Glossary: Climate Change and the Food System

Key terms and concepts on the connection between food systems and climate change

Key Terms to Understand the Food System and Global Warming

You don’t have to become a climate scientist to understand climate change, but there are a few key terms that are important to understand to ensure you’re not bogged down by jargon. So in case you’re still scratching your head when you read “carbon-dioxide equivalent” or you can’t name the key greenhouse gases, here’s your cheat sheet.

Greenhouse gases

Any gas in the atmosphere capable of absorbing infrared radiation (heat) reflected from the earth’s surface. Greenhouse gases occur naturally in the environment and are also generated by human actions, like burning fossil-fuels or raising livestock. The main greenhouse gases are carbon dioxide, methane, and nitrous oxide. Today, increasing levels of manmade greenhouse gases in the atmosphere are causing temperature increases and contributing to climate change. (You may sometimes see this term referred to as GHGs).


Greenhouse effect
Certain gases – called “greenhouse gases” – present in the Earths’ atmosphere trap energy from the sun as infrared radiation (or heat) that has been reflected off Earth’s surface. As these gases build up in the atmosphere, more and more heat is trapped, warming the Earth’s surface and leading to fluctuations in the climate. The greenhouse effect is a natural phenomenon in the atmosphere; it is a vital part of maintaining normal temperatures on the planet. But the last century’s exponential rise in greenhouse gases has led to significant increases in this greenhouse effect on the planet. The Earth system as a whole works much like the human body with respect to temperature; The overall increase of a few degrees has major impacts on the way the entire system functions. 


Global warming
Greenhouse gases naturally occur in the environment. Water Vapor is actually the most abundant GHG that occurs both naturally and as part of the feedback loop with other GHGs, many of which are released into the environment by humans. The Nobel-Prize winning Intergovernmental Panel on Climate Change report, the Fourth Assessment, on global warming confirms that the current atmospheric concentration of carbon dioxide and methane, two important heat-trapping gases, “exceeds by far the natural range over the last 650,000 years.” Since the beginning of the Industrial Revolution, the IPCC notes, concentrations of both gases have increased at a rate that is “very likely to have been unprecedented in more than 10,000 years.” This increase in atmospheric greenhouse gas is leading to higher temperatures that are destabilizing the planet’s climate – what is commonly called global warming.  But global warming might more aptly be dubbed “climate chaos” because its effect is not just “warming” but actually more erratic and extreme weather, including more acute droughts and flooding. The IPCC has found that the intensity of hurricanes in the North Atlantic, for instance, has increased over the past thirty years, related to increases in the temperatures of tropical seas. At the same time, droughts have become longer and more intense and have affected larger areas throughout the tropics and subtropics. 

Carbon dioxide equivalent, CDE, or CO2eq
You may notice one of these three terms in articles talking about greenhouse gas emissions. So what do they mean? First, it’s important to realize that there are many different greenhouse gases out there, not just carbon dioxide. To understand the food system’s role in global warming, for instance, the most important greenhouse gases are methane and nitrous oxide. Each greenhouse gas has different levels of potency, or global warming effect. In order to compare these gases and measure greenhouse gas emissions, climate scientists standardize these potencies. Because carbon dioxide is the most common and least potent greenhouse gas, these other gases are benchmarked to carbon dioxide. For example, the carbon dioxide equivalent for nitrous oxide is 296. In other words, nitrous oxide has a global warming effect 296 times more potent than carbon dioxide. Sometimes, however, to simplify their language people will, as I do, use the term “greenhouse gas emissions” to describe all the greenhouse gases measured by these equivalencies.

Fossil fuels
A hydrocarbon deposit, such as oil, coal, or natural gas, formed from the decayed remains of prehistoric animals or plants and used for fuel. Note that fossil fuels play a huge role in the food system: petroleum is used as the base of many of the chemicals used in industrial farming, fossil fuels are used to power on-farm machinery and processing, and natural gas is used to make the artificial nitrogen fertilizer, just to mention a few connections.

Coined by colleague Jennifer Wilkins at Cornell University, “foodprint” refers to the impact of our food choices on global warming based on our food’s emissions during growing, processing, packaging, and transporting our food. Some ideas for reducing our foodprint include choosing plant-centered, organic, locally grown foods and by limiting the amount of processed foods that we eat.

Rising Temperatures
The IPCC estimates that the global average temperatures will increase 2 to 4.5 degrees Celsius, which is between 3.6 and 8.1 degrees Fahrenheit, by the end of the century. Note that often articles about global warming and rising temperatures will just give the degrees in Celsius and you will need to convert to Fahrenheit.

One of the reasons livestock has such a significant global warming toll is that many animals raised for meat are ruminants – like sheep, goats, and cattle. Ruminants are mammals distinct in how they digest their food. They do it differently than we humans: they digest in two steps. First, ruminants semi-digest their food – the raw plant material – then they regurgitate it and the “cud,” as it’s called, is chewed again to break it down further. (This step is called ruminating and is the inspiration for our use of “ruminate” to mean mulling something over.) This quality of cattle is also why you may have noticed if you’ve ever stumbled on a field of cows munching away on tall grass, they all seem to be in a constant state of chewing. The climate change downside to rumination is that this process produces methane in the gut of ruminants, a greenhouse gas 296 times more powerful than carbon dioxide. As they digest, ruminants must release this gas and do so through belching or, to a lesser degree, flatulence. While this rumination is what allows cattle to digest fibrous grasses that we humans can’t convert into digestible form, it also adds to ruminants’ climate change toll. Cattle production has been drastically scaled up within the last half-century and production is only forecasted to expand as the dietary demands of an emerging middle class increase. It is also worth noting that landuse has been drastically altered to make room for meat production. Deforestation for the use of herding is also a major contributer to global warming. 

Wetlands include swamps, bogs, fens, and marshes, areas of land that are saturated with water and filled with diverse vegetation. Wetlands can sequester more greenhouse gases than forests, savannas, grasslands, or croplands and therefore are an important factor in global warming.