C3 plants are those whose method of photosynthesis is adapted to cooler and wetter climates. They represent the majority of plants globally and include rice, soybean, and wheat. C3 plants are less efficient at creating energy for growth than C4 type plants in hot and dry climates.

C4 plants are those whose method of photosynthesis is adapted to hotter and dryer climates. They represent only a small fraction of plants globally. Examples include some grasses, maize, sugar cane, millet, and sorghum. In hot and dry climates, it is more efficient at creating energy for growth than C3 plants.

Carbon dioxide equivalent (CO₂.eq) is a measure used to compare and combine the warming effect of emissions from different greenhouse gases, using single measure of impact. This is done on the basis of a conversion factor known as the Global Warming Potential (GWP), which is the ratio of the total energy trapped by a unit of greenhouse gas (e.g. a tonne of methane) over a specific period of time (normally 100 years), to that trapped by carbon dioxide over the same time period.

Carbon intensity refers to the amount of carbon emissions that are produced to achieve a specific outcome. For example, the carbon intensity of electricity is the emission produced per unit of electricity supply.

A carbon price is a cost that must be paid for the right to produce a unit of carbon pollution. This may take the form of a carbon tax on pollution or an obligation to buy permits from a carbon market. In either case, the goal is to promote investment by polluters to reduce emissions of carbon dioxide and other greenhouse gases.

Carbon sequestration is any process by which carbon dioxide is removed from the atmosphere and stored elsewhere, whether by biological or technological means. There are two main types of carbon sequestration, terrestrial (carbon plants and soils), and geologic (carbon stored in rock formations) . One classic example of carbon sequestration is reforestation.

A carbon sink is a reservoir (natural or artificial) which accumulates and stores carbon over time. The process of removing carbon dioxide from the atmosphere by increasing the sink capacity of the reservoir (which could be a soil) is called carbon sequestration

Carbon stock refers to the amount of carbon stored in plants, soils, and ecosystems.

Carrying capacity, in ecology, refers to the maximum population of a species that can be sustained by a particular environment. The concept can also be applied to people, for example in attempts to calculate how many humans the earth can sustain indefinitely.

Cellular agriculture refers to the production of agricultural products (foods or food ingredients as well as fuel or fibre) using cell cultures. Cell-based meat is a well-known example of cellular agriculture.

Choice architecture refers to the design of which choices are made available or not to people in a given context, and how these different choices are presented to them. In any context, there is always a choice architecture affecting decision making, whether deliberately designed or not. For example people's purchasing decisions in a shop are dictated by the products available to buy in a grocery shop, their price, their presentation and visibility, the extent to which they are advertised and promoted and so forth: these collectively constitute the choice architecture.

Climate smart agriculture (CSA) was first introduced by the FAO in 2010 as an integrated approach geared at reorienting and redesigning agricultural systems to address and build resilience to climate change, and is often discussed in the context of low-income countries. CSA involves three interconnected elements: increasing agricultural productivity and incomes; adapting and building resilience to climate change; and the mitigation of greenhouse gas emissions. It aims to identify context specific agricultural strategies supporting these elements and guide coordinated actions among stakeholders (e.g. farmers, researchers, private sector, civil society and policy makers) from the farm to the global level. CSA is criticised for justifying nearly any form of agriculture (thereby ‘greenwashing’ unsustainable practices) and for failing to address enduring inequalities in food production and distribution. CSA is closely related to the concepts of sustainable intensification and ecological intensification but differs from them in its strong focus on planning and implementation for climate change adaptation and mitigation, and less on reducing environmental impacts beyond emissions.

A cohort study, commonly used in medical and nutritional epidemiology, is a longitudinal study that samples a cohort (a group of people that is defined by having experienced the same event, e.g. birth or graduation, in a selected time period) and follows it over time to investigate people’s exposure to certain factors (e.g. the consumption of certain foods) and the occurrence of particular health outcomes. For example, a cohort study may measure the dietary patterns over time of a group of people who were born between 1960 and 1970 to find out which dietary patterns are associated with the development of diabetes or particular cancers. There are two types of cohort studies. Prospective studies follow a cohort of people who differ by certain factors (e.g. smokers and non-smokers) to study which medical conditions appear in what part of the cohort (e.g. after 20 years more smokers than non-smokers have developed lung cancer). Retrospective studies study a cohort after a medical condition (e.g. lung cancer) has occurred in a part of the group to trace back which factors (e.g. smoking) may have contributed to this.

