From the Climates of the Past to the Climates of the Future

International audienceThis chapter connects everything we have learned about past climates (both from the analysis of natural archives and from numerical simulations), and future climate projections. The models used to explore the future are similar to those used for past climates, except that the results are based on emission scenarios of greenhouse gas emissions whereas past climate simulations may be compared to reconstructions from the natural archives described in volume 1. The climate of the past 1,000 years can be seen as the ‘background noise’ of the recent natural evolution of theclimate system. On this basis, the current climate change can be analyzed. Over the longer term, analysis of ice cores allows us to trace back the history of atmospheric CO2 concentration over the last 800,000 years, and shows that the anthropogenic disturbance (producing an atmospheric CO2 concentration currently in excess of 410 ppm) is completely outside the documented glacialinterglacial variations over the last million years, ranging from 180 to 280 ppm. With this awareness you are well equipped to now explore the climate of the future