| The present study focuses on regional climate simulations carried out with the community
model CCLM forced with lateral boundary conditions taken from the AOGCM ECHO-G.
Simulations have been carried out as time slice experiments each covering 40 years for the
periods 6,000 years before present [ BP ] with changes in earth’ orbital parameters [
CO2=270 ppm ], 1750 AD [ CO2=270 ppm ], 1990 AD [ CO2=360 ppm ] and for the IPCC
greenhouse gas [ GHG ] change experiment B2 for the period 2050–2079 [ CO2~510 ppm ]
.
Hypotheses addressed with the regional simulations, specifically for climatic changes
between 6,000 years BP and pre-industrial times, relate to hydrological changes
based on reconstructed lake levels in southeastern Patagonia. In this respect the
simulations indicate most notable precipitation changes over the Andes Mountains
and towards the subtropical regions of the Pampas. The eastern parts of the Andes
Mountains, i.e. the Patagonian steppe, shows however no clear-cut precipitation
changes.
More recent changes, i.e. between the climate of the late 20th century and pre-industrial
times, show remarkable near-surface temperature and precipitation changes. Again, largest
changes occur over the Andes Mountains, but due to the large magnitude of these changes
also other regions show statistically significant values. The magnitude of the differences
outreaches the mid-Holocene minus pre-industrial changes by a factor of approximately two.
Another interesting feature appears when comparing present-day minus pre-industrial
changes with the IPCC B2 scenario minus present-day. Here changes are in the same order of
magnitude as for the present-day minus pre-industrial period. This result indicates that the
increase in GHG concentrations does not linearly project on the increase in temperatures, but
under-proportional. It is hypothesized that based on theses simulations climatic change has
already attained a large order of magnitude compared to the – in terms of GHG
concentrations – anthropogenically undisturbed climate over central and southern South
America. |