Credit: Brent Parker Jones
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The Hill of Grace vineyard lies in a quiet, out-of-the-way corner of Eden Valley, the hilly region to the east of the Barossa wine zone in South Australia.
The vineyard produces what many consider to be Australia's greatest red: the Henschke Hill of Grace shiraz, a wine so revered that the latest vintage will cost you close to $400 a bottle, while classic older vintages such as 1990 can set you back almost twice that much.
The quality of this wine is due to a unique combination of factors: the vineyard site's deep sandy loam soils; the extreme old age of the vines (some planted as far back as the 1860s); and the climate - crucially, it's cooler here than down on the Barossa Valley floor.
Viticulturist Prue Henschke is doing her best to protect her priceless inheritance and pass it on to her children in even better condition. She has adopted organic practices in the vineyard - mulching under the vines, and planting native grasses between the rows to retain precious moisture. And she's painstakingly replanting the vineyard using cuttings taken from the best of the old vines.
But there's one thing she has no control over whatsoever, and that's the climate.
According to a growing body of evidence, in 50 years time - perhaps as soon as 30, or even in just one generation - the Hill of Grace vineyard may well be too hot to produce a wine worthy of its $400 price tag.
The inescapable fact is that grapes ripen earlier in warmer climates, and early ripened grapes simply don't get a chance to develop the extraordinary, subtle complexities of flavour that have built the reputation of the Hill of Grace shiraz over the last 50 years.
"Scary, isn't it?" says Henschke. "This is a mammoth issue for us. The oldest vines at Hill of Grace have survived for 146 years, but now they're threatened by this manmade change. And I think, well, Hill of Grace is just nine hectares of the whole of Australia. I wonder how many other irreplaceable sites will be affected as things get warmer.
It's a question many others in the Australian wine industry are asking. Over the last 12 months, climate change has jumped the queue of concern among grape growers and winemakers - as it has for the rest of us - taking precedence, even, over the well-publicised grape and wine glut.
A recent report from the University of Melbourne and the CSIRO unequivocally predicts that â€œclimate change will dramatically alter the growing season for Australian grapes and affect the wine styles produced. It's a prediction that has resonated with grape growers suffering unprecedented drought conditions.
An inconvenient truth
"God bless Al Gore," says Richard Smart, the internationally renowned Tasmania-based viticultural consultant who dubs himself "the flying vine doctor". "Now, finally, we're starting to see the industry talking about global warming.
Smart has been talking about it for almost two decades; he gave his first paper on climate change and its possible impact on the New Zealand industry in 1988.
"In a lot of ways, you see, the wine industry is the canary in the mine of agriculture," says Smart. "Because wine is based on such a tight interaction between temperature and grape variety, even small changes in temperature can have immediate effects on wine style and quality. And it's the temperature requirements of certain grapevine varieties that have determined where the wine regions are."
One way of measuring the climate of each of Australia's 60-plus wine regions is by referring to its mean January temperature (MJT), a measurement which has a direct relationship to wine quality and style.
Coonawarra in South Australia, for example, is considered cool, with an MJT of 19.1ºC. It is the region's long, cool growing season that is the key to its elegant cabernet and spicy shiraz.