In this study, a novel optics scheme for cloud and precipitation modeling is introduced. Based on the Mie theory and existing datasets on ice crystals, the scheme offers an open-source package for generating data for user-defined gas bands, particle size distributions, and crystal habits. This approach ensures continuity across wide spectral bands and from small particle sizes (i.e., clouds) to large particle sizes (i.e., precipitation). It overcomes biases in existing schemes caused by numerical accuracy and inconsistency. Results are evaluated using an offline version of radiation codes used in a global circulation model. Using the flexible new scheme, it is found that cloud radiative effects are sensitive to microphysics variables such as particle size and habit distribution, which have an impact on effective radius. Systematic biases in radiation fluxes may occur if the effective radius is not fully predicted in microphysics processes due to predefined size and habit distributions. We show that when models assume spherical ice crystals, they dramatically underestimate radiative effects in ice clouds. The biases can be addressed by improving the effective radius approximation with a volume-to-radius ratio calculated from in-situ measurements. Combining these findings, we propose that numerical models can use a set of optics parameterizations for each type of hydrometer while accurately accounting for radiation effects caused by variations in size and habit distributions. Uncertainties due to this simplification are evaluated. This study offers a pathway towards a simple, consistent, and physical representation of radiative processes of clouds and precipitation in weather and climate simulations.

Greenhouse gases (GHGs) are gases that absorb and emit thermal energy. In a warming climate, GHGs modulate the thermal cooling to space from the surface and atmosphere, which is a fundamental feedback process that affects climate sensitivity. Previous studies have stated that the thermal cooling to space with global warming is primarily emitted from the surface, rather than the atmosphere. Using a millennium-length coupled general circulation model (Geophysical Fluid Dynamics Laboratory’s CM3) and accurate line-by-line radiative transfer calculations, here we show that the atmospheric cooling to space accounts for 12 % to 50 % of Earth’s clear-sky longwave feedback parameter from the poles to the tropics. The atmospheric cooling to space is an efficient stabilizing feedback process because water vapor and non-condensable GHGs tend to emit at higher temperatures with surface warming as the thermodynamic structure of the atmosphere evolves. A simple yet comprehensive model is proposed in this study for predicting the clear-sky longwave feedback over a wide range of surface temperatures. It achieves good spectral agreement when compared to line-by-line calculations. Our study provides a theoretical way for assessing Earth’s climate sensitivity, with important implications for Earth-like planets.