The early Eocene (~55 to 50 Ma) is a time period which has been explored in a large number of modelling and data studies. Here, using an ensemble of previously published model results, making up "EoMIP" – the Eocene Modelling Intercomparison Project – and syntheses of early Eocene terrestrial and sea surface temperature data, we present a self-consistent inter-model and model–data comparison. This shows that the previous modelling studies exhibit a very wide inter-model variability, but that at high CO2, there is good agreement between models and data for this period, particularly if possible seasonal biases in some of the proxies are considered. An energy balance analysis explores the reasons for the differences between the model results, and suggests that differences in surface albedo feedbacks, water vapour and lapse rate feedbacks, and prescribed aerosol loading are the dominant cause for the different results seen in the models, rather than inconsistencies in other prescribed boundary conditions or differences in cloud feedbacks. The CO2 level which would give optimal early Eocene model–data agreement, based on those models which have carried out simulations with more than one CO2 level, is in the range of 2500 ppmv to 6500 ppmv. Given the spread of model results, tighter bounds on proxy estimates of atmospheric CO2 and temperature during this time period will allow a quantitative assessment of the skill of the models at simulating warm climates. If it is the case that a model which gives a good simulation of the Eocene will also give a good simulation of the future, then such an assessment could be used to produce metrics for weighting future climate predictions

Past studies of the end-Permian extinction (EPE), the largest biotic crisis of the Phanerozoic, have not resolved the timing of events in southern high-latitudes. Here we use palynology coupled with high-precision CA-ID-TIMS dating of euhedral zircons from continental sequences of the Sydney Basin, Australia, to show that the collapse of the austral Permian Glossopteris flora occurred prior to 252.3 Ma (~370 kyrs before the main marine extinction). Weathering proxies indicate that floristic changes occurred during a brief climate perturbation in a regional alluvial landscape that otherwise experienced insubstantial change in fluvial style, insignificant reorganization of the depositional surface, and no abrupt aridification. Palaeoclimate modelling suggests a moderate shift to warmer summer temperatures and amplified seasonality in temperature across the EPE, and warmer and wetter conditions for all seasons into the Early Triassic. The terrestrial EPE and a succeeding peak in Ni concentration in the Sydney Basin correlate, respectively, to the onset of the primary extrusive and intrusive phases of the Siberian Traps Large Igneous Province.

The early Eocene (~55 to 50 Ma) is a time period which has been explored in a large number of modelling and data studies. Here, using an ensemble of previously published model results, making up "EoMIP" – the Eocene Modelling Intercomparison Project, and syntheses of early Eocene terrestrial and SST temperature data, we present a self-consistent inter-model and model-data comparison. This shows that the previous modelling studies exhibit a very wide inter-model variability, but that at high CO₂, there is good agreement between models and data for this period, particularly if possible seasonal biases in some of the proxies are considered. An energy balance analysis explores the reasons for the differences between the model results, and suggests that differences in surface albedo feedbacks, water vapour and lapse rate feedbacks, and prescribed aerosol loading are the dominant cause for the different results seen in the models, rather than inconsistencies in other prescribed boundary conditions or differences in cloud feedbacks. The CO₂ level which would give optimal early Eocene model-data agreement, based on those models which have carried out simulations with more than one CO₂ level, is in the range 2000 ppmv to 6500 ppmv. Given the spread of model results, tighter bounds on proxy estimates of atmospheric CO₂ during this time period will allow a quantitative assessment of the skill of the models at simulating warm climates, which could be used as a metric for weighting future climate predictions

No abstract

The Paleocene-Eocene Thermal Maximum (PETM; 55 Ma) is of particular interest since it is regarded as a suitable analog to future climate change. In this study, the PETM climate is investigated using the Community Climate System Model (CCSM3) with atmospheric CO 2 concentrations of 43, 83, and 163 the preindustrial value.Simulated climate change from 43 to 83 atmospheric CO 2 concentration, possibly corresponding to an environmental precursor of the PETM event, leads to a warming of the North Atlantic Ocean Intermediate-Water masses, thus lowering the critical depth for methane hydrate destabilization by ;500 m. A further increase from 83 to 163CO 2 , analogous to a possible massive methane hydrate release, results in global oceanic warming and stratification. The increase in the radiative surface warming, especially at high latitudes, is partially offset by a decrease in the ocean heat transport due to a reduced overturning circulation. Surface temperature values simulated in the 163CO 2 PETM run represent the closest match to surface temperature reconstructions from proxies for this period.Simulated PETM precipitation, characterized by a slight northward shift of the intertropical convergence zone, increases at higher CO 2 concentrations, especially for the northern midlatitudes as well as the high latitudes in both hemispheres. Data-inferred precipitation values and gradients for North America and Spain, for instance, are in good agreement with the 163CO 2 simulation. Increasing atmospheric CO 2 concentrations might also have favored the release of terrestrial methane through warmer and wetter conditions over land, thus reinforcing the greenhouse gas concentration increase.

Abstract. A range of proxy observations have recently provided constraints on how Earth's hydrological cycle responded to early Eocene climatic changes. However, comparisons of proxy data to general circulation model (GCM) simulated hydrology are limited and inter-model variability remains poorly characterised. In this work, we undertake an intercomparison of GCM-derived precipitation and P − E distributions within the extended EoMIP ensemble (Eocene Modelling Intercomparison Project; Lunt et al., 2012), which includes previously published early Eocene simulations performed using five GCMs differing in boundary conditions, model structure, and precipitation-relevant parameterisation schemes. We show that an intensified hydrological cycle, manifested in enhanced global precipitation and evaporation rates, is simulated for all Eocene simulations relative to the preindustrial conditions. This is primarily due to elevated atmospheric paleo-CO2, resulting in elevated temperatures, although the effects of differences in paleogeography and ice sheets are also important in some models. For a given CO2 level, globally averaged precipitation rates vary widely between models, largely arising from different simulated surface air temperatures. Models with a similar global sensitivity of precipitation rate to temperature (dP∕dT) display different regional precipitation responses for a given temperature change. Regions that are particularly sensitive to model choice include the South Pacific, tropical Africa, and the Peri-Tethys, which may represent targets for future proxy acquisition. A comparison of early and middle Eocene leaf-fossil-derived precipitation estimates with the GCM output illustrates that GCMs generally underestimate precipitation rates at high latitudes, although a possible seasonal bias of the proxies cannot be excluded. Models which warm these regions, either via elevated CO2 or by varying poorly constrained model parameter values, are most successful in simulating a match with geologic data. Further data from low-latitude regions and better constraints on early Eocene CO2 are now required to discriminate between these model simulations given the large error bars on paleoprecipitation estimates. Given the clear differences between simulated precipitation distributions within the ensemble, our results suggest that paleohydrological data offer an independent means by which to evaluate model skill for warm climates.

No abstract

Rapid climate change was a major contributor to the end-Permian extinction (EPE). Although well constrained for the marine realm, relatively few records document the pace, nature, and magnitude of climate change across the EPE in terrestrial environments. We generated proxy records for chemical weathering and land surface temperature from continental margin deposits of the high-latitude southeastern margin of Gondwana. Regional climate simulations provide additional context. Results show that Glossopteris forest-mire ecosystems collapsed during a pulse of intense chemical weathering and peak warmth, which capped ~1 m.y. of gradual warming and intensification of seasonality. Erosion resulting from loss of vegetation was short lived in the low-relief landscape. Earliest Triassic climate was ~10–14 °C warmer than the late Lopingian and landscapes were no longer persistently wet. Aridification, commonly linked to the EPE, developed gradually, facilitating the persistence of refugia for moisture-loving terrestrial groups.