# Large discrepancies in dominant microphysical processes governing mixed-phase clouds across climate models

## TL;DR

Climate models differ in how they represent ice formation processes in clouds, leading to inconsistent predictions of cloud composition.

## Contribution

The study reveals large discrepancies in how climate models prioritize microphysical processes affecting mixed-phase clouds.

## Key findings

- All models agree that primary ice nucleation dominates in cold high-latitude clouds.
- Model responses to a unified secondary ice production parameterization varied significantly.
- Divergences suggest models prioritize different processes, affecting cloud phase predictions.

## Abstract

The balance between liquid and ice in clouds remains a major challenge in climate modeling, largely due to uncertainties in ice-related processes. We investigate the relative importance of four microphysical processes—primary ice nucleation (PIN), secondary ice production (SIP), sedimentation, and transport of ice crystals—for the supercooled liquid fraction (SLF) in mixed-phase clouds using three global climate models: EC-Earth3-AerChem, NorESM2-MM, and ECHAM6.3-HAM2.3. All models identify PIN as the dominant influence on SLF at cold temperatures in high northern latitudes, but diverge elsewhere and for higher temperatures. Implementing a unified SIP parameterization produced varied model responses, revealing fundamental differences in how microphysical processes interact within each model framework. These discrepancies suggest that each model prioritizes different processes in shaping the cloud phase. Such divergence may limit the reliability of conclusions regarding microphysical processes drawn from any single model.