This year has been a record-breaking one for high temperatures. Starting in January, Australia experienced two major heatwaves that saw temperatures approach 50°C in parts of the country. The following month, Argentina and Chile experienced extreme summer heat accompanied by serious wildfires. In South Africa, the unusually hot and dry summer helped produce what Reuters called the “most severe” fire season in the country in a decade.
As the global summer began to move from south to north, a heatwave hit the US Southwest, breaking highest March temperature records in Arizona and Southern California. In April, large parts of northern India experienced sustained “severe heat episodes” with temperatures in New Delhi reaching 45°C. Later in May, a heatwave tore across western and central Europe; France, the UK, Portugal and Spain all set new May temperature records.
Then came June and July, when a series of heatwaves shattered climatological records across the globe. The World Weather Attribution described the late-June heatwave as the “most severe ever recorded” in western Europe. By 4 July, more than half of the population of the US were under heat alerts.
A report from Columbia University released in April had already predicted that 2026 “is likely to be the warmest year in the period of instrumental data”.
What’s more, heatwaves are becoming increasingly commonplace; the Intergovernmental Panel on Climate Change (IPCC) found in 2021 that since 1950, “it is virtually certain that there has been increases in the intensity and duration of heatwaves and in the number of heatwave days at the global scale”.
LOWER YIELDS
All of this should ring alarm bells for winemakers. Grapes are among the most temperature-sensitive agricultural crops. While mature vines are relatively robust and able to withstand extended periods of heat and drought, the grape harvest itself is highly quality sensitive. Typically, heatwaves lower yields, accelerate ripening, and vines may shed leaves, exposing the fruit to direct scorching sunlight. According to the Australian Wine Research Institute, severe heat events can reduce grape yields by 35%.
The International Organisation of Vine and Wine (OIV) described two such occurrences of reduced harvest size in its State of the World Wine Sector in 2025 report.
“France, the world’s second-largest wine producer, produced 36.1 mhl in 2025,” says the OIV. “This volume is 16% below its five-year average. The low level in French wine production for 2025 is mainly attributable to adverse weather conditions across the country from flowering to harvest, impacting all wine regions. In particular, the heatwave and drought in August curtailed production potential by accelerating grape ripening while stunting their growth.”
Spain produced “a 2025 production volume of 28.7 mhl. This figure represents a decrease of 2.4 mhl (−7.7%) compared to 2024, and it remains 17% below the five-year average. A third consecutive year of drought and heatwaves led to a marked contraction in yields, resulting in one of the lowest harvest levels observed in recent decades.”
A 2023 study by Hewitt, S., Hernández-Montes, E., Dhingra, A. et al. that appeared in Scientific Reports described the impact of heat on grapes themselves. It found that: “Exposure to a seven-day episode of heat stress… increased berry pH, decreased titratable acidity, and generally decreased organic acid content, but did not alter sugar content, in the berries of two distinct wine grape varieties [Cabernet Sauvignon and Riesling].”
In short, grapes exposed to a week-long heatwave will likely produce wine higher in alcohol and lower in acidity. But the risk is greater than vintages of flabby Pauillac.
When it comes to extreme viticulture, Greece is often Europe’s canary in the coalmine. The IPCC places the country in Europe’s highest-risk tier for extreme heat, with warming trends coinciding with declining summer rainfall, often resulting in prolonged drought periods. Unlike other Mediterranean climates, Greece also experiences less overnight cooling due to the massive heat-storing capacity of the surrounding sea.
These compounding factors have forced Greek viticulturalists to find ways to adapt to warmer and drier vineyards. The broad strategy has been a return to native, heat stress-resistant grape cultivars like Assyrtiko, Plytó and Mavrodafni, higher elevation sites and greater research into targeted irrigation.
But despite efforts to mitigate damaging effects, there are upper limits. The Greek island of Santorini has become a warning. On the island, Assyrtiko, a highly heat-resistant variety, has comprised the majority of vines, but consecutive hot and dry years have decimated production.
Between 2022 and 2025, yields fell from 2,500 to 500 tonnes as the vines were unable to continue compensating for an exhausted water supply. The correct variety can only take you so far.
The French National Committee for Wine AOCs (CNAOV) has introduced a scheme under the name Varieties of Interest for Adaptation (VIFA), wherein growers are able to trial promising grapes while retaining their protected status so long as the trial grapes account for at most 5% of the vineyard’s varieties.
To date, around 20 appellations have planted cultivars under the system, including Bordeaux, where six climate-adaptation varieties, predominantly from the Iberian Peninsula, have been approved for limited use in Bordeaux and Bordeaux Supérieur. The reds Touriga Nacional, Marselan, Castets and Arinarnoa, and whites Alvarinho and Liliorila have been selected for later ripening, drought resilience, acidity retention or suitability for warmer conditions.
The trend is clear. Summers are changing and heatwaves will be something that will increasingly trouble winemakers across the viticulture atlas. It’s a bitter pill for an industry that has de ned itself through regional character, and perhaps wine’s next great climate struggle will be how to adapt while retaining its identity.
