In recent years, industry also developed new chemicals as alternatives to CFCs, HCFCs, and HFCs. One category of such chemicals are HFOs (hydrofluoroolefins). These are HFCs which are broken down rapidly after being emitted, avoiding accumulation in the atmosphere. Their greenhouse effect is therefore minimal; per kilogram emission comparable with that of CO2. An HFO is now being used as refrigerant in the air conditioner of cars as a replacement for HFC-134a which has a greenhouse effect of approximately 1300 times that of CO2.
The effect of HFCs or other substances on the total greenhouse effect depends not only on the substance itself, but also on the application. A refrigeration system uses electricity which, depending on the manner of generation, results in emissions of CO2.
In some applications, the CO2 emissions associated with the energy use are more significant for the overall greenhouse effect of the system than that caused by the
The choice for an alternative substance or technique depends not only on the greenhouse effect of the substance and the energy efficiency of the application, but also on the possible flammability and toxicity, availability, cost, etc.