Fig. 2: Vertical profiles of globally averaged ocean temperature and
salinity in the last 400 years of the 500 years of piControl simulation
(relative to the beginning of this 400 year time period). The last 400
years cover all simulations branched off since the first branch-off
point is in year 150 of the piControl simulation, i.e. 350 years before
the end of the piControl simulation (see Table 1).
In the last 100 years of the 500 year piControl simulation, which
followed the 500 year spinup simulation, there are still imbalances in
the top-of-atmosphere (TOA) and net surface radiation. Averaged over
these 100 years the TOA radiation imbalance amounts to 0.34
W/m2 whereas the net surface energy flux consisting of
radiation and turbulent heat fluxes amounts to 0.84
W/m2. Given that changes in the atmospheric energy
content on this time scale are much smaller, the discrepancy implies an
unphysical atmospheric energy non-conservation of about 0.5
W/m2. By using the delta approach in the evaluation of
the climate change signal as briefly introduced in section 2.2, this
non-conservation is cancelled out although one needs to keep in mind the
non-linearity of the system.
The gradual energy loss of the ocean over the same time period,
diagnosed from changes in the 3D ocean temperature (and sea-ice mass
changes), corresponds to a global surface energy flux of -0.01
W/m2. The deviation from the atmospheric surface flux
imbalance by 0.85 W/m2 cannot be explained by changes
in the continental heat content, but points to further deviations from
energy conservation that can be related to mismatching grids and
coastlines between the model components, inconsistent treatment of
temperature, precipitation and runoff (Mauritsen et al. 2012), or other
inconsistencies. The atmosphere-related and the surface-related
non-conserving energy terms partly compensate each other, resulting in
an overall unphysical energy sink of -0.35 W/m2, and
both of them are relatively constant over all simulations (when averaged
over decades and longer; not shown).