A cold chain is a supply chain or part of a supply chain where products and raw materials are stored or transported at low temperatures (either frozen or refrigerated at a temperature generally lower than 8°C).

Colorectal cancers are those of the bowel and colon.

A companion crop is a plant grown in close proximity to another crop plant in order to provide some benefit. Such benefits include legumes grown to provide nitrogen fixation and lower the need for synthetic nitrogen inputs, densely growing undercrops that do not compete with the crop but cover the soil and prevent weed growth, plants with insect-repelling properties to reduce pests, flowering plants which attract pollinators, and others. By replacing other, artificial interventions to achieve these goals, companion planting can be considered an example of a 'nature-based solution'. Companion crops might themselves also be food crops, or be grown solely for these benefits to the primary crop. Companion planting is a form of polyculture, and is typical of permaculture and agroecological growing.

See companion crop.

A confounding factor is a factor that influences the relationship between variables that are investigated. In dietary research, for example, a lack of physical exercise may potentially confound the association between the consumption of soda beverages and overweight: when those who drink the most soda beverages are generally more overweight, but also exercise less, the association between the consumption of soda beverages and overweight may be caused partly or entirely by a lack of exercise. Other common confounding factors include age, gender, whether people smoke or drink alcohol, occupation, educational attainment, or income. Confounding factors are a potential bias in statistical research and may lead to over- or under-estimating the relationship between variables. While theoretically their number can be infinite, statistical research often accounts for a set of known potential confounding factors.

Often described as a mission-driven discipline, conservation biology is a field of study concerned with the protection and maintenance of the earth’s biodiversity. Research in conservation biology draws on other disciplines including ecology, biology and the social sciences and humanities.

Conservation grazing is the use of grazing livestock to maintain or increase the biodiversity of natural pastures and other habitats.

The concept of the ‘corporate food regime’ was developed by political economist Phillip McMichael, in his work identifying different historical phases in the political economy of food and agriculture. He characterises the period from the late 1980s onwards as the ‘corporate food regime’ due to the increasingly prominent role played by large transnational corporations in all aspects of food provisioning, including through their influence on  market prices and the establishment of new regulations and trade policies. The idea is widely used by academics, particularly proponents of food sovereignty, to critically refer to the various actors and processes that facilitate the dominance of an export-led global food system.

Cost-benefit analysis looks to inform policy decisions by calculating all related costs and benefits associated with a given decision. For example, a government wanting to reduce meat consumption, could propose various policy options including banning meat advertising, taxing meat products, or subsidising the production of alternative protein. A cost-benefit analysis would estimate the costs and benefits of each option by using estimated economic values for any social and environmental benefits (like potential reductions in greenhouse gas emission and diet-related hospital admissions). The results of this cost-benefit analysis could then be used to inform policy. The process of cost-benefit analysis often involves discounting when estimating the benefits of a policy decision, because whilst costs are often upfront, any benefits tend to arise in the future. Cost-benefit analysis and discounting are both important approaches used in the creation of nature markets that place an economic value on the environment.

Cover crops are crops that are grown with the purpose of protecting or improving the soil, rather than for harvest. Cover cropping can prevent soil erosion, improve soil fertility and quality, and help prevent pests and diseases. This practice can reduce the need for chemical inputs and is commonly associated with agroecology, regenerative agriculture and organic farming.

Crop rotation is the practice of growing different types of crops in sequence across the same area of land. It is designed to optimize nutrients in the soil, improve soil health, and counter pressure from pests and weeds. This practice can reduce the need for chemical inputs and is commonly associated with agroecology, regenerative agriculture and organic farming.

Crop-livestock integration refers to the practice of combining the cultivation of one or more crop with at least one type of livestock. This integration is designed to reduce reliance on external inputs, as the crops provide feed for the animals, and the animal manure provides nutrients that foster crop production. Integrated crop-livestock farming is associated with agroecology, regenerative agriculture and organic farming.