Which climate change path are we following? Bad news from Scots pine

<div><p>Current expectations on future climate derive from coordinated experiments, which compile many climate models for sampling the entire uncertainty related to emission scenarios, initial conditions, and modelling process. Quantifying this uncertainty is important for taking decisions that are robust under a wide range of possible future conditions. Nevertheless, if uncertainty is too large, it can prevent from planning specific and effective measures. For this reason, reducing the spectrum of the possible scenarios to a small number of one or a few models that actually represent the climate pathway influencing natural ecosystems would substantially increase our planning capacity. Here we adopt a multidisciplinary approach based on the comparison of observed and expected spatial patterns of response to climate change in order to identify which specific models, among those included in the CMIP5, catch the real climate variation driving the response of natural ecosystems. We used dendrochronological analyses for determining the geographic pattern of recent growth trends for three European species of trees. At the same time, we modelled the climatic niche for the same species and forecasted the suitability variation expected across Europe under each different GCM. Finally, we estimated how well each GCM explains the real response of ecosystems, by comparing the expected variation with the observed growth trends. Doing this, we identified four climatic models that are coherent with the observed trends. These models are close to the highest range limit of the climatic variations expected by the ensemble of the CMIP5 models, suggesting that current predictions of climate change impacts on ecosystems could be underestimated.</p></div

Agreement between observed responses by tree ring analyses and expected responses by habitat suitability models under different GCMs for <i>Pinus sylvestris</i>.

<p>Agreement between observed responses by tree ring analyses and expected responses by habitat suitability models under different GCMs for <i>Pinus sylvestris</i>.</p

Models explaining the observed responses.

<p>Each column shows results for one of the four models with the highest level of agreement between expected and observed responses. In the upper row, the current range of <i>Pinus sylvestris</i> (thin grey line) and its future climate suitability are shown (grey-yellow-green scale; 0 < HS < 1000). In the lower row, the expected variation of climate suitability is shown (grey-yellow-green scale), together with the observed responses of <i>Pinus sylvestris</i> populations: green points represent populations with positive responses, grey points represent neutral responses, and red points represent negative responses. The small histograms within lower maps show the results of the null-model tests of agreement between expected and observed responses: when the vertical red line is on the left of the black line, <i>P{A</i>_<i>sim</i> <i>> a</i>_<i>obs</i><i>}</i> > 0.05, when the red line is on the right of the black one, <i>P{A</i>_<i>sim</i> <i>> a</i>_<i>obs</i><i>}</i> < 0.05. All the maps are Albers equal-area conic projections and coordinates are metric. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189468#pone.0189468.s005" target="_blank">S5 Table</a> for model details.</p

Potential improvement in future suitability predictions.

<p>Difference between habitat suitability under future climatic conditions as predicted by the entire set of models and by the selected four. The colour scale is the difference between the consensus model of the entire set of 59 models and the consensus of the selected four models. The darker area within the red line indicates where the difference is significant.</p

Schematic idea behind the experiment.

<p>Five hypothetical range shifts are shown with the relative expected effects on local populations. Let’s suppose only one of the five hypothesized range shifts is actually occurring. In the case an appropriate set of local data on population responses being available, it is possible to identify which specific range shift is actually occurring on the basis of the spatial pattern of positive, neutral, and negative responses.</p