|Global warming has, for a significant time, been a topical subject which attracts the attention of different interest groups and the influence on agriculture can be substantial. Global warming is the result of increasing concentrations of the so called greenhouse gasses – carbon dioxide, methane, nitrogen sub oxide and ozone – which are liberated in the atmosphere. These gasses are absorbed in the atmosphere where the contained heat is then liberated. It leads to a temperature increase of the atmosphere. Different indicators are utilised to monitor the temperature change like the increase in soil surface temperature, atmospheric temperature, ocean temperature and sea levels and the decrease in the appearance of glaciers, snow coverage and ice formation.
Global agriculture industries had to adjust out of sheer necessity over years due to changing climatic conditions or natural disasters like droughts, floods, fires or diseases. This is also applicable to different international wine industries. Phylloxera as an insect or a fungal disease like downy mildew has for example nearly destroyed some wine industries if the necessary solutions were not found. Global warming is also a natural reality which needs to be addressed by different wine industries. Seeing that wine industries are only one of different agricultural industries, governments will be nationally responsible to attend to global warming.
The extremity of global warming.
If the average temperature of the global soil surface will be 1.5°C higher in 2030 than in 1900 different changes will occur. The suitability of certain cultivars in certain regions will for example change considerably. The cultivation of a climate sensitive cultivar like Pinot noir will for example be limited to only a few areas. Climate change may however also lead to a more reliable climate in certain regions with potentially better harvests and opportunities for new cultivars and wine styles. In Anatolia, Turkey, where the average maximum temperatures during the harvest range from 42 – 45°C and the annual rainfall is only slightly more than 100 mm, the cultivars Emir, Bogaskere and Okuzgozu are cultivated successfully.
Rainfall projections until 2030 indicate that drier winters but wetter summers can be expected due to global warming. This can lead to wetter conditions during ripening and the harvest, as well as possible floods during these periods. Seeing that the potential occurrence of fungal diseases can be promoted by these conditions, the managing of sound quality grapes, as well as the resulting wines will become a challenge. In general ripening will be earlier, harvest times will be compressed, an increased need for irrigation and increased frost risk will develop. More heat radiation as result of higher soil temperatures may lead to earlier ripening, grapes and juice with higher sugar and potassium concentrations and lower concentrations of total acid, nitrogen and flavour precursors. Viticulture practices to delay ripening can be applied as counter actions for the influence of high temperatures. Increased canopy to protect the grapes against heat waves can however create more humid conditions which will increase the pest and disease risks in the vineyard.
The management of vineyards during heat waves as result of global warming, in order to maintain the grape quality is one of the most important challenges. The South Australian definition of a heat wave is five successive days with a maximum daily temperature above 35°C or three successive days with a maximum daily temperature above 40°C.
Heat damage can influence the yield and quality of the grapes and cultivars also differ regarding the magnitude of the damage. The potential damage includes acid reductions and less colour development which cannot necessarily be compensated by additional irrigation. It is essential that the irrigation equipment of farms function well and is also maintained properly to manage heat waves successfully. Prior to heat waves the following actions must be implemented:
- Sufficient irrigation must be applied to saturate the root zone area.
- The possible application of a sunscreen spray like Surround™ must be considered. It must however be ensured that these products are approved for use on grapes for winemaking.
- Actions like leaf removal or canopy manipulation must be reconsidered if it may lead to increased berry exposure.
During heat waves sufficient irrigation should be applied to ensure that the turgor of the vines is recovered during the night prior to another heat wave. If overhead irrigation is applied it must be done overnight to avoid foliage burn. Sufficient irrigation after a heat wave is also important to replace lost soil moisture and decrease the soil temperature.
The later pruning of vineyards can also delay ripening, which can decompress the harvest and delay the maturation of certain cultivars to cooler periods (Krstic & Barlow, 2014).
Global warming will have an important influence on grapes, but cellar activities will also have to be adjusted to accommodate the changes in the grapes. The cooling burden of cellars will most probably be increased, but acid adjustments by means of acid additions or pH adjustment will also become more important. New additives, which are presently unknown, will most probably be developed to neutralise the negative impact of global warming.
Krstic, Mark & Barlow, Snow, 2014. Vintage 2030 and beyond: Producing quality wines in warmer times. Wine & Viticulture Journal, March/April 2014: 52 – 57.