State and timescale-dependency of surface climate variability from the last Glacial to present day (STACY)

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I propose to establish an Emmy Noether group to investigate, whether, how and why the variability of our planet's climate depends on its mean temperature. This is important because changes in the probability distribution of temperature and precipitation lead to changes in the frequency of the occurrence of extreme climatic events, and are thus more important for society than mean shifts.Future climate projections are based on complex climate models and thus the assessment of their reliability is imperative. The instrumental record is, however, too short and limited to close-to-present day conditions to constrain modelled variability changes beyond the decadal scale. Benchmarking climate models against indirect paleoclimatic evidence derived from natural archives, such as ice cores, speleothems or fossil pollen preserved in lake sediments, is the only solution for this at present. Yet model simulations display in general far less temperature variability on all timescales beyond the interannual than paleoclimate proxy data.To improve our understanding of centennial climate variability, my group will derive robust estimates of climate over the last 80,000 years. This period is particularly suitable because it extends back into the last Glacial, and covers the transition into the current warm period, the Holocene. The deglaciation was the last time Earth's global mean temperature underwent a large-scale climate shift by more than 3°C, comparable to that projected for the next 300 years.The group's main aims will be to quantify the changes of climate variability between these cold and warm climate periods, and within the Glacial state, and to assess the underlying changes in climate dynamics. This will constrain the gap between modelled and reconstructed variability. We will investigate the changes in total centennial-scale variability, as well as the linkage between annual, centennial and millennial-scale climate variability, and evaluate, if and how the sensitivity of the climate system to volcanic eruptions is influenced by seasonality and global mean temperature.To achieve these goals, the group will (a) improve current models of the formation process of speleothem and ice core records, (b) perform innovative experiments with water isotope-enabled climate models, (c) derive a spatio-temporal reconstruction of past climate based jointly on model and proxy data linked through the improved process models and (d) constrain the amplitude of change in the reconstruction using a new multivariate Bayesian climate reconstruction framework.This will allow, for the first time, a fair test of consistency between the proxy-estimated and the modelled change in variability from the interannual to the millennial scale, and will improve our understanding of the longterm predictability of the climate system.