Climate Change and Wine Production in Britain

The work presented has been researched and developed by Dr Paula Harrison and Dr Ruth Butterfield of the Environmental Change Institute, University of Oxford. The work was funded by the European Commission’s Environment programme as part of a large European consortium (16 Institutes from across Europe) which investigated the potential effects of climate change on agriculture in Europe. The project was called CLIVARA.

The scenarios used for the model results are projections for 2050 provided by the UK Meteorological Office’s HADCM2 model using a IS92a-type forcing scenario with a global mean temperature change of 2^o C. This assumes that the atmospheric CO₂ will have increased to 515ppmv (from a current level of 353ppmv).

The summer mean temperature is projected to be 2⁰C higher than at present in the south-east of England decreasing to 1.6^oC in Scotland (there is a gradient of warming from south-east to north-west). Winter temperature will again be 2 ⁰C higher than present in the SE decreasing to 1.8 ⁰C in Scotland based on this scenario (see Table 1). This is classified as a medium-high scenario, meaning it is a ‘high’ greenhouse gas forcing scenario which is the equivalent of a 1% increase per annum in equivalent carbon dioxide concentration. Lower forcing scenarios produce lower temperature increases for 2050.

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Currently wine production in this country is limited by first, summer temperatures, which are sometimes too cool and the season is too short for good maturation, and secondly the risk of spring frosts, which kill the growing buds. Climate change will mean an increase in summer temperatures, causing the vines to develop more quickly so that harvesting can happen earlier – before the onset of cooler wetter weather – meaning less fungal disease (which is damaging to the quality of the wine) and better harvesting conditions.

Climate change may therefore mean that the enterprise is less risky in the future.

Warmer summers will also allow the UK to grow a wider choice of varieties originating from southern Germany and central France (for 2050). As it gets warmer the choice will increase.

An increase in CO₂ concentration has a fertilizing effect on the crop by increasing the rate of photosynthesis (photosynthesis is more efficient at higher CO₂ concentrations). This means more carbohydrates are fixed by the crop resulting in larger grapes, possibly higher sugar comtent and higher overall yield per m².

The quality of wine is largely determined by the composition of the fruit. Sugar and pH level are the main parameters which determine the final alcohol content and its influence on wine flavour, while the acid content is important in the balance or acidity of the wine. At present only one study in the Chianti region, central Italy, on one variety has been conducted so it is difficult to estimate possible impacts on yields. A possible increase in sugar content (and therefore alcohol content) due to enrichment with CO₂ might be expected to result in a heavier wine.

In all cases in the Italy experiments an increase in temperature and CO₂ resulted in an increase in fruit dry matter (ie harvested yield). In general effects on yield and quality are expected to increase.

In the UK wine is already grown as far north as south Wales, Cheshire, West Yorkshire, and Humberside. According to our new grapevine model (calibrated to UK conditions) this northern limit will shift to southern coastal Scotland by 2050 (see maps). Bud burst and flowering will occur earlier by approximately 15 to 25 days (varying spatially). Maturity will occur between one month and a month and a half earlier in most places (from a median maturity date across the current region of mid October). Although the crop will develop more quickly (giving it less time to intercept solar radiation) the beneficial effects of elevated carbon dioxide result in 10 to 25% increases in yield. (The effects of changes in precipitation have not been analysed).

Figure 1 Results for the baseline climate (1961-90) from the grapevine model: (a) date of maturity; and (b) potential yield (fruit dry matter).

Figure 2 Changes in grapevine model output from the baseline climate (1961-90) under the core climate change scenarios: (top left) date of maturity for HCGG*; (top right) date of maturity for HCGS*; (bottom left) potential yield for HCGG; and (bottom right) potential yield for HCGS.

*The core scenarios were constructed from two experiments of the UK Hadley Centre’s unified GCM (HadCM2). These experiments were the greenhouse gas only experiment (abbreviated to HCGG) and the greenhouse gas plus sulphate aerosol experiment (abbreviated to HCGS).

Table 1 Overview of the core climate change scenarios used in the CLIVARA project.

3 Second Hadley Centre coupled ocean-atmosphere experiment for GHGs plus sulphate aerosols (SA)

Further information will be available (currently being printed):

Butterfield, R.E., Harrison, P.A., Orr, J., Gawith, M. and Lonsdale, K.G. (1999). Modelling climate change impacts on wheat, potato and grapevine in Great Britain. In: T.E. Downing, P.A. Harrison, R. E. Butterfield, and K.G. Lonsdale (Eds.) Climate Change, Climate Variability and Agriculture in Europe: An Integrated Assessment. Research Report No. 21, Environmental Change Institute, University of Oxford, Oxford. pp. 265-287.