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ENSI Erfahrungs- und Forschungsbericht 2011

rentide ice sheet and additionally the ice sheet of

the Nordic Sea is removed (MWNS). An overview

of the ice sheet topography and the different areas

of the reduction is presented in Fig. 1.

Other boundary conditions (e.g., aerosols and veg-

etation) are generally kept at the preindustrial val-

ues in the glacial simulations.

Evaluation of the LGM climate state

Before focusing on the results of the sensitivity ex-

periments, the model's ability to generate a rea-

sonable glacial climate state is investigated. To do

so we compare the surface air temperature (SAT)

and the precipitation in the LGM simulations with

other LGM simulations and with climate recon-

structions [4].

The global mean SAT in LGM1 and LGM2 is re-

duced by 4.45 °C and 5.55 °C with respect to PI, re-

spectively. This is consistent with other models that

show a cooling in the range of 3.6 °C to 5.7 °C [5].

The simulated cooling is more pronounced in the

mid- and high-latitudes, while the temperatures in

the tropical regions are less affected (Fig. 2).

For the European sector the simulated cooling in

both simulations is mostly within the 90 % confi-

dence interval of the reconstruction for the annual

mean and also for January temperature. For July,

however, the temperature changes are generally

overestimated in the simulations.

Similar to the SAT, the global mean precipitation

is reduced in the LGM (in the order of 10–15 %).

Apart from a general drying, several regions with

positive anomalies occur, namely at the western

coast of Europe and North America, in a band at

35°N across most of the Atlantic and in some re-

gions at the edges of the major ice sheets. As for

SAT the large-scale precipitation anomaly pattern

is consistent with the multi-model mean of [5].

For the precipitation the uncertainties in the re-

construction are large so that only at one location

in the Pyrenees the anomaly is significantly differ-

ent from the present. Due to the large uncertain-

ties the simulated precipitation anomalies are con-

sistent with the reconstruction at most locations.

To summarize the large-scale feature of the simu-

lated SAT and precipitation anomaly patterns for

LGM are consistent with other simulations. In Eu-

rope the results are also mostly within the large

confidence intervals of reconstructed continental

temperature and precipitation anomalies except

for summer SATs. No evidences are found that one

of the two LGM simulations lead to a much better

agreement with the reconstruction.

Impact on temperature and precipitation

a) Sensitivity to the ocean surface and the

radiative forcing

The climate state in the three simulations that have

the LGM ice sheet height implemented (LGM1,

LGM2 and MWLGM) are compared for the North

Atlantic region to assess the influence of differenc-

es either in the ocean surface forcing or in the ra-

diative forcing.

The annual mean SAT difference patterns between

LGM1/LGM2 and PI agree on the major character-

istics of the changes. The strongest differences be-

Figure 2:

Annual mean surface air

temperature differences

between LGM2 and PI.

Only values that are

statistically significant

at the 5 % level based on

the two-sided Student's

t test are colored.

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