Climate change threatens olive oil production in the Levant.

The olive tree (Olea europaea L.) is one of the species best adapted to a Mediterranean-type climate 1-8 . Nonetheless, the Mediterranean Basin is deemed to be a climate change 'hotspot' by the Intergovernmental Panel on Climate Change 9,10 because future model projections suggest considerable warming and drying 11,12 . Within this context, new environmental challenges will arise in the coming decades, which will both weaken and threaten olive-growing areas, leading to a loss of productivity and changes in fruit and oil quality 13-15 . Olive growing, a core of the Mediterranean economy, might soon be under stress. To probe the link between climate and olive trees, we here report 5,400 years of olive tree dynamics from the ancient city of Tyre, Lebanon. We show that optimal fruiting scales closely with temperature. Present-day and palaeo data define an optimal annual average temperature of 16.9 ± 0.3 °C for olive flowering that has existed at least since the Neolithic period. According to our projections, during the second half of the twenty-first century, temperature increases in Lebanon will have detrimental consequences on olive tree growth and olive oil production, especially in the country's southern regions, which will become too hot for optimal flowering and fruiting. These data provide a template to understand present and future thresholds of olive production under climate change.