When it comes to protecting the environment, most refrigerants just aren’t that cool. That’s been the conclusion of environmental groups and international treaty organizations for decades, and so the EPA is progressively phasing out the use of certain refrigerants. Here’s what you need to know about these refrigerants and their phase outs.

Refrigerants are fluids or gases with certain thermodynamic qualities that make them useful for the “refrigeration cycle,” which is a physical process for moving cooler heat to a location of warmer heat. Air conditioning units that employ refrigerants compress the fluid to its boiling point so that it changes phase and evaporates into a cold gas that circulates within a piping system, and then a fan blows over those cold pipes into the target environment. Finally, a condenser changes the gas back into a fluid and the cycle continues. Throughout the process, the refrigerant slowly leaks out of the system and into the wider environment, and being lighter than air, ultimately ends up in the Earth’s atmosphere.

Two kinds of refrigerants, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), were identified in the 20s and popularized in the 50s for AC units as ideal because because of their inert properties such as non-inflammability, stability and low toxicity, unlike the relatively dangerous refrigerants used at the time like ammonia. These are the refrigerants commonly called “freon,” which is a trademark registered by a joint venture between General Motors and DuPont in the 30s. DuPont also developed the R- numbering system that’s now used for coding the various refrigerants based on their molecular structure. R-22 is the name of the most common HCFC, which is distributed in light green cylinders.

In the 70s, scientists began identifying CFCs and HCFCs as the cause of ozone layer depletion, and in 1987, the United Nations universally ratified an international treaty to phase them out, known as the Montreal Protocol. This led to the EPA implementing a multi-stage phase out of these refrigerants, including R-22. In 2010, production and import of R-22 was halted in the U.S., except for the amount needed for units that were manufactured earlier. In 2020, production and import of R-22 will be halted entirely.

In the meantime, prices for R-22 are exploding. “New refrigerant will not be produced after 2019 and the cost of a recharge is expected to skyrocket even further,” says Steve Lewis, president and CEO of an AC repair company in Las Vegas.

Following the Montreal Protocol, the refrigerant industry moved to using perfluorocarbons (FCs) and hydrofluorocarbons (HFCs). The most common of these in use for air conditioning today is called R-410A, which comes in pink cylinders. Since R-410A does not contribute to ozone depletion, it’s a likely replacement for R-22.

Unfortunately, scientists now identify R-410A and other HFCs as having a high potential for causing global warming. This begs the question: When will R-410A get phased out? That’s an open question. In 2016, the Obama administration signed on to an agreement to begin phasing out HFCs in 2019. In 2017, a federal court decided that the EPA was overstepping its authority, but that decision was later suspended until an appeal is reviewed.