The US Environmental Protection Agency announced a rule Monday that would phase out hydrofluorocarbons (HFCs), the potent greenhouse gases that are widely used as refrigerants.

Though HFCs aren’t intentionally emitted in the regular use of refrigerators and air conditioners, they often leak out at various phases in an appliance’s life cycle, from manufacturing through disposal. One of the most widely used HFCs, R-134a, causes 1,430 times more warming than an equivalent amount of carbon dioxide over 100 years. Another that is commonly used in supermarkets, R-404A, has a global warming potential of 3,900. Eliminating the use of HFCs worldwide would reduce emissions enough to avoid up to 0.5˚C (0.9˚F) of warming by 2100. //

Once again, countries from around the world came together to address the issue, signing the Kigali Amendment that updated the Montreal Protocol to include HFCs. Notably, neither the US nor China has ratified the agreement, but last month, the two largest greenhouse gas emitters both agreed to eliminate the use of HFCs. //

there are already substitutes available for new refrigerators and air conditioners. One substitute that is already in many models of refrigerators is isobutane. Known in the industry as R-600a, it’s inexpensive, it has almost no ozone depletion potential, and it has a small global warming potential (three instead of R-134a's 1,430). //

Almost a decade ago, isobutane and other hydrocarbon refrigerants seemed poised for use in the market. In 2011, Underwriters Laboratories (UL) gave the refrigerants the go-ahead, and the EPA followed soon after. But then UL slashed their limits, citing a risk of fire if hydrocarbon refrigerants were to leak in a small room that also contained an open flame, like from a gas-fired water heater. //

Ultimately, the fire issue may be moot as some grocery stores have begun switching to using carbon dioxide as a refrigerant. Though it requires higher pressures throughout the cooling system, carbon dioxide is not detrimental to the ozone layer. And its global warming potential? One.