1 Climate Change, Viticulture, and Wine
The grapevine is one of the oldest cultivated plants that, along with the process of making wine, have
resulted in a rich geographical and cultural history of development (Johnson, 1985; Penning-Roswell, 1989;
Unwin, 1991). Today’s viticultural regions for quality wine production are located in relatively narrow
geographical and therefore climatic niches that put them at greater risk from both short-term climate variability
and long-term climate change than other more broad acre crops. In general, the overall wine style that a region
produces is a result of the baseline climate, while climate variability determines vintage quality differences.
Climatic changes, which influence both variability and average conditions, therefore have the potential to bring
about changes in wine styles. Our understanding of climate change and the potential impacts on viticulture and
wine production has become increasingly important as changing levels of greenhouse gases and alterations in
Earth surface characteristics bring about changes in the Earth’s radiation budget, atmospheric circulation, and
hydrologic cycle (IPCC, 2001). Observed warming trends over the last hundred years have been found to be
asymmetric with respect to seasonal and diurnal cycles with greatest warming occurring during the winter and
spring and at night (Karl et al., 1993; Easterling et al., 2000). The observed trends in temperatures have been
related to agricultural production viability by impacting winter hardening potential, frost occurrence, and growing
season lengths (Carter et al., 1991; Menzel and Fabian, 1999; Easterling et al., 2000; Nemani et al., 2001;
Moonen et al., 2002; Jones, 2005c).
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 (Gladstones,
1992). For example, average growing season temperatures typically define the climate-maturity ripening
potential for premium quality wine varieties grown in cool, intermediate, warm, and hot climates (Jones, 2006;
Figure 1). 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 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 hot climate maturity type and warms beyond
what is considered viable, then grape growing becomes challenging and maybe even impossible. Furthermore,
observations and modeling has shown that climate change will not just be manifested in changes in the mean,
but also in the variance where there are likely to be more extreme heat occurrences, but still swings to
extremely cold conditions. Therefore, even if average climate structure gets better in some regions, variability
will still be very evident and possibly even more limiting than what is observed today.
Overall the wine quality impacts and challenges related to climate change and shifts in climate maturity
potential will likely be evidenced mostly through more rapid plant growth and out of balance ripening profiles.
For example, if a region currently experiences a maturation period (véraison to harvest) that allows sugars to
accumulate to favorable levels, maintains acid structure, and produces the optimum flavor profile for that variety,
then balanced wines result. In a warmer than ideal environment, the grapevine will go through its phenological
events more rapidly resulting in earlier and likely higher sugar ripeness and, while the grower or winemaker is
waiting for flavors to develop, the acidity is lost through respiration resulting in unbalanced wines without greater
after-harvest inputs or adjustments in the winery.