Assume that we have borrowed the Earth from our children, and that we one day shall give it back to them and account for what we have done to it. Then we would have to try to restore the damage we have caused. Further, we would have to offer compensation for the damage we have done that we cannot repair at a lower cost. The generational environmental debt (GED) is a measure of these costs. In this paper we define and discuss the concept of GED and calculate GED for emissions of the greenhouse gas CO2. The global GED for CO2 emissions is estimated to 10 000 billion US dollars and the Swedish GED for CO2 emissions is estimated to 60 billion US dollars.