Recent accelerated climate change has exacerbated existing environmental problems in the Mediterranean Basin that are caused by the combination of changes in land use, increasing pollution and declining biodiversity. For five broad and interconnected impact domains (water, ecosystems, food, health and security), current change and future scenarios consistently point to significant and increasing risks during the coming decades. Policies for the sustainable development of Mediterranean countries need to mitigate these risks and consider adaptation options, but currently lack adequate information — particularly for the most vulnerable southern Mediterranean societies, where fewer systematic observations schemes and impact models are based. A dedicated effort to synthesize existing scientific knowledge across disciplines is underway and aims to provide a better understanding of the combined risks posed.

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Climate change and interconnected risks to sustainable development in the Mediterranean

Anthropogenic warming is anticipated to increase soil moisture drought in the future. However, projections are accompanied by large uncertainty due to varying estimates of future warming. Here, using an ensemble of hydrological and land-surface models, forced with bias-corrected downscaled general circulation model output, we estimate the impacts of 1–3 K global mean temperature increases on soil moisture droughts in Europe. Compared to the 1.5 K Paris target, an increase of 3 K—which represents current projected temperature change—is found to increase drought area by 40% (±24%), affecting up to 42% (±22%) more of the population. Furthermore, an event similar to the 2003 drought is shown to become twice as frequent; thus, due to their increased occurrence, events of this magnitude will no longer be classified as extreme. In the absence of effective mitigation, Europe will therefore face unprecedented increases in soil moisture drought, presenting new challenges for adaptation across the continent. Severe drought plagued Europe in 2003, amplifying heatwave conditions that killed more than 30,000 people. Assuming business as usual, such soil moisture deficits will become twice as frequent in the future and affect up to two-thirds of the European population.

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Anthropogenic warming exacerbates European soil moisture droughts

Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.

https://hal-amu.archives-ouvertes.fr/hal-01870934/document

Past and future global transformation of terrestrial ecosystems under climate change

The observed trend towards warmer and drier conditions in southern Europe is projected to continue in the next decades, possibly leading to increased risk of large fires However, an assessment of climate change impacts on fires at and above the 15 °C Paris target is still missing Here, we estimate future summer burned area in Mediterranean Europe under 15, 2, and 3 °C global warming scenarios, accounting for possible modifications of climate-fire relationships under changed climatic conditions owing to productivity alterations We found that such modifications could be beneficial, roughly halving the fire-intensifying signals In any case, the burned area is robustly projected to increase The higher the warming level is, the larger is the increase of burned area, ranging from ~40% to ~100% across the scenarios Our results indicate that significant benefits would be obtained if warming were limited to well below 2 °C

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Exacerbated fires in Mediterranean Europe due to anthropogenic warming projected with non-stationary climate-fire models.

Recent Mediterranean droughts have highlighted concerns that climate change may be contributing to observed drying trends, but natural climate variability in the region is still poorly understood. We analyze 900 years (1100-2012) of Mediterranean drought variability in the Old World Drought Atlas (OWDA), a spatiotemporal tree-ring reconstruction of the June-July-August self calibrating Palmer Drought Severity Index. In the Mediterranean, the OWDA is highly correlated with spring precipitation (April-June), the North Atlantic Oscillation (January-April), the Scandinavian Pattern (January-March), and the East Atlantic Pattern (April-June). Drought variability displays significant east-west coherence across the basin on multi-decadal to centennial time scales and north-south anti-phasing in the eastern Mediterranean, with a tendency for wet anomalies in the Black Sea region (e.g., Greece, Anatolia, the Balkans, etc) when coastal Libya, the southern Levant, and the Middle East are dry, possibly related to the North Atlantic Oscillation. Recent droughts are centered in the Western Mediterranean, Greece, and the Levant. Events of similar magnitude in the Western Mediterranean and Greece occur in the OWDA, but the recent 15-year drought in the Levant (1998-2012) is the driest in the record. Estimating uncertainties using a resampling approach, we conclude there is an 89% likelihood this drought is drier than any comparable period of the last 900 years and a 98% likelihood it is drier than the last 500 years. These results confirm the exceptional nature of this drought relative to natural variability in recent centuries, consistent with studies that have found evidence for anthropogenically forced drying in the region.

Spatiotemporal drought variability in the Mediterranean over the last 900 years

The United Nations Framework Convention on Climate Change Paris Agreement of December 2015 aims to maintain the global average warming well below 2°C above the preindustrial level In the Mediterranean basin, recent pollen-based reconstructions of climate and ecosystem variability over the past 10,000 years provide insights regarding the implications of warming thresholds for biodiversity and land-use potential We compare scenarios of climate-driven future change in land ecosystems with reconstructed ecosystem dynamics during the past 10,000 years Only a 15°C warming scenario permits ecosystems to remain within the Holocene variability At or above 2°C of warming, climatic change will generate Mediterranean land ecosystem changes that are unmatched in the Holocene, a period characterized by recurring precipitation deficits rather than temperature anomalies

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Joël Guiot

Papers

Climate change: The 2015 Paris Agreement thresholds and Mediterranean basin ecosystems