Anne Dallmeyer

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

Vegetation, climate, man—Holocene variability in monsoonal Central Asia

We have investigated the Holocene climate and vegetation change in the Asian monsoon region using climate model simulations and proxy derived vegetation and climate reconstructions. The simulated mid-Holocene climate is qualitatively in good agreement with the reconstructions. Both methods reveal no systematic and uniform large-scale climate shifts, but asynchronous moisture changes in different sub-areas of the Asian monsoon region. The atmospheric response to the Holocene insolation forcing is strongly modified by ocean-atmosphere interactions, while the interaction between vegetation and atmosphere has minor influence on the large-scale Holocene climate change and is only important at a regional level. Nevertheless, sensitivity simulations reveal that large-scale forest decline in the Asian monsoon region leads to substantial losses in regional precipitation. During the Holocene, substantial vegetation changes are confined to the fringe zone of the Asian monsoon area and to the Tibetan Plateau, where simulated forest fraction has decreased by approx. 15 % and 30 % since mid-Holocene, respectively.