Climate change in recent times has become a major issue and talking point globally because of its effects on the environment and the repercussions this could be having or possibly have. The effects of climate change on Viniculture (wine production) are described in this article.
Grapevines (Vitis vinifera) are very responsive to their surrounding environment with a seasonal variation in yield of 32.5%. Climate is one of the key controlling factors in grape and wine production, affecting the suitability of certain grape varieties to a particular region as well as the type and quality of the wine produced. Wine composition is largely dependent on the mesoclimate and the microclimate and this means that for high quality wines to be produced, a climate-soil-variety equilibrium has to be maintained. The interaction between climate-soil-variety will in some cases come under threat from the effects of climate change. Identification of genes underlying phenological variation in grape may help to maintain consistent yield of particular varieties in future climatic conditions.
Climate data of the last 100 years has shown that global temperatures are gradually beginning to rise with a linear warming trend of 0.74 ⁰C per hundred years and this is anticipated to affect viticulture all over the world having both positive and negative effects on the various wine regions of the world. Despite climate change uncertainties, the gradual temperature rise is projected to continue in the future. This has meant growers will have to adapt to climate change using various mitigation strategies.
Adding to rising temperatures is the increase in carbon dioxide (CO2) concentration that is expected to continue to increase and have an effect on agroclimatic conditions. Shifts in the amount of, distribution, and seasonality of rainfall are also anticipated, as well as increases in surface level of ultraviolet UV-B radiation due to ozone layer depletion.
The advent of global warming is anticipated to raise average temperatures according to various climate models. These effects are expected to be more pronounced in the northern hemisphere and will change the margins and suitability for grape growing of certain cultivars.
Of all environmental factors, temperature seems to have the most profound effect on viticulture as the temperature during the winter dormancy effects the budding for the following growing season. Prolonged high temperature can have a negative impact on the quality of the grapes as well as the wine as it affects the development of grape components that give colour, aroma, accumulation of sugar, the loss of acids through respiration as well as the presence of other flavour compounds that give grapes their distinctive traits. Sustained intermediate temperatures and minimal day-to-day variability during the growth and ripening periods are favourable. Grapevine annual growth cycles begin in spring with bud break initiated by consistent day time temperatures of 10 degrees Celsius. The unpredictable nature of climate change may also bring occurrences of frosts which may occur outside of the usual winter periods. Frosts cause lower yields and effects grape quality due to reduction of bud fruitfulness and therefore grapevine production benefits from frost free periods.
Organic acids are essential in wine quality. The phenolic compounds such as anthocyanins and tannins help give the wine its colour, bitterness, astringency and anti-oxidant capacity. Research has shown that grapevines exposed to temperature consistently around 30 degrees Celsius had significantly lower concentrations of anthocyanins compared to grapevines exposed to temperatures consistently around 20 degrees Celsius. Temperatures around or exceeding 35 degrees Celsius are found to stall anthocyanin production as well as degrade the anthocyanins that are produced. Furthermore, anthocyanins were found to be positively correlated to temperatures between 16 – 22 degrees Celsius from veraison (change of colour of the berries) to harvest. Tannins give wine astringency and a “drying in the mouth” taste and also bind onto anthocyanin to give more stable molecular molecules which are important in giving long term colour in aged red wines. High tannin levels are positively correlated to commercial quality grading.
As the presence of phenolic compounds in wine are affected heavily by temperature, an increase in average temperatures will affect their presence in wine regions and will therefore affect grape quality.
The gradually increasing temperatures will lead to a shift in suitable growing regions. It is estimated that the northern boundary of European viticulture will shift north 10 to 30 kilometres (6.2 to 18.6 mi) per decade up to 2020 with a doubling of this rate predicted between 2020 and 2050. This has positive and negative effects, as it opens doors to new cultivars being grown in certain regions but a loss of suitability of other cultivars and may also risk production quality and quantity in general.
Altered precipitation patterns are also anticipated (both annually and seasonally) with rainfall occurrences varying in amount and frequency. Increases in the amount of rainfall have will likely cause an increase in soil erosion; while occasional lack of rainfall, in times when it usually occurs, may result in drought conditions causing stress on grapevines. Rainfall is critical at the beginning of the growing season for the budburst and inflorescence development while consistent dry periods are important for the flowering and ripening periods.
Increased CO2 levels will likely have an effect on the photosynthetic activity in grapevines as photosynthesis is stimulated by a rise in CO2 and has been known to also lead to an increase leaf area and vegetative dry weight. Raised atmospheric CO2 is also believed to result in partial stomatal closure which indirectly leads to increased leaf temperatures. A rise in leaf temperatures may alter ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCo) relationship with carbon dioxide and oxygen which will also affect the plants' photosynthesis capabilities. Raised atmospheric carbon dioxide is also known to decrease the stomatal density of some grapevine varieties.
UV-B radiation have also reached high levels and this known to impact upon chlorophyll and carotenoid concentration, which will decrease photosynthesis and may alter aroma compounds (Schultz, 2000). UV-B radiation also effects the activation of genes of the phytopropanoid pathway, which will affect the accumulation of flavanoids and anthocyanins and therefore affect the colour and composition of wine (Schultz, 2000).
Systems have been developed to manipulate the temperatures of vines. These include a chamber free system where air can be heated or cooled and then blown across grape bunches to get a 10 degree Celsius differential. Mini chambers combined with shade cloth and reflective foils have also been used to manipulate the temperature and irradiance. Using polyethylene sleeves to cover cordons and canes were also found to increase maximum temperature by 5-8 degrees Celsius and decrease minimum temperature by 1-2 degrees Celsius.