Many countries commit to rapid climate action, but their ambitions are not enough to reach the Paris goals. It is not trivial to define which countries should do more. This is a matter of fairness. But what is fair in this context? Should rich countries mitigate more, because they have the means to do so? Or the countries that have emitted a lot in the past? Clearly, there is no single answer, because it depends on what you think is fair. However, these principles can be quantified. The Carbon Budget Explorer allows navigating through the implications of different views on fairness.