It is August and it is hot outside. Right on cue, the press is full of stories about record setting heat waves at both the local and global level. I’m not a climate scientist or a meteorologist, but I have no reason to doubt the accuracy of these articles. From my limited research, the overwhelming scientific consensus seems to be that the earth is warmer now than it has ever been since people started measuring temperatures on a systematic basis (roughly 150 years ago) and probably warmer than it has been for at least 120,000 years (according to paleoclimate scientists).
Where I sit at the moment, however, is a comfortable 72 degrees thanks to a wonderful invention known as air conditioning. I suspect I could live without this invention – after all, billions of people currently do – but I really don’t want to find out. It is central to my comfortable lifestyle. As an urban planner, I also know that air conditioning is central to the development of modern cities and to the migration patterns that have shaped our country.
Unfortunately, the pleasure I take from air conditioning was undermined recently by an article in the Washington Post entitled “Addicted to Cool: How the dream of air conditioning turned into the dark future of climate change.” The article pointed out the huge demand air conditioning places on our electrical supply grid and the greenhouse gasses created by our current generation sources – not to mention the leaking refrigerants which are greenhouse gasses in their own right. In effect, the more we use air conditioning the more we need air conditioning. It went on to view this situation with almost existential angst:
“It’s possible to see a future in which we are dependent on the perfect, continuous performance of air conditioning the way many people are dependent on lifesaving drugs, planes are dependent on air traffic control, and a colony on the moon or Mars would be dependent on perpetual sources of oxygen and water. It is a technology so deeply embedded in our daily lives, and so increasingly important to our survival, that when we think of it, it is not with pleasure, as a luxury, or with pride, as an exemplar of our technical ingenuity. Rather, it reminds us of our frailty.” [1]
Other articles have used terms like “climate antihero” [2] and “absolutely disastrous” [3] to describe our dependence on air conditioning. Exactly how guilty should I feel? I decided to dig a little deeper to learn more about a technology I have largely taken for granted, and then to take several steps back to gain some much needed perspective on how it fits into our society and economy, rather than simply viewing air conditioning through an environmental lens.
The History
Ancient Romans experimented with buildings that had double walls and the ability to circulate water in the space in between to keep the indoor rooms cooler. Clever, but expensive and tricky to maintain. People have long known that allowing a big chunk of ice to melt lowers the temperature of the surrounding air. It is even more effective if you can blow air across the melting ice and circulate that throughout the building. The first “air conditioned” buildings – such as Chicago’s Auditorium Building and New York’s Carnegie Hall – used this technique in the late 1800s.
Unfortunately, ice was expensive, particularly in the hot climates where it was needed the most. Enter John Gorrie, an Apalachicola, Florida doctor who noticed that his patients symptoms became more severe during hot weather. In order to help cool them, he invented a machine in 1851 that used compressed air to make ice in a 10” x 10” x 4” mold. Despite the ingenuity of his device, it never became popular with the public. In fact, he was mocked because what he was producing was not “God’s ice” and he ended up dying penniless a few years later.
Technology (and public opinion) moved on, however, and in a few decades mechanical ice production was far more efficient and more accepted. In fact, the modern system for rating the capacity of an air conditioning system is referred to as “tons” of capacity. One ton of capacity is technically the ability to remove 12,000 British Thermal Units (or BTUs) from a given space in one hour. But it originated as the amount of heat necessary to melt a one-ton block of ice!
The next major step forward occurred in 1902 when Willis Carrier invented a mechanical way to cool and dehumidify a printing plant in Brooklyn, New York. The plant did color printing which entailed running paper through a printing press multiple times – once for each layer of color. The problem was that the heat and humidity would fluctuate during the day and cause the paper to expand or contract, thus ruining the quality of the color image. Carrier's invention solved both problems.
Air conditioning was initially popular primarily with industrial buildings that produced products that were sensitive to heat and humidity (e.g. pasta, chocolate, printing and chewing gum, etc.). Industries that previously had to shut down for the summer could now operate year-round. [4]
Two decades later it started showing up in commercial buildings frequented by the public such as movie theaters and hotels. On a hot day, people would buy a ticket to an air conditioned theater regardless of what movie was showing. In 1928, the Milam Building in San Antonio became the first air conditioned, high-rise office building in the country. Traditionally, urban office buildings were built in a “U” or “H” shape and covered with operable windows so that they could capture breezes on hot days. Unfortunately, when it was really hot or the air was still you ended up with lots of sweaty (and unhappy) office workers. Again, air conditioning became a boon to productivity.
