Climate change means major ecosystem shifts for the Mediterranean Basin

As temperatures around the world increase, some regions will feel the heat more than others. Already, regional temperatures in the Mediterranean basin are about 1.3°C higher than they were between 1880 and 1920, compared with an increase of roughly 0.85°C worldwide during the same period.

Considering that Mediterranean basin ecosystems are a hotspot for the world's biodiversity and supply numerous services to people, including clean water, flood protection, carbon storage, and recreation, this extra increase in temperature is critical.

Here, to further consider the effects of different Paris Agreement temperature thresholds on the Mediterranean basin, Joel Guiot and Wolfgang Cramer used pollen cores from sediments, which provide rich detail about Mediterranean climate and ecosystem variability over the past 10,000 years. They applied this data in models as a baseline to estimate future climate and vegetation scenarios based on different temperature increases.

In both the "business as usual" simulations and a second set of simulations that reflected intended national goals proposed by the governments at the 2015 United Nations Climate Change Conference in Paris, the amount of ecological change that's predicted vastly exceeds that which has occurred during the Holocene. In the "business as usual" case, all of southern Spain turns into desert, deciduous forests invade most of the mountains, and shrubland vegetation replaces most of the deciduous forests in a large part of the Mediterranean basin.

Only under the scenario where the global warming is limited to 1.5°C above pre-industrial temperatures do ecosystem shifts remain inside the limits experienced during the last 10,000 years.

This analysis does not account for other human impacts on ecosystems, such as land-use change, urbanization, and soil degradation, many of which are more likely to increase in the future because of the expanding human population and economic activity, the authors note.