Updated climate models are clouded by scientific biases, researchers find

Clouds can cool or warm the planet, a radiative effect that contributes significantly to the global energy budget and can be altered by human-caused pollution. About 80% of the world's southernmost ocean is covered by clouds. How does this body of water affect the climate?

Thanks to an international collaboration identifying compensation errors in climate model protocols, researchers are one step closer to figuring it out. The researchers published their findings in a journal.

The problem of cloud and radiation biases over the Southern Ocean has been a problem in the past generations of global climate models. After the latest CMIP6 models were released, we were anxious to see if the old problems were still there.

The World Climate Research Program's CMIP6 allows for the systematic assessment of climate models to illuminate how they compare to each other and real-world data. Five of the CMIP6 models were analyzed by Wang and the researchers.

The Southern Ocean's cloud coverage is thought to be a contributing factor to some CMIP6 models' high sensitivity when simulations predict a surface temperature that rises too quickly for the rate of increased radiation. The Southern Ocean clouds could cast a shadow of doubt on the projection of future climate change.

The paper emphasizes compensating errors in the cloud physical properties despite the improvement of radiation simulation over the Southern Ocean. We can quantify the errors in the simulations of the cloud microphysical properties, including cloud fraction, cloud water content, cloud droplet size and more, and show how each contributes to the total bias in the cloud radiative effect.

Physical properties of the cloud determine the cloud radiative effect. The cloud radiative effects in CMIP6 are comparable to satellite observations, but there are biases in the cloud fraction liquid water path. Even though the latest CMIP models improve the simulation of their mean states, such as radiation fluxes at the top of the atmosphere, the detailed cloud processes are still uncertain.

The model climate sensitivity assessments use model detailed physics instead of the mean state performance to evaluate the effect on the climate.

Wang said that their future work would aim to pin down individual parameters that are responsible for biases. Hopefully, we can work together with model developers to solve them. The ultimate goal of the study is to improve the models.

The Division of Geology and Planetary Science is one of the contributors.

More information: Compensating Errors in Cloud Radiative and Physical Properties over the Southern Ocean in the CMIP6 Climate Models, Advances in Atmospheric Sciences (2022). DOI: 10.1007/s00376-022-2036-z Journal information: Advances in Atmospheric Sciences