Monday, August 30, 2021

An underestimated negative cloud feedback from cloud lifetime changes

Scientists still do not even understand the complex phenomenon of cloud formation! This major deficiency has been well known for decades, but the general public has been kept in the dark about it.

Apparently, the climate models have for years underestimated the very significant cooling effect of clouds meaning their dire long-term forecasts (up to 100 years or to the end of the century) are garbage!

"As the atmosphere warms, part of the cloud population shifts from ice and mixed-phase (‘cold’) to liquid (‘warm’) clouds. Because warm clouds are more reflective and longer-lived, this phase change reduces the solar flux absorbed by the Earth and constitutes a negative radiative feedback. This cooling feedback is weaker in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) than in the fifth phase (CMIP5), contributing to greater greenhouse warming. Although this change is often attributed to improvements in the simulated cloud phase, another model bias persists: warm clouds precipitate too readily, potentially leading to underestimated negative lifetime feedbacks. In this study we modified a climate model to better simulate warm-rain probability and found that it exhibits a cloud lifetime feedback nearly three times larger than the default model. This suggests that model errors in cloud-precipitation processes may bias cloud feedbacks by as much as the CMIP5-to-CMIP6 climate sensitivity difference. Reliable climate model projections therefore require improved cloud process realism guided by process-oriented observations and observational constraints."

An underestimated negative cloud feedback from cloud lifetime changes | Nature Climate Change (no public access)

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