Clouds at mid/high latitudes often consist of a mixture of ice and liquid and are thus referred to as mixed-phase clouds. When the atmosphere warms, these clouds gradually transition to liquid clouds, which leads to a cloud brightening (increase in cloud albedo, and thus a negative climate feedback). Advances in spaceborne remote sensing (CALIPSO) have revealed that climate models have a phase bias, such that the simulated clouds generally contain too much ice and not enough liquid. Past research (e.g., Tan, Storelvmo and Zelinka, Science 2016) has demonstrated that fixing this bias in climate models would lead to an increased climate sensitivity. Consistent with this, the CMIP6 model ensemble has a significantly higher climate sensitivity than CMIP5, due to a more positive extratropical cloud feedback as modeling groups have addressed the phase bias (Zelinka et al., GRL, 2020). In a recent follow-up study (Bjordal, Storelvmo, Alterskjær, Carlsen, Nature Geosci., 2020) we demonstrated that the negative cloud phase feedback changes with climate state. While it is strongly negative in mid/high latitudes in the present climate, this feedback will weaken with further warming, until it completely vanishes when the majority of the clouds are all liquid. This change in cloud feedback thus represents a shift to higher climate sensitivity with warming, and with that potentially a transition to a different climate state with largely ice-free extratropical clouds.

Bio: https://www.mn.uio.no/geo/english/people/aca/metos/truds/