English Abstract The last two important periods of climate warming (at
c. 14.7 and 11.5 kyr BP) in NW and Central Europe are characterized
quantitatively by their shifts especially in winter and summer temperature,
but also in effective precipitation. Two independent methods are used:
simulations with the ECHAM4 atmospheric general circulation model and
reconstructions based on geological and palaeoecological data. In both
climatic transitions, January temperatures increased by as much as 20
degrees Celcius from -25 degrees a -15 degrees Celcius to -5 degrees a +5
degrees Celcius. During July the changes were smaller: temperatures
increased on the average by 3-5 degrees from 10 degrees -15 degrees Celcius
to 13-17 degrees Celcius during both warming phases. In both transitions an
increase in precipitation was balanced by a comparable increase in
evapotranspiration so that the effective precipitation remained rather
stable or increased slightly. The strong increase in January temperatures
was forced by changes in the N Atlantic Ocean, as the variations in sea
surface temperatures and the position of the sea ice margin determined the
temperature change over land. The increase in July temperatures was mainly
driven by the small increase in insolation and the deglaciation of Scotland
and Scandinavia. The latter effects were much less than the changes in the
N Atlantic Ocean. In addition, the magnitude of the two climate shifts was
geographically changing as a result of different distances to the Atlantic
Ocean and the land ice. Moreover, the timing of the major warming phases is
spatially different, as this timing is mainly determined by the relative
distance to the sea ice and land ice margins.
