A big thank you to Andrew Isaacs, Senior Lecturer at UC Berkeley’s Haas School of Business and Natàlia Costa i Coromina, Graduate Student Instructor at UC Berkeley’s Haas School of Business for their expertise!
Modern Carbon During the growing season, vineyards will take a considerable amount of carbon dioxide out of the atmosphere through the process of photosynthesis. The carbon in that CO2 is what we refer to as “modern carbon," or carbon in the form of CO2 that is already in the atmosphere.
Using photosynthesis, the plants will build tissues and ultimately wine grapes. At the end of the growing season, after we harvest the grapes, these vines will slowly go back into dormancy. They'll drop their leaves, and in the winter, we’ll prune them to get ready for the next season.
All of that plant material - the grapes, the canes, the leaves, and so on – are compounds made from carbon that came out of the atmosphere. And all of that plant material will also return its carbon naturally back into the atmosphere, mostly as CO2, through the process of microbial decay, and mostly during the winter months.
So – over the course of a year, the plants will have made no net change to the CO2 concentration in the atmosphere through the cycle of first photosynthesis and then microbial decay.
Fossil Carbon The impact to the climate in grape growing is primarily through our farming practices, such as the use of tractors that burn diesel fuel, and trucks and other equipment that burn gasoline. Those do add CO2 to the atmosphere, and therefore add to the problem of climate change.
The reason for that is that the carbon in the fuel used to be in the ground in the form of oil and gas deposits, and that carbon had been in the ground for millions of years. That's why we refer to them as fossil fuels - the word “fossil” just means “old”.
By using fossil fuel, we're taking carbon out of the ground and putting that carbon into the atmosphere, mostly in the form of CO2. It does not somehow go back into sequestration in the ground. And, that fossil carbon will stay in the atmosphere for 1000s of years, and possibly 10s of 1000s of years.
CO2 simply does not break down in the atmosphere – basically, it just stays there. And since CO2 is a greenhouse gas, that accumulation of CO2 is warming the planet.
Nitrous Oxide
The use of nitrogen fertilizer, either in the form of nitrate, ammonia, urea, or other fixed nitrogen compounds, also adds to the problem of climate change.
Every pound of nitrogen that we add to farmland will eventually be converted by microbes into nitrous oxide, or N2O. Some of the nitrogen that we apply will wind up in the plants we are growing, but even that nitrogen will sooner or later wind up as N2O in the atmosphere.
Nitrous oxide is a much more potent greenhouse gas than carbon dioxide - by a factor of about 300, molecule for molecule! It does have a half-life in the atmosphere, fortunately, but it's a pretty long half-life, about 100 years.
And just as the amount of CO2 in the atmosphere is accumulating because we're taking fossil carbon out of the ground and putting it into the atmosphere as CO2, the amount of nitrous oxide in the atmosphere is also growing year by year, mainly from the use of nitrogen fertilizer on farmland.
The Bottom Line...
If we want to do something as farmers to reduce our impact on the climate, we should try to reduce our use of:
How much fossil fuel we're burning
How much nitrogen fertilizer we’re using (to the *bare minimum* that will allow us to produce a good crop.)
