Abstract
Climate models taking part in the coupled model intercomparison project phase 5 (CMIP5) all predict a global mean sea level rise for the 21st century. Yet the sea level change is not spatially uniform and differs among models. Here we evaluate the role of air–sea fluxes of heat, water and momentum (windstress) to find the spatial pattern associated to each of them as well as the spread they can account for. Using one AOGCM to which we apply the surface flux changes from other AOGCMs, we show that the heat flux and windstress changes dominate both the pattern and the spread, but taking the freshwater flux into account as well yields a sea level change pattern in better agreement with the CMIP5 ensemble mean. Differences among the CMIP5 control ocean temperature fields have a smaller impact on the sea level change pattern.
Highlights
During the last hundred years, global mean sea level has been rising
The future sea level change pattern is characterized by a meridional dipole in the North Atlantic with higher sea level rise north of 40◦N and lower to the south, a meridional dipole in the Southern Ocean with higher sea level rise north of 50◦S and lower to the south, and higher sea level rise in the Western North Pacific. These features can be seen in the model mean of coupled model intercomparison project phase 5 (CMIP5) simulations under the idealized 1% CO2 scenario (figure 1(a)). (In all figures showing sea level change, the quantity plotted is the difference between local sea level change and the global mean, because in this analysis we are concerned only with the geographical pattern.) We choose to analyse results for this scenario, in which the atmospheric CO2 concentration is increased by 1% each year, because it gives minimal differences in radiative forcing among models
There are five other CMIP5 models for which the data were available but it was not possible to run stable simulations with all three fluxes simultaneously, because they caused too large a perturbation when imposed together; we found the stable simulations could be achieved in those cases if the applied flux changes were scaled down
Summary
During the last hundred years, global mean sea level has been rising. The rate of rise was ∼2 mm year−1 for 1972– 2008 (Church et al 2011), and ∼3 mm year−1 since the early 1990s (Cazenave and Nerem 2004, Llovel et al 2011). (In all figures showing sea level change, the quantity plotted is the difference between local sea level change and the global mean, because in this analysis we are concerned only with the geographical pattern.) We choose to analyse results for this scenario, in which the atmospheric CO2 concentration is increased by 1% each year, because it gives minimal differences in radiative forcing among models They tend to show these common features, the individual models disagree on the details and the magnitude of the regional changes (Yin et al 2010, Pardaens et al 2011, Yin. 2012, Bouttes et al 2012), with the spread between the models being greatest at high latitudes (figure 1(b); see figure S2 of Bouttes et al 2012, for individual models). We investigate the contribution to the model spread which arises from their having different control climate states of the 3D ocean temperature field
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