Climate change is one of the biggest challenges facing humankind for the next century. We expose how we build a Model about the Dynamics of Inertia and Adaptability in energy systems (DIAM) to study the question \"Shall we wait another decade before taking costly measures to curb greenhouse gases emissions\". Using primarily Mathematica, we had to use also the GAMS language, not only to be understood by other researchers in our field, but also to gain access to a powerful non linear constrained optimisation solver. It seems urgent to bridge the gap between these kind of solvers and Mathematica because when one builds models of complex systems, intertemporal optimisation is often preferred to recursive simulation.