Abstract. 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 CO 2 (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.
The mid-Piacenzian climate represents the most geologically recent interval of long-term average warmth relative to the last million years, and shares similarities with the climate projected for the end of the 21st century. As such, it represents a natural experiment from which we can gain insight into potential climate change impacts, enabling more informed policy decisions for mitigation and adaptation. Here, we present the first systematic comparison of Pliocene sea surface temperature (SST) between an ensemble of eight climate model simulations produced as part of PlioMIP (Pliocene Model Intercomparison Project) with the PRISM (Pliocene Research, Interpretation and Synoptic Mapping) Project mean annual SST field. Our results highlight key regional and dynamic situations where there is discord between the palaeoenvironmental reconstruction and the climate model simulations. These differences have led to improved strategies for both experimental design and temporal refinement of the palaeoenvironmental reconstruction.
Aim To understand the impact of glacial refugia and migration pathways on the modern genetic diversity of Pinus sylvestris. Location The study was carried out throughout Europe. Methods An extended set of data of pollen and macrofossil remains was used to locate the glacial refugia and reconstruct the migrating routes of P. sylvestris throughout Europe. A vegetation model was used to simulate the extent of the potential refugia during the last glacial period. At the same time a genetic survey was carried out on this species. Results The simulated distribution of P. sylvestris during the last glacial period is coherent with the observed fossil data, which showed a patchy distribution of the refugia between c . 40°N and 50°N. Several migrational fronts were detected within the Iberian and the Italian peninsulas, and outside the Hungarian plain and around the Alps. The modern mitochondrial DNA depicted three different haplotypes for P. sylvestris. Two distinct haplotypes were restricted to northern Spain and Italy, and the third haplotype dominated most of the present-day remaining distribution range of P. sylvestris in Europe. Main conclusions During the last glacial period P. sylvestris was constrained under severe climatic conditions to survive in scattered and restricted refugial areas. Combining palaeoenvironmental data, vegetation modelling and the genetic data, we have shown that the long-term isolation in the glacial refugia and the migrational process during the Holocene have played a major role in shaping the modern genetic diversity of P. sylvestris in Europe
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