Tim Brücher

Were Rivers Flowing across the Sahara During the Last Interglacial? Implications for Human Migration through Africa

Human migration north through Africa is contentious. This paper uses a novel palaeohydrological and hydraulic modelling approach to test the hypothesis that under wetter climates c.100,000 years ago major river systems ran north across the Sahara to the Mediterranean, creating viable migration routes. We confirm that three of these now buried palaeo river systems could have been active at the key time of human migration across the Sahara. Unexpectedly, it is the most western of these three rivers, the Irharhar river, that represents the most likely route for human migration. The Irharhar river flows directly south to north, uniquely linking the mountain areas experiencing monsoon climates at these times to temperate Mediterranean environments where food and resources would have been abundant. The findings have major implications for our understanding of how humans migrated north through Africa, for the first time providing a quantitative perspective on the probabilities that these routes were viable for human habitation at these times.

Europe on fire three thousand years ago: Arson or climate?

The timing of initiation of human impacts on the global climate system is actively debated. Anthropogenic effects on the global climate system are evident since the Industrial Revolution, but humans may have altered biomass burning, and hence the climate system, for millennia. We use the specific biomarker levoglucosan to produce the first high-temporal resolution hemispheric reconstruction of Holocene fire emissions inferred from ice core analyses. Levoglucosan recorded in the Greenland North Greenland Eemian ice core significantly increases since the last glacial, resulting in a maximum around ~2.5 ka and then decreasing until the present. Here we demonstrate that global climate drivers fail to explain late Holocene biomass burning variations and that the levoglucosan maximum centered on ~2.5 ka may be due to anthropogenic land clearance.

Fire in the Earth System: Bridging Data and Modeling Research

This is a preliminary PDF of the author-produced manuscript that has been peer-reviewed and accepted for publication. Since it is being posted so soon after acceptance, it has not yet been copyedited, formatted, or processed by AMS Publications. This preliminary version of the manuscript may be downloaded, distributed, and cited, but please be aware that there will be visual differences and possibly some content differences between this version and the final published version.

Comprehensive Earth system models of the last glacial cycle

Much of modern climate science fails to consider millennium-scale processes, many of which may prove to be important for predicting the climate trajectory in the shorter term.

Diving into the past – A paleo data-model comparison workshop on the Late Glacial and Holocene

What: An international group of approximately 30 scientists with background and expertise in global and regional climate modeling, statistics, and climate proxy data discussed the state of the art, progress, and challenges in comparing global and regional climate simulations to paleoclimate data and reconstructions. The group focused on achieving robust comparisons in view of the uncertainties associated with simulations and paleo data. WheN: 16–18 April 2018 Where: Hamburg, Germany U nderstanding changes in the climate of the late Pleistocene and the Holocene has long been a research topic. Studies rely on different sources of information, ranging from terrestrial and marine archives to a hierarchy of climate modeling activities. In contrast to the climate of the last millennium, novel approaches are necessary to bridge the different temporal and spatial representations of the various archives and the climate models, and to achieve a robust understanding of climate variability and climate processes on centennial-to-millennial time scales. On the one hand, paleoclimate archives typically have a coarser temporal and spatial resolution on longer—for example, glacial—time scales than on shorter—late Holocene—time scales. They also commonly have poorer age constraints and are more uncertain. However, larger climate forcing occurred, giving a better signal-to-noise ratio for these longer time scales. On the other hand, climate modeling approaches based on comprehensive Earth system models (ESMs) need to take into account additional components and processes within the Earth system that are either not present or of secondary importance within the late Holocene, our current interglacial period, such as the emergence and vanishing of vast ice sheets or continental uplift. Indeed, the climate modeling community has yet to prove the feasibility of transient fully coupled ESM simulations over a complete glacial cycle. Addressing these issues requires expert knowledge from different fields, including critical assessment of paleoclimate data quality; technical and statistical tools to compare and analyze archives; and the exploitation of presently available and upcoming transient simulations with comprehensive ESMs. Experts of the respective fields gathered in Hamburg, Germany, for a 3-day workshop1 to discuss long-standing