The Effects of Climate Change on the California Wine Industry – My Latest Contribution to SOMM Journal

The following article is my latest contribution to the print magazine SOMM Journal. I feel very honored to have been given the opportunity to write for this fantastic periodical and encourage each and every one of you to check it out when you get a chance.  With 6 issues per year, subscriptions are FREE to those in the wine industry.  There is a fee for non-industry folks.  Please visit the SOMM Journal site to download the latest issue of the journal, as well as read web-only exclusives.  You may also subscribe to SOMM Journal on their website or go there directly by clicking here.

Printed for the first time online with permission.

Without further ado, here is my piece (unedited) for SOMM Journal:


Editor’s Note: The effects of climate change on the global wine industry are not at all uniform. Each individual region may suffer its own unique effects, some of which will be described in more detail in subsequent articles in this magazine. This piece highlights the general effects of climate change on the wine regions of California. Since the amount of information available is too vast for a single article, this article highlights major points of interest and we encourage you to read as many of the “selected references” that are listed at the end of this piece for even more details.

Climate change is a threat not only to viticulture but to every living system worldwide. We’ve discussed some general global trends in past issues, but today the focus will be on the effects of climate change on some of the wine regions of California.

With increasing temperatures in regions that are already on the brink of being too hot for winegrape production, studies estimate that suitable vineyard area of premium wine production in the US could decrease as much as 81% by the year 2100. According to the Wine Institute’s most recent figures, the California wine industry has a $61.5 billion impact on the state’s economy, as well as a $121.8 billion impact on the national economy. An 81% reduction in premium wine production sites, most of which are located in California, would have disastrous effects not only the economy of California, but also the nation.


In general, California is expected to see increases in temperatures as a result of climate change. For the Central Coast, models are predicting a 0.6-1.7oC increase, while the

Figure 5 from Jones et al (2010)

Figure 5 from Jones et al (2010) (click to enlarge)

North Coast is expected to see increases of 0.5-1.1oC. Research funded by the Napa Valley Vintners found that since 1931, temperatures have been increasing in that region by about 0.03oF every year, though there is significant variation between urban and non-urban areas within the valley.

Between 2000 and 2039, some models are predicting increases in growing degree days from 140 to 340 in the Central Coast, and from 60 to 220 on the North Coast. Additionally, the number of growing degree days over 35oC are expected to increase by up to 17.5 and 10 days on the Central and North Coasts, respectively.

One major problem with increasing temperatures in California is that many regions are already at the upper limit in terms of optimal temperatures for premium winegrape growing. Most wine grapes are grown within a 10oC range, between 12oC and 22oC, while some varieties are more sensitive and can only grow within a much smaller temperature range in order to produce premium quality wines.

Using the Winkler Index for vineyard suitability, which evaluates an area based on growing degree days, a 2010 study found that there are several places in California, particularly in the Central Valley, that are already bordering on “too hot” for grapes and that further warming would be detrimental for grape growing in these regions.

For example, 78% of the vineyard sites in the Lodi AVA fall into the Winkler Index Class IV (hot), with the remaining 22% falling into Class V (very hot). The Madera AVA is even hotter, with 100% of the vineyard sites falling into Class V, the hottest class possible before an area is considered unsuitable for winegrape growing. As a comparison, 56% of sites in Napa Valley AVA fall into Class III, right in the middle of “too cold” and “too hot”, with just 30% falling into Class IV. Similarly, in Paso Robles AVA, 49% of vineyard sites are considered to be Class III, while 37% are in Class IV. As of 2010, none of the sites in Napa Valley or Paso Robles fell into the “very hot” category.

With increasing temperatures and the associated increases in growing degree days, many vineyard sites in Class IV and in particular Class V may find themselves producing lower quality grapes and wine, necessitating immediate mitigation and adaptation.

Precipitation and Soil Moisture

It is unclear exactly how precipitation will change in California, but the general consensus is that some regions may see increased precipitation, while others (e.g. more southern

Photo By NPS Photo [Public domain], via Wikimedia Commons

Photo By NPS Photo [Public domain], via Wikimedia Commons

regions) might see less. Additionally, changes in ocean dynamics due to climate change may affect fog production, a meteorological phenomenon important for some grape growing regions in California, though more research on this is needed.

