What does a 2°C change in global surface temperature represent? How much do different activities contribute to the increase in greenhouse gases? On what timescales is the climate adjusting? What solutions exist? What can we do about this? What is being done at Ecole Polytechnique regarding teaching? Elements of answers to these different questions will be given, drawing from reports from the Inter-Governmental Panel on Climate Change, and from personal experience in teaching. Time will be kept for discussion.