Description: Central Asia is one of the largest arid regions in the world, however, multiple lakes have existed here since the Neogene. These lakes were able to sustain themselves despite the aridification trend in Asia through the PlioPleistocene. For example, long-term geological multiproxy records, including carbonate δ18O, from lake sediments of the Qaidam, Gaxun Nur, and Orog Nuur Basins indicate multiple changes in the hydrological cycle of the region with alternate phases of prevailing evaporation and precipitation. These changes are attributed either to Neogene global climate change or regional tectonic events. In this study, we use the isotope-equipped atmospheric general circulation model ECHAM5-wiso for modeling of Asia climate evolution and associated changes in precipitation δ18O during key periods of the Neogene. High-resolution simulations (T159L31, ca. 0.8°x0.8° and 31 vertical levels, 6 hour output frequency) with Mid-Holocene, Pleistocene, Pliocene and Miocene boundary conditions allow us to estimate the contributions of global climate change into the hydrological budget over the Central Asia. We complement this work with a Lagrangian Trajectory analysis (wind back-trajectories) applied to the ECHAM5-wiso outputs to trace changes in the origin of precipitation-producing air masses. We show that in addition to precipitation amount variations associated with changes in large-scale atmosphere dynamics, considerable changes in moisture sources between the time slices considered contribute to the isotopic signature of precipitation within the Qaidam, Gaxun Nur, and Orog Nuur Basins. Finally, comparison of simulated δ18O results to wind backtrajectory analysis suggests that local process, such as moisture recycling, exert an increasing control for more recent time periods.

Description: Understanding the dynamics of warm climate states has gained increasing importance in the face of anthropogenic climate change. During the Last Interglacial (LIG, ∼128 to 116 ka), greenhouse gas concentrations and high latitude insolation were higher than pre-industrial levels, causing a high-latitude warming (Turney and Jones, 2010; Pfeiffer and Lohmann, 2016). We present a suite of climate model results (COSMOS, MPI-ESM, AWI-CM, EC-Earth) to evaluate the patterns and compare the simulations with the above-mentioned surface temperature reconstructions, seasonal archives (Felis et al., 2015; Brocas et al., 2017), and sea ice reconstructions (Stein et al., 2017). As a result of this modestly warmer climate, polar ice sheets were smaller and estimates report that the global mean sea level was 6-9 meters higher than today (Dutton et al., 2015). The sensitivity of the Antarctic Ice sheet is related to the local temperature around the West Antarctic Ice Sheet (WAIS) (Sutter et al., 2016). Our ice sheet model experiments indicate that a 2-3°C local warming causes already a partially collapsed, irreversible WAIS. A pronounced subsurface oceanic warming can destabilize the WAIS, resulting in an oceanic gateway between the Ross and Weddell Seas. A sensitivity study using the new oceanic gateway between the Atlantic and Pacific Oceans as a bathymetrical boundary condition indicates that this region would be covered by sea ice. Mixing due to sea-ice formation prevents a pronounced warming around the WAIS and would stabilize the WAIS. Thus, the disintegration of the WAIS is probably related to non-local influences like in Hellmer et al. (2017) where the shelves of West Antarctica are warmed from below by Circumpolar Deep Water.

Description: In this manuscript we describe the experimental procedure employed at the Alfred Wegener Institute in Germany in the preparation of the simulations for the Pliocene Model Intercomparison Project (PlioMIP). We present a description of the utilized Community Earth System Models (COSMOS, version: COSMOS-landveg r2413, 2009) and document the procedures that we applied to transfer the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) Project mid-Pliocene reconstruction into model forcing fields. The model setup and spin-up procedure are described for both the paleo- and preindustrial (PI) time slices of PlioMIP experiments 1 and 2, and general results that depict the performance of our model setup for mid-Pliocene conditions are presented. The mid-Pliocene, as simulated with our COSMOS setup and PRISM boundary conditions, is both warmer and wetter in the global mean than the PI. The globally averaged annual mean surface air temperature in the mid-Pliocene standalone atmosphere (fully coupled atmosphere-ocean) simulation is 17.35 °C (17.82 °C), which implies a warming of 2.23 °C (3.40 °C) relative to the respective PI control simulation.

Description: Climate and environments of the mid-Pliocene warm period (3.264 to 3.025 Ma) have been extensively studied. Whilst numerical models have shed light on the nature of climate at the time, uncertainties in their predictions have not been systematically examined. The Pliocene Model Intercomparison Project quantifies uncertainties in model outputs through a coordinated multi-model and multi-model/data intercomparison. Whilst commonalities in model outputs for the Pliocene are clearly evident, we show substantial variation in the sensitivity of models to the implementation of Pliocene boundary conditions. Models appear able to reproduce many regional changes in temperature reconstructed from geological proxies. However, data/model comparison highlights that models potentially underestimate polar amplification. To assert this conclusion with greater confidence, limitations in the time-averaged proxy data currently available must be addressed. Furthermore, sensitivity tests exploring the known unknowns in modelling Pliocene climate specifically relevant to the high latitudes are essential (e.g. palaeogeography, gateways, orbital forcing and trace gasses). Estimates of longer-term sensitivity to CO2 (also known as Earth System Sensitivity; ESS), support previous work suggesting that ESS is greater than Climate Sensitivity (CS), and suggest that the ratio of ESS to CS is between 1 and 2, with a "best" estimate of 1.5.

