John Gladstones on wine, terroir and climate change

Wine, Terroir and Climate Change
John Gladstones, Wakefield Press, Adelaide, 2011

John Gladstones wrote this mesmerising book for the world’s grape growers and winemakers. But it’ll appeal to a wider audience – including those interested in the concept of wine and “terroir”, or readers looking for a concise but painstaking discussion on natural and human-induced climate change.

Gladstones outlines the ambitious scope of the book at the outset. He writes, “This book tackles two contentious subjects that underlie the future of viticulture. Terroir is much spoken of, but nobody, to the best of my knowledge, has attempted a comprehensive definition and integration of its elements in the light of modern science. To do so is an ambitious task, given the many remaining gaps in knowledge. Some of my conclusions may prove to be wrong. But I trust at least that they will help lead to a fuller understanding.

Climate change, which makes up much of the book’s latter half, must obviously influence all planning for future viticulture. But in approaching the subject it became evident that neither public understanding nor the ‘official’ position of the Intergovernmental Panel on Climate Change was necessarily accurate. Much in the argument for global warming by anthropogenic (man-caused) greenhouse gases appeared questionable. I therefore undertook as deep a study of the basic scientific evidence as I was able. The result was disturbing, though more as to the science underlying the global warming thesis than to the future of viticulture”.

The book, like Gladstones earlier Viticulture and Environment (1992), places temperature at the centre of grape growing. He sets out the reasons for this in chapter two of the new book, titled Temperature: The Driving Force. The theme weaves through the book and crystallises into practical advice for grape growers in maturity rankings of grape varieties, viticultural climate tables and reference climate tables.

For the general reader, as opposed to vignerons and grape growers, Gladstones’ methodical dissection of “terroir” is wonderfully enlightening.

The French word, for which there is no English equivalent, has become part of the mainstream wine vocabulary and stands for the environmental forces behind a wine’s individuality. The idea is central to France’s appellation system – based on distinctive regional wines, and drills down even to individual vineyard sites.

Gladstones defines “terroir” as “the vine’s whole natural environment, the combination of climate, topography, geology and soil that bears on its growth and the characteristics of its grapes and wines”. And he links these forces to the practicality of the market, writing, “The important thing is that a wine’s defined origin conveys a meaningful message to buyers and consumers, mostly as to its style though not necessarily as to its quality”.

We then read compellingly through the elements of terroir: temperature, broken into sections on vine phenology (physiological development), diurnal temperature range, day length, growing season temperature summations, individual sites, growth and fruiting, ripening temperatures, temperature variability and within-season variability.

A controversial conclusion from this section is that the best wines come from regions with the “lowest diurnal temperature range” – seemingly at odds with the notion of great wines coming from continental climates like Canberra’s. Clonakilla’s Tim Kirk quipped to me, “I haven’t forgiven him for what he said about Canberra [in his 1992 book]”.

Gladstones then discusses light intensity and exposure, rainfall, atmospheric humidity, wind and ripening period ideals for wine styles. Next under his gaze come geography, topography and soil, broken into several sections: latitude, altitude, topography, air drainage and frosts, aspect and slope, soil and above ground microclimate, proximity to water bodies – concluding with the common threads running through known best viticultural sites.

After this, Gladstones moves underground, examining soil water relations, soil and root temperatures, development of the vine root system, the root system and fruit ripening and an hypotheses (and objections to it) on hormone-driven root control of ripening.

The next two chapters study vine balances and management (soil-atmosphere water balance, vines and root maturity, vine size and crop load and irrigation strategies) and vine nutrition (nitrogen, potassium and other nutrient elements).

Finally, he arrives at geology and soil types, two of the most mentioned but perhaps most problematic aspects of “terroir”. He presents the challenge: “associations between wine characteristics and soil type alone, and likewise to some extent geology, have nevertheless proved elusive when studied objectively”.

After looking at soils and geology in literature, soil structure and drainage, soil thermal properties, soil types and vine nutrition and relationships to geology, Gladstones concludes that there probably is a geological flavour element to “terroir” – most plausibly from deep roots of mature vines tapping elements close to bedrock.

A chapter on organic and biodynamic viticulture charts the many advantages of organic management and concludes that it probably aids the expression of “terroir”. However, biodynamics appears to add no advantage and, writes Gladstones “at worst, they represent an unhealthy retreat into irrationality and mysticism… they have no place in an enlightened 21st century”.

Unquestionably Gladstones’ conclusions on climate change are the most controversial element of the book. The section, however, is a magnificent read for its broad sweep across a complex topic. It’s written concisely, logically and expansively and is accessible to non-scientists like me. It’s richly referenced for further exploration of the issues.

Gladstone discusses pre-industrial climates, the evidence of sea levels and early history, including viticultural records, natural causes of climate change, including earth-sun geometry, volcanic activity, solar irradiance and magnetic field, and modelling pre-industrial temperatures.

He then examines anthropogenic causes of climate change, including carbon dioxide and water vapour, aerosols and other pollutants, and land uses and effects. Next he examines modelled temperature feedbacks, principally ice and snow cover and clouds.

After a detailed study of the attribution of causes, including and examination of data sources, statistical methods and climate modelling, he concludes that “warming by anthropogenic greenhouse gases has been much over-estimated”, and “The 20th century’s true warming, as recorded in sea surface temperatures, is at least largely accounted for by natural climate fluctuations, for which the most credible cause on decadal to centennial timescales is fluctuation in solar output and magnetic field”.

He also concludes that we’re likely to be now dipping into a natural cooling period to about mid century. He anticipates this will likely offset admitted human-induced warming in that period.

Gladstones’ controversial conclusions underline the inherent uncertainty in predictions of any kind. His calculations put human-induced warming at much less alarming levels than those driving public policy. He could be right. But then, he could be wrong, too. Nobody knows with certainty.

Gladstones’ views on climate change lead to his conclusions that the world’s great wine “terroirs” will ride out any changes. He also concludes “rising atmospheric CO2 concentration will itself probably increase the optimum minimum and mean temperatures for vines”, and that “Sustainable production methods and improving quality and reliability across both market segments will help further establish wine as a world beverage of preference and moderation. The 21st century stands to become wine’s golden age”.

Copyright © Chris Shanahan 2011