As a vineyard owner in Southern California, I am of course very interested in all of this. How do I prepare for the future? Will my vineyard end up as part of the Mojave desert in 30 years? Should I rip out all of our Cabernet Sauvignon vines and replace them with warm climate varietals, like Zinfandel and Nebbiolo? Or maybe switch to producing raisins?
Californian vineyard owners know for quite some time by first hand experience that the Californian coastal wine area climate is actually getting cooler. This season's dramatic pictures of Paso Robles vineyards covered in snow during Spring, and low overall yield due to low temperatures at blooming and fruit set were no exceptions. While I am of the opinion that Temecula can have pretty hot days in the Summer with temperatures over 100 degrees Fahrenheit, folks who lived here for decades told me that this year was actually cool.
So what's going on? I used data from The California Irrigation Management Information System (CIMIS) to see the trend of Winkler Scale growing degree days. The Winkler scale, developed by the university of Davis, is a method to quantify heat available for vine development during the growing season.
2,500 degree days or less: Region I.
Similar to Côte d'Or and Champagne, the Rhine, Willamette Valley
2,501–3,000 degree days: Region II.
Similar to Bordeaux.
3,001–3,500 degree days: Region III.
Similar to the Rhône
3,501–4,000 degree days: Region IV.
Similar to Spain
Greater than 4,000 degree days: Region V.
Similar to North Africa
One clarification that sounds pretty plausible to me, is that Global Warming leads to higher inland temperatures. The warm inland air rises in the atmosphere and results in an area of low air pressure. Cool air from the ocean (Pacific High) will flow inland and bring cooler temperatures to coastal areas. This effect can clearly be observed in Temecula where ocean breezes flow into the Temecula valley later in the morning when inland temperatures rise. Early in the morning there is virtually no wind, and the many Temecula balloon rides take advantage of that landing close to where they took off.
So based on what I know today, I do not expect having to graft to Nebbiolo or start growing raisins in Temecula, Southern California. Actually, slightly lower temperatures will help me get even better quality fruit. Will stick to being a happy Cabernet Sauvignon grower!!