The PROHIBLUX project comprises three main scientific activities. The first scientific activity involves developing a normative theory of limits on the permissible uses of sustainable emissions allowances. Adopting a specific global mitigation target means having a finite global budget for greenhouse gas emissions that is consistent with the chosen target, based on probability. The project aimed to justify an emissions ceiling for the emissions budget, distinguishing between uses of the budget that should be subject to price constraints equal for all, and those that should be the focus of special policy measures. In order to provide a robust justification for the emissions ceiling, the PROHIBLUX project had to satisfy two requirements. Firstly, it had to explain why producing a certain amount of emissions above the ceiling (e.g. by chartering a superyacht) is morally distinct from producing the same quantity of emissions below the ceiling (e.g. by taking repeated car journeys). Secondly, it had to demonstrate that producing emissions above the ceiling is morally wrong, even when equivalent carbon offsetting measures are implemented, whether nature-based or technological. Building on a theory of the just distribution of a finite emissions budget, named emissions limitarianism, and on two pro tanto arguments concerning positional consumption and moral disengagement, the project provided a justification for the emissions ceiling that satisfied both requirements. The second scientific activity takes the form of a comparative analysis of the three main policy proposals for implementing the emissions ceiling, based on both ethical considerations and feasibility constraints. The policies in question include bans, luxury carbon taxation and progressive carbon taxation. Bans prohibit the sale and/or possession of certain goods and services from a specified date onwards. Luxury carbon taxation involves a surcharge on the purchase or ownership of certain carbon-intensive luxury goods. Progressive carbon taxation is a carbon pricing system in which the tax rate on carbon emissions increases as individuals move from lower to higher emission brackets. The analysis was based on both normative and non-normative criteria. These include emissions justice, expressive justice, social efficiency, the non-frustration of legitimate expectations, administrative feasibility, and the prevention of carbon leakage. The main outcome of this analysis is a grid that evaluates the three policy instruments against each of the aforementioned criteria. The third scientific activity is an investigation into whether the fact that the very rich have consistently exceeded the emissions ceiling, coupled with their substantial financial resources, imposes additional climate justice responsibilities on them beyond those applicable to all individuals. The PROHIBLUX project supported this view by distinguishing between the weighty and frivolous interests of emitters and investors and by adopting a broad and objective conception of equal sacrifice for climate action. Furthermore, the project proposed a global policy toolbox through which countries could synchronise their efforts to ensure that the very rich fulfil their special climate responsibilities, while also preventing carbon leakage. The toolbox consists of taxes on extreme wealth, carbon taxes on the financial assets of the very rich, and carbon taxes on luxury and emission-intensive consumption.
