With the help of the sun, plants take carbon dioxide out of the air and convert it into carbohydrates or food, giving off oxygen as a by-product. It is absolutely essential that there be carbon dioxide in the atmosphere in order for us and other animals to survive on this earth. Depending on the type of metabolic pathway, some plants are actually more productive with higher concentrations of atmospheric carbon dioxide. Coincidentally, most major food crops belong to this category. As a result, increased atmospheric carbon dioxide results in increased food production from plants.
Amidst all the talk and debate over whether or not global warming is real, it is interesting that carbon dioxide has become one of the targeted enemies to the environmentalist movement. Carbon dioxide is essential to life. Unlike animals, plants have the ability to create their own food. With the birth of agriculture in world history, humans have cultivated and genetically selected plants through the ages that are highly productive, which allows us to not only survive but to thrive and support large populations, even in geographically small spaces.
This is all made possible by the miracle of photosynthesis: the process whereby plants make food out of atmospheric carbon dioxide with energy from the sun, water, and minerals from the soil. Photosynthesis itself is a very complicated biochemical process but at its most basic, carbon dioxide is food via plants. The science behind the discovery of plants’ ability to photosynthesize is by no means modern and the facts concerning photosynthesis have been upheld by modern experiments.
If there was no carbon dioxide in the atmosphere plants would starve and so would we. If we tried to drastically reduce carbon dioxide in the atmosphere would it decrease crop yields? This is a trick question because the answer is both yes and no.
There are different metabolic pathways plants use for catching and converting carbon dioxide into carbohydrates; plants are divided into groups according to their CO2 catching methods. The categories are: C3 plants, C4 plants, and CAM plants. CAM plants are plants adapted to very dry climates such as succulents and cacti. As a group, the CAM plants contribute little to us in the way of food so they won’t be discussed at length here. The main difference between C3 plants and C4 plants is that C4 plants have an internal carbon dioxide concentrating mechanism while C3 plants do not. This allows C4 plants to survive and grow even in very low atmospheric carbon dioxide concentrations; fluctuations in carbon dioxide concentrations have little affect on C4 plant survival. C3 plants, by contrast, are greatly affected by atmospheric carbon dioxide concentrations. Higher carbon dioxide concentrations result in greater plant productivity while lower carbon dioxide concentrations have the reverse effect.
So to answer the above question: lower carbon dioxide concentrations would not affect yields from C4 plants but would definitely decrease C3 crop yields. If there was no carbon dioxide in the air even C4 plant yields would fall because C4 plants can’t possibly concentrate carbon dioxide if there is none in the air to begin with.
The entire world is fed on about 10 major crops: wheat, rice, corn, potatoes, soybeans, oats, rye, barley, hay (cattle feed for beef and dairy, which then becomes food for us), and sugarcane. There are other food crops, of course, but these 10 are the major sources of food that sustain the human population. There are only two from this list that are C4 plants: corn and sugarcane. All the other plants are C3 plants, which means their production is influenced by atmospheric carbon dioxide levels: more carbon dioxide means greater yields. Greater crop yields mean more carbon dioxide is pulled out of the atmosphere and turned into food. Is this a good thing? With ever increasing human populations around the world this may be a welcome result. It makes me wonder why environmentalists never talk about this undeniable benefit of increased atmospheric carbon dioxide.
As a note of interest, to read about how this difference between C3 and C4 plants led to the discovery that honey was being adulterated by corn syrup, read the article on “Pure Honey?“.