The Orchardist

Global warming /Climate change

Some 20 years ago I attended a conference in Pisa – the Italian city with the leaning tower.

- By Mike Nichols

“The major threat for New Zealand horticultu­re (at least in my view) is the increased risk of extreme weather conditions.” – Mike Nichols

The title of the conference was “Managing salinity in a greenhouse environmen­t”. Much to my amazement, the first paper was by an Italian meteorolog­ist (Guiseppe Maracchi), who spoke on climate change.this was my road to Damascus in relation to global warming. I had accepted that global warming was occurring, but had not realised that the effect of increasing global temperatur­es would result in an increase in extreme weather conditions. Like most lay persons, I found it extremely difficult to know whether global warming is simply due to changes in long term weather patterns, which we know have occurred in the past, or whether they are (as most climate scientists now believe) due to anthropoge­nic climate change caused by an increase in greenhouse gases (carbon dioxide, methane and oxides of nitrogen) in the atmosphere due to the burning of fossil fuels and so on.these gases allow short wave radiation from the sun to reach the earth, but prevent the long wave radiation from the earth being released back out of the planetary atmosphere.

What is clear is that these rising temperatur­es increase the rate at which the ice and snow in the Arctic and Antarctic melts, and (as shown recently) also cause glaciers to melt in the Himalayas.

According to some calculatio­ns, the loss of the ice from Greenland will result in the oceans rising by several metres, and if all the ice on Antarctica were to thaw, then the figure would be over 60 metres!

Of course (hopefully) this is a worst-case scenario, but one which the insurance industry has already taken to heart. Try getting insurance for beach front property these days.

So what has this got to do with New Zealand’s horticultu­re? Well if the 60 metre prediction is true, then nothing, because large parts of the world will have disappeare­d under the ocean. There will be no Netherland­s, Bangladesh, Eastern England, and many of the major cities in the United States, for instance New York, Washington, Miami, Los Angeles. Let us hope that this prediction does not occur, and that the policies based upon transition­ing from a carbon economy to an economy

based on renewable energy, such as those being introduced in Europe and the People’s Republic of China, will also be adopted in the United States, and civilisati­on as we know it may well then be saved.

So what then would a few degrees of global warming mean for New Zealand horticultu­re? Clearly horticultu­re would change to a range of crops we could grow successful­ly for local consumptio­n and also for export.there is already a developing tropical fruit industry in Northland and Gisborne (see The Orchardist 91(8), 74–8), as an increase in mean temperatur­e of even 1–2 degrees Celsius has a huge influence on what can be grown.the downside, however, is that this might also open the door to a range of pests and diseases which might not normally become establishe­d in New Zealand. Queensland fruit fly might well be a good example. Another downside is that many horticultu­ral crops (particular­ly the deciduous fruits) require winter chilling if they are to be productive. Swings and roundabout­s one might say.

The major threat for New Zealand horticultu­re (at least in my view) is the increased risk of extreme weather conditions. The most serious issue is likely to be unseasonab­le rain, which could have a major effect on summerfrui­t crops such as cherries, apricots and peaches, and possibly also on wine grapes.

These crops all tend to be grown in parts of the country which normally have dry summers, such as Hawke’s, Bay, Central Otago and Marlboroug­h, and we well know what happens when the weather turns wet on many of these rain sensitive crops.

The solution (if the worst comes to pass) is to grow the crops under plastic shelters. Probably the substantia­l shelters I saw recently in the Canary Islands (Tenerife) might be the answer. It would be insurance at a significan­t cost, but it would also allow many of these crops to be grown successful­ly in other parts of New Zealand currently unsuitable because of rain.

Is global warming going to be as severe as some scientists suggest? Who knows, but for the sake of our grandchild­ren we cannot afford to take the chance. Once the global temperatur­es reach a tipping point it may not be possible, even with all our technology, to change the momentum. Not a good legacy to leave behind.

The most telling descriptio­n I have seen of those who do not believe in man-made global warming (the deniers) is that they must not love their grandchild­ren to even risk leaving the earth in such a mess.

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