Fairness critically conditions the carbon budget allocation across countries

•Study derives carbon budget allocations when fairness concerns are considered.•Key concerns are basic needs, past emissions and benefits from historical emissions.•Fairness concerns identify critiques about current budget allocation principles.•A qualified equal-per-capita approach is a promising way to address such concerns. Countries’ nationally determined contributions to mitigate global warming translate to claims of country specific shares of the remaining carbon budget. The remaining global budget is limited by the aim of staying well below 2 °C, however. Here we show how fairness concerns quantitatively condition the allocation of this global carbon budget across countries. Minimal fairness requirements include securing basic needs, attributing historical responsibility for past emissions, accounting for benefits from past emissions, and not exceeding countries’ societally feasible emission reduction rate. The argument in favor of taking into account these fairness concerns reflects a critique of both simple equality- and sovereignty-principled reduction approaches, the former modelled here as the equal-per-capita distribution from now on, the latter as prolonging the inequality of the status-quo levels of emissions into the transformation period (considered a form of “grandfathering”). We find the option most in line with fairness concerns to be a four-fold qualified version of the equal-per-capita approach that incorporates a limited form of grandfathering.