Does the receipt of benefits from some common resource create an obligation to contribute toward its maintenance? If so, what is the basis of this obligation? I consider whether individual contributions to climate change can be impugned as wrongful free riding upon the stability of the planet's climate system, when persons enjoy its benefits but refuse to bear their share of its maintenance costs. Two main arguments will be advanced: the first urges further modification of H.L.A. Hart's 'principle of fairness' as the basis for demanding that would-be free riders pay their fair share in the context of climate change, while the second claims that remedial action on climate change is better captured through collective action analysis than through harm principles that seek to connect individual actions to bad environmental outcomes.