With around 130 peaks exceeding 3000 m in altitude the Pyrenees Mountains represent a natural border between France and Spain. The range is more than 450 km long and ~100 km wide, spanning in a west-east direction from the Atlantic Ocean to the Mediterranean Sea. The Pyrenees' biodiversity is rich and unique, with more than 4500 vascular plant species and 180 endemic species. The Pyrenees is one of the European plant biodiversity centers, threatened by climate change.
According to our new climate simulations, the warming effect is more marked in mountain areas (the Alps and the Pyrenees). Here, the average temperature change will exceed 2°C by the middle of the century under a scenario with strong future growth in greenhouse gas emissions (RCP8.5). Climate change has strong geographic variations with 20% less precipitation on the Mediterranean side and 20% more on the Atlantic side, when comparing two extended periods for the past (1961-1991) and the future (2041-2051). Results are highly sensitive to large-scale circulation change: we rely solely on one model and one climatic scenario (RCP8.5 with the EURO CORDEX simulation by WRF-IPSL-CMIP5). We will include a wider spectrum of climate projections to reduce the associated degree of uncertainty in the next phase of the project.
Generally, we expect more extended droughts, more severe heatwaves and more frequent extreme precipitation events. More heatwaves are likely to cause more frequent high ground-level ozone events, potentially increasing plant stress and damage. Other pollutants, such as nitrogen deposition, can significantly influence plant growth over the region where nitrogen deposition currently greatly exceeds critical loads.
Assessing the combined effect on the mountain ecosystem of pollution and climate change is critical. With increased temperature, the Pyrenees' vegetation is likely to change. Our studies show marked differences in plant communities across the entire Pyrenees Mountains, with vegetation zones climbing higher up in altitude, likely resulting in reduced habitat availability for species adapted to the higher altitudes.
Although it is highly unlikely that efforts to combat climate change will have a significant effect by the middle of the century, air quality can be improved more rapidly. Our focus in the coming months of the projects will be to assess whether the benefits in air pollution could partly compensate the negative impacts of climate change.