Simple functional representations of gas absorption for efficient climate model radiation schemes

Understanding climate-relevant radiative processes requires radiation-transfer tools that balance physical fidelity, computational efficiency, and interpretability. Existing approaches span a broad but sparse hierarchy: idealized models miss key radiative processes, operational schemes trade physical tractability for accuracy and efficiency, and although line-by-line models are physically accurate, their computational cost prohibits direct coupling to Earth system models. This leaves a critical gap for models that are physically tractable, asymptotically convergent, and efficient.

We investigate alternative representations of gas absorption, a key component for clear-sky radiation transfer. Using simple functional forms per frequency, we represent the pressure–temperature scaling of absorption. Absorption cross sections, radiative fluxes, and heating rates are evaluated for representative atmospheric profiles and compared against a benchmark line-by-line reference model. We show that these functional forms can reproduce  the pressure–temperature dependence of gas absorption, thus replacing large multidimensional lookup tables. Combined with monochromatic spectral quadrature points (Czarnecki et al., 2023), this approach will enable highly efficient, physically tractable gas absorption calculations in climate models.