Should climate models go on a low-sodium diet ?

Cloud formation in polar regions is controlled by the presence of natural aerosols, including sea salt aerosol which is emitted when strong winds blow over the open ocean. Therefore, the proper representation of the Arctic and Antarctic climate in models relies on adequate marine aerosol parameterizations. However, these have not been evaluated in the last generation of climate models, CMIP6. We performed this missing evaluation in a study published in May 2023 in Journal of Geophysical Research : Atmospheres.

In this work we show that :
(1) sea salt aerosol mass is overestimated in climate models compared to surface measurements, both in the Arctic and Antarctic, by one order of magnitude
(2) the model diversity leads to an uncertainty of up to a factor of 3 on concentrations
(3) the present-day and future uncertainty on concentrations, along with the sensitivity of polar climate to sea salt aerosol, leads to an uncertainty on the polar energy budget of around 1W/m2.

As a result, this work suggests that sea salt aerosol parameterizations should be revised in climate models, in particular when it comes to including polar-specific sources related to sea ice regions.

Missing sources from sea ice regions in climate models lead to a distorted seasonal cycle of surface concentrations, particularly for locations closer to the poles. In addition, size distribution of sea salt aerosols in models lead to a positive bias on emissions.

Marine aerosol concentrations could double in the Arctic by 2100, in connection with accelerated sea ice melting, and could increase by at least 50% even in a moderate climate change scenario. Therefore, the uncertainty on the radiative impact of sea salt aerosols leads to a large uncertainty for both present-day and future polar climate.

Contact : Rémy Lapere

Reference : Lapere, R., Thomas, J. L., Marelle, L., Ekman, A. M. L., Frey, M. M., Lund, M. T., et al. (2023). The representation of sea salt aerosols and their role in polar climate within CMIP6. Journal of Geophysical Research : Atmospheres, 128, e2022JD038235. https://doi.org/10.1029/2022JD038235