Fig. 22: Difference of the sea surface height (SSH) between the mean over 2071–2100 (SPP370) and the mean over 1985–2014 (historical run) averaged over five ensemble members. Only the dynamical sea level part is shown (i.e. contributions from thermal expansion and water mass changes are not considered).

5.5 Changes in the energy budget

The global-mean net total TOA radiative imbalance remains, on decadal timescales, close to zero in the historical simulation until around 1970, after which it increases to ~0.7 W/m2 for present-day conditions (Fig. 23a, black solid curve), reflecting the uptake of heat by the climate system. This is less than the observational estimate of 0.9 W/m2 for the period 2005–2014 by Trenberth et al. (2016), but within the uncertainty bounds (+/- 0.3 W/m2. It matches the observational estimate by Johnson et al. (2016) who report 0.71 ± 0.1 W/m2. Compared to CMIP5 and to other CMIP6 models, our simulated 0.7 W/m2 are below the average (see Wild, 2020, their Figure 6). After the historical period, the net total TOA radiative imbalance decreases gradually in our SSP126 scenario simulation, stabilizes at ~0.9 W/m2 in the SSP245 scenario simulation, and continues to increase to up to 2.0 W/m2 in the SSP370 and SSP585 scenario simulations toward the end of the 21st century (Fig. 23a, coloured solid curves). In contrast to the net total TOA radiation, its shortwave component exhibits a negative imbalance varying between 0.0 W/m2 and -1.0 W/m2 over the course of the historical simulation (Fig. 23a, black dashed curve), which implies an increased planetary albedo (Fig. 23b, black solid curve). The increased planetary albedo, particularly pronounced during the second half of the 20th century (+0.2%; the absolute simulated planetary albedo is ~28.9%), is not due to changes in surface albedo (Fig. 23b, black dashed curve), but is likely for the largest part due to anthropogenic aerosols that have compensated for a similarly strong positive longwave-radiative imbalance due to increased greenhouse-gas concentrations.