Wine grapes are a climatically sensitive crop grown in a fairly narrow geographic range. Growing season temperatures for high-quality wine production are generally limited to 13-21C on average.
This encompasses the Old World appellation regions of France, Italy, Germany, Spain and the Balkans, and developing New World regions in California, Chile, Argentina, southern Australia and New Zealand.
Speaking at the International Masters of Wine Symposium last month in Florence in Italy, Professor Greg Jones, the wine climate specialist from the University of Southern Oregon, noted the overall growing season temperature trend was upwards.
This increase, by 1.3C, was for numerous wine regions around the world between 1950 and 2000. Greater growing season heat accumulation with warmer and longer seasons has occurred.
There has been a decline in the number of days of significant frost in the dormant period and spring - earlier last spring frosts and later first frosts in autumn with longer frost-free periods.
For example, in Tuscany, the Chianti region of Italy, summer temperatures have increased by 2C between 1955 and 2004.
The warming is extending the world's wine map into new areas such as British Columbia in Canada, Exmoor in England and into the southern Baltic.
The effect in the Old World regions has been earlier bud-burst and flowering and altering ripening profiles which affect wine styles. For example, potential alcohol levels of Riesling at harvest in the Alsace region of France have increased by 2.5 per cent (by volume) over the past 30 years and are closely correlated to significantly warmer ripening periods, earlier bud-break and flowering.
In Napa, California, average alcohol levels rose from 12.5 per cent to 14.8 per cent between 1971 and 2000, while acid levels fell and the pH climbed. Soil temperatures are increasing in the wake of air temperatures, and this will probably present numerous additional issues.
Similar warming trends are being observed in viticulture areas in New Zealand. For example, in Marlborough, mean annual temperatures over the past 80 years have increased by 0.9C, and the number of summer days (days above 25C) at Blenheim has increased from 24 to 36 a year. Frost days (days below 0C) have decreased from 40 to around 12 a year.
Greg Jones noted that climate model projections by 2100 predict growing season warming of an additional 2.0-4.5C on average. Niwa mid-range projections for the New Zealand wine grape areas are for a warming of 1C by 2030 and 2C by 2090.
The Florence symposium turned its attention to how the European wine industry is preparing for a warmer world - and these lessons are very pertinent to our wine industry.
While challenges exist for all New Zealand wine regions, opportunities for a more sustainable industry are being addressed in the overseas industry and research communities. At the vineyard level the terrain slope (using north- rather than south-facing slopes), training systems and vineyard design can be changed.
For example, many vine rows have been oriented to maximise sunshine in places where this is no longer the optimal objective, and shade will become a positive rather than a negative in many places.
Another option is wine variety diversification. The Piedmont region of Italy is noted for its red wines which are made from Dolcetto or Nebbiolo varieties. Although both varieties are grown over a narrow climate range, Nebbiolo performs better in a warmer climate (17.8 to 20.4C) with a long growing season. Dolcetto does better in a slightly cooler climate (16.4 to 18.4C). This is an expansion in quality and production potential.
About 5000 or so varieties of grape are now known. In Bordeaux (France) the Parcelle 52 project, under way since 2009, is monitoring the performance of all sorts of locally unfamiliar grapes such as Grenache, Tempranillo and Georgia's Saperavi to prepare for a hotter climate.
Other tips for a more glorious future in wine production from researchers include Rabigato and Alfrocheiro in Portugal, Sumoll, Escursac and one of the two different Maturanas in Spain, Counoise and Verdesse in France, Lagrein on the Italian mainland and Nieddera in Sardinia.
The fastest growing varieties globally have been away from the cooler wine styles to Syrah, Cabernet Sauvignon, Merlot and, especially, Tempranillo.
The New Zealand wine industry can seize the opportunities with similar evaluations for each region with different varieties.
Finally the traditional appellation regions in Europe are in areas of significant topography and research programmes have been mapping potential new areas for production at higher elevations. New Zealand has a long latitude range and the South Island, in particular, has significant areas above 300m that can be used. This enables the migration of warmer wine styles south, with the cooler wine styles to higher elevations. For example, the MacKenzie Basin in inland Canterbury probably has a significant potential as a future viticulture area - with a dry climate, hot summers and cold winters.
The earth's climate is changing much more quickly than the wine business - and virtually every other business - is preparing for. The gradual nature of climate change should give the industry sufficient time to develop and use some of the adaptation strategies discussed in Florence. A warming world represents opportunities for the New Zealand wine industry - both producers and growers.
Jim Salinger, a visiting scientist at IBIMET-CNR in Rome, is conducting research on climate and wine quality in Tuscany.