Introduction

Viticulture is changing substantially as the world warms. Phenology is advancing (Quénol et al., 2017) and growing seasons are lengthening (Jones and Davis, 2000), all of which can impact yield, quality and wine characteristics (Jones, 2007; Quénol et al., 2017). Wine producers in traditional viticulture regions in Europe are concerned with mitigating the negative impact on their crops from factors such as heat stress and drought (Jones and Schultz, 2016) and are considering how to adapt to future climate change (Neethling et al., 2017). In contrast, other regions' climates are becoming more favourable for viticulture as the viticulture belt shifts progressively northward in the northern hemisphere and southward in the southern hemisphere (Nesbitt, 2016).

Climate change has already benefitted viticulture in England and Wales (Nesbitt et al., 2018), with a fivefold increase in vineyard hectarage from 2004 to 2021 (approximately 3800 ha; WineGB, 2021). This has been accompanied by a move away from hardy German grape varieties that are suited to the coldest possible climates under which grapes can grow, such as Muller-Thurgau, towards French varieties such as Chardonnay, Pinot noir and Pinot meunier that require warmer growing season temperatures (Ashenfelter and Storchmann, 2016; Nesbitt et al., 2019). Chardonnay is one of the most popular white wine grape varieties, accounting for around 6.7 % (332,000 hectares) of all vineyards worldwide (Easton, 2015). It can produce popular ‘everyday' wines as well as some of the greatest wines that fetch some of the highest prices at auction.

The potential for UK viticulture and wine production has been investigated previously. Georgeson and Maslin (2017) used a ‘middle-of-the-road scenario’ climate model (a further 2.2 °C warming and 5.6 % increase in rainfall) to predict the UK’s suitability for new vineyards of nine grape varieties in 2100. Their map of potential Chardonnay growing areas in 2100 included large areas of the Midlands and East of England, though they warned that production of high-quality sparkling wine in Southern England might be threatened by temperatures that are too high. Another approach applied Jones’ climate/maturity threshold for Chardonnay of a 14 °C Growing Season Temperature (GST; mean temperature from 1 April to 31 October) (Jones, 2006) to the UK (Nesbitt, 2016). Nesbitt (2016) found that only 10 % of vineyards (≥1 ha) in England and Wales, as of November 2015, were within areas with mean GST > 14 °C for the 30-year period from 1981 to 2010.

Nesbitt et al. (2018) considered UK wine production from a yield perspective and concluded that a significant number of existing UK vineyards were sub-optimally located. They also reported that the transition to French grape varieties had made UK wine production more susceptible to inter-annual variations in climate, threatening the sustainability of the industry. The sustainability of yield is thus, in large part, dependent on having a climate with an average GST that is considerably above the lower threshold of its range for the grape variety so that ripe berries are still produced in relatively cold years.

Little research, however, has considered whether the UK (or other cool regions that are warming) will have the potential to produce high-quality single-variety still wines equivalent to the Chardonnay and Pinot noir wines of Burgundy. The Burgundy region of Chablis is of particular interest. Its white wines are produced exclusively from Chardonnay grapes, and it is the most northerly major producer (47°49'19"N latitude), and the nearest area to England, of non-sparkling Chardonnay wine.

English wine producers are already using Chardonnay extensively, it and Pinot noir being the most-grown grape varieties in the UK (WineGB, 2020). This is almost entirely to produce sparkling wines, with Chardonnay usually blended with Pinot noir and Pinot meunier to make a classic Champagne-style wine, which requires grapes that are only just barely ripe (Clarke, 2020). Doubt remains, however, as to how consistently the UK will be able to produce high-quality still wine from these varieties over the coming decades (Nesbitt et al., 2016). Chardonnay is rarely used to make still white wines in the UK, though the proportion of still wine has been steadily increasing since the exceptional high-quality and high-yielding vintage of 2018 (Olsen, 2021; WineGB, 2021).

