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GRAPEGROWING
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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
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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BY
Kimberly Nicholas Cahill,
Christopher B. Field Stanford University and Carnegie Institution for Science Stanford, CA kncahill@stanford.edu 
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.)
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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
Figure II. Historical temperature trends observed over the earth. Note
that warming (darker red colors) has been observed over nearly all
continents.
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