Following publications have been announced by our department Climate Extremes and Impacts. For further information please contact the marked authors of the publications:
Lyu, Z., Goosse, H., Dalaiden, Q., Klein, F., Shi, F., Wagner, S., & Braconnot, P. (2021): Spatial patterns of multi–centennial surface air temperature trends in Antarctica over 1–1000 CE: Insights from ice core records and modeling. Quaternary Science Reviews, Volume 271, 2021, 107205, doi:10.1016/j.quascirev.2021.107205
Abstract:
The spatial pattern of Antarctic surface air temperature variability on multi–decadal to multi–centennial time scales is poorly known because of the short instrumental records, the relatively small number of high–resolution paleoclimate observations, and biases in climate models. Here, changes in surface air temperature over Antarctica are reconstructed over the past two millennia using data assimilation constrained by different ice core water isotope records in order to identify robust signals. The comparison between previous statistically based temperature reconstructions and simulations covering the full Common Era driven by natural and anthropogenic forcings shows major discrepancies occurring in the period 1–1000 CE over East Antarctica, with the reconstructions displaying a warming over 1–500 CE that is not reproduced by the simulations. This suggests that the trends in the first millennium deduced from the statistically based reconstructions are unlikely to be entirely forced by external forcings. Our reconstructions show the high sensitivity of the 500-year temperature trend in Antarctica and its spatial distribution to selection of the records for the reconstructions, especially during 1–500 CE. A robust cooling over Antarctica during 501–1000 CE has been obtained in three data assimilation–based reconstructions with a larger magnitude in the WAIS than elsewhere over Antarctica, in agreement with previous estimates with the larger changes than simulated in climate models. The reconstructions for atmospheric circulation indicate that the pattern of temperature changes over 501–1000 CE is related to the positive trend of Southern Annular Mode and a deepening of Amundsen Sea Low. This confirms the role of internal variability in the temperature trends on multi–centennial scales.
Xoplaki, E., Luterbacher, J., Luther, N., Behr, L., Wagner, S., Jungclaus, J., Zorita, E., Toreti, A., Fleitmann, D., Izdebski, A., & Bloomfield, K. (2021): Hydrological Changes in Late Antiquity: Spatio-Temporal Characteristics and Socio-Economic Impacts in the Eastern Mediterranean. In: Erdkamp, P., Manning, J.G., & Verboven K. (eds): Climate Change and Ancient Societies in Europe and the Near East. Palgrave Studies in Ancient Economies, Palgrave Macmillan, Cham., doi:10.1007/978-3-030-81103-7_18
Abstract:
Until now, proxy records have been the primary tool for quantitative reconstructions of the physical world of the ancient and late antique Mediterranean. This chapter demonstrates the combined use of proxy datasets and the hitherto underutilized potential of earth system models in the scientific and historical study of past environmental variations and impacts on human societies. Results from model simulations are able to explain hydroclimatic anomalies observed in the proxy records and provide links to relevant mechanisms. The Late Roman Dry Period and the Late Roman Wet Period of the mid-fourth to early eighth centuries AD are each associated with the increase in the frequency of subsistence crises and with the accelerated infrastructural adaptations of communities and agricultural expansion, respectively. The chapter concludes with an examination of the historical and climatic contexts behind one such anomaly, a subsistence crisis in Cappadocia in the late 300s AD.
Sherriff-Tadano, S., & Klockmann, M. (2021): PMIP contributions to understanding the deep ocean circulation of the Last Glacial Maximum. Past Global Changes Magazine, 29(2), 84-85, doi:10.22498/pages.29.2.84
Abstract:
Simulations of the Last Glacial Maximum (LGM) within PMIP significantly improved our understanding of the mechanisms that control the Atlantic Meridional Overturning Circulation (AMOC) in a glacial climate. Nonetheless, reproducing the reconstructed shallowing of the LGM AMOC remains a challenge for many models.
The Last Glacial Maximum (LGM; ca. 21,000 years ago) was a period within the last glacial cycle with very low greenhouse gas concentrations and maximum ice volume. The global climate was much colder than the modern climate, and the state of the Atlantic Meridional Overturning Circulation (AMOC) was very different as a consequence of the glacial climate forcings. In the modern climate, North Atlantic Deep Water (NADW), which forms in the Nordic and Labrador Seas, fills the deep North Atlantic basin. In contrast, proxy data such as carbon and neodymium isotopes, suggest that during the LGM, a large fraction of NADW in the deep Atlantic basin was replaced by Antarctic Bottom Water (AABW), which is formed in the Southern Ocean. As a result, the glacial AMOC was shallower than the modern AMOC (Lynch-Stieglitz 2017). The strength of the LGM AMOC is harder to reconstruct; proxies of AMOC strength support a glacial AMOC state ranging from weaker than or similar to today (e.g. Lynch-Stieglitz 2017). Nonetheless, the LGM provides a good opportunity to understand the AMOC response to climate changes as well as to evaluate the capability of comprehensive atmosphere-ocean coupled general circulation models (AOGCM) to reproduce AMOC states which are very different from today.
Jungclaus, J.H., Bothe, O., Garcia-Bustamante, E., González-Rouco, J.F., Neukom, R., & Schurer, A. (2021): Simulating the Common Era: The Past2K working group of PMIP. Past Global Changes Magazine, 29(2), 72-73, doi:10.22498/pages.29.2.72
Abstract:
Simulations of Common Era climate evolution coordinated by PMIP’s „Past2K“ working group together with multi-proxy reconstructions from the PAGES 2k Network provide pivotal understanding for the evolution of the modern climate system and for expected changes in the near future.
Knowledge of past climate evolution is essential for understanding natural variability and for providing context for current and future climate change. One example is the Common Era (CE, i.e. approximately the last 2000 years) with its vast collection of proxy, observational, and documentary datasets, which often feature annual or sub-annual resolution. Simulations covering the CE or the last millennium (LM, i.e. the 1000 years before the industrial era, 850 to 1850 CE) are essential to identify plausible mechanisms underlying paleoclimatic observations and reconstructions. Applying the same models to study past, present, and future climate and its response to external forcing enables the community to use paleodata for the evaluation of the Earth system models that we use for climate projections.