Neither category of cost can be estimated with any precision for fossil fuels, fission or fusion fifty years hence, but the present understanding is outlined below. Thus the conventional costs of electricity generated by fusion will be dominated by capital costs. These range from parity between fission, fusion and fossil fuels, to a factor two to fusion's disadvantage. Fusion has the advantage when one turns to the costs associated with safety and environmental concerns. Such costs comprise the costs of any harm done and the costs of complying with measures designed to prevent harm being done.
Fossil fuels are at the opposite extreme.
So also will be the costs of complying with measures designed to limit the emissions responsible for the harm. For fission, given the appropriate regulatory environment and safety culture, the expected costs of harm done are known to be small. The real problem is the costs associated with complying with measures needed to secure public acceptance. Public concern, and the associated compliance costs, may increase if it becomes necessary for fission to replace fossil fuels on a large scale all over the world. In order to obtain the benefits of the availability of fusion, at the time when those benefits are likely to be urgently required, the option should be established by about 2040.