Climatic Change and The Greenhouse Effect
Climatic Change and The Greenhouse Effect
The last ice age occurred 25 000 to 14 000 years ago. The earth then warmed rapidly, and in Australasia 8000 to 10 000 years ago reached temperatures 1?C to 2?C higher than those of today, before progressive waves of cooling and warming ultimately produced the regime of the late twentieth century.
On a shorter time scale, there is considerable evidence to suggest that the period from the late 1400s to the mid-1500s was exceptionally warm in Europe. In 1509 there were 139 vineyards recorded in England, of which 11 were owned by Henry VIII, 67 by noblemen and 52 by the Church. In Germany there were a series of abundant and high-quality vintages, culminating in the fabulous vintage of 1540. In that year the Rhine stopped flowing and could be crossed by foot: wine was cheaper than water. As in 1989 in France, there were two vintages: a `normal' vintage, albeit early, followed by a second harvest four to six weeks later of the secondary bunches which usually fail to ripen.
The worm then turned in dramatic fashion. Between 1625 and 1715 the coldest weather recorded in the last 1000 years struck the vineyards of Europe. It put an end to English viticulture for centuries to come, but it was no less severe in France. The 1690s saw a catastrophic run of vintages: Chateau Latour sold no wine at all in the four vintages up to 1693, and 1694 and 1695 were terrible years. Then in the winter of 1709 the great freeze struck: even at Marseilles, in the warmest part of France, the temperature dropped to 17.5?C below zero. It caused near total destruction of the French vineyards, although the wisdom of hindsight tells us that the wholesale replanting which followed gave rise to Bordeaux as we know it today.
I recount these swings in fortune simply to put the events of today, and in particular the Greenhouse effect, into some kind of perspective. It is not to say we should not be concerned about our environment and the damage or change - the two words are in effect used interchangeably - mankind's occupation of earth causes to the environment. Perspective is also needed when we look at the causes. The Greenhouse gases (so-called because along with water vapour and clouds they trap heat energy which would otherwise be re-radiated into space), are carbon dioxide, methane and chlorofluorocarbons (CFCs).
All one hears about is CFCs, yet methane accumulation is increasing at 2 per cent per year - largely due to the internal combustion mechanics of the ever-increasing herds of beef and dairy cattle. Carbon dioxide is increasing at the rate of 0.5 per cent per year, and its concentration is now 25 per cent higher than it was 200 years ago. And carbon dioxide is the base building block for all plant growth via the process of photosynthesis: increase the concentration of carbon dioxide and you increase the rate of growth of the plant. Studies have predicted a 10 to 15 per cent increase in the growth rate of vines, while Pinus radiata (pine tree) seedlings have shown a 30 per cent increase. No one other than those directly profiting supports the destruction of the world's rainforests, but nature may outsmart us all yet by accelerating the growth of all other vegetation and hence pull the carbon dioxide levels back into balance.
In a lecture delivered at the University of Western Australia in October 1990, Dr John Gladstones pointed out that were it not for the Greenhouse gases the average temperature would be minus 18?C rather than the present plus 15?C; says Dr Gladstones, `We need the Greenhouse effect'.
The principal Greenhouse gases are carbon dioxide and water vapour, which gases are fully transparent to incoming short-wave solar radiation, but absorb certain wavelengths of the long-wave radiation given off by the earth, thus forming the so-called blanket. Any increase in the amount of Greenhouse gases will have minimal effect, because at present levels they already trap virtually all of the heat in the outgoing wavelengths they absorb. The only gases capable of trapping wavelengths which now escape freely are the chlorofluorocarbons, which are additionally suspected of harming the ozone layer. `Pending better evidence it seems prudent they should be quickly phased out of use,' Dr Gladstones observes.
The computer models which have predicted an up to 4.5?C increase in temperature over the next 50 years assume a rise of only 1?C as a direct result of projected Greenhouse gas increases. This is in fact at the extreme upper end of the range of estimates in the literature. It is then held to be magnified by what are termed positive feedbacks, involving more water vapour yet less cloud, meaning less solar radiation is reflected away before it reaches the earth. It is principally in the assumptions regarding the feedback that the disagreement among scientists emerges. Dr Gladstones has this to say: `But as best I (and many others) have been able to interpret the evidence, any worldwide feedback through the water cycle and cloud is more likely to be negative. That is, it will moderate any initial heating tendency, not magnify it. The greater probability is therefore that any Greenhouse warming by the middle of the next century will be less than a degree.
`If global temperatures rise by, say 3?C by the mid-twenty-first century as the viridomologists have forecast, the effects on vines may largely or wholly be offset by the direct effects of greater carbon dioxide concentrations. Viticulture will undoubtedly become possible well beyond its present cool margin, but I suggest that the biggest benefits will be in areas with at present only moderately cool viticultural climates. Temperatures there will still be within reasonable limits by today's standards, and the optimum temperatures for yield and wine quality may well have risen in parallel with actual temperatures.
`Whether present hot areas, such as the Swan Valley, suffer would depend on how far high temperatures are damaging in their own right, and how far the extra carbon dioxide is protective. Present hot climate vineyards are probably safe enough for some decades to come under this scenario, but the wisdom of further plantings might be questioned.
`The more likely future, however, is that carbon dioxide concentration will continue to rise, with temperature rising, at most, only a little. In that case the optimum conditions for all types of wine will probably continue their historic migration to warmer and sunnier climates. In Western Europe the quality centre of gravity might shift to the south-eastern region of France, and perhaps Portugal. Existing Northern European vineyards will become less competitive.
`California will benefit greatly, especially the intermediate valleys, which have unlimited sunshine, currently sub-optimal relative humidities, and moderate to warm temperatures. So will South Africa and Chile. Most parts of Australia will benefit, including north-east Tasmania for strictly cool climate styles, but probably not southern Tasmania or the cooler or less sunny parts of New Zealand.'