The Chablis vintage model is an empirical model of inter-annual variation in Chablis vintage quality (Biss and Ellis, 2021). It estimates the vintage quality of still Chardonnay wine as a function of mean temperature from April to September (curvilinear relation, maximum score at 16–17 °C), mean minimum temperature in September (cool night index (CNI) during ripening; negative relation), and total rainfall from June to September (from around flowering and fruitset to harvest; negative relation). That model is applied here to identify climatically suitable sites for the production of still Chardonnay wine in the UK for the periods 1981–2000, 2010–2019, and out to 2040–2059 to understand the potential for producing high-quality still Chardonnay wine in the UK. No consideration of soils, topography, or viticultural and winemaking skill is made as part of this paper.

Results

1. Change in Model climate indices from 1981–2000 to 2010–2019

1.1. CNI versus TmeanApr-Sep

From 1981–2000 to 2010–2019, CNI rose by 0.48 °C (SD 0.28 °C) and Tmean_Apr-Sep by 0.55 °C (SD 0.11 °C) for the UK as a whole. The increase in CNI, however, was more varied geographically than for Tmean_Apr-Sep, becoming progressively greater going north and west from the South-East and East of England (Figure 2a and Table S2). In certain isolated areas, CNI decreased in absolute terms (red and reddish areas in Figure 2a).

For example, while Tmean_Apr-Sep rose in North West England and East of England by 0.5 and 0.7 °C, respectively, CNI increased by 0.5 °C in North West England but only by 0.1 °C in the East of England (Table S2). This distribution was consistent with changes in the Diurnal Temperature Range (DTR) for September (Figure 2b), where mean maximum temperatures increased more than mean minimum temperatures in the East of England, South East England, and the Midlands, but vice versa for Cornwall, North West England, Northern Ireland, Western and Northern Scotland, and South Wales.

When considering inter-annual variation rather than climatic trends, it is important to note that the two variables did not always move in the same direction or with the same magnitude of change. That is, higher Tmean_Apr-Sep did not necessarily translate into higher CNI. For example, the 2018 season value for Tmean_Apr-Sep was 1.6 ° C warmer than the mean for 1981–2000, yet CNI was 0.3 °C cooler (mean of the top 30 counties, Table S3).

1.2. Precipitation (PJun-Sep)

Rainfall (P_Jun-Sep) increased from 1981–2000 to 2010–2019 by between 2.0 and 21.9 %. The increase was small (< 10 %) in southern regions and large (> 20 %) in the North East and North West of England (Table S2).

Figure 2. Change in climate indices from 1981–2000 to 2010–2019 in the UK.

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(a) change in mean CNI as a percentage of change in mean Tmean_Apr-Sep; (b) change in mean Diurnal Temperature Range (DTR) for the month of September. Colours are graduated in the maps, from red to black to green (and to blue in (a)), to reflect the non-discrete variation in change.

2. Applying the Model retrospectively

2.1. The UK, 1981–2000

According to the Model, only areas in inner London and around Heathrow airport in west London were capable, on average, of producing Good Chardonnay still wine (“Chardonnay wine”) between 1981 and 2000 (Figure 3a). The maximum score achieved was 6.5, but only 0.2 % of UK land achieved a score of ≥ 6 (Table 3). Existing vineyards would have experienced, on average, Tmean_Apr-Sep that was too cold compared to the ideal Chablis climate, though CNI and P_Jun-Sep were within the ideal range (empty triangles, Figure 4).

2.2. The UK in 2010-19

The climate for the period 2010 to 2019 was, on average, incapable of producing Good Chardonnay wine over 98 % of the UK land area (Figure 3b and Table 3).

Places that would have been suitable for producing Good Chardonnay wine between 2010 and 2019 would be land in and around London (including parts of south Hertfordshire, north Surrey, and south Essex), areas that fringe the Thames Estuary (south Essex and north Kent), and some isolated areas in the East of England and Midlands, such as in Cambridgeshire, Suffolk, and Oxfordshire (Figure 3b). Existing vineyards would have experienced similar CNI and P_Jun-Sep in 2010–2019, and marginally better Tmean_Apr-Sep, compared to 1981–2000, but still c. 0.5 to 1.0 °C lower than the ideal climate projected by the Model (solid circles, Figure 4).

