Thursday, April 20, 2006
Climate change and wine: Observations, predictions, and potential implications
Grape growing and wine production are largely weather and climate driven enterprises. Extreme weather events such as hard winter freezes, spring or fall frosts, and hail can result in major losses in a given vintage, while long term changes in climate can result in changes in ripening potential and the style of wine that a region can produce. In addition, grapevines are typically grown in regions and under conditions that are considered narrow for a specific variety's optimum quality, ultimately putting it at a greater potential risk from climatic variations and change. This presentation summarizes a series of regional and global studies that examine observed climate structure, variability, and trends, along with climate model projections in relation to viticultural viability and quality issues.
On the global scale, recent research—the first to examine the effects of both past and future climate change on the world's high quality wine regions—finds that warmer growing season climates have allowed many regions to produce better wine, while future climate projections indicate more benefits for some regions and challenges for others. Observed growing season warming rates during 1950-2000 in 27 regions averaged 2.3°F, while climate model projections for 2000-2049 predict growing season warming of an additional 3.6°F. In addition, phenological changes observed for numerous locations and varieties in Europe indicate (over the last 50 years) that grapevines have responded to the observed warming with earlier events (bud break, bloom, véraison, and harvest) and shorter intervals between events that range from 6-17 days depending on variety and location.
In the western United States grapes are grown over an extensive north-south gradient of climate types. Recent research has examined the structure, variability, and trends in climate for the principal grape growing regions in California, Oregon, and Washington by analyzing dormant season, growing season and ripening period rainfall, temperatures and degree-days, annual and seasonal frost frequencies, the dates of last spring and first fall frost occurrence, and the length of the frost-free period for 1948-2002. Results reveal that, on average, most regions have experienced warmer growing seasons, driven mostly by changes in minimum temperatures, with greater heat accumulation, a decline in frost frequency that is most significant in the dormant period and spring, earlier last spring frosts, later first fall frosts, and longer frost-free periods. For the grape growing regions in eastern Washington and Oregon, this has translated into a growing season warming of 1.2°F driven mostly by significant changes in minimum temperatures which has resulted in an increase of360 growing degree-days over 1948-2002. In addition, the warming has resulted in 14 fewer days below freezing on an annual basis (most occurring during the spring) with a 25 day longer frost-free period driven by a 16 day earlier average last frost in the spring and a 9 day later first frost in the fall. Examining winter extreme temperatures in these same regions shows a decline in the occurrence and frequency of the number of days below 15°F. While many of these trends may have been beneficial to grape growing and wine production in the western United States, an examination of possible future climate change in these same regions indicate an average growing season warming of 3.1°F in the next 50 years.
Depending on the seasonal structure and magnitude of climate change in the future, important issues for the wine industry include potential shifts in regional varietal viability and achieving optimum varietal ripeness and wine balance in a warmer environment. While much uncertainty still exists in the magnitude and rate of climate change, the wine industry will need to assess the impacts, adapt accordingly by altering varieties and management practices, or mitigate wine quality differences by developing new technologies. Other potential issues affecting grape and wine quality include changes in vine growth due to a higher CO 2 concentration, added moisture stresses in water-limited regions, and changes in the presence or intensity of pests and vine diseases.
Gregory V. Jones is an associate professor and research climatologist in the Geography Department at Southern Oregon University who specializes in the study of how climate variability and change impact natural ecosystems and agriculture. He holds a BA and Ph.D. from the University of Virginia in Environmental Sciences with a concentration in the Atmospheric Sciences. His research interests include climatology, hydrology, and agriculture; phenology of plant systems; biosphere and atmosphere interactions; climate change; and quantitative methods in spatial and temporal analysis. His dissertation was on the climatology of viticulture in Bordeaux, France with a focus on the spatial differences in grapevine phenology, grape composition and yield, and the resulting wine quality. He conducts applied research for the grape and wine industry in Oregon, has given hundreds of international, national, and region presentations on wine-related research, and is the author of numerous book chapters, reports, and articles on wine economics, grapevine phenology, site assessment methods for viticulture, climatological assessments of viticultural potential, and climate change.