During the growing season, plants like corn, soybeans and other annual crops take in carbon dioxide and discharge oxygen back into the air while storing carbon in their plant material such as seeds, stalks, leaves and roots. An acre of corn yielding 180 bushels removes 8 tons of CO2 from the air during an average growing season and produces enough oxygen to supply 131 people with their year’s needs of this essential for life, according to a Monsanto website which cited USDA information: www.americasfarmers.com/2014/01/29/everything-you-ever-wanted-to-know-about-corn/
This is article one of a two-part series. Today we take a look at how oxygen is produced, carbon is removed (sequestered) from the atmosphere, and how carbon dioxide is added back in what is called the carbon cycle, with an eye to how agriculture contributes to, or detracts from, the warming of the earth’s atmosphere.
While greatly simplified for this article, the production of oxygen and carbon only partially regulate global temperatures, but we concentrate on these factors because they are influenced by agriculture and affect agricultural producers in terms of weather and potentially through government regulations. Metabolizing carbon dioxide through photosynthesis into oxygen and carbon has been going on since algae and other microbes, and eventually plants, emerged eons ago on our planet.
While well over half of earth’s oxygen is produced by oceanic phytoplankton, plants – especially trees and other perennials – produce most of the remaining oxygen. Annual plants, like most agricultural crops, contribute noticeably, however.
Annual agricultural crops take in sufficient carbon dioxide, release oxygen while growing, and store enough carbon during the growing season that oxygen rises somewhat and carbon dioxide (CO2) declines slightly in the northern hemisphere where the majority of the world’s crops are grown each year. CO2 concentrations decrease measurably during the summer and rise during the winter, yielding a small net advantage for our planet.
Annual plants like corn, wheat, soybeans and most vegetables produce a lot of oxygen while growing, but the amount of carbon stored in their decaying fodder and roots is small in comparison to most perennials like prairie forbs, grasses and trees that have large plant masses and root systems and don’t die during winter.
“The fact that farming feeds the carbon cycle does not mean it’s making climate change worse. But growing wheat or corn does less to sequester carbon in the ground than growing a forest or grassland,” said Boston University scientist Joshua Gray: www.harvestpublicmedia.org/article/corn-belt-farming-boosts-global-carbon-cycle
Carbon dioxide comprises about 80 percent of the greenhouse gases that are blamed for warming up the earth’s atmosphere, according to a 2014 EPA publication: www.epa.gov/ghgemissions/overview-greenhouse-gases
Carbon dioxide enters the atmosphere mostly through burning fossil fuels like coal, natural gas, and oil, but also through decomposition of wastes, fires, and some chemical reactions such as the curing of cement.
Methane accounts for 11 percent of greenhouse gases. Methane gases have two main contributors: human-caused sources (64%) and natural sources (35%).
Human activities that enhance methane accumulation include the production of fossil fuels (natural gas is released at oil drilling sites, refineries, and when mining coal), natural gas losses during transportation and by consumers, raising livestock (ruminants like cattle especially get blamed), landfill and other waste decompositions, burning of biomasses such as forest fires and wood for fuel, rice farming which uses paddies that give off methane as submerged materials decompose, gases from manure storage, and biofuels.
Natural contributors of methane include wetlands that release the gas as matter decomposes, thawing of tundra which allows methane to escape, termites, and many lesser sources: www.whatsyourimpact.org/greenhouse-gases/methane-emissions
Before the industrial era began, oxygen from photosynthesis offset the natural production of methane and CO2.
Nitrous oxides and fluorinated gases are products of modernization that account for about 6 and 3 percent of the remaining greenhouse gases respectively. Nitrous oxides are furnished mostly by agriculture, various industries, and burning fossil fuels, causing atmospheric nitrous oxide gases to increase slowly. Fluorinated gases, which are produced mainly by industrial and refrigeration processes, are becoming highly regulated and appear to be holding steady.
It’s apparent from this greatly simplified discourse on the carbon cycle that human activities are altering the amount of CO2, methane, nitrous oxides and fluorinated gases on our planet. Activities of modern humans are making our lives easier, but with costs.
Next week we will look at what agricultural scientists and farmers around the world are doing to generate oxygen, remove carbon, and help manage global warming. Some solutions cost nothing.
Besides many scientific publications that I reviewed for this series, over Thanksgiving I conferred with and thank several family members/guests who know more than me about this subject, including one who measures carbon footprints around the world for UN agencies and other entities interested in what happens – for example – if several thousand hectares of perennial forest are converted into the production of palm oil, soybeans and other crops.