Importance of the mixed-phase cloud distribution in the control climate for assessing the response of clouds to carbon dioxide increase: a multi-model study

Abstract

We have conducted a multi-model intercomparison of cloud-water in five state-of-the-art AGCMs run for control and doubled carbon dioxide climates. The most notable feature of the differences between the control and doubled carbon dioxide climates is in the distribution of cloud-water in the mixed-phase temperature band. The difference is greatest at mid and high latitudes. We found that the amount of cloud ice in the mixed phase layer in the control climate largely determines how much the cloud-water distribution changes for the doubled carbon dioxide climate. Therefore evaluation of the cloud ice distribution by comparison with data is important for future climate sensitivity studies. Cloud ice and cloud liquid both decrease in the layer below the melting layer, but only cloud liquid increases in the mixed-phase layer. Although the decrease in cloud-water below the melting layer occurs at all latitudes, the increase in cloud liquid in the mixed-phase layer is restricted to those latitudes where there is a large amount of cloud ice in the mixed-phase layer. If the cloud ice in the mixed-phase layer is concentrated at high latitudes, doubling of carbon dioxide might shift the center of cloud water distribution poleward which could decrease solar reflection because solar insolation is less at higher latitude. The magnitude of this poleward shift of cloud water appears to be larger for the higher climate sensitivity models, and it is consistent with the associated changes in cloud albedo forcing. For the control climate there is a clear relationship between the differences in cloud-water and relative humidity between the different models, for both magnitude and distribution. On the other hand the ratio of cloud ice to cloudwater follows the threshold temperature which is determined in each model. Improved measurements of relative humidity could be used to constrain the modeled representation of cloud water. At the same time, comparative analysis in global cloud resolving model simulations is necessary for further understanding of the relationships suggested in this paper.

Lower-Tropospheric Mixing as a Constraint on Cloud Feedback in a Multiparameter Multiphysics Ensemble

“…Uncertainty in cloud feedback, the most important factor for the spread of CS , has been examined by decomposing into different cloud properties including regionality, height, and optical depth (e.g., Zelinka et al 2012aZelinka et al ,b, 2013hereafter Z13). For example, negative cloud feedback over the high latitudes associated with a phase change from ice to liquid cloud is physically consistent and robust among models (e.g., Tsushima et al 2006;Zelinka et al 2012b;Z13). In contrast, low cloud amount feedback over the ocean, the largest contributor to the total spread of cloud feedback (Bony and Dufresne 2005;Webb et al 2006), still scatters substantially even in the state-of-the-art climate models [archived in phase 5 of the Coupled Model Intercomparison Project (CMIP5); Taylor et al 2012] both in sign and magnitude (Vial et al 2013;Z13;Qu et al 2014).…”

Linking glacial and future climates through an ensemble of GCM simulations

“…Therefore a higher value should correspond to a higher total amount of ice in the clouds. The relationship of ice, clouds and sensitivity is complex, but Tsushima et al (2006) find less cloud ice to be linked to in a larger pole-ward shift in cloud water and therefore a reduced cloud albedo effect, amplifying the overall warming. However, at least for the two versions of MIROC considered in that work (among other GCMs) and an intermediate unpublished version, their overall sensitivity to LGM boundary conditions is rather similar, indicating that this change in model formulation has little effect under strong cooling conditions.…”

Two-moment bulk stratiform cloud microphysics in the GFDL AM3 GCM: description, evaluation, and sensitivity tests

“…These effects could potentially outweigh the influences of IN on cirrus clouds (Lohmann and Feichter, 2005), but their magnitudes are still very uncertain. Furthermore, a recent study by Tsushima et al (2006) suggests that the representation of mixed-phase clouds in climate models plays an important role for the response of clouds to carbon dioxide increase.…”