Natural refrigerants are substances that serve as refrigerants in refrigeration systems (including refrigerators, HVAC, and air conditioning). They are alternatives to synthetic refrigerants such as chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), and hydrofluorocarbon (HFC) based refrigerants. Unlike other refrigerants, natural refrigerants are non-synthetic and can be found in nature. The most prominent of these include various natural hydrocarbons, carbon dioxide, ammonia, and water. Natural refrigerants are preferred to their synthetic counterparts for their higher degrees of sustainability. With the current technologies available, almost 75 percent of the refrigeration and air conditioning sector has the potential to be converted to natural refrigerants. Background Synthetic refrigerants have been used in refrigeration systems since the creation of CFCs and HCFCs in 1929. When these refrigerants leak out of systems and into the atmosphere they can have adverse results on the ozone layer and global warming. CFC refrigerants contain carbon, fluorine, and chlorine and become a significant source of inorganic chlorine in the stratosphere after their photolytic decomposition by UV radiation. Released chlorine also becomes active in destroying the ozone layer. HCFCs have shorter atmospheric lifetimes than CFCs due to their addition of hydrogen, but still have adverse effects on the environment from their chlorine elements. HFCs do not contain chlorine and have short atmospheric lives, but still absorb infrared radiation to contribute to the greenhouse effect from their fluorine elements. In 1987 the Montreal Protocol first acknowledged these dangers and banned the use of CFCs by 2010. A 1990 amendment included agreements to phase out the use of HCFCs by 2020 with production and import being eliminated by 2030. HFC refrigerants, which have a negligible impact on the ozone layer, were seen as viable replacements, but these too have a high impact on global warming. The Kigali amendment of 2016 calls for these HFCs to be cut back by 80% over the next 30 years. Natural refrigerants are one of the potential options for replacement of HFCs, and are growing in usage and popularity as a result. The natural refrigerant industry is expected to have a compounded annual growth rate of 8.5% over the next 4 years, and is expected to become a US$2.88 billion industry by 2027. Sustainability metrics Refrigerants are typically evaluated on both their global warming potential (GWP) and ozone depletion potential (ODP). The GWP scale is standardized to carbon dioxide, where the refrigerant's value is the multiple of the heat that