Changes in soil moisture will be inevitable simply based upon predicted increasing temperatures. As temperature increases, evaporation rates will increase, leading to drier soils and ultimately more stress on the plants themselves.


A big question facing growers when they are faced with a changing climate is what they can do to adapt and maintain a successful operation.

First and foremost is to make changes within their growing and winemaking procedures to help reduce their overall carbon footprint. While this is not a quick fix, it will help minimize the effects of climate change for everyone. Reducing water usage in the vineyard and winery and adopting newer and more efficient technologies are a couple of ways to do this.

For those in more troubled areas such as those regions already on the brink of being too hot for grape production, the need for more rapid change may be necessary. Planting new varieties or clones that are more heat-tolerant is an option, as is moving the vineyard all together to location higher in elevation.

In the vineyard, adopting more efficient irrigation systems or practicing dry farming may be necessary. Additionally, changing vineyard management practices to improve water use efficiency in the plants themselves will be necessary to continue producing high quality wine. Examples on ways to achieve this are changing trellis techniques and changing canopy pruning strategies to increase shade protection on the grapes.

Problems with Accepting Climate Change and Limitations to Action

Unfortunately, despite the overwhelming evidence of a changing climate, there are still often barriers to action by grape growers which are both physical and psychological. Because of the variability from AVA to AVA, and even within individual AVAs, it becomes difficult to accept that what scientists say might happen in a particular area is actually going to happen in one individual vineyard. Growers are highly knowledgeable about their

Photo By Mark Smith (Flickr: Pinot Grigio harvest, vintage 2012) [CC BY 2.0 (], via Wikimedia Commons

Photo By Mark Smith (Flickr: Pinot Grigio harvest, vintage 2012) [CC BY 2.0 (], via Wikimedia Commons

particular sites and how it relates to grape growing and winemaking, but are sometimes less understanding and accepting of less tangible predictions in terms of how that land may or may not be suitable in the future.

In addition to distrust and general decreased awareness of climate change within the growers themselves, there are some physical barriers that exist that make it difficult for growers to adapt even if they wanted to. For example, planting more heat-tolerant grape varieties becomes difficult when these new grape varieties have yet to be developed or when the financial costs of such massive changes becomes too much for an individual winery to bear.

Finally, collaboration between scientists, growers, and government agencies will be necessary to maximize participation in any climate change adaptation programs. Creating tax incentives, government financial assistance programs, or other government policies, and encouraging participation in groups like the California Sustainable Winegrowing Alliance and the California Association of Winegrape Growers are all ways to help increase individual vineyard and winery participation in the mitigation of the effects of climate change.


In general, it is predicted that California will see increased temperatures as well as decreases in soil and plant moisture, leading to overall greater stress to the grapes and a reduction in overall wine quality. Some regions of California already on the brink of being too hot for winegrape production may find themselves sooner than later unable to produce high quality wine, necessitating rapid change and adaptations not only at the individual vineyard level, but also at the state level.

In order to maintain high quality wine production in California for the foreseeable future, it is of utmost important for the growers and for the overall economic health of the state to start taking action. It will become necessary at the state level to create policies and programs to provide support for wine growers to make the necessary adaptations required to maintain economic health. With a $61.5 billion state-wide economic impact, addressing climate change effects on wine production and taking immediate action is of critical importance for the economic health of not only California, but also for the nation.

Selected References:

Cahill, K.N. Global Changes in Local Places: Climate Change and the Future of the Wine Industry in Sonoma and Napa, California. PhD Dissertation, Stanford University, 2009, 226, 3343947.

Cayan, D.R., Nicholas, K., Tyree, M., and Dettinger, M. 2011. Climate and Phenology in Napa Valley: A Compilation and Analysis of Historical Data. Napa Valley Vintners.

Diffenbaugh, N.S., White, M.A., Jones, G.V., and Ashfaq, M. 2011. Climate adaptation wedges: a case study of premium wine in the United States. Environmental Research Letters 6: 024024.

