A warming limit for the Mediterranean basin
Pollen cores from sediments provide rich detail on the history of vegetation and climate in the Mediterranean during the Holocene (the most recent ~10,000 years). Guiot and Cramer used this information as a baseline against which to compare predictions of future climate and vegetation under different climate-change scenarios. Vegetation and land-use systems observed in the Holocene records may persist under a 1.5°C warming above preindustrial temperature levels. A 2°C warming, however, is likely over the next century to produce ecosystems in the Mediterranean basin that have no analog in the past 10,000 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 1.5°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.