Early ripening of grapes "pinned to warming"

Yarra Valley

So the planet has got a little warmer in the last 200 years, and grapes are ripening a little earlier. Just as it got colder before the Little Ice Age and, no doubt, grapes ripened a little later. It’s called climate and it’s what the planet does.

Maybe it’s because for the first time in history we are examining our planet in such microscopic detail, something that has really only happened in the last hundred or so years (which just happens to coincide with a period of warming) that we are continually worrying about where we are headed.

Grapes were grown in the north of England during the Roman Warm Period, but there isn’t a chance of any decent Château Harrogate or Côtes du Humber in the near future.

Add this to the fact that the range of climates in which grapes are grown would exceed many times over the tiny change in global temperature in the last 200 years, and it should be obvious that adaptation should not be a big issue.

But despite all this, pinning it on global warming (as many scientists, and AAP, are all too eager to do on many occasions) makes it newsworthy, apparently:

RESEARCHERS in Australia say they have pinpointed key factors in the early ripening of grapes, providing potential answers for wine growers threatened by global warming.

In Australia and Western Europe, there is an abundance of anecdotal evidence linking higher temperatures with earlier grape maturation, a phenomenon that can affect the quality of table wine. 

But wine growing and climate change are each highly complex questions.

Until now, no one has sorted out how the variables – warming, sunlight, soil moisture and vineyard management – each play a role in grape maturation.

A team led by Leanne Webb at the CSIRO looked at 10 sites in southern Australia where there were highly detailed records, stretching from 1985 to 2009, for all of these factors.

Only at one site – at Margaret River on Australia’s southwestern tip – did the grapes ripen later. For the others, maturation occurred between six to 34 days earlier.

The commonest driver of earlier ripening was higher temperature, deemed a significant factor at seven sites.

Lower soil moisture, particularly in the drought-stricken southeast, was a major factor for earlier harvests at five sites. Drier soils lead to higher levels of a stress hormone called abscisic acid in vine roots, which drives the plant’s fruit to earlier ripening.

But vineyard management was also important.

In four sites, pruning and fertilisation methods that lowered crop yields contributed strongly to earlier maturation.

And there may be other technological innovations in these and other sites, such as improved disease and pest control, that could have been a ripening factor, says the study. (source)

So out of just 10 sites, warming was “deemed” a significant factor at seven, soil moisture at five, pruning and fertilisation at four, plus there “may be” other unknown factors which they were unable to attribute. Make of that what you will.

But it’s not all doom and gloom, as the study shows that vineyards can (dirty word warning) adapt, like humanity has been doing for centuries.

Call me cynical, but making “global warming” so prominent in this report seems to be purely to sensationalise the story. Its connection to “global warming” is tangential and the focus is clearly more on factors that are important for adaptation.

But let’s not forget this is CSIRO after all – and they have already made up their minds on climate change.

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