Radiative efficiency is a measure of ‘greenhouse strength’ for different greenhouse gases, defined as the change in radiative forcing per change in atmospheric concentration of a gas (in Watts per metre square per part per billion; W m^-2 ppb^-1).

Radiative forcing is the measure of how different factors (including greenhouse gases) change the balance between incoming and outgoing energy in the atmosphere. Expressed as the change in energy balance per unit area (in Watts per metre square; W m^-2) over a given timeframe – typically contemporary compared to preindustrial conditions.

Reconstituted meat is a paste- or liquid-like meat product that is produced from ground meat. Fat and excess water are separated from the meat using a centrifuge or an emulsifier (a machine used to produce the meat into a fine and homogeneous paste or liquid of a desired thickness). Reconstituted meat is mostly used as a basis for pet food and as a supplement in some meat products for human consumption (e.g. chicken nuggets and some sausages).

A reduction fishery catches wild fish to be converted into fishmeal and fish oil (often to supply the aquaculture sector), rather than catching fish for direct human consumption.

Reforestation refers to the spontaneous or intentional return of trees in an area that has lost its forest cover either as a result of deforestation by humans or in other ways such as wildfire or drought.

Reformulation refers to changes food manufacturers make to the production recipes of processed and ultra-processed food products to improve their nutritional profile. Examples of reformulation include replacing sugar with artificial sweeteners (e.g. aspartame or sucralose) to reduce the food’s energy content or reducing the amount of salt or saturated fat in a food product.

Regenerative agriculture aims to generate farming systems that improve soil health, increase biodiversity and sequester carbon through the use of practices such as cover crops, crop rotations, minimal tillage, organic compost, agroforestry and crop-livestock integration. Many of these practices are also associated with organic farming and agroecology. Various certification schemes are being developed which will specify the processes and outcomes required for products to be classified as ‘regenerative’

See regenerative agriculture, conservation grazing, rotational grazing, mob grazing and crop-livestock integration.

Reintroduced species are species that are introduced by humans into an ecosystem to replace a species of the same type that has gone (locally) extinct. A reintroduced species can either be of the same species type as the species that was lost or a related species with similar appearance and/or behaviour.

The concept of resilience, in the context of food system sustainability, refers to the ability of the food system to cope with and recover from socio-economic or environmental shocks and pressures. A resilient system has a certain degree of toughness and is able to bounce back against or adapt to disturbances. A resilient food system, for example, is able to keep providing food or other outputs such as livelihoods for farmers, drinking water, and biodiversity conservation under conditions of drought, a drop in food prices, war, climate change, the spread of virus in plants or animals, and so on. Resilience can be thought of at different scale levels. For example, what may be considered as resilient on a national level may not be understood to be resilient at a farm level. While some see resilience as synchronous with sustainability, others point out that a resilient system may also be one that resists needed transformation; an unsustainable status quo may in fact be resilient to change.

Rewilding is a broad concept that emerged in the 1990s in the field of conservation biology and which has evolved in recent years to encompass a range of visions on nature and the management of ecosystems. Rewilding revolves around the understanding that ‘nature’ has become marginalised throughout human history. The ambition of rewilding is to turn the tide: it aims to give land back to nature and change the management of ecosystems for them to become more resilient and autonomous. In doing so, rewilding aims to kickstart the restoration of global biodiversity and strengthen ecosystem functions such as flood protection and carbon sequestration. An important underlying objective for many rewilders is to create a ‘wilder’ Earth where humans will be able to experience nature more frequently and in new, more diverse ways. Common rewilding strategies include trophic rewilding (the restoration of complex trophic interactions between species kickstarted by the reintroduction of keystone species such as large carnivores or large herbivores) and passive rewilding (the spontaneous rewilding of ecosystems when land is left to its own devices). Rewilding is a contested term. Debate centers on the implications of rewilding for food production and for rural and indigenous communities. An important topic of discussion concerns the extent to which rewilding is compatible with farming and whether its large-scale adoption would require a substantial downscaling of agricultural land use. Further topics of debate include the goal of some rewilders to restore landscapes to a pre-human baseline (see Pleistocene and Holocene rewilding) and various proposals to reintroduce large carnivores (e.g. wolves and tigers) in places where these went extinct. While rewilders today do not always see their own approaches reflected in these discussions, critics of rewilding are in favour of alternative visions that seek to restore nature and biodiversity through approaches that they see to be more clearly based on the principle of social justice.

The right to food was initially recognised in the 1948 Universal Declaration of Human Rights. It has since been developed by the Food and Agriculture Organisation of the United Nations, who now recognise the importance of the right to adequate food, defining this as ‘regular, permanent and unrestricted access, either directly or by means of financial purchases, to quantitatively and qualitatively adequate and sufficient food corresponding to the cultural traditions of the people to which the consumer belongs, and which ensure a physical and mental, individual and collective, fulfilling and dignified life free of fear’.

Rotational grazing is a system in which pasture is split up into paddocks and grazing animals moved from paddock to paddock over time. The result of this is that any individual part of the pasture is not being grazed for a significant portion of the year, allowing it time to recover. See conservation grazing, regenerative grazing, and mob grazing.

A ruminant is a mammal with a four-compartmented stomach which enables it to acquire nutrients from plant-based food such as grasses, husks, and stalks. Examples of ruminants include cattle, sheep, goats, deer, giraffes, and camels. After swallowing, microbes in the ruminant’s rumen (its first stomach compartment) begin fermenting the food. This process generates fatty acids (nutrients which the ruminant absorbs through its rumen walls) and methane, which the ruminant eructs or burps. Through this process, ruminants are able to digest coarse cellulosic material which monogastrics and people cannot. Methane emissions from ruminants are a significant source of greenhouse gasses from ruminant-based livestock systems.