Alcohol is rising!!! It is just because of the climate?

I have, in the window of my store, some bottles from different vintages of Ridge Montebello. I call the window my cemetery, because it is where the bottles I've killed find their final repose. The Montebello is fantastic wine - I'm a big fan of it, and I drink it whenever I have excuse to do so. And then sometimes when I don't.
A few days ago Matt was browsing through the graveyard, perusing the evidence of exploits past. For those that don't know Matt, he is a young but skilled connoisseur that helps me in the store and has edited many of the posts on this blog for me, including this one. While he was browsing the Montebello corpses, he noticed a big difference in the wine's alcohol content, lighter in older bottles and higher on more recent vintages. In 1977, for instance, the percentage by volume was 11.7, and 12.9% in 1988. It climbed to 13% in 1999 and 13.2% in 2003. He mentioned global warming as explanation for the constant alcohol escalation, which does play a big part, in light of the direct proportion between sugar and alcohol. In fact, through the fermentation process the sugars are transformed directly into alcohol with the help of enzymes contained in the yeast. But is it just that... or there is more?
I remembered a conversation I had with a winemaker a while ago, regarding the help that science has contributed with grape clone selection, making more information available to agronomists, in order to select the best clones for the area of production. This information variably increases the quality and the health of the grapes. A big breakthrough happened along these lines in Montalcino, where it has been discovered that Sangiovese Grosso wasn't the best clone for Montalcino conditions and soils. In the past 30 years, the weather has gotten warmer but the grapes got healthier, the grains got smaller, and the vines got older, losing some vigor but gaining concentration and potency. Concentration of the grape from water distress coupled with better and older vines result in a higher content of polyphenols, which is a good thing for a wine. It also results in higher sugars and lower acidity levels which is not so good (distressingly high alcohol levels, and wines with shorter aging potential). Today I think we are in a sweet spot where the climate is more temperate. In Piedmont, for instance, we had a stretch of 6 good to excellent vintages from 1996 and 2001. The level of technology gave the winemakers more information than ever, including the latest creation of the grape's genome map. If this is like drinking a wine at its peak, let's hope we are still far from descending.
Buona Bevuta a Tutti.