The mean score for 2010–2019 (Table 3) hides significant vintage score variation: 2012 would likely have been Poor everywhere (maximum score achieved for any one 5 × 5 km grid square 5.9), 2018 Excellent at the best sites (maximum score 9.0), with the other eight years scoring in-between (maximum score 6.8 to 7.3). The highest-scoring existing vineyard of size (> 1 hectare) for 2010–2019 was Forty Hall Vineyard in Enfield, London (its grid square scoring a mean 6.6 for the 2010–2019 period; 4.7 for 2012, 8.4 for 2018, and 5.9 to 6.8 for the other eight vintages).

2.2.1. The 2012 vintage

No land was deemed capable of producing Good Chardonnay wine in 2012 (Figure 3c). Of the sizeable vineyards (> 1 hectare), Forty Hall Vineyard came closest (4.7). For all existing vineyards, 2012 would have been too cold and wet (crosses, Figure 4b).

Figure 3. Chardonnay still wine quality score estimates across the UK provided by the Chablis vintage model.

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(a) 1981 to 2000 (percentage of UK land where wine quality rated Good 0.2 %, Excellent 0.0 %); (b) 2010–2019 (Good 1.8 %, Excellent 0.0 %); (c) 2012 (Good 0.0 %, Excellent 0.0 %); (d) 2018 (Good 25.2 %, Excellent 8.8 %). Green is Good; purple is Excellent.

Table 3. Estimates of UK vintage scores for Chardonnay still wine quality and percentage of UK land scoring ≥ 6 (i.e., Good or Excellent) from the Chablis vintage model for 1981 to 2000, 2010 to 2019, and RCP 4.5 projections (UKCP18) for 2040–2059 at the 5th, 50th and 95th percentiles; CNI2 indicates estimates with a modified CNI (see text). The two right-hand columns show the highest-scoring existing UK vineyard (> 1 ha) and its score in each period or scenario.

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Period		Mean Scorea	Max Scoreb	UK Land (%) scoring ≥ 6c		Highest-Scoring Vineyard (> 1 ha)d	Top Vineyard Scoree
1981 to 2000		–7.4	6.5	0.2	Forty Hall Vineyard, Enfield, Londonf		5.3
2010 to 2019		–4.8	7.2	1.8	Forty Hall Vineyard, Enfield, Londonf		6.6
2040–2059 (RCP 4.5)	5 %	–5.6	7.1	1.0	Forty Hall Vineyard, Enfield, Londonf		6.2
	5 % (CNI2)	–5.8	7.0	0.8	Forty Hall Vineyard, Enfield, Londonf		6.1
	50 %	–1.0	7.5	20.7	Bothy Vineyard, Oxfordshire		7.4
	50 % (CNI2)	–0.9	8.3	24.8	Bardsley Farms Vineyard, Kent		8.2
	95 %	2.3	7.7	39.1	Wolf Oak Vineyard, Berkshire		7.6
	95 % (CNI2)	2.7	9.1	42.4	Mereworth Wines, Kent		9.1

^a Mean of mean vintage score (for the stated period) across all 5 × 5 km grid squares.

^b Maximum mean score (for the stated period) achieved by any one 5 × 5 km grid square.

^c Percentage of UK 5 × 5 km grid squares with a mean score equal to or greater than 6.

^d Highest-scoring vineyard based on the mean score of its 5 × 5 km grid square for a stated period

^e Mean score for a stated period of highest-scoring vineyard’s 5 × 5 km grid square.

^f The administrative area designated London is the Greater London region, which includes considerable areas of farmland and woodlands at its extremities which are protected from urban development. Hence, there are suitable sites for viticulture, which benefit already from the urban heat island effect, and with a considerable number of potential customers for their wines nearby. The Forty Hill vineyard, for example, is only 20 km north of the centre of London.

Figure 4. Comparison of climates for the top 30 UK counties (Table 4) in 1981–2000, 2010–2019, 2012 and 2018, and the Chablis region, France, from 1963 to 2018. Contours (vintage score) and dashed lines from Biss and Ellis (2021).

