4.2 Greenland Ice Sheet (GrIS)

Figure 2 indicates a near-linear sea level trend for the GrIS versus average temperature (2051-2100: 0.8±0.2 mm/yr/K), which, as discussed below, is likely a result of mass loss being dominated by surface mass balance (SMB) over ice dynamics in the models. In a subset of ISMIP6 model simulations it is possible to separate the role of these two components of mass loss. We do this using the results presented in (Payne et al., 2021), and find that the dynamic component of mass loss is both limited and insensitive to average temperature, whereas the SMB component has a positive linear relationship with GMST (Fig. 3). As a result, SMB becomes an increasingly dominant component of mass loss under SSP5-8.5, from being approximately equal to the dynamic component in the earlier part of the century, to being a factor of 2-3 greater in the second half. The ISMIP6 simulations apply a SMB-elevation feedback, such that melt increases as elevation decreases (Nowicki et al., 2020). This acts to enhance SMB losses with surface lowering, contributing to the increasing dominance of this component over the century.