July 14 2014

WITCH: the story of FEEM's most famous model



The book Climate Change Mitigation, Technological Innovation and Adaptation is the attempt to transparently lay out the story of FEEM's most famous model: WITCH.

Integrated assessment models (IAMs) represent an aspiration, that of describing the full cycle of environmental externalities. Starting from what causes environmental externalities (human activities), to the positive or negative feedbacks these have on humans, IAMs are increasingly at the basis of key policy decisions.

We use the term “aspiration” because the complexity of the phenomena that these models try to portray is such that some processes and links are always left unmodelled. What is essential and what can be left out depends, ultimately, on what questions the modeler is set out to answer.

We wrote the first equations of the WITCH model in 2005 and the model has since grown in complexity and richness. WITCH is a moving target, which develops and unfolds over time as new requests arrive from policy, new topics acquire research relevance, new data and methods become available and new people with new skills join or leave the team.

In WITCH, economic activity generates greenhouse gas emissions, a simplified model of carbon and climate dynamics translates emissions into temperature increases and a damage function provides a feedback of climatic change on economic activities. This is the core, common to many other IAMs.

What is maybe the trade mark of this model is its game theoretic structure as well as the endogenous representation of technological change. Indeed, these features are reflected in the name itself: World Induced Technical Change Hybrid model, or WITCH.

WITCH is an open project and new additions as well as developments will follow in future years. A final consolidated version will probably never exist and the latest developments are always posted at the WITCH project website. Researchers and policy makers are able to consult all the background material as well as the output of a number of representative scenarios using the WITCH Policy Simulator, a section of the website that provides user-friendly access to an interesting dataset. The model code is also available for download, as a way to foster community research in the field.

We hope that researchers and policy makers who are interested in applied climate economics will find this book a source of useful information. We are perfectly aware of the fact that numerical tools like WITCH have many limits and must be applied with caution. However, they are extremely valuable to appreciate the many subtleties of the climate change challenge.

Interdisciplinary and applied economic work in this field is exciting and to a great extent new: much more work lies ahead of us all in order to carry out informative and insightful analyses.

by Valentina Bosetti, Carlo Carraro, Emanuele Massetti, Massimo Tavoni

Link to the book Climate Change Mitigation, Technological Innovation and Adaptation


Fondazione Eni Enrico Mattei

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