Climate controlled historic olive tree occurrences and olive oil production in southern Spain

Future climate projections of temperature increases and precipitation decreases over southern Europe pose an enormous challenge not only for the natural environment but also agricultural practices there. Adaptation and prediction are thus necessary to reduce the impact of climate change on future societies. The study of past environments and climate change can be used to improve our understanding of future climate scenarios, providing information about how former environments responded under past climatic conditions. Olive (Olea europaea) fruits and oil have a significant place among the Mediterranean culture where cultivation of olive is an important agricultural activity in the region, particularly in Spain, where commercial olive trees cover 2.5 million ha. Thus it is instructive to understand the primary climatic factors controlling past olive production in this area. In this study we present a synthetic record of Olea occurrences based on seven lake and wetland sediment pollen records from the Sierra Nevada area of southern Spain, for the last ~4500 cal yr BP, which could be used to evaluate the natural and anthropogenic variability of Olea in this area, particularly during the last millennia. Comparison of pollen data with paleoclimatic records strongly suggests that natural millennial-scale variability in Olea is controlled in large part by persistent centennial-scale North Atlantic Oscillation (NAO) fluctuations. Our fossil data demonstrate that olive cultivation in this area expanded rapidly at ~950 cal yr BP (1000 CE) and its subsequent variability depended on climate conditions. This study also shows that olive oil production since the beginning of the 20th century was conditioned by climate, suggesting that olive oil industry will be affected by the present aridification tendency in the Mediterranean climates areas.