Gatto, J., Kim, B., Mahdavi, P., Namekawa, H., and Tran, H. 2009. The Future Impact of Climate Change on the California Wine Industry and Actions the State of California Should Take to Address It. International Policy Studies Program, Stanford University Report.

Hannah, L., Roehrdanz, P.R., Ikegami, M., Shepard, A.V., Shaw, M.R., Tabor, G., Zhi, L., Marquet, P.A., and Hijmans, R.J. 2013. Climate change, wine, and conservation. PNAS 110(17): 6907-6912.

Jones, G.V., Duff, A.A., Hall, A., and Myers, J.W. 2010. Spatial Analysis of Climate in Winegrape Growing Regions in the Western United States. American Journal for Enology and Viticulture 61(3): 313-326.

Lambert, K. 2013. An overview of climate change studies and impacts for Sonoma wine grape growers. Community Alliance with Family Farmers. (PDF)

Nemani, R.R., White, M.A., Cayan, D.R., Jones, G.V., Running, S.W. Coughlan, J.C., and Peterson, D.L. 2001. Asymmetric warming over coastal California and its impact on the premium wine industry. Climate Research 19: 25-34. (PDF)

White, M.A., Diffenbaugh, N.S., Jones, G.V., Pal, J.S., and Giorgi, F. 2006. Extreme heat reduces and shifts United States premium wine production in the 21st century. PNAS 103(30): 11217-11222.

3 comments for “The Effects of Climate Change on the California Wine Industry – My Latest Contribution to SOMM Journal

  1. October 15, 2015 at 7:06 pm

    Hi Becca. Very interesting post. Though, allow me to add a couple of questions and facts.
    It is said that some regions in CA may fall in the “too hot” category. How about finding out that there are grape growing regions already above that rather arbitrary limit? Let me tell you that the Central Texas area, where the Texas Hill Country AVA (THC) is, needs the Winkler scale to have an VIII zone to describe it (Winkler himself is not to blame, because he was cautious enough to say “more than” for his 5th zone).
    Let me tell you another thing. As we know, Vitis vinifera, the specie, comes from the stripe of land that goes from Armenia to current Iran in the Middle East. Have you wondered what’s the weather like over there, and how it has been over thousands of years?
    Well, you’d find that it’s pretty hot and dry and yet vines could thrive and develop there just fine without any human support. When THC weather is compared to those regions it can be seen how similar they are.
    It’s true that high temperatures negatively affect plants….in a cool region. They don’t affect them negatively in a hot region, but let me tell you why. Vines (and other plants) are loaded with a set of genes called “Heat Shock Genes” (HSG) that are triggered by temperatures above 95ºF. They express Heat Shock Proteins (HSP) that protect plant parts and molecules from the effects of higher temperatures. This is why we don’t see any heat related damage on plants in the THC after two months of maximum temperatures equal or exceeding 95ºF (and some getting 105ºF).
    Since HSP demand energy for their production, they are not present if temperatures are mild and this is why heat waves in cool climates find unprotected plants that later show the symptoms being hurt by heat.
    As a result, I think California vintners are going to be just fine no matter how hot it gets.
    Quality wise, I can’t convince anybody by writing, but if you can, make a virtual stroll around Texas wineries. Some may ship to Colorado!. You can start with ours, Fall Creek Vineyards.
    Sergio Cuadra
    Director of Winemaking
    Fall Creek Vineyards

    • Donn Rutkoff
      October 20, 2015 at 7:26 pm

      can you provide more info on the HSG and HSP? A lot more info., references, who and when discovered them. I am keenly interested, even tho I don’t own any vines.

      • November 5, 2015 at 10:54 am

        Sorry, I didn’t see your reply until today.
        There is a good paper about it that goes: “Heat Shock Protein Expression in
        Leaves of Cabernet Sauvignon” by Anne Morrell et al. published in Am. J. Enol. Vitic., Vol 48, No. 4, 1997.
        There is a very good review about it here: “Plant heat-shock proteins: A mini review” by Mohamed H. Al-Whaibi, published in Journal of King Saud University – Science (2011) 23, 139–150
        If you give me an address I can send them to you.

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