How ACs are Heating Up the World

Beads of sweat drip down your face as the sun beats down on your neck and the humid air makes it difficult to catch your breath. You seek refuge in the nearest building, swinging open the door to an instant wave of cold air that washes over you in a refreshing breeze. From schools to homes to grocery stores, many buildings had their air conditioning (AC) cranked to the max over the summer to battle this year’s record-breaking heat. But what if the same ACs providing refuge from the heat actually contribute to it?

All ACs are made of three main parts: the evaporator coil, the compressor, and the condenser coil. Hot air from inside the building is blown into the AC by a fan and passes the evaporator coil, which contains a liquid refrigerant. The refrigerant absorbs so much heat from the air that the refrigerant evaporates entirely. The gaseous refrigerant flows through the compressor, which pressurizes it, making the refrigerant easier to transport and treat. As the refrigerant flows into the condenser coil, air from the outdoors is sucked into the AC. This air absorbs the heat from the refrigerant, causing the refrigerant to undergo another phase change, this time from gas to liquid. Now that the refrigerant is once again a liquid, it flows back to the condenser coil and the process is repeated until the desired temperature is reached.

Though ACs might seem harmless at first, they are large contributors to climate change. As previously described, ACs are able to lower indoor temperatures by transferring heat from the air indoors to the air outdoors. With enough air conditioners running at the same time in a concentrated area, the temperature difference created by AC usage becomes noticeable. In large cities at night, when temperatures are cooler, the heat from ACs makes the air 1.8 degrees Fahrenheit, or 1 degree Celsius, hotter on average.

In addition, many ACs use refrigerants that contain hydrofluorocarbons (HFCs). HFCs are extremely potent greenhouse gasses and can be anywhere between 140 to 11,700 times more effective at trapping heat in our atmosphere than carbon dioxide. HFCs can escape into the atmosphere through AC leaks that occur due to old age, poor maintenance, and poor manufacturing. Though AC leaks are often small, the sheer quantity of ACs with potential leaks, especially in large cities, adds up to become a significant contributor to HFC emissions: around 40 to 60 percent of HFC emissions are a result of AC leaks.

HFCs aren’t the only greenhouse gasses emitted by AC usage. The vast quantity of ACs also require a massive amount of energy to operate. For instance, ACs can contribute up to 60 percent of electricity consumption in Hong Kong during the summer months. Electricity is most often generated by burning fossil fuels, which creates greenhouse gases. AC usage directly accounts for around four percent of global annual greenhouse gas emissions. These greenhouse gasses absorb some of the heat that would’ve been reflected back into outer space by Earth’s atmosphere and surface. This absorbed heat is trapped within the greenhouse gasses and contributes to increasing temperatures.

Many actions have been taken to try to reduce ACs’ effect on the environment. These actions come primarily in the form of the Kigali Amendment to the Montreal Protocol. The Montreal Protocol is an international treaty that regulates the production and consumption of substances that contribute to climate change. The Kigali Amendment was ratified in 2016 and aims to reduce the production and consumption of HFCs by 80 percent in the next 30 years. The United States ratified the Kigali Amendment in 2022, and almost all new ACs manufactured since then use alternative refrigerants, such as R-454B. R-454B has a similar efficiency to previous refrigerants with HFCs, but a 78 percent lower capacity to trap heat. This means that comparatively, R-454B has a much lower impact on the environment.

As temperatures rise, the incentive to use ACs will rise as well. This creates a feedback loop, as ACs contribute to hotter temperatures and hotter temperatures lead to higher AC usage. Recent trends have shown that the coming years will be even hotter than 2023, turning ACs from a luxury to a necessity in many areas as more people suffer from the effects of extreme heat. While we should accept that ACs will become more prevalent, we must also mitigate the negative effects that they will have on the environment. With new alternative refrigerants being developed and implemented, the future of environmentally-friendly and efficient AC usage is showing more and more promise.