In the first post of this series we looked at the evidence for climate change occurring in Portuguese vineyards, and based on what we saw it seems to be undeniable. This part, however, is more important to you, the reader. It affects what you pour into your wineglass and then drink.
We'll subdivide the section into what's in your glass, and then also try to tie it in with what's going on in the vineyard. The last example in Part 1 showed how much alcohol levels have been increasing in wine over the last few years - to which the obvious reply would be 'Simple then - just pick the grapes earlier before they get too ripe.'
Only it's not that simple of course, because actually there are two ways of looking at ripeness. The first, known as technological ripeness (or even just sugar ripeness) will indeed determine how much alcohol gets into the bottle. But the alcohol is only a small part of what the wine tastes like. The flavour itself depends on a whole different type of ripeness, which winemakers call phenolic ripeness, and these two both need to develop in tandem.
Imagine a green pepper or a green tomato. When they turn red, you would think that they should be ripe. But even when their flesh or juice becomes sweet, without phenolic ripeness their skins would still have the tart, slightly bitter and aggressive vegetal tang of green peppers or green tomatoes. Climate change throws the two sorts of ripeness out of kilter, with the sugar getting ripe well before the skins of the grapes. Normally it's due to dehydration, with excessive summer temperatures shrivelling the grapes (and therefore concentrating their sugars) before the skins are ripe.
This in turn causes a second problem, particularly for red wine. The colour in these unripe skins is less developed, less intense and less stable - so after a couple of years the wines lose their colour, and the tannins which would normally enable them to age gracefully. In short, hot summer wines turn brownish and fall apart a couple of years after bottling.
Curiously, drought brought on by irregular precipitation patterns can also have the opposite effect - it can stop ripening altogether. When it's just too hot the vines can't afford to lose any more water so they stop producing sugar and the berries just don't get sweet at all.
Extreme temperatures can also cause the vines to lose their leaves, exposing the grapes to direct sun. Like us, grape skins can also get sunburn and dry up. These desiccated shells will never develop a nice ripe flavour, and extreme sunburn just after fruit set will burn up entire bunches before they even form properly. And since the leaves are responsible for photosynthesis, leaf-less vines cannot produce any sugar at all.
Extreme sunburn in the Touriga Nacional.
A more obvious consequence of climatic fluctuations is that the size and number of grape bunches (and indeed, the size of the grapes themselves) becomes much more variable, leading to more variation in crop size between years. In dry regions, wetter years will generally increase yields because the vines have more water. However, cooler climates may suffer greater losses than usual to fungal diseases which thrive in the damp.
Unpredictable harvests cause all sorts of logistical problems. How many pickers will we need to hire to collect the crop? How long will it take? How much fermentation space will I need in the winery? Will I have enough wine to meet my sales targets or should I already have signed contracts to purchase grapes months ago? If I am making fortified wines, have I ordered enough grape spirit? And so it goes on.
But in many ways, perhaps obviously, climate change is even more of a problem for the viticulturist than it is for the winemaker. Winters that turn out to be warmer than expected lead to earlier budburst which in turn puts the young shoots at greater risk of a spring frost - which can all but wipe out the entire year's crop.
Controlling pests and diseases becomes unpredictable, and changing weather patterns may lead to problematic insects and fungi colonising new areas that couldn't previously sustain them. Drier years could be beneficial as they might reduce the amount of herbicide that is used in the vineyard but extreme precipitation events increase soil erosion.
Another major issue that has been making dramatic headlines over the last few years is the increasing incidence of wild fires in hotter grape producing regions. Australia and California have been particularly badly affected. Whilst it is relatively unusual for the actual vineyards to burn, the smoke in the air is taken in by the vines and has a devastating effect on grape quality. To make matters worse, smoke taint is only revealed after fermentation, so potentially huge amounts of money can be wasted picking grapes and making wine only for it to turn out to be unsellable. In Australia 60,000 tonnes of grapes (4 % of national production) were lost this way in the 2020 harvest.
The picture is not pretty. But with ingenuity there are some mitigating steps that can be taken, and we'll have a look at them in Part 3.