“Grand Paris” is a study carried out by ten teams of researchers and city planners in the aim of putting forward general guidelines for Paris urban area’s evolution by 2030. All the teams suggest making the area “greener” in some way, to combat climate warming by CO2 sequestration. Our team also shows that extending the nearby forests by 30 %, favouring short farm-to-consumer circuits and using lighter coloured building materials will decrease the urban heat island, reducing the mortality during heat waves as well as the need for air-conditioning. These results lead us to reverse the way of thinking urban planning: the geographic and natural aspects should replace the urban infrastructure as a driver for planning urban development. This new strategy allows city changes on quite a large scale, that will have a favourable impact in terms of economics, leisure activities, greenhouse gas emissions and the local microclimate