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knowledge is essential to assess confidence of the simulated
tendencies.
Figure 2 summarizes the simulated climate changes for
temperature and precipitation calculated from all six
comparisons of the two periods. The areas between the
upper and lower curves represent the uncertainty ranges of
the simulated climate changes for the monthly means and
the annual average. The values in this figure refer to the area
average of Germany.
5
4
3
Temperatur change for Germany
outside of the calculated natural variability. This
documents that the higher resolved regional simulations
can significantly modify the projections of the global
model.
relative change in %
50
40
30
20
10
0
-10
-20
-30
-40
Precipitation change for Germany (GCM)
ΔT in K
2
-50
-60
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
1
0
50
40
30
Precipitation change for Germany (RCM)
relative change in %
-1
50
40
30
20
10
0
-10
-20
-30
-40
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Precipitation change for Germany
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
relative change in %
20
10
0
-10
-20
-30
-40
-50
-60
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Figure 3. Precipitation changes for Germany form
global (top) and regional (bottom) model
simulations for the A1B-scenario.
Figure 2. Climate change of 2-meter temperature (top,
absolute change in K) and precipitation (bottom, relative
change in %) for Germany from different realizations
of the A1B-scenario. Values represent differences
between the periods 2051-2080 and 1961-1990.
The increase of annual mean temperature varies between 2.2
and 2.8 K. The strongest warming occurs in August with
values of 3 to 4 K. A reduced warming with less than 1 K
seems possible in spring, but here the range of uncertainty
with up to 2 K is larger than in other seasons. Despite the
partly large spread of temperature changes a significant rise
of temperature throughout the year seems very likely
The simulated changes of precipitation show a different
behavior during the year. The annual sum does not change
within the range of uncertainty. Summer precipitation,
however, considerably decreases with maximum values in
June and August between -14 and -28 %. Because the
reduction is much stronger than the range of uncertainty, the
drying in summer has to be regarded as confidential. The
reduction in summer is compensated by an increase of
precipitation during the other seasons particularly from
October to May. The increase in winter and spring, however,
is connected with a large range of uncertainty (up to 30 %)
which reduces the level of confidence.
4. Conclusions
The analysis of a small single model ensemble of climate
simulations for Europe with the regional climate model
CLM provides a first estimate of the effect of internal
variability on the simulated climate changes for temperature
and precipitation. The knowledge of this unavoidable
natural uncertainty is a necessary precondition to assess
the reliability (confidence) of climate change signals. The
results further show, that the changes of climatological
means as simulated by the regional model can
significantly differ from those of the driving global
simulation. “Significantly” means in this context that the
deviations between global and regional projections are
larger than explained by their internal variability.
References
Hollweg, H.-D., U. Boehm, I. Fast, B. Hennemuth, K.
Keuler, E. Keup-Thiel, M. Lautenschlager, S. Legutke,
K.Radtke, B. Rockel, M. Schubert, A. Will, M. Woldt,
C. Wunram, Ensemble simulations over Europe with
the regional climate model CLM forced with IPCC
AR4 global scenarios. M&D Technical Report, No. 3,
145 pp. Max-Planck-Institute for Meteorology, 2008,
www.mad.zmaw.de/projects-at-md/sg-adaptation/
The precipitation changes of the corresponding global
climate simulations calculated for the same region show a
similar seasonal cycle (figure 3). However, the reduction in
summer with up to -50 % is significantly stronger and
expands over a longer period than in the regional simulation.
Furthermore, the decrease is not fully compensated by the
increase during the rest of the year. This leads to an overall
reduction of annual precipitation by 10 %, which lies well