In this book some options concerning the greenhouse effect are assessed from a welfarist point of view: business as usual, stabilization of greenhouse gas emissions and reduction by 25% and by 60%. Up to today only economic analyses of such options are available, which monetize welfare losses. Because this is found to be wanting from a moral point of view, the present study welfarizes (among others) monetary losses on the basis of a hedonistic utilitarianism and other, justice incorporating, welfare ethics. (...) For these welfarist evaluations information about the social consequences of the four options are collected from the literature and eventually corrected; then the consequences for individual well-being are assessed based on psychological research about well-being dependent on the social situation of the individual; finally the aggregation formulas of the respective welfare ethics are applied to these data. Assessments by other types of ethics, e.g. Kantian ethic, are included. The strongest abatement option is found to be optimum with great unanimity. - In addition a cost-welfare analysis of greenhouse gas abatement is undertaken revealing efficient cost-welfare ratios for these measures and the most efficient ratio for the strongest option. - A final, more theoretical part discusses the moral obligations following from such evaluations. The notion of 'moral obligation' is explained in a way that, apart from moral goodness of the required act, reinforcement by formal or informal sanctions is another necessary condition for moral obligations. This leads to a conception of a historical morality according to which the demands of morality rise in the long run. Applying this conception to the greenhouse effect implies that presently we have the moral duty to raise the standards of greenhouse gas abatement as much as is politically feasible. (shrink)