Description: Climate patterns are influenced by internal variability and forcing. A major forcing is carbon dioxide that influences, together with other greenhouse gases, the equilibrium temperature of the Earth system. Over millions of years, carbon dioxide concentrations in the atmosphere have been regulated by a fine balance between outgassing from the Earth’s mantle – via volcanic activity – and removal and sequestration – via chemical weathering. Small disturbances of this equilibrium have been amplified by climate system feedbacks and caused, over millions of years, a transition of the Earth system from a nearly ice free “hothouse” state to the modern glaciated “icehouse”, with major ice sheets at high latitudes. Over the last two million years, orbital forcing, i.e. the astronomical configuration of the Earth-Sun-system – that is related to quasi-periodical climate transitions at multi-millennial time scale – had strongest control on climate. Variations of the Earth’s orbital elements create pronounced oscillations between more and less extensive glaciation in particular of the Northern Hemisphere. These are known as the glacial-interglacial cycles of the Pleistocene. Since the dawn of the industrial era climate has been deteriorated at a rate that is unique during the recent geologic history of the last 50-60 million years. Current rise in carbon dioxide occurs at a rate that is unprecedented, bringing us from the stage of Pleistocene glacial cycles again closer to a hothouse climate. Current levels of carbon dioxide excite the climate/earth system to a state far beyond its natural equilibrium. Climate system components with large thermal inertia, including ice sheets and oceans, cause delayed reaction of the climate and earth system to anthropogenic activity, and cause continued warming even if current levels of anthropogenic greenhouse forcing are stabilized. Recent research highlights that the climate system’s reaction to anthropogenic forcing intensifies. Related to distortion of the probability density function of climate variables, e.g. temperature, formerly extreme weather conditions become more abundant. Record-breaking ocean heat content, accelerated retreat of smaller ice masses like alpine glaciers, and minimum sea ice extent show that climate is changing at a pace so far not experienced by modern societies. In this talk we will review recent climate change and survey methods of climate research. This will be put into context of future climate projections.

Description: Climate patterns are influenced by internal variability and forcing. A major forcing is carbon dioxide that influences, together with other greenhouse gases, the equilibrium temperature of the Earth system. Over millions of years, carbon dioxide concentrations in the atmosphere have been regulated by a fine balance between outgassing from the Earth’s mantle – via volcanic activity – and removal and sequestration – via chemical weathering. Small disturbances of this equilibrium have been amplified by climate system feedbacks and caused, over millions of years, a transition of the Earth system from a nearly ice free “hothouse” state to the modern glaciated “icehouse”, with major ice sheets at high latitudes. Over the last two million years, orbital forcing, i.e. the astronomical configuration of the Earth-Sun-system – that is related to quasi-periodical climate transitions at multi-millennial time scale – had strongest control on climate. Variations of the Earth’s orbital elements create pronounced oscillations between more and less extensive glaciation in particular of the Northern Hemisphere. These are known as the glacial-interglacial cycles of the Pleistocene. Since the dawn of the industrial era climate has been deteriorated at a rate that is unique during the recent geologic history of the last 50-60 million years. Current rise in carbon dioxide occurs at a rate that is unprecedented, bringing us from the stage of Pleistocene glacial cycles again closer to a hothouse climate. Current levels of carbon dioxide excite the climate/earth system to a state far beyond its natural equilibrium. Climate system components with large thermal inertia, including ice sheets and oceans, cause delayed reaction of the climate and earth system to anthropogenic activity, and cause continued warming even if current levels of anthropogenic greenhouse forcing are stabilized. Recent research highlights that the climate system’s reaction to anthropogenic forcing intensifies. Related to distortion of the probability density function of climate variables, e.g. temperature, formerly extreme weather conditions become more abundant. Record-breaking ocean heat content, accelerated retreat of smaller ice masses like alpine glaciers, and minimum sea ice extent show that climate is changing at a pace so far not experienced by modern societies. We will approach the characteristics of a warmer than modern world, as it is projected for the future, from the perspective of the geological past. Earth history contains examples of climate states both colder and warmer than the current one. We will learn about potential future climate conditions by means of combining inference from geological and glaciological records with climate modelling. Records, or archives, provide detailed, but very localized, information on past environmental conditions. These can be translated into information on the climate of the past. Climate models, on the other hand, enable the direct study of dynamics of past, present and future climates. Marrying models and archives enables us to learn about both characteristics and dynamics of the climate of the past. Furthermore, we may identify those characteristics of past climates that may be expected again in the future. Last but not least, we will learn that the past provides a test-bed where we can evaluate climate models with respect to their applicability for future warmer-than-present climate states.