What does climate change do to wine?

More alcohol and less acidity. In the Languedoc the alcohol content of the wine rose from 11 to 14 percent between 1984 and 2018.

In the same series of measurements, total acidity fell from 6.0 to 4.5 grams per litre and the pH rose from 3.50 to 3.75. Acidity is what makes a wine feel fresh; less acidity and more alcohol give a different kind of wine from the same vineyard.

You can see it on the label. A bottle that used to say 12.5 percent now more often states 14 percent or more.

In Alsace the harvest now falls 25 days earlier than seventy years ago, and in Beaune on average 13 days earlier since 1988.

The series from Beaune runs from 1354 to 2018 and is the longest there is. Between 1354 and 1987 the harvest began on average on 28 September, in the years after on 15 September.

In Alsace, it was not only the harvest that shifted. Budburst moved forward by 10 days, flowering by 23 days and veraison by 39 days.

Warmth lets the grape build up more sugar, and yeast converts sugar into alcohol. More sugar in the grape therefore means more alcohol in the bottle.

In Bordeaux the average temperature of the growing season has risen by about 2 degrees over seventy years. As a result the grape reaches its sugar level earlier in the season, while the pips and skins still have to ripen.

The grower then chooses between picking early with less ripe tannin, or picking later with more alcohol.

The Earth's surface is now on average 1.3 degrees warmer than at the end of the nineteenth century, reports the KNMI.

The KNMI attributes the global rise of about 1 degree since the second half of the nineteenth century entirely to human activities. In the Netherlands, the temperature on the warmest day of the year has risen by more than 3 degrees since 1900.

Viticulture responds to exactly that measure. A growing season a few degrees warmer shifts all the stages of the vine.

Growers adapt with other grape varieties, other rootstocks, parcels at higher altitude or in cooler spots and adjusted pruning.

Researchers describe those adjustments as a package: late-ripening varieties, more leaf cover against sunburn, a different planting density and, in the cellar, a different approach to fermentation.

The size of the harvest is also shifting. The OIV reports that the weather in both hemispheres depressed the 2025 harvest, the third year in a row with a small worldwide harvest.