The Arctic Ocean in CMIP6 models: Biases and projected changes in
temperature and salinity
We examine the historical evolution and projected changes in the
hydrography of the deep basin of the Arctic Ocean in 23 climate models
participating in the Coupled Model Intercomparison Project Phase 6
(CMIP6). The comparison between historical simulations and an
observational climatology shows that the simulated Atlantic Water (AW)
layer is too deep and thick in the majority of models, including the
multi-model mean (MMM). Moreover, the halocline is too fresh in the MMM.
Overall our findings indicate that there is no obvious improvement in
the representation of the Arctic hydrography in CMIP6 compared to CMIP5.
The climate change projections reveal that the sub-Arctic seas are
outstanding warming hotspots, causing a strong warming trend in the
Arctic AW layer. The MMM temperature increase averaged over the upper
700 m at the end of the 21st century is about 40\% and
60\% higher in the Arctic Ocean than the global mean in
the SSP245 and SSP585 scenarios, respectively. Salinity in the upper few
hundred meters is projected to decrease in the Arctic deep basin in the
MMM. However, the spread in projected salinity changes is rather large
and the tendency toward stronger upper 400 m ocean stratification in the
MMM is not simulated by all the models. The identified biases and
projection uncertainties call for a concerted effort for major
improvements of coupled climate models.