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2.2.2. The 2018 vintage

Estimates of the 2018 vintage were exceptional (Figure 3d) because the weather that year had the potential to produce high-quality Chardonnay wine throughout most of England (34.0 percent of the UK land area). In fact, the weather in 2018 had the potential to produce Excellent Chardonnay wine across a greater area of the UK (8.8 % of UK land area) than all but one (95th percentile projection with CNI2) of the mean projections for 2040–2059 considered in this study (see below). The highest-scoring existing vineyard of size (> 1 hectare) was Laithwaites’ Windsor Great Park Vineyard in Berkshire (8.8).

Near-ideal high-quality Chardonnay wine production conditions were met by the majority of existing vineyards in 2018: Tmean_Apr-Sep was sufficiently high whilst CNI remained below 10.75 °C (open squares, Figure 4a). Moreover, P_Jun-Sep was some 50 to 100 mm lower than is typical for the Chablis region (open squares, Figure 4b).

3. Alternative method: applying a 14 °C GST threshold

According to the application of a 14 °C GST threshold (Jones, 2006), Chardonnay viticulture was not possible, on average, throughout most of the UK during the 1981 to 2000 period except for in and around London, parts of the Thames Estuary and a small part of southern Hampshire (Figure 5a). The 2010 to 2019 period was, on average suitable for Chardonnay viticulture in large parts of the South East and East of England and along the Severn Estuary (Figure 5b). The 2012 vintage was similar in distribution to 1981 to 2000 (Figure 5c), whereas the 2018 vintage stood out for the considerable extent of land suitability, accounting for 34.1 percent of the UK and covering most of England as far north as Lancashire and Yorkshire (Figure 5d).

Figure 5. UK land suitability (in green) for Chardonnay viticulture, based on 14 °C GST threshold (Jones, 2006).

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a) 1981 to 2000 (1.1 % of UK area); b) 2010 to 2019 (11.0 %); c) 2012 (0.7 %); d) 2018 (34.1 %).

4. Medium-term projections for the UK in 2040–2059

4.1. 5th percentile projection

Under the RCP 4.5 5th percentile projections for 2040 to 2059, the vintage score estimates provided by the Model were similar to those presented in Figure 3b for the 2010–2019 period, with only 1.0 % of UK land area capable of producing Good Chardonnay wine (Table 3). Hence this projection is not described in detail.

The 5th percentile mean scores for the top 30 counties (by existing vineyard area) for 2040–2059 were all < 6, marginally lower than, or similar to, the 2010–2019 period (Table 4).

4.2. 50th percentile projection

Applying the median RCP 4.5 projections resulted in a considerable area of climatically-suitable UK land (20.7 % Good, 0.0 % Excellent) with the greatest potential vintage scores for Chardonnay still wine focused around the South East and East of England (Figure 6a).

The majority of existing vineyards from the top 30 counties provided Good Chardonnay wine in 2040–2059, narrowly missing or just clipping the boundary for producing Excellent Chardonnay wine because CNI was too high (solid circles, Figure 7a). Rainfall (P_Jun-Sep) was not a limiting factor to high vintage scores (solid circles, Figure 7b).

Eastern and South East England (especially Essex and Kent) had the most suitable climate for producing Good to Excellent Chardonnay wine (Table 4). However, areas of high-quality potential wine production were found throughout the South of England, Midlands and East of England, including some counties with relatively small areas of vineyard at present (as of November 2020), such as Buckinghamshire, Cambridgeshire, Hertfordshire, Suffolk, and Worcestershire.

The lower limit of the estimated 10-year inter-annual range was between 4.0 and 5.0 for most counties in South East England and East of England with currently large areas of planted vineyards (>100 ha), namely East Sussex, Essex, Kent, and West Sussex (Table 4). All counties outside of South East England and East of England, except for Gloucestershire (3.6) and Somerset (3.1) in South West England and Worcestershire (4.1) in the West Midlands, provided a lower limit score below 3.0 (Table 4).

