Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
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March/April 2008
subject, when they have pressing issues with their own operations on the ground. This article attempts to answer some questions that growers and winemakers must address as they try to understand and evaluate the application of climate science to winegrowing.
WHAT IS CLIMATE? At any location, the daily, seasonal, and annual patterns of temperature, precipitation, wind, and humidity characterize the weather.Aweather forecast is useful to address questions like, "Should I bring an umbrella tomorrow?"
Climate is the statistical summary of weather over 10 to 30 years. In addition to average properties, climate covers questions such as, "How many days over 100°F are there in a typical growing season? What's the difference between January and July likely to look like here? What grape varieties are likely to do well here, based on where they thrive in
other parts of the world?"
WHAT DRIVES THE EARTH'S CLIMATE? Essentially, the temperature of the Earth is controlled by the balance between input from the sun (some of which our eyes can see as visible light) and reflection and heat radiation from the ground. Clouds, ice, and snow reflect much of the energy from the sun. Land and water absorb most of the high-energy, shortwavelength energy from the sun, and then emit longer-wavelength energy as heat, with hotter surfaces emitting more.
This heat energy can't be seen with our eyes, unless assisted by thermal imaging technology such as night-vision binoculars. The heat energy is released in the direction of space, but
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Kimberly Nicholas Cahill,
Christopher B. Field
Stanford University and
Carnegie Institution for Science
Stanford, CA
limate is clearly important to the viability and success of the wine industry worldwide. A map of the world's winegrowing regions shows that large-scale cultivation of grapevines happens in particular places and not others. We know that these places share certain climatic features, such as winters without killing freezes and generally moderate summer temperatures.
Growers and connoisseurs around the world are familiar with generalizations about both climate and winegrowing (for example, you can expect about 110 days from bloom to harvest) and specifics about certain regions or grape varieties (for example, warm Rutherford is well-suited to producing highquality Cabernet Sauvignon, while Pinot Noir thrives in cooler Carneros).
What, then, warrants all the recent attention to the issue of global climate change, including several articles in PWV? (Robinson, May/June 2007; Jones, July/August 2007; Smart, January/ February 2005.)
Aren't growers accustomed to dealing with changes in weather conditions as part their everyday job? How can we know what the climate is going to be like in the future, when weather forecasts are famously fickle? How is it possible that humans could be affecting something as vast as the climate system of the entire planet?
These are frequent questions from those in the wine industry, who have reason to view climate change as a huge-scale and far-off
Temperture Trend around the globe
Figure II. Historical temperature trends observed over the earth. Note that warming (darker red colors) has been observed over nearly all continents.