A zonally averaged energy balance climate model is used to generate zonal temperature variability through fluctuating meridional energy transports. In the base model, stochastic transport fluctuations are introduced by multiplying the eddy diffusion coefficients by Gaussian random deviates. For eddy coefficient variability of 50%, the base model generates an interannual temperature variability of 0.03 K for the global temperature, and 0.04 and 0.05 K for the Northern and Southern Hemispheric temperatures, respectively. The sensitivity to modeling assumptions of the model generated variability and its meridional distribution are investigated through a series of numerical experiments. For the range studied, the temperature variability level generated is linearly related to the transport variability level introduced. Switching from the multiplicative noise model of the base to an additive noise model results in an increase in the level of model generated temperature variability and a change in the shape of variance spectra of temperature anomaly time series. These model results are compared with a time series of central England temperatures as well as GCM generated climate variability. Because the level of variability is so dependent on the form of stochastic forcing parameterization, we conclude that great caution is needed before ascribing physical reality to such stochastic fluctuations.
Recent climate and societal changes have increased wildfire activity and prolonged the fire season in many regions of the world. The precision of fire seasonality analysis from tree-ring records can be improved by complementing the subjectively determined intra-ring position of fire scars with more precise studies of wood formation. With this aim, we monitored the wood formation dynamics of Pinus nigra J.F. Arnold (black pine) trees along a climatic gradient in western Anatolia to better understand the wood formation for the interpretation of fire seasonality. Wood microcores were collected from April to November 2021 from trees at four sites across (from north; the Black Sea climate in Bolu to the south; and the Mediterranean climate in Isparta) the areas where previous fire history reconstructions were conducted. These previous studies showed that most fires occurred during the latewood formation period. We found that matured latewood tracheids were observed between September (August) and November, thus suggesting that these fires occurred during late summer and fall. Our results show the importance of temperature and water availability for the timing of earlywood and latewood formations. These findings can be used to better inform planning activities for fire management and as a proxy to reconstruct past fire seasonality.
Species distribution models can help predicting range shifts under climate change. The aim of this study is to investigate the late Quaternary distribution of Oriental beech ( Fagus orientalis ) and to project future distribution ranges under different climate change scenarios using a combined palaeobotanical, phylogeographic, and modelling approach. Five species distribution modelling algorithms under the R-package `biomod2`were applied to occurrence data of Fagus orientalis to predict distributions under present, past (Last Glacial Maximum, 21 ka, Mid-Holocene, 6 ka), and future climatic conditions with different scenarios obtained from MIROC-ESM and CCSM4 global climate models. Distribution models were compared to palaeobotanical and phylogeographic evidence. Pollen data indicate northern Turkey and the western Caucasus as refugia for Oriental beech during the Last Glacial Maximum. Although pollen records are missing, molecular data point to Last Glacial Maximum refugia in northern Iran. For the mid-Holocene, pollen data support the presence of beech in the study region. Species distribution models predicted present and Last Glacial Maximum distribution of Fagus orientalis moderately well yet underestimated mid-Holocene ranges. Future projections under various climate scenarios indicate northern Iran and the Caucasus region as major refugia for Oriental beech. Combining palaeobotanical, phylogeographic and modelling approaches is useful when making projections about distributions of plants. Palaeobotanical and molecular evidence reject some of the model projections. Nevertheless, the projected range reduction in the Caucasus region and northern Iran highlights their importance as long-term refugia, possibly related to higher humidity, stronger environmental and climatic heterogeneity and strong vertical zonation of the forest vegetation.
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