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proxy climate. Socio-ecological adaptations to climate change are modeled with
GLUES (Lemmen et al. 2011 ; Wirtz and Lemmen 2003 ); and the land-use feedback
on population is simulated by overexploitation of land and resources. Characteristic
traits of technology, substance, and economic potential exhibit adaptation and
continuous innovation (Lemmen 2014 ).
Paleovegetation and paleoclimate forcings of GLUES, expressed as net primary
production and growing degree days, are derived from PLASIM. After successfully
testing vegetation
fields (Haberkorn 2013 ), we ran GLUES to obtain socio-tech-
trajectories for regional subdomains, worldwide and over the entire
3 Key Findings
The average size of regionally coherent climate variability derived from paleocli-
mate proxies is around 3,000 km; it signi
cantly increased over Western South and
North America, and decreased over the Arabian Sea and the Southwest Asian
monsoon region. Centennial (but not millennial) scale variability decreased over the
North Atlantic: this reinforced our earlier hypothesis (Wirtz and Lemmen 2003 ) that
regional climate variability may have led to unequal probabilities for crises in early
human civilizations in the Old and the New World.
The high-resolution vegetation distribution during the 6 ka BP time slice, based
on the PLASIM climate, reveals generally deciduous and temperate vegetation
types in Western, South and Central Europe (Fig. 1 ). Such a high-resolution veg-
etation reconstruction can improve the prediction of suitability of the land for past
agricultural activities (Kaplan et al. 2011 ).
We successfully reconstructed a North Atlantic SST that
taken as a boundary
condition for PLASIM
replicates the terrestrial temperature (i.e., the temperature
relevant to societies) in Central Europe as represented by a high-resolution lake
proxy. This novel method applies an inverse modeling algorithm to nudge the
simulated land temperature in the climate model to a proxy-reconstructed temper-
ature; its central element is the inverse climate sensitivity in Central Europe to
North Atlantic SST anomalies (Haberkorn 2013 ; Haberkorn et al. 2012 ). We can
now provide past SST
fields that are in agreement with reconstructed land tem-
perature, thus allowing the reconstruction of a dynamically consistent European
climate throughout the Holocene.
We calculated the prehistoric GHG emissions from anthropogenic land use; we
produced estimates for land demand for crops (Gaillard et al. 2010 ) and associated
carbon emissions (Lemmen 2010 ) for the Holocene. Calculated emissions (world
total 30 Gt by 4 ka BP from deforestation) could not have contributed to a sig-
ciencies, however, we
arrived at much larger emissions on the order of 340 Gt by 100 years BP (AD 1850)
(Kaplan et al. 2011 ), consistent with the stable carbon isotope signature from ice
cores. Thus, our two studies provide extreme low and high estimates of the possible
cant warming. By considering past technological inef
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