The Grapes of Climate Wrath

Published December 13, 2019


The implication is that more carbon dioxide—produced from driving your car instead of taking the Metro—will have the effect of making grapes smaller and therefore affect wine production levels and perhaps quality. This 2014 paper, “The impact of climate change on the global wine industry: Challenges & solutions,” suggests a wide range of negative effects on the wine industry due to “climate change” resulting from increased CO2, but it also offers solutions.

The source of this concern is an abundance of research articles published in recent years that suggest crop yields will be reduced as ambient atmospheric CO2 concentrations increase. Yet in spite of these warnings, we have clear evidence that crop yields of all types throughout the planet have dramatically increased in the past 50 years, while CO2 levels have increased. Some of these  trends are due to better farming and irrigation practices, some due to selective breeding to make better varieties that have higher yields and increased resistance to diseases, and, yes, some of it is due to increasing CO2 in our atmosphere that allows for more efficient photosynthesis and better internal plant water management.

After all, isn’t the latter reason why many greenhouse operations inject highly elevated levels of CO2 into their greenhouse operations? Here is an excerpt from a Canadian report on Carbon Dioxide in Greenhouses:

Carbon dioxide (CO2) is an essential component of photosynthesis (also called carbon assimilation). Photosynthesis is a chemical process that uses light energy to convert COand water into sugars in green plants. These sugars are then used for growth within the plant, through respiration. The difference between the rate of photosynthesis and the rate of respiration is the basis for dry-matter accumulation (growth) in the plant. In greenhouse production the aim of all growers is to increase dry-matter content and economically optimize crop yield. CO2 increases productivity through improved plant growth and vigour. Some ways in which productivity is increased by COinclude earlier flowering, higher fruit yields, reduced bud abortion in roses, improved stem strength and flower size. Growers should regard COas a nutrient.

That said, I looked specifically at how grape size would be affected and found a University of California Davis paper that specifically addressed this issue. In “Berry Size and Yield Paradigms on Grapes and Wines Quality,” the researchers concluded:

Myths are creative explanations similar to scientific hypotheses, and when not subjected to scientific tests they can become perfect hypotheses that explain perfectly what they are supposed to explain. Here we evaluated with data two longstanding and widely held paradigms of viticulture for which there had previously been little quantified observations: large berries and high yields are inferior. The data are clear in that the results of independent means of changing berry size and yield produced qualitatively different results. This renders the generalizations asserted in both of the paradigms untenable. The high yield, low quality paradigm may be applicable to environments in which sugar accumulation is limiting factor because reducing crop generally increases the rate of increase in sugar concentration in the remaining clusters. We draw these conclusions about the dependence of composition on yield and berry size: the viticultural practices used to control yield in a vineyard are more important than the yield values per se in determining the quality of the resulting grapes and wines; and the environmental conditions determine berry size are more important the size per se in determining the quality of the grapes and resulting wines.

In other words, the practices of the viticulturalist have more of an impact on the quality of berries than anything else, and larger grapes sizes aren’t necessarily better for wine production, despite what the myths promoted by the DC Metro might suggest.

So, whom would I trust on wine? The DC metro or the vitculturalists and researchers themselves?

I’ll go with the vitculturalists every day of the week and twice on Sundays. Salud!