Agriculture Reference
In-Depth Information
Any one of these could affect the suitability of a given cultivar for a particular
region or subregion.
Temperature records around the globe show that the average surface tem-
perature has increased by about 0.8
o
C during the 20th century, with most of this
increase occurring in the last 50 years of that century. Climate scientists have used
global circulation models (GCMs) to simulate this warming trend, which has
been attributed to an increase in the atmospheric concentrations of greenhouse
gases, produced mainly by human activities. Using these models, projections have
been made of future temperature increases and of other changes, as suggested in
the aforementioned points. Some winegrowing companies in Australia and over-
seas have acted on these projections and bought vineyards in cooler maritime
regions, or at higher elevations, in an attempt to mitigate any adverse effects of
climate change.
Nevertheless, it must be remembered that forecasts, for example, of an aver-
age temperature increase of 0.4
o
to 2
o
C
2
by 2030 are simply model projections,
with inherent uncertainties depending on how well the climate system, with
its complex biophysical processes and feedback mechanisms, is understood and
what the actual values of the numerous input variables will be during the next
17 years. Indeed, a recent analysis of the transient climate response to forcing
factors between 1970 and 2009 shows the actual temperature increase to be
tracking at the lower level of the ensemble of GCM projections (Otto et al.,
2013). Similarly, Hawkins (2013) concluded from a comparison of 42 GCM
projections with global temperature records that “global temperatures have not
warmed as much as the mean of the model projections in the past decade or
so,” an observation that is consistent with the “flat” trend in the earth's sur-
face temperature for the past 15 years (Anon., 2013). Climate change and its
potentialimpactsarediscussedinmoredetailin“ClimateChangeandPossible
Consequences” in chapter 6.
The effect of climate change on vine performance is not only confined to
an effect of temperature increase during the growing season on vine growth and
fruit ripening but also can involve the effect of higher atmospheric CO
2
con-
centrations on vine growth, possible increased stress in water-limited regions,
and possible changes in pest and disease pressure. The interaction of these
climate-related uncertainties reinforces the concept that site selection should be
based on a more comprehensive suite of factors than climate alone, as discussed
in the next section.
2
The wide range in the projected increase is due to the different GCMs used to make the
projections.
