Fig. 13: Mean 2 m temperature anomaly (°C) for (a) the whole globe, (b)
Northern Hemisphere, and (c) Southern Hemisphere from piControl,
historical, and scenario simulations. Anomalies were computed relative
to the period 1951–1980. The purple line indicates the observed 2 m
temperature anomaly from Goddard Institute for Space Studies (GISS)
Surface Temperature Analysis (GISTEMP v4) (GISS, 2019; Hansen et al.,
2010; Lenssen et al., 2019).
Fig. 14 shows the spatial distribution of simulated temperature and
precipitation changes until the end of the 21st century according to the
strongest emission scenario SSP585. Temperature changes are very robust
and exceed the 2 standard deviations of interannual variability of the
control simulation over the whole globe (Fig. 14a). Generally,
precipitation changes are less robust (Fig. 14b) with the Arctic and the
Southern Ocean as well as the African tropics being prominent
exceptions. Simulated precipitation changes can be regarded as less
robust than temperature changes not only because of large internal
variability of the precipitation but also because of large biases in
present-day climate which amount to more than 7 mm/day in some tropical
areas. Bias patterns for both 2 m temperature and precipitation as well
as the magnitude of the biases for present-day climate are not
surprisingly very similar to the ones in MPI-ESM (Müller et al., 2018,
their Fig. 7f).
The well-known feature of Arctic Amplification, and to a lesser extent
also Antarctic Amplification, can clearly be seen from Fig. 14a.
According to the SSP585 scenario, the temperature increases as much as
11°C over the Northern Barents Sea and around Spitsbergen. In the
northernmost parts of the European and American continents the warming
exceeds 7°C at the end of the century compared to the historical
reference period. Large continental areas are affected by temperature
increases of more than 5°C. Also over the Weddell Sea and over parts of
Antarctica temperature increases of more than 5°C are simulated. Over
the ocean, the warming generally amounts to 2 to 3°C.
Over large areas of central Africa and over the tropical Pacific,
precipitation increases of more than 50% are simulated. Other areas,
with comparable precipitation increases, include the ocean northwest of
South Africa as well as northeastern parts of Greenland. Over the whole
Arctic a substantial precipitation increase of more than 40% is
simulated; over the Southern Ocean adjacent to the Antarctic continent
extended areas are affected by precipitation increases of 20 to 30%.
These precipitation changes are very robust since they exceed twice the
interannual standard deviation of the control simulation. Except for
parts of the Amazonas region, simulated precipitation decreases are less
robust and are mainly concentrated in subtropical areas. They do not
exceed 50% of present-day precipitation.
Compared to the multi-model CMIP5 ensemble (IPCC, 2014, Summary for
Policymakers, their Fig. SPM.8), the temperature response in AWI-CM
looks very similar, both regarding magnitude (11°C over Northern Barents
Sea, more than 5°C over large continental areas as well as Weddell Sea
and parts of Antarctica, 2 to 3°C over large parts of the ocean) and
pattern of response. However, the warming hole, i.e. a lack of warming
over the North Atlantic subpolar gyre, that is present in the CMIP5
ensemble (e.g. Menary and Wood, 2018; Chemke et al., 2020), hardly
exists in AWI-CM. Furthermore, the precipitation increase in AWI-CM over
the Arctic is less pronounced and the precipitation increase over Africa
clearly more pronounced compared to the multi-model CMIP5 ensemble
(IPCC, 2014, Summary for Policymakers, their Fig. SPM8). Otherwise, the
precipitation response pattern is quite consistent.
It can be concluded that especially the temperature response pattern
with strong Arctic and continental as well as weak ocean warming agrees
very well with the multi-model ensemble mean of CMIP5 simulations, even
in terms of magnitude. Also the feature of wetting polar, subpolar and
tropical regions as well as drying subtropical regions agrees with
patterns from the multi-model ensemble of CMIP5 simulations although the
magnitude of the response is not as consistent as the magnitude of the
temperature response.
(a)