J. Geophys. Res. Atmos. http://doi.org/cvp2 (2018)

Climate models do not typically simulate the radiative effects of precipitating hydrometeors — that is, falling snow. Previous studies have demonstrated that systematic model biases arise in the tropical Pacific due to this exclusion, including excessive atmospheric instability, a corresponding increase in deep convection and warmer sea surface temperatures. Chao-An Chen from Academia Sinica, Taiwan, and colleagues further investigate these biases in light of anthropogenic forcing, using simulations with the Community Earth System Model (CESM1) in which snow radiative effects are either ‘on’ or ‘off’, and CO2 concentrations that increase by 1% per year.

With anthropogenic forcing, it is found that convective regions in the Pacific are intensified and shifted eastwards. However, when snow radiative effects are included, these changes — radiative balance, circulation and precipitation — are all amplified, leading to reduced precipitation around the maritime continent, but a near doubling over the western Pacific. Snow ‘off’ simulations compare well to CMIP5 output, suggesting that projected changes in the tropical Pacific may presently be underestimated. Thus, future work should aim to incorporate the impacts of falling snow into coupled climate models.