In Messini, a sleepy Greek town in the south-west Peloponnese, Panagiotis Mitseas’s oil mill hums with activity on an autumn afternoon. Locals bearing sacks of freshly harvested olives wait patiently for their produce to be weighed, washed, sliced, and crushed. It is a convivial scene that has been repeated in Greece for millennia. But Mitseas is not happy. “I haven’t seen such a bad year in my six decades of work,” said the 78-year-old miller. Production had fallen by more than two-thirds because of unusually warm weather, he explained.

“The olive trees didn’t rest as they should have during the winter months,” he said, grabbing a few olives from a sack. “They’re dehydrated.” The impact of global warming on this staple of Greek life since ancient times extends far beyond Messini. Crop yields have fallen across the Mediterranean region over the past two years because of the weather, while farmers on the island of Rhodes were hit by the destruction of some 50,000 olive trees in forest fires during the summer.  

Bulk prices of olive oil — described by Homer as “liquid gold” — have soared as a result, doubling in a year to about €9,000 per tonne. That in turn has pushed up retail prices and triggered a rise in thefts of olives and olive oil, along with incidents of adulteration with cheaper products.

But the crisis also has a positive side for Greece, with the rising value of their olive oil prompting entrepreneurs to market it as a luxury product in foreign markets rather than letting better-known Spanish and Italian brands profit from their bulk purchases of high-quality Greek oil.

Olive trees have deep roots in Greek history and mythology. Legend has it that Athens was so named because when Poseidon and Athena were competing for the favour of the city, the goddess of wisdom’s offering of an olive tree for the Acropolis is said to have triumphed over the saltwater spring offered by the sea god.

The recent spike in prices, however, is starting to disrupt the olive trade central to Greek life. Mitseas said his mill was burgled — the thieves took 100 litres of oil worth hundreds of euros — for the first time in his career.

Some farmers have experimented with GPS trackers concealed in plastic olives to track thefts of their crops, and supermarkets have begun fitting antitheft mechanisms to olive oil containers as if they were bottles of whisky or expensive wine.

Until last year, the authorities did not even keep separate data on olive oil thefts because they were so rare. “Now, there are three or four incidents a week,” said Constantina Dimoglidou, a Greek police spokesperson. “We’ve never seen such incidents of theft before.”

The climate impact and spike in prices have, however, at least prompted Greeks to consider how to extract more value from a crop that has long been taken for granted — an opportunity boosted by Greece’s relatively good harvest the previous season.

Greece, the world’s third-largest producer, has traditionally sold high-quality olive oil in bulk to its larger rivals Spain and Italy, who brand it and sell it on to the world’s consumers.

And at home, Greeks acquire most of their own household olive oil from an untaxed informal market valued at €500mn. The crucial ingredient of Greek cuisine usually comes with scant quality control in unlabelled bottles, cans or plastic containers from relatives or friends with an olive grove. Such sales are now sometimes negotiated over social media platforms.

Emmanouil Giannoulis, president of the National Olive Oil Interprofessional Organisation, said some olive oil was adulterated with other products — a problem likely to worsen with higher prices — and more than two-thirds of randomly sampled oil fails to meet Greek quality standards.

Some 82 per cent of Greece’s 300,000 tonnes of typical annual oil output is nevertheless high-quality extra virgin olive oil, which is largely used not for branded Greek exports but by Italian and Spanish producers to add flavour to their own oil, according to Giorgos Economou, director-general of Sevitel, an Athens-based group of olive oil companies.

“Let’s not blame the wicked Spanish and Italians, but our own inability to add value to Greek olive oil and sell it,” he said.