Variations in global ice volume and temperature over the Cenozoic era have been investigated with a set of one-dimensional (1-D) ice-sheet models. Simulations include three ice sheets representing glaciation in the Northern Hemisphere, i.e. in Eurasia, North America and Greenland, and two separate ice sheets for Antarctic glaciation. The continental mean Northern Hemisphere surface-air temperature has been derived through an inverse procedure from observed benthic δ18O records. These data have yielded a mutually consistent and continuous record of temperature, global ice volume and benthic δ18O over the past 35 Ma. The simple 1-D model shows good agreement with a comprehensive 3-D ice-sheet model for the past 3 Ma. On average, differences are only 1.0˚C for temperature and 6.2 m for sea level. Most notably, over the 35 Ma period, the reconstructed ice volume–temperature sensitivity shows a transition from a climate controlled by Southern Hemisphere ice sheets to one controlled by Northern Hemisphere ice sheets. Although the transient behaviour is important, equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric, providing limited evidence for hysteresis. Furthermore, the results show a good comparison with other simulations of Antarctic ice volume and observed sea level.

Marine sediment records from the Oligocene and Miocene reveal clear 400,000-year climate cycles related to variations in orbital eccentricity. These cycles are also observed in the Plio-Pleistocene records of the global carbon cycle. However, they are absent from the Late Pleistocene ice-age record over the past 1.5 million years. Here we present a simulation of global ice volume over the past 5 million years with a coupled system of four threedimensional ice-sheet models. Our simulation shows that the 400,000-year long eccentricity cycles of Antarctica vary coherently with d 13 C data during the Pleistocene, suggesting that they drove the long-term carbon cycle changes throughout the past 35 million years. The 400,000-year response of Antarctica was eventually suppressed by the dominant 100,000-year glacial cycles of the large ice sheets in the Northern Hemisphere.

Stable isotope records of benthic foraminifera from ODP Site 1264 in the southeastern Atlantic Ocean are presented which resolve the latest Oligocene to early Miocene (~24–19 Ma) climate changes at high temporal resolution (<3 kyr). Using an inverse modelling technique, we decomposed the oxygen isotope record into temperature and ice volume and found that the Antarctic ice sheet expanded episodically during the declining phase of the long-term (~400 kyr) eccentricity cycle and subsequent low short-term (~100 kyr) eccentricity cycle. The largest glaciations are separated by multiple long-term eccentricity cycles, indicating the involvement of a non-linear response mechanism. Our modelling results suggest that during the largest (Mi-1) event, Antarctic ice sheet volume expanded up to its present-day configuration. In addition, we found that distinct ~100 kyr variability occurs during the termination phases of the major Antarctic glaciations, suggesting that climate and ice-sheet response was more susceptible to short-term eccentricity forcing at these times. During two of these termination-phases, &delta;¹⁸O bottom water gradients in the Atlantic ceased to exist, indicating a direct link between global climate, enhanced ice-sheet instability and major oceanographic reorganisations

This study investigates likely changes in mean and extreme precipitation over southern Africa in response to changes in radiative forcing using an ensemble of global climate models prepared for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Extreme seasonal precipitation is defined in terms of 10-yr return levels obtained by inverting a generalized Pareto distribution fitted to excesses above a predefined high threshold. Both present (control) and future climate precipitation extremes are estimated. The future-to-control climate ratio of 10-yr return levels is then used as an indicator for the likely changes in extreme seasonal precipitation.A Bayesian approach to multimodel ensembling is adopted. The relative weights assigned to each of the model simulations is determined from bias, convergence, and correlation. Using this method, the probable limits of the changes in mean and extreme precipitation are estimated from their posterior distribution.Over the western parts of southern Africa, an increase in the severity of dry extremes parallels a statistically significant decrease in mean precipitation during austral summer months. A notable delay in the onset of the rainy season is found in almost the entire region. An early cessation is found in many parts. This implies a statistically significant shortening of the rainy season.A substantial reduction in moisture influx from the southwestern Indian Ocean during austral spring is projected. This and the preaustral spring moisture deficits are possible mechanisms delaying the rainfall onset in southern Africa. A possible offshore (northeasterly) shift of the tropical-temperate cloud band is consistent with more severe droughts in the southwest of southern Africa and enhanced precipitation farther north in Zambia, Malawi, and northern Mozambique.This study shows that changes in the mean vary on relatively small spatial scales in southern Africa and differ between seasons. Changes in extremes often, but not always, parallel changes in the mean precipitation.

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Abstract.Relative sea-level variations during the late Pleistocene can only be reconstructed with the knowledge of icesheet history. On the other hand, the knowledge of regional and global relative sea-level variations is necessary to learn about the changes in ice volume. Overcoming this problem of circularity demands a fully coupled system where ice sheets and sea level vary consistently in space and time and dynamically affect each other. Here we present results for the past 410 000 years (410 kyr) from the coupling of a set of 3-D ice-sheet-shelf models to a global sea-level model, which is based on the solution of the gravitationally selfconsistent sea-level equation. The sea-level model incorporates the glacial isostatic adjustment feedbacks for a Maxwell viscoelastic and rotating Earth model with coastal migration. Ice volume is computed with four 3-D ice-sheet-shelf models for North America, Eurasia, Greenland and Antarctica. Using an inverse approach, ice volume and temperature are derived from a benthic δ 18 O stacked record. The derived surface-air temperature anomaly is added to the present-day climatology to simulate glacial-interglacial changes in temperature and hence ice volume. The ice-sheet thickness variations are then forwarded to the sea-level model to compute the bedrock deformation, the change in sea-surface height and thus the relative sea-level change. The latter is then forwarded to the ice-sheet models. To quantify the impact of relative sea-level variations on ice-volume evolution, we have performed coupled and uncoupled simulations. The largest differences of ice-sheet thickness change occur at the edges of the ice sheets, where relative sea-level change significantly departs from the ocean-averaged sea-level variations.

Abstract. In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals in Earth history is of fundamental importance. The late Pliocene warm period (also known as the PRISM interval: 3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions. Here, we present results from simulations of the Antarctic ice sheet by means of an international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP-ANT). For the experiments, ice-sheet models including the shallow ice and shelf approximations have been used to simulate the complete Antarctic domain (including grounded and floating ice). We compare the performance of six existing numerical ice-sheet models in simulating modern control and Pliocene ice sheets by a suite of five sensitivity experiments. We include an overview of the different ice-sheet models used and how specific model configurations influence the resulting Pliocene Antarctic ice sheet. The six ice-sheet models simulate a comparable present-day ice sheet, considering the models are set up with their own parameter settings. For the Pliocene, the results demonstrate the difficulty of all six models used here to simulate a significant retreat or re-advance of the East Antarctic ice grounding line, which is thought to have happened during the Pliocene for the Wilkes and Aurora basins. The specific sea-level contribution of the Antarctic ice sheet at this point cannot be conclusively determined, whereas improved grounding line physics could be essential for a correct representation of the migration of the grounding-line of the Antarctic ice sheet during the Pliocene.

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