How will a changing climate affect olive trees?

One of the Mediterranean's oldest and most symbolic crops is threatened by the effects of climate change. How will rising temperatures and an unstable climate affect this prized crop?

'The Phoenicians were the ones who developed the cultivation of the olive tree in the Mediterranean,' explains Joan Mayol, farmer and president of the Regulatory Council of the Oil of Mallorca. 'And then it began to be grown in Spain, which is now the largest producer and exporter in the world. There was already a Roman writer from Cadiz (South of Spain) in the 1st century who perfectly described how the cultivation of the olive tree and all the varieties of olives should be.'

As Joan tells us from his olive grove in the Serra de Tramuntana in Mallorca, Spain is the largest producer and exporter of olive oil in the world, even ahead of Italy and Greece.¹ Olive groves have evolved with the Mediterranean climate and are known for their resistance to water scarcity. Yet recent years have shown that even the olive tree, a symbolically resilient tree, could be one of the crops severely affected by the effects of climate change, endangering a millennia-old source of subsistence, culture and commerce.²   

Photo: Olive trees submerged in floodwater. Extreme weather events and shifting climate patterns have caused heavy rainfall in olive-producing regions. As olive trees are adapted to dry soil conditions, this can cause crop failure and root rot.

From the Mediterranean Levant to Spain: the history and present of olive oil  

The olive tree's geographical origin lies in the eastern Mediterranean (corresponding to present-day Lebanon, Jordan, Syria, and adjacent areas) between 4000 and 3000 BCE. Its great value has been said to partly reflect and determine the history of the great Phoenician and Roman empires. From the beginning of its history, the tree brought much more than olives and oil.⁵ 'It was also a substance used for medicinal values, fuel, cosmetics...' explains Joan. 

The history of the olive tree goes hand in hand with the history of the Mediterranean and its gastronomy: Biologist Georges Duhamel said that 'the Mediterranean ends where the olive tree stops growing.''³  Together with vines and wheat, it forms part of the so-called 'Mediterranean trilogy', crops that were among the first to occupy its coastal lands.⁴ 

The current crop in Spain, occupying 14% of the country’s agricultural area, represents almost half (45%) of world production.⁶ Large areas of olive groves, as with any large plantation of trees, absorb a considerable amount of CO2.⁷ Joan describes that 'each olive tree, on average, as there are larger and smaller olive trees, absorbs 30 kg of CO2 per year, which makes the olive grove an important factor in curbing climate change'. 

Photo: Olive trees growing in Andalusia, Spain. Spain produces 45% of the world's olives. 

A tree that affects and is affected by the climate 

Although olive trees can, to some extent, mitigate the effects of climate change through their absorption of CO2, they are also victims of climate change.⁷ Rising greenhouse gas emissions are causing an increase in temperatures as well as the frequency of extreme weather events such as droughts, storms or unseasonal temperatures.⁸  A study published in 2019 found that climate change, mainly due to drier and hotter weather in summer and autumn, is expected to reduce the area where olive growing is possible in Andalusia, Spain's largest oil-producing region, and probably in other olive-growing regions.⁹ The lack of rain and expected dry spells will cause water stress to the olive tree and, at the same time, higher temperatures will cause heat stress. This 'stress' damages trees physiologically, compromising flowering and, thus, olive production.

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Photo: Olives wrinkled from insufficient water and heat stress.

Olive trees have been perceived as indestructible historically and mythologically.¹¹ However, temperature increases and irregular seasonal changes are affecting key processes that result in a good season. The processes in the olive orchard most affected by climate change are olive flowering, which occurs during the spring and its onset is very susceptible to temperature, and the stage where the fruit (olive) develops and ripens, which occurs in mid to late summer. Patterns in recent years show that flowering is advancing and that ripening is accelerating, which results in the flower dropping before setting into a fruit. In addition, the number of olives per tree has declined, and the quality of these olives' oil has been said to have changed. In addition, the risk of climate-related stress due to high temperatures and lack of water resources in summer is increasing. All of these factors contribute to less productive harvests.^2,10,11 

Olives are often harvested by shaking the tree branches with either tools or machinery and caught in nets underneath the trees. 

Researchers at the Consejo Superior de Investigaciones Científicas (CSIC), due to the difficulty of making reliable forecasts on the response of olive orchards to climate change, have developed a biophysical model called OliveCan 2.0 that simulates several of the processes that could occur due to the effects of climate change. The model shows, for example, the decrease in flowering percentage in a scenario of higher temperatures or the tendency of flowering dates to advance in weeks or months in this same scenario with higher temperatures.¹² 

Possible adaptations

In the short term, there is an increased likelihood of crop failure and in the long term, the risk is in an overall reduction in yield quantity and quality.⁷ Adaptations exist for both scenarios. Following the OliveCan 2.0 projection, where flowering occurs earlier in the year under warmer weather, growers can adapt in the short term by changing their cropping patterns. Preventing water stress will require large investments in irrigation and adjusting the times of the year to apply it.¹³ On the other hand, there will be circumstances that will not be so easy to adapt to. Joan tells us that 'in 2020 there was a small localized tornado [in Mallorca] that wiped out 80% of the oil crop of the largest producer on the island. I lost a lot in a few hours with that tornado. If these become more and more frequent, there is a lot of risk to production.' 

Extreme weather events like this, new suboptimal average growing temperatures, more frequent cold or heat waves, and severe and unexpected pest outbreaks will require extreme transitions in olive farming. To cope with these changes, it will be necessary to research the most resilient and robust olive varieties, consider intercropping techniques, in which different species are grown at the same time on the same area of land, conserve soil health to maintain or improve water retention, and, in some cases, even shift the area of olive orchards to more suitable areas altogether.¹⁰ Because of the latter, it could be argued that, as areas in central Europe, New Zealand or California can easily accommodate olive groves, the competitiveness of the Mediterranean coastal strips will diminish, and with it Spain's leading status in global olive oil production.^11,14 

Photo: 'Global blend' olive oil, made from olives sourced outside of Spain, on the shelf of an American grocery store. 

The real consequences of the threat to the olive tree

Before worrying about how you will dress your salads and cook your food in the future, keep in mind that the repercussions, at least initially, will be mainly for producers and farmers. Given the complexity and magnitude of the food chain, there is a time lag between what happens in the field and what we find in the supermarket.¹⁵ That is not to say that we can sit back and relax because what the vulnerability of the olive tree to climate change is telling us is highly significant. It shows that, in the future, even those crops that we have relied on for thousands of years and that have survived so many changes over the centuries are not likely to be readily and cheaply available. A period of agricultural and, therefore, social change and uncertainty could lie ahead.⁸ Joan acknowledged that 'maybe [climate change] can be a bigger threat, but not to the oil, but to our livelihoods. We will have to roll up our sleeves and work to adapt and protect the landscapes tied to our Mediterranean past and present.'