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Aim To understand the impact of glacial refugia and migration pathways on the modern genetic diversity of Pinus sylvestris . LocationThe 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. ResultsThe 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 conclusionsDuring 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. Editor: Martin Sykes BIOSKETCHESRachid Cheddadi is a senior research scientist at CNRS. He is a palaeoecologist with particular focus on quantitative past climate reconstructions and vegetation dynamics from pollen records.

Abstract. In 2008 the temporal focus of the Palaeoclimate Modelling Intercomparison Project was expanded to include a model intercomparison for the mid-Pliocene warm period (ca. 2.97 to 3.29 Ma BP). This project is referred to as PlioMIP (Pliocene Model Intercomparison Project). Two experiments have been agreed upon and comprise phase 1 of the PlioMIP. The first (Experiment 1) will be performed with atmosphere-only GCMs. The second (Experiment 2) will utilise fully coupled ocean-atmosphere GCMs. This paper describes the experimental design and boundary conditions that will be utilised for Experiment 1 of the PlioMIP project.

Abstract. The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ~ 400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution and based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.4 and 4.7 °C relative to pre-industrial with a multi-model mean value of 2.8 °C. Annual mean total precipitation rates increase by 6 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases are 1.3 °C greater over the land than over the oceans, and there is a clear pattern of polar amplification with warming polewards of 60° N and 60° S exceeding the global mean warming by a factor of 2.4. In the Atlantic and Pacific Oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. Although there are some modelling constraints, there is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (Equilibrium Climate Sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble earth system response to doubling of CO2 (including ice sheet feedbacks) is approximately 50 % greater than ECS, consistent with results from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea-surface temperatures are used to assess model estimates of ECS and indicate a range in ECS from 2.5 to 4.3 °C. This result is in general accord with the range in ECS presented by previous IPCC Assessment Reports.

Abstract. Accurate estimates of past global mean surface temperature (GMST) help to contextualise future climate change and are required to estimate the sensitivity of the climate system to CO2 forcing during the geological record. GMST estimates from the latest Paleocene and early Eocene (~ 57 to 48 million years ago) span a wide range (~ 9 to 23 °C higher than pre-industrial) and prevent an accurate assessment of climate sensitivity during this extreme greenhouse climate interval. Here, we develop a multi-method experimental framework to calculate GMST during three target intervals: 1) the latest Paleocene (~ 57 Ma), 2) the Paleocene-Eocene Thermal Maximum (56 Ma) and 3) the early Eocene Climatic Optimum (EECO; 49.4 to 53.3 Ma). Using six independent methodologies, we find that average GMST estimates during the latest Paleocene and PETM are 11.7 °C (±0.6 °C) and 18.7 °C (±0.8 °C) higher than pre-industrial, respectively. GMST estimates from the EECO are 13.3 °C (±0.5 °C) warmer than pre-industrial and comparable to previous IPCC AR5 estimates (12.7 °C higher than pre-industrial). Leveraging the extremely large "signal" associated with these extreme warm climates, we combine estimates of GMST and CO2 from the latest Paleocene, PETM and EECO to calculate a gross estimate of the average climate sensitivity between the early Paleogene and today. This yields gross climate sensitivity estimates for the latest Paleocene, PETM and EECO which range between 2.8 to 4.8 °C (66 % confidence). These largely fall within the range predicted by the IPCC (1.5 to 4.5 °C per doubling CO2), but appear incompatible with low values (between 1.5 and 2.8 °C per doubling CO2).