Table 4. Estimated mean vintage scores (1981–2000; 2010–2019; 2040–2059) and ranges (2010–2019 only; in parentheses) with estimated 10-year inter-annual variation (2040–2059 only; in parentheses) for Chardonnay still wine for the 30 UK counties with the largest areas of planted vineyards. Scores (out of 10, where 6.0–8.0 is Good and >8.0 Excellent) provided by the Chablis vintage model (Biss and Ellis, 2021) with historical weather records (1981–2000; 2010–2019), and projected climate change (2040-2059; RCP 4.5 at the 5th, 50th and 95th percentiles). Vintage scores for each of the 819 constituent vineyards are provided in Table S4.

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			Mean Vintage Score
		Area of Planted Vines	1981–2000	2010–2019b	2040–2059 (RCP 4.5)a
County	Region	(ha)			5 % CNI	5 % CNI2	50 % CNI	50 % CNI2	95 % CNIc	95 % CNI2c
Berkshire	South East England	34.4	2.0	4.1 (0.4 – 8.0)	3.8 (0.4 – 7.7)	3.6 (0.3 – 7.6)	6.5 (3.6 – 8.7)	6.9 (4.1 – 9.1)	7.3 (5.0 – 7.7)	8.5 (6.1 – 8.9)
Buckinghamshire	South East England	19.8	2.5	4.7 (1.3 – 8.3)	4.2 (1.0 – 8.0)	4.0 (0.8 – 7.8)	6.6 (3.9 – 8.7)	7.1 (4.4 – 9.2)	7.2 (5.0 – 7.4)	8.4 (6.2 – 8.7)
Cambridgeshire	East of England	10.0	2.7	5.0 (2.0 – 8.0)	4.2 (1.0 – 7.9)	4.1 (0.9 – 7.8)	6.6 (3.8 – 8.6)	7.1 (4.3 – 9.1)	7.2 (5.0 – 7.6)	8.4 (6.2 – 8.8)
Cornwall	South West England	30.4	0.6	2.0 (–1.8 – 5.9)	2.2 (–0.8 – 6.3)	1.8 (–1.4 – 5.9)	5.1 (2.1 – 7.3)	4.8 (1.8 – 7.1)	6.2 (3.4 – 6.7)	6.2 (3.4 – 6.7)
Devon	South West England	84.4	1.2	2.6 (–1.8 – 6.3)	2.7 (–0.6 – 7.0)	2.4 (–1.0 – 6.7)	5.5 (2.4 – 8.0)	5.7 (2.6 – 8.2)	6.5 (3.7 – 7.3)	7.2 (4.4 – 8.0)
Dorset	South West England	73.2	0.8	2.7 (–1.7 – 6.6)	2.5 (–1.1 – 6.8)	2.2 (–1.1 – 6.5)	5.5 (2.5 – 8.3)	5.7 (2.7 – 8.5)	6.8 (4.0 – 7.8)	7.6 (4.8 – 8.6)
