Ron Smith: Climate change and the growing of the grape

A report in The Guardian (UK), a few days ago (8 April), was headed ‘Climate change will threaten wine production’.  A few days later (10 April), the New Zealand Herald carried a similar story,  ‘Warming likely boost to vineyards’.  Of course, the two reports are not as incompatible as they seem. 
The Guardian report notes that a warming climate will favour grape cultivation in the more northerly regions of Europe, at the same time as it makes it more problematic in traditional areas, bordering on the Mediterranean.  In New Zealand the move will be to the South.  The theory is unimpeachable.  If the climate warms, areas too cool to presently cultivate grapes, will have that potential.  Archaeological data shows that two thousand years ago the Roman occupiers of Britain grew grapes around Hadrian’s Wall.  That activity stopped around fifteen hundred years ago, as the climate cooled, in what we now know as the ‘Dark Ages’.  There was a similar temperature switch five hundred years later (the ‘Medieval Warm Period’), when Greenland really was ‘green’ (relatively) and this, in turn, was followed by the ‘Little Ice Age’ when English folk enjoyed winter fairs on a frozen Thames.

This is the rub.  A period of cooling may come again and, if it does, expensively-developed vineyards will become unproductive as did those on the Scottish borders.  It all depends on how much confidence an intending developer might have in the predictions of the Intergovernmental Panel on Climate Change and their enthusiastic supporters, on which the Guardian and the Herald stories are based.  If it were my money, I should want to be pretty sure that they were right.

Of course, we know what the theory is.  Human activity is resulting in increasing quantities of carbon dioxide being released into the atmosphere and that, through the ‘greenhouse effect’, has the potential to cause an increase in global temperatures.  On the other hand, we might also know that global temperatures have not risen appreciably for the last fifteen to twenty years and wonder how sure we can be that the predicted warming will occur.  In this connection it would be appropriate to ask the experts, who are authoring these predictions, what caused the ‘Roman’ warming and the Medieval Warm Period, given that it could not have been the smoking stacks of an Industrial Revolution, or the products of General Motors.

In fact, this is not an easy question.  The patterns of climate change down through the millennia seem to have a plethora of explanations which range from, extra-terrestial causes, such as the place of the Solar system in our local galaxy, the eccentricity of the earth’s orbit around the sun (and the earth’s wobble on its axis), and variations in the sun’s energy output, to volcanic and plate-tectonic activity, and variations in the circulation-patterns in of the oceans of the world, for example the ‘southern oscillation’ (which brings us la niña).   There are also the consequences of human activity: forest-clearing, city-building, and the possible impact of ‘greenhouse’ gases, as noted above.  The mechanisms in many of these cases are not completely understood and the interactions between them are difficult to evaluate, so that there is plenty of potential for honest differences of opinion.

However, there is one factor in the list above which might be worth noting by the intending investor in new viticultural opportunities and that is the relatively short-period variation in the output of the sun.  The Little Ice Age that ended the Medieval Warm Period, and lasted until the beginning of the Nineteenth Century, seems to have been associated with a reduced number of sun-spots on the sun’s disc (the so-called Maunder Minimum).  Scientists are presently drawing our attention to a similar sun-spot minimum, and wondering whether we might not plausibly expect a period of cooling that could last several hundred years.  (There is a mechanism for this that has to do with the so-called ‘solar wind’ and its effect on cloud formation, and thus global temperature.)

There are persons who are constitutionally disposed to think that human beings are having too big an impact on the environment and that this ought to be reduced, on what really amounts to moral grounds.  In many ways, this is an affluent indulgence, which is largely not shared by those in the non-western world, who still have aspirations for their children and their societies. 

In our society there seem to be many persons who are willing to accept the assurances of official agencies and ‘experts’ that the theory of global warming is sound and that, even if there is a pause now, warming will resume at some point in the future.  They claim that we thus need to take precautions through carbon-charges and the subsidisation of ‘alternative’ (‘green’) energy sources to avoid catastrophe.  The situation of the potential speculator in the growing of the grape is different.   He can’t do anything about the carbon charges but he really needs to find out what happened to the ‘Chateau Hadrian’ enterprise and make quite sure it doesn’t happen to him.