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.