East Sussex	South East England	379.9	2.9	4.7 (2.1 – 7.7)	4.5 (1.5 – 8.1)	4.4 (1.4 – 8.0)	6.6 (4.1 – 8.5)	7.2 (4.6 – 9.1)	6.9 (4.8 – 7.0)	8.2 (6.1 – 8.3)
East Yorkshire	Yorkshire and Humber	8.6	–2.1	1.1 (–3.6 – 5.1)	–0.2 (–4.1 – 4.3)	–0.4 (–4.3 – 4.1)	3.7 (0.1 – 6.7)	3.9 (0.3 – 6.9)	5.9 (2.8 – 7.5)	6.6 (3.4 – 8.2)
Essex	East of England	249.1	3.9	5.8 (3.4 – 8.2)	5.2 (2.4 – 8.3)	5.1 (2.4 – 8.2)	7.0 (4.8 – 8.5)	7.6 (5.3 – 9.1)	7.0 (5.4 – 7.0)	8.3 (6.6 – 8.2)
Gloucestershire	South West England	84.7	2.5	4.3 (0.4 – 7.5)	4.0 (0.7 – 7.9)	3.7 (0.5 – 7.6)	6.4 (3.6 – 8.6)	6.8 (4.0 – 9.0)	7.0 (4.6 – 7.6)	8.1 (5.7 – 8.7)
Hampshire	South East England	340.3	2.6	4.3 (0.8 – 7.8)	4.3 (1.1 – 8.1)	4.1 (1.0 – 8.0)	6.6 (3.9 – 8.7)	6.9 (4.2 – 9.1)	7.1 (4.8 – 7.4)	8.0 (5.7 – 8.3)
Herefordshire	West Midlands	31.0	1.8	3.6 (–0.7 – 6.9)	3.2 (–0.3 – 7.2)	3.0 (–0.5 – 7.0)	6.0 (2.9 – 8.4)	6.4 (3.4 – 8.8)	7.0 (4.4 – 7.9)	8.1 (5.5 – 9.0)
Hertfordshire	East of England	12.2	2.7	5.0 (2.0 – 8.1)	4.2 (1.0 – 7.8)	4.0 (0.9 – 7.7)	6.6 (3.9 – 8.5)	7.0 (4.3 – 9.0)	7.2 (5.0 – 7.4)	8.3 (6.1 – 8.5)
Isle of Wight	South East England	10.2	4.5	5.7 (3.5 – 7.8)	5.7 (3.4 – 8.5)	5.5 (3.2 – 8.3)	6.8 (4.9 – 8.0)	6.9 (5.1 – 8.1)	5.9 (4.6 – 5.4)	6.4 (5.1 – 5.9)
Kent	South East England	1012.9	3.4	5.2 (2.7 – 7.8)	4.9 (2.2 – 8.2)	4.8 (2.1 – 8.2)	6.9 (4.6 – 8.6)	7.6 (5.4 – 9.3)	7.0 (5.2 – 7.0)	8.6 (6.8 – 8.6)
Lincolnshire	East Midlandsd	16.1	–0.2	2.8 (–1.0 – 6.6)	1.7 (–1.9 – 6.0)	1.6 (–2.1 – 5.8)	5.1 (1.9 – 7.8)	5.4 (2.2 – 8.1)	6.8 (4.0 – 8.0)	7.7 (4.8 – 8.8)
Monmouthshire	Wales	19.6	1.6	3.3 (–1.2 – 6.6)	2.8 (–0.8 – 7.0)	2.6 (–1.0 – 6.8)	5.6 (2.3 – 8.2)	5.9 (2.7 – 8.5)	6.7 (3.8 – 7.7)	7.6 (4.7 – 8.6)
Norfolk	East of England	52.0	2.4	4.8 (2.1 – 7.4)	3.9 (0.9 – 7.5)	3.8 (0.8 – 7.4)	6.3 (3.8 – 8.3)	6.9 (4.3 – 8.9)	7.0 (4.9 – 7.3)	8.3 (6.2 – 8.6)
