Climate change: new challenges.

Summary Hervé Le Treut, French climatologist and member of the International Panel on Climate Change (IPCC), gave a lecture on the theme of climate modeling. Since January 2009, he has been the director of the Institut Pierre Simon Laplace (IPSL), a federation that coordinates the work of nine research laboratories in the Paris region.From the outset of his talk, Hervé Le Treut explained how the issues associated with climate change are evolving: because of the passing of certain key dates and the crossing of critical thresholds, the deadlines - once distant and unclear - are becoming clearer and closer. After illustrating this state of affairs on diagrams that specify the associated time scales, the speaker presents the various elements necessary for climate modeling, distinguishing between what we can say for sure and what is a matter of uncertainty, and then he discusses future risks.This lecture, given on June 18, 2015 on the occasion of the Inria scientific days, before an audience mainly composed of researchers, ends with an invitation addressed to all citizens. Hervé Le Treut suggests that everyone should take an interest in climate change on a territorial scale, to allow for more concrete observation and greater awareness.