The energy transition will be costly, but it will reduce much larger climate damages in the future without it. In order to compare these immediate costs with their future benefits, one must estimate the “carbon value”, which is ideally equal to the discounted value of the flow of marginal climate damages. This raises the issue of the rate at which very distant climate damages should be discounted. I will explore the economic and moral issues behind our discounting systems in relation to our responsibilities towards future generations, and how they translate into a climate discount rate. I will be particularly interested in the role of the deep uncertainties surrounding the fate of our civilization on this Planet, the intensity of climate change, and the speed of green technological progress.