This paper offers a comprehensive description of the integrated assessment model (IAM) RESPONSE developed at CIRED. RESPONSE aims at providing a consistent framework to appraise alternative modelling choices made by the main existing IAMs. It is designed as a flexible tool able to take different modelling structures in order to compare results from the modelling frameworks that have driven the so-called ''when flexibility'' controversy since the early 1990s dealing with the optimal timing of mitigation efforts and the optimal time profile of the social cost of carbon. RESPONSE is both sufficiently compact to be easily tractable and detailed enough to be as comprehensive as possible in order to capture a wide array of emblematic modelling choices, namely the forms of the damage function (quadratic vs. sigmoid) and the abatement cost (with or without inertia), the treatment of uncertainty, and the decision framework (one-shot vs. sequential).
