Climate models and earth system models often comprise submodels composed via a `coupler’, a software component that enables interaction between submodel components. The continuous exchange of data through couplers creates the risk of subtle errors propagating across components, potentially distorting scientific conclusions. In this paper, we argue for lightweight formal verification techniques to tackle coupler correctness. We abstract general design principles for couplers and propose verifiable subsystems. Using an example of a real-world bug, we illustrate a hybrid verification strategy that integrates module-level contracts, verified through both static and runtime techniques. We aim to offer a practical pathway for both existing and future couplers, ultimately enabling auditable and formally verifiable couplers.