After World War II, air conditioning technology became cheaper and more compact. It became a standard feature of most new commercial buildings outside of areas that were traditionally cool such as the Northwest and Northeast. In the 1950s, inexpensive window units became widely available in stores which made home air conditioning economically feasible for the first time. It gradually was incorporated into suburban tract housing as “central air” and by 1957 ten percent of all households had some form of air conditioning. By 1975, that number was over 50 percent of all households, and air conditioning was commonplace not only in buildings but in transportation vehicles such as personal automobiles. In fact, the iconic features of suburban development – long commutes, enclosed shopping malls, and high-rise office buildings – would not have been nearly as popular absent the rise of air conditioning.
The Ripple Effects
Air conditioning did not just make us cooler, it changed our lives and our society. The increase in productivity was mentioned briefly above, but it is hard to overstate the economic impact on our country. People are simply more productive at working, thinking or learning when they are housed in a building with a relatively stable temperature range regardless of the outdoor weather.
This was a point that was not lost on the air conditioning and advertising industries. Ads in the 50s and 60s depicted indoor workers as elegantly dressed in modern surroundings (made possible by air conditioning, of course) while outdoor workers were gritty and sweaty as they struggled with the heat. A 1949 Carrier ad in the Saturday Evening Post showed a man sleeping outside under a sombrero with text that read: “Temperature 102° – Productivity 0.” [1] Executives of the day might have missed the subtle racism, but they certainly understood the potential impact on their bottom line.
The fact is that productivity drives the quality of life that we enjoy. If we didn’t have air conditioning (and other productivity enhancing technologies), we also wouldn’t have many of the other perks that come with living in a country that is an economic powerhouse.
The productivity we have gained from air conditioning is not just an important technical detail, it is also an important geographic detail. Air conditioning helped transform the southern swath of the United States from a sleepy backwater into an economic dynamo. Hot, humid locales that many people found unlivable for much of the year suddenly became attractive as air conditioning became ubiquitous. As an example, look at the chart below which shows the growth rate over the past 80 years for Florida, Texas and Arizona.
For comparison, the population of the United States went up by 250 percent during the period from 1940 to 2020. The rate of growth in Texas over the same period was almost double that amount (455%), Florida grew by more than 1,100 percent, and Arizona grew by more than 1,400 percent. The migration from north to south has been one of our country’s biggest demographic stories of the past century.
Air conditioning not only promoted migration to the south, it also facilitated migration from rural to urban areas. Cities lost their image as hot, treeless deserts and became both literally and figuratively “cool.” The urban heat island effect – which results in inner city temperatures that are 5 to 10 degrees warmer than surrounding rural areas in the summer – is certainly a real thing but it became irrelevant with air conditioning.
It didn’t make any difference what the local weather patterns were like or that the west facade and the north facade looked exactly the same despite wildly different solar heat gain coefficients. Architects were focused on building construction costs – the cost of running an air conditioner in a poorly designed building was an operating cost that many architects chose to ignore.
It also meant that residential construction in Phoenix, Las Vegas and Palm Springs moved away from adobe and other forms of masonry to the same type of wood frame construction that was used in Minneapolis, Chicago and other northern cities. Fast and cheap were the key parameters when comfort was simply an issue of twisting the thermostat dial a little bit further.
The Bad News and the Good News
Most current air conditioners use what is known as the vapor compression cycle. A refrigerant vapor is compressed and sent to a condenser outside the building where it releases heat into the atmosphere and changes from a vapor into a vapor/liquid mix. The refrigerant is then routed through an expansion valve where it drops in pressure and expands. This change in pressure and form (the refrigerant is now about 75% liquid) causes the refrigerant to drop in temperature. It is then run through an evaporator (inside the building) where it absorbs heat (i.e., cools the building) while converting from mostly liquid back to a vapor.
This is a reliable and effective form of cooling technology, but it has three environmental drawbacks. First and foremost, the process uses a considerable amount of electricity. It is estimated that roughly 6 percent of the electricity generated in the U.S. is used for cooling (globally it is closer to 10 percent). Since about 60 percent of our electrical capacity comes from burning fossil fuels, it means that keeping cool contributes to the greenhouse gasses that in turn contribute to global warming.
Secondly, the heat that air conditioners release into the atmosphere actually makes a hot day even hotter. The impact is pretty minimal, but in dense urban areas the combined heat from air conditioners could raise the ambient outdoor temperature by perhaps one degree. Finally, many air conditioners use hydrofluorocarbons as refrigerants which are far more potent greenhouse gasses than carbon dioxide. Of course, air conditioners are designed not to leak and refrigerants are designed to be recycled, but as equipment ages, leaks do occur and there are a lot of old air conditioners still in use.
