A recent 4 year study led by Dr. Daniel R. Cayan, of Scripps Institution of Oceanography at UC San Diego, found that average temperatures had only increased by a degree or two (Fahrenheit) over the past several decades, mainly affecting overnight temps rather than daytime temps. That really doesn't surprise me, especially seeing as it is possible for the diurnal/nocturnal temperature differential in Napa to be as much as 40 to 50 degrees.
Vinoland's Cabernet sauvignon vines are approximately 80% through veraison. Due to persistent cool temperatures (our second below average summer in a row), it's hard to tell if my pruning experiment this year has had any impact on the maturation of the Cabernet vines. With possibly two full months still until harvest I can only cross my fingers and hope for warm, dry weather during September and through October.
Whilst I do understand that the San Francisco Bay Area is well known for it's diverse micro climates - and it is indeed the cool marine layer that aids in quality grape production in this part of the world - I long for more typical summer temps...it is California after all.
Global warming is awfully cold!