The sunny side of the Ice Age: Solar insolation as a potential long-term pacemaker for 3 demographic developments in Europe between 43 and 15 ka ago

Abstract

After a decade of research under the auspices of the project ‘Population dynamics: Land use 18 patterns of populations between the Upper Pleistocene and Middle Holocene in Europe and 19 the Middle East’, a consistent sequence of high-resolution palaeodemographic datasets has 20 been compiled, spanning the entire Upper Paleolithic from roughly 43 to 15 ka ago. When 21 viewed in a diachronic perspective, long-term trends of increasing and decreasing population 22 sizes and densities, as well as expanding and contracting areas of settlement activities (Core 23 Areas) become evident. An environmental parameter with potentially strong impact on 24 hunter-gatherers societies is solar insolation. The sun’s energy available at a certain time 25 and place is one of the main factors influencing plant growth. The amount of plant biomass, 26 in turn, largely determines the amount of animal biomass in a landscape. The latter is the 27 most important source of energy for European Upper Palaeolithic hunter-gatherers. Here, we 28 aim to assess the potential influence of changes in solar insolation on palaeodemographic 29 development in Western and Central Europe between 43 and 15 ka ago. To this end, we 30 present estimates on the number, density and spatial distribution of hunter-gatherers for five 31 consecutive Upper Paleolithic periods in Europe. Based on regional climate model data for 32 the Last Glacial Maximum and solar insolation data, we calculate (1) differences in the 33 amount of Megajoule per square meter (MJm-²), (2) start, end, and length of the growing 34 season, as well as (3) summed temperatures during the entire duration and during the first 35 30 days of the growing season. A comparison shows that a moderate, steady increase of 36 population size and an extension of the Core Areas between 43 and 29 ka coincides with an 37 increase in the summed temperature, particularly during the first 30 days of the growing 38 season. The period between 29 and 25 ka shows a pronounced population decline, a strong 39 contraction of Core Areas and a withdrawal from higher latitudes. This coincides with a 40 markedly delayed growing season, a decrease in summed temperatures, and a marked 41 reduction in solar insolation during the early part of the growing season. Between 25 and 20 42 ka, we see consolidation and renewed growth in both numbers and densities of people and 43 an expansion and merging of Core Areas in Western Europe. There is a slight gain in the 44 energy available during the first half of the year. The growing season starts earlier and is of 45 increasingly longer duration, coupled with rising summed temperatures. Between 20 and 15 46 ka, the meta-population grows strongly, Core Areas expand and the higher latitudes become 47 repopulated. This coincides with further increasing summed temperatures and an ever-earlier 48 start to the growing season. Additionally, the gain in available solar energy during the early 49 phase of the growing season is particularly pronounced. These findings indicate that solar 50 insolation and its effects on an ecosystem’s phenological configuration over different trophic 51 levels is indeed an important factor in the long-term demographic development of Paleolithic 52 hunter-gatherers.

• europe
• human-environment interaction
• insolation
• palaeodemography
• upper palaeolithic

Resources

• Maier_et_al_PaleoAnthropology_accept_ms.pdf

Bibliography

Maier, A., Ludwig, P., Zimmermann, A., Schmidt, I. (in press.): The sunny side of the Ice Age: Solar insolation as a potential long-term pacemaker for 3 demographic developments in Europe between 43 and 15 ka ago. – In: PaleoAnthropology