Wine Grape Production as a Climate Change Indicator

Russ Steele

In November of 2007 I wrote a post at NC Media Watch Why should grape growers worry about a cold phase PDO? This was in responses to a paper written by Gregory V. Jones and  Gregory B. Goodrich Influence of climate variability on wine regions in the western USA and on wine quality in the Napa Valley 

ABSTRACT: [emphasis added] Trends in climate variables important to wine grape production in the western United States include fewer frost days, longer growing seasons and higher spring and growing season temperatures. These trends have been related to a steady increase in wine quality and a decrease in year to year variability. While the trends in climate have been linked to increasing sea surface temperatures (SSTs) in the eastern Pacific, it is unknown whether this is caused by climate change or may be part of natural oscillations in the Pacific. In this study, fifteen climate variables important to wine grape production were analyzed for ten wine regions over the western USA. The variables were stratified by phases of the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) both separately and then in combination (modulation effect) to determine if there are any significant differences between teleconnections. Wine Spectator vintage ratings for Cabernet Sauvignon wines from the Napa Valley were also stratified in the same method and multivariate statistics were used to determine which variables are most important to wine quality. ENSO phase by itself was not found to be important to either climate variability in wine regions in the western USA or wine quality in Napa Valley, but the cold phase of the PDO was found to be associated with increased spring frosts and a shorter growing season that results in lower ratings relative to warm PDO. The combination of neutral ENSO conditions during the cold phase of the PDO was nearly always associated with low quality wine in the Napa Valley, which is a function of cold springs with increased frost risk, cool growing seasons, and ripening period rainfall (cold PDO) and above average bloom and summer rainfall (neutral ENSO). While climate trends to generally warmer growing seasons with less frost risk have occurred, this research highlights the impact of climate variability on wine quality where, should the PDO return to a multi-decadal cold phase, wine growers in the Napa Valley and across the western USA will likely experience greater variability in wine quality.

We are now in a cold phase PDO with a La Niña weather pattern. During cold phases the La Niña is the dominate pattern, and we can expect more of these cold events like we have had in 2010 and 2011 over the next twenty to thirty years. The impact of cool phase PDO could be amplified by the return of another grand minmum.

Lisa Baertlein, wrote about the current impact of the cool and wet conditions in Reuters on the 19th of October, Cool California weather keeps winemakers waiting

Growers around the Golden State are harvesting grapes later than usual this year. The take is anticipated to be smaller than normal, due to heavy spring rains and the second summer in a row of cooler-than-normal temperatures.

Here in Nevada County the wine grape production in 2010 dropped by 31 percent. Yields were significantly down, due primarily to hail and frost at critical moments, according to a County Ag Report.  A cool phase PDO is not uniformly cold, the climate will vary from warm to cold and back again, riding on a declining temperature trend. This uncertainty will make wine grape growing a risky business. The Reuters article has some insight into 2011 crop decline, and 2012 has the potential to be repeat of 2010. Stay tuned, as we maybe on the cusp of the next grand minimum. The last grand minimums restricted grape growing in England and other northern countries in Europe due to shortened growing season and cool to cold summers.  I will continue to track the decline in wine grape production as a climate change indicator.