Understanding does not imply predictive power -- We always make models for something, not of something -- Time means are more predictable than the instantaneous state -- The large scale dynamics are reasonably well understood, un-certainty lies in the parametrization of small-scale processes -- It is the poor and the marginalized that are hit hardest by climate change -- When deciding about long-term strategies, irreversibility is a key point -- The Montreal Agreement is a good example of how to deal with a global environmental problem.