North Yorkshire	Yorkshire and Humbere	10.7	–1.1	1.5 (–3.6 – 5.6)	0.7 (–3.3 – 5.1)	0.5 (–3.5 – 4.9)	4.3 (0.7 – 7.2)	4.4 (0.8 – 7.4)	6.3 (3.1 – 7.8)	6.8 (3.6 – 8.3)
Northamptonshire	East Midlands	14.4	0.4	3.3 (–1.0 – 7.4)	2.3 (–1.5 – 6.6)	2.2 (–1.6 – 6.4)	5.5 (2.2 – 8.2)	5.9 (2.6 – 8.5)	7.0 (4.2 – 8.0)	8.0 (5.1 – 9.0)
Nottinghamshire	East Midlands	9.0	1.7	4.0 (–0.1 – 7.6)	3.4 (–0.3 – 7.5)	3.2 (–0.5 – 7.3)	6.1 (2.9 – 8.7)	6.4 (3.2 – 8.9)	7.2 (4.5 – 8.1)	7.9 (5.3 – 8.9)
Oxfordshire	South East England	41.8	1.5	3.8 (–0.1 – 7.8)	3.4 (–0.1 – 7.4)	3.3 (–0.2 – 7.3)	6.3 (3.3 – 8.6)	6.9 (3.9 – 9.2)	7.3 (4.8 – 7.9)	8.7 (6.2 – 9.2)
Shropshire	West Midlands	18.5	–0.6	1.6 (–3.0 – 5.3)	1.0 (–3.1– 5.6)	0.7 (–3.3 – 5.4)	4.6 (1.0 – 7.6)	4.9 (1.2 – 7.9)	6.5 (3.3 – 7.9)	7.3 (4.0 – 8.7)
Somerset	South West England	19.9	1.9	3.7 (–0.4– 7.2)	3.4 (0.2 – 7.4)	3.1 (0.0 – 7.1)	5.9 (3.1 – 8.2)	6.2 (3.4 – 8.5)	6.7 (4.2 – 7.2)	7.6 (5.1 – 8.1)
Staffordshire	West Midlands	20.1	0.7	2.8 (–1.8 – 6.8)	2.2 (–1.8 – 6.6)	1.9 (–2.1 – 6.3)	5.4 (2.0 – 8.2)	5.8 (2.3 – 8.5)	6.9 (4.0 – 8.0)	7.9 (4.9 – 8.9)
Suffolk	East of England	48.8	2.9	5.1 (2.3 – 7.9)	4.3 (1.1 – 7.9)	4.2 (1.0 – 7.8)	6.6 (3.9 – 8.5)	7.1 (4.5 – 9.0)	7.1 (5.0 – 7.3)	8.4 (6.3 – 8.5)
Surrey	South East England	126.9	1.7	3.9 (0.5 – 7.9)	3.6 (0.2 – 7.6)	3.5 (0.1 – 7.5)	6.4 (3.4 – 8.7)	7.0 (4.0 – 9.3)	7.4 (4.8 – 7.8)	8.8 (6.3 – 9.3)
West Sussex	South East England	456.6	2.9	4.5 (1.3 – 7.8)	4.5 (1.4 – 8.4)	4.3 (1.2 – 8.2)	6.8 (4.0 – 8.9)	7.2 (4.4 – 9.3)	7.2 (4.9 – 7.4)	8.2 (5.9 – 8.5)
Wiltshire	South West England	31.8	1.2	3.3 (–0.8 – 7.3)	2.9 (–0.7 – 7.1)	2.6 (–1 – 6.8)	5.8 (2.6 – 8.3)	6.1 (2.9 – 8.6)	7 (4.3 – 7.8)	7.9 (5.1 – 8.6)
Worcestershire	West Midlands	23.3	3.5	4.9 (1.0 – 7.9)	4.7 (1.4 – 8.4)	4.5 (1.2 – 8.1)	6.8 (4.1 – 8.9)	7.2 (4.5 – 9.3)	7.1 (4.9 – 7.6)	8.2 (6.0 – 8.7)