Fortunately, not all the news is bad. We have steadily improved our air conditioning technology with better compressors, better heat exchangers, better refrigerants and better thermostats. It is estimated that a modern air conditioning system is roughly 50 percent more energy efficient than a similar capacity unit from 30 years ago. In addition, progress is being made on replacements for the vapor compression style of air conditioner that have the potential to improve efficiency by another 50 percent in the next 10 to 15 years.
At the same time, the sources of electrical power are getting greener each year. As recently as 2007, nearly half of all U.S. electricity was generated by coal-fired plants – the dirtiest source we have. As of 2023, that share was down to just 16 percent and it will continue to fall. Most of that loss in electrical capacity was replaced by power plants fueled by natural gas – another fossil fuel – but one which is far cleaner than coal.
In addition, the use of renewable sources for electricity has been booming. The amount of electricity generated by renewables has increased by more than 250 percent between 2007 and 2023, and that share will continue to grow. [5] In the first half of 2024, just over 20 gigawatts of commercial-scale generating capacity was added to the electrical grid. Of that amount, approximately 60 percent was solar, 12 percent was wind, and 21 percent was utility-scale battery storage. Just 2 percent of new capacity was powered by natural gas. [6] Assuming those trends continue, in 10 years the US electrical grid will have very little contribution from coal-fired plants, and renewables plus nuclear will account for well over half of total capacity.
The Bottom Line
The end result is that we have become lazy and complacent in the use of air conditioning, and that is indeed a bad thing. It is not that difficult to design buildings that have lower air conditioning (and heating) loads, and the resulting buildings not only have lower operating costs and a reduced environmental impact but often are more interesting to look at. Building owners and developers need to insist that architects pay more attention to those details.
On the other hand, while we certainly could be more efficient in our use of air conditioning, I have a hard time understanding why air conditioning should make us feel any more guilty than Bitcoin mining or massive AI server farms or any of hundreds of other power-intensive activities. Air conditioning has had enormous benefits for human health and productivity that seem to more than offset the environmental impact.
I find it fascinating that articles decrying our dependence on air conditioning seem far more common than articles advising a reduction in our dependence on furnaces to keep warm in the winter. At least air conditioning has the potential to get “greener” as the electrical grid continues to shift toward renewables, while heating technology is still reliant to a considerable degree on the direct burning of fossil fuels such as natural gas, heating oil and even wood. Yes, global warming is slowly increasing the need for air conditioning and reducing the need for furnaces, but the disparity is hard to understand.
Given that countries around the globe have missed climate target after climate target, I think the goal of stopping or reversing global warming at any time in the foreseeable future is mostly wishful thinking. Realistically, I think we need to start thinking about adapting to a warmer world and air conditioning seems like a key technology in that regard. We should, of course, continue to improve its efficiency and continue to expand the use of renewable energy sources, but disparaging a technology that might be crucial to our societal well-being seems silly.
A more rational approach would be to encourage greater energy efficiency in all of our daily activities. If anything, we should favor technologies that are largely electrical like air conditioning since the impact of renewable power sources for electricity are likely to decrease our overall carbon footprint over time. City planners have a role in encouraging urban design strategies that reward energy efficient buildings and lessen the urban heat island effect – but that is a topic for a different post. In the meantime, I’m not going to feel guilty about keeping the AC on until fall weather arrives.
Notes:
1. Philip Kennicott; “Addicted to Cool: How the dream of air conditioning turned into the dark future of climate change”; The Washington Post; September 2023; https://www.washingtonpost.com/style/of-interest/interactive/2023/air-conditioning-climate-change/
2. Casey Crownhart; “Why air-conditioning is a climate antihero”; MIT Technology Review; July 2023; https://www.technologyreview.com/2023/07/27/1076774/air-conditioning-climate-antihero/?gad_source=1&gclid=Cj0KCQjwiOy1BhDCARIsADGvQnCMq3it_HKW4UAv2n1JL0EIV_xkwAWV4uR0-XmVMjAjoDT01SxdeigaAmb0EALw_wcB
3. Charlotte Elton; “Absolutely Disastrous: Air conditioners take horror toll on the environment, campaigners warn”; EuroNews; July 2022; https://www.euronews.com/green/2022/07/30/absolutely-disastrous-air-conditioners-take-horror-toll-on-the-environment-campaigners-war
4. Matt Largey; “Birth of the cool: A brief history of air conditioning”; KUT News; July 2018; https://www.kut.org/science/2018-07-17/heat-hot-weather-invention-of-ac
5. “Electricity explained”; U.S. Energy Information Administration; March 2024; https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php
6. “Today in Energy: U.S. power grid added 20.2 GW of generating capacity in the first half of 2024”; U.S. Energy Information Administration; August 2024; https://www.eia.gov/todayinenergy/detail.php?id=62864#:~:text=Plans%20for%20changes%20in%20capacity,and%20wind%20(4.6%20GW).
