This article discusses existing principles that systematise climate responsibility and offers an economic activity principle as alternative. The economic activity principle presented here focuses on the economic link between the polluter-pays, beneficiary-pays, and abilityto-pay principles. It argues that agents’ climate responsibility should be based progressively on the emissions intensity of their income and expenditures above an abilityto-pay threshold and after an excusable ignorance threshold. The proposed principle offers a systematised understanding of the norm of common but differentiated responsibilities which might help address some of the problems related to its current lack of conceptual clarity and empirical measurability.