^a Figures in brackets for the RCP 4.5 projections are estimated 10-year inter-annual variation at an approximate 80 % confidence level, i.e., 1 in 10 years can be expected to be worse than the lower limit and 1 in 10 years above the upper value.

^b Figures in brackets are the 2010–2019 range, from the lowest-scoring vintage (2012) to best scoring vintage (2018).

^c For Essex, Kent, and Isle of Wight the mean and the upper limit have the same score, or the latter is lower than the mean score. This is because the warming for the upper limit of TmeanApr-Sep is so great that it exceeds the peak of the curvilinear relation, and so the regime is supra-optimal for quality.

^d Parts of Lincolnshire are located in Yorkshire and Humber. However, all the vineyards in the dataset used here are found in the East Midlands.

^e Parts of North Yorkshire are located in North East England. However, all the vineyards in the dataset used here are found in Yorkshire and Humber.

Figure 6. Model predictions for the vintage score of Chardonnay still wine across the UK in 2040-2059 under RCP 4.5 (median and 95th percentiles).

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(a) 2040–2059 using the median RCP 4.5 projection (UK area rated Good 20.7 %, Excellent 0.0 %); (b) 2040–2059 using the median RCP

(b) 4.5 projection but with CNI2, a smaller increase than CNI projections (Good 24.5 %, Excellent 0.3 %); (c) 2040–2059 using the 95th percentile RCP 4.5 projection (Good 39.1 %, Excellent 0.0 %); (d) 2040–2059 using the 95th percentile RCP 4.5 projection but with CNI2 (Good 24.5 %, Excellent 17.9 %). Green is Good; purple is Excellent.

Figure 7. Comparison of climates between the top 30 UK counties (Table 4) in 2040–2059 and the Chablis region, France, from 1963 to 2018. Contours (vintage score) and dashed lines from Biss and Ellis (2021).

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Alternative 95th percentile projection that assumes simultaneously hotter (95th percentile TmeanApr-Sep) and wetter (95th percentile PJun-Sep) summers, as opposed to the standard 95th percentile projection that assumes hotter (95th percentile TmeanApr-Sep) and drier summers (5th percentile PJun-Sep).

4.3. 95th percentile projection

The 95th percentile RCP 4.5 projections (Figure 6c,d) led to a substantial area of UK land with high-quality ratings (39.1 % Good, 0 % Excellent). There was a noticeable expansion over the median projection of areas predicted to produce high-quality wine, moving beyond the South East and East of England into the Midlands and parts of the South West (compare Figure 6c with 6a). Estimated vintage scores for the Isle of Wight (Table 4) and London (Figure 6), however, were noticeably lower than those provided by the median projection.

Existing vineyards (for the top 30 counties) were all warm and dry (solid triangles, Figure 7b), ideal for Good Chardonnay and, other than East Yorkshire and Isle of Wight, all the counties with large areas of vineyards currently provided scores that were at least Good (Table 4).

The lower limit of the 10-year range for the 95th percentile projection increased by between +0.6 and +2.7 over that for the 50th percentile (except Isle of Wight, which had a small reduction of -0.3 in the lower limit) (Table 4). Conversely, the upper limit of the range was generally reduced by between –0.2 and –1.5 for the 95th over the 50th percentile projections, except for Isle of Wight, which experienced a larger drop (–2.6) and the more northerly counties, which showed an increase in the upper limit (East Yorkshire (+0.8), Lincolnshire (+0.2), North Yorkshire (+0.6) and Shropshire (+0.3), Table 4). The overall effect is that the estimated 10-year inter-annual range for 25 of the 30 counties (98 % of the area of planted vines considered here) was narrower, with the worst vintages not being as poor and the best vintages not being as good for the 95th as the 50th percentile projection.

Discussion

Conclusions

This study suggests:

1) The production of high-quality Chardonnay still wine was rarely possible throughout most of the UK in recent times (1981–2000 and 2010–2019). This would remain to be the case under the 5^th percentile projection for climate change (RCP 4.5).

2) Considerable areas of England and Wales, particularly the South East, East of England, and Central England, should be able to produce high-quality still Chardonnay wine, on average, in 2040–2059, with the 50th and 95th percentile projections for climate change (RCP 4.5).

3) The average climate in 2040–2059 (RCP 4.5, 50th percentile projections) should be sufficiently above the threshold for Chardonnay viticulture to allow ripening even in relatively cool years in the South East and East of England, especially Essex, Kent, and the Isle of Wight, extending to Central England under the 95th percentile projection, provided inter-annual variation remains similar to, or less than, recent times.

4) If CNI rises less than that projected by UKCP18 and instead continues along its current path (CNI2), the potential quality of wine may increase further.

Aside from the uncertainties associated with emissions scenarios and climate projections, further uncertainty arises from i) generalisations and inaccuracies with the Chablis vintage model, ii) the extent to which the Model can be applied to the UK, iii) the effect of soil type on the quality of UK Chardonnay still wines and iv) how climate change will affect the incidence of frost, intense small-scale weather events and the transmission of fungal and viral disease, none of which are modelled here.

More generally, beyond its application to the UK and despite the abovementioned caveats, the Chablis vintage model provides an approximate tool for locating sites with suitable climates for Chardonnay viticulture for the purpose of producing still white wine.

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