Le 14/01/2010 à 15h00
bibliothèque Vallée, Gif sur Yvette
Climate, Grapes, and Wine: Structure and Suitability in a Variable and Changing Climate
Gregory V Jones
Southern Oregon University
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. To understand climate’s role in growing winegrapes and wine production one must consider 1) the weather and climate structure necessary for optimum quality and production characteristics, 2) the climate suitability to different winegrape cultivars, 3) the climate’s variability in wine producing regions, and 4) the influence of climate change on the structure, suitability, and variability of climate. 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 in the future.
To place viticulture and wine production in the context of climate suitability and the potential impacts from climate change, various temperature-based metrics (e.g., degree-days, mean temperature of the warmest month, average growing season temperatures, etc.) can be used for establishing optimum regions. For example, average growing season temperatures typically define the climate-maturity ripening potential for premium quality wine varieties grown in cool, intermediate, warm, hot, and very hot climates. For example, Cabernet Sauvignon is grown in regions that span from intermediate to hot climates with growing seasons that range from roughly 16.5-19.5ºC (e.g., Bordeaux or Napa). For cooler climate varieties such as Pinot Noir, they are typically grown in regions that span from cool to lower intermediate climates with growing seasons that range from roughly 14.0-16.0ºC (e.g., Northern Oregon or Burgundy). From the general bounds that cool to very hot climate suitability places on high quality wine production, it is clear that the impacts of climate change are not likely to be uniform across all varieties and regions, but are more likely to be related to climatic thresholds whereby any continued warming would push a region outside the ability to produce quality wine with existing varieties. For example, if a region has an average growing season average temperature of 15ºC and the climate warms by 1ºC, then that region is climatically more conducive to ripening some varieties, while potentially less for others. If the magnitude of the warming is 2ºC or larger, then a region may potentially shift into another climate maturity type (e.g., from intermediate to warm). While the range of potential varieties that a region can ripen will expand in many cases, if a region is a very hot climate maturity type and warms beyond what is considered viable, then grape growing becomes challenging and maybe even impossible.
While the average climate structure in a region determines the broad suitability of winegrape cultivars, climate variability influences issues of production and quality risk associated with how equitable the climate is year in year out. Climate variability in wine regions influences grape and wine production through cold temperature extremes during the winter in some regions, frost frequency and severity during the spring and fall, high temperature events during the summer, extreme rain or hail events, and broad spatial and temporal drought conditions. Climate variability mechanisms that influence wine regions are tied to large scale atmospheric and oceanic interactions that operate at different spatial and temporal scales. The most prominent of these is the large scale Pacific sector El Niño-Southern Oscillation (ENSO), which has broad influences on wine region climates in North America, Australia and New Zealand, South Africa, South America, and Europe. While each of the known climate variability mechanisms reveals some temporal periodicity, increases in climate variability for many wine regions have been observed. In general increases in climate variability would bring about greater risk associated climate extremes, which in turn would strain the economic viability of wine production in any region. Both observations and models indicate that climates experience changes in both the mean and the variability of temperatures in wine regions and elsewhere. For example, if the change response of a warming climate was only in the mean, then there would be less cold weather and more hot and record hot weather. On the other hand, increases in the temperature variance alone would result in more cold and hot weather and record conditions. However, evidence points to concomitant increases in both the mean and variance which would bring about less change for cold weather events and much more hot weather and record hot weather. For example, research has demonstrated that the European summer climate might experience a pronounced increase in year-to-year variability in response to greenhouse-gas forcing. Such an increase in variability might be able to explain the unusual European summer 2003, and would strongly affect the incidence of heat waves and droughts in the future. Evidence of changing climate variability in many other wine regions has also been found where the coefficient of variability in the growing season climates throughout the western US and many other wine regions globally has increased over the last 50 years.
On the global scale trends in wine region climates has found 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. The observed growing season warming rates for numerous wine regions across the globe during 1950-2000 averaged 1.3°C, with the warming 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. However, climate model projections by 2050 for the same wine regions predict growing season warming of an additional 1.5-2.5°C on average with spatial analyses showing the potential for relatively large latitudinal shifts in viable viticulture zones with increasing area on the poleward fringe in the Northern Hemisphere (NH) and decreasing area in the Southern Hemisphere (SH) due to the lack of land mass. Within regions, spatial shifts are projected to be toward the coast, up in elevation, and to the north (NH) or south (SH). Furthermore, climate variability analyses have shown evidence of increased frequency of extreme events in many regions, while climate models predict a continued increase in variability globally. In addition, phenological changes observed over the last 50 years for numerous locations and varieties globally indicate 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.
Overall, winegrapes are a climatically sensitive crop whereby quality production is achieved across a fairly narrow geographic range. In addition, winegrapes are grown largely in mid-latitude regions that are prone to high climatic variability that influence relatively large vintage differences. On top of the knowledge of the climate structure and variability in wine regions worldwide are the projected rate and magnitude of future climate change which will likely bring about numerous potential impacts for the wine industry, including – added pressure on increasingly scarce water supplies, additional changes in grapevine phenological timing, further disruption or alteration of balanced composition in grapes and wine, regionally-specific needs to change the types of varieties grown, necessary shifts in regional wine styles, and spatial changes in viable grape growing regions. While uncertainty exists in the exact rate and magnitude of climate change in the future, it would be advantageous for the wine industry to be proactive in assessing the impacts, invest in appropriate plant breeding and genetic research, be ready to adopt suitable adaptation strategies, be willing to alter varieties and management practices or controls, or mitigate wine quality differences by developing new technologies.
Gregory V. Jones is a professor and research climatologist in the Department of Environmental Studies 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 teaching and research interests include meteorology, 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 and has given hundreds of international, national, and regional presentations on climate and wine-related research. He is the author of numerous book chapters, including being a contributing author to the 2008 Nobel Peace Prize winning Intergovernmental Panel on Climate Change Report, and other reports and articles on wine economics, grapevine phenology, site assessment methods for viticulture, climatological assessments of viticultural potential, and climate change. He was recently named to Decanter Magazine’s 2009 Power List representing the top 50 most influential people in the world of wine and the Oregon Wine Press’s 2009 Wine Person of the Year.