The characteristics of wine grapes when harvested, and the quality of the wine made from them, are extremely sensitive to climate conditions during the growing season, especially temperature. Wine grape harvest dates are already weeks earlier than what they have been historically in many parts of the world, which means that temperatures are higher as the grapes ripen. That trend will continue and, as average temperatures continue to rise, winegrowers will need to adapt their vineyard management practices to compensate for that. In addition, when a vineyard is replanted, they will want to consider other clones, or even varieties, that are more tolerant of higher temperatures. Ultimately, some varieties will no longer be suitable in regions where they have been grown for centuries, while new wine regions farther north (farther south in the Southern Hemisphere) will blossom.
The graph below shows projected growing season temperature for a vineyard on a Napa Valley hillside relative to the lower and upper limits of the historical sweet spot for Cabernet Sauvignon, a relatively heat tolerant variety. The key takeaway is that, taking year to year variability into account, the winegrower should plan to implement adaptation measures within the next ten to fifteen years. Vineyards on the Valley floor, especially those growing more heat sensitive varieties, will likely need to take action considerably sooner.