Air conditioning: The climate-change dilemma

Posted: August 13, 2024

The world has both too much and not enough air conditioning. On the one hand, hundreds of thousands of people die every year from lack of adequate cooling. On the other hand, just powering the air conditioning we already have constitutes nearly 10% of the world’s electricity consumption. As emerging markets—particularly China, India and Thailand—begin using more air conditioning, the International Energy Agency (IEA) estimates that the amount of energy used for cooling will double in the next 25 years, assuming we do nothing to mitigate it. And that's before accounting for the increased cooling needs of new cloud-computing and AI data centers.

Paradoxically, while using air conditioning releases greenhouse gasses (GHG), the failure to use it contributes to GHG emissions as well. That’s because about 500 million tons of food goes to waste every year because it’s not kept cool enough during storage and transport. Not only could that spoiled food feed nearly half the 2 billion people who are food insecure, it also contributes 4.4 gigatons of CO2 equivalent GHG emissions—a full 8% of all the GHG emissions worldwide. As a result, expanding cold chains—the refrigerated transit and storage infrastructure— would decrease carbon emissions by ten times the amount it increases them.

As heat waves become longer, more frequent and severe—such as those scorching Europe this summer—the race is on to find a way to both expand the availability of cooling while cutting its carbon footprint.

The high cost of cooling

Only 15% of people who live in hot climates have air conditioning—and that percentage is even lower in the developing economies of sub-Saharan Africa and south Asia. As of 2019, the lives, health and productivity of  a quarter to half of the world’s population—2 to 4 billion people—were in danger because of heat stress.

Between 2002 and 2021, heat-related deaths of people 65 and older increased by 61% to 345,000 in 2019. Another 420,000 people die every year after eating food that hasn’t been kept properly refrigerated. More air conditioning could prevent those deaths, but it would also create more carbon emissions, from both electric power and refrigerant chemicals.

Refrigerants

Traditionally, air conditioning and refrigeration have used fluorocarbon chemicals to transfer heat from interior to exterior spaces. Many of these chemicals are greenhouse gasses thousands of times more potent than carbon dioxide. For example, the most commonly used refrigerant for motor vehicle air conditioning, has a global warming potential (GWP) of 1,430. That means that each molecule of HFC-134a contributes 1,430 times as much to the greenhouse effect as one molecule of carbon dioxide.

Because these refrigerants leak from air conditioning systems and often escape into the atmosphere when they’re decommissioned, replacing them with alternative refrigerants could prevent about 45 gigatons of CO2-equivalent emissions over 30 years. That’s 1.5 gigatons each year—as much as the emissions produced by 200 million homes or 4,000 natural gas power plants in that same time.

In 2022, the United States joined 137 other countries in ratifying the Kigali Amendment to the Montreal Protocol, which calls on countries to replace high-GWP refrigerants with alternatives. Compared to fluorocarbons with GWPs in the thousands, Ammonia has a GWP less than one and propane and isobutane have GWPs less than four. Even CO2 itself works as a refrigerant, with a GWP of just one. The U.S. expects that global adoption of the Kigali Amendment could avoid half a degree C of warming over the next century.

Electric grid burden

As global temperatures rise, the energy that air conditioning requires to keep up increases exponentially. That’s just a hard cold fact of thermodynamics. Just a small increase in temperature outside from 35.6 C (96 F) to 37.8 C (100 F) requires your air conditioner to use 42% more energy just to keep the temperature inside at 24 C (75 F).

Moreover, when everyone cranks their air conditioning up at once during a heat wave, they put an extra burden on the electric grid, which can lead to blackouts and extra energy spent fixing the grid. It also can prompt utilities to fire up older, less efficient power plants to keep up with demand.

Intelligent appliances managed in the cloud that use adaptive-predictive control to automatically reduce energy use based on grid conditions have improved electricity savings by 24%. Passive cooling techniques, like creating shade and cool roofs can help reduce the need for air conditioning.

Humidity

But, just cooling the air is not sufficient to keep people comfortable. As they say: as often as not, it’s not the heat—it’s the humidity. Using air conditioning to control humidity actually contributes more to climate change than controlling temperature. New technology that uses dessicants (like the silica packets that keep packages dry) instead of refrigerants to dehumidify the air could further reduce the energy needed for air conditioning.

As the world continues to heat up, we’ll need to use air conditioning more than ever—to both save lives and preserve food. As with so many solutions to climate change, many tools already exist that can help—we just need to use them.