Highlights: 

Extreme heat is the deadliest weather-related hazard in the United States, and climate change is driving up its frequency and intensity.
While conventional air conditioning does save lives, it also produces greenhouse gas emissions, exacerbates urban heat, and is inaccessible to many. 
Passive cooling strategies reduce indoor temperatures without increasing electricity demand.
Transitioning from high global warming potential refrigerants to low global warming alternatives can significantly reduce cooling-related emissions while maintaining performance.  

 

As the United States experiences record-breaking summer heat, safe and sustainable cooling has become a matter of increasing urgency. Extreme heat claims roughly 2,000 lives every year, making it the deadliest weather-related hazard in the United States. Heat-related deaths nearly doubled in recent years, rising from 1,156 in 2020 to 2,394 in 2024. Some cities, like Phoenix, Arizona, experience a disproportionate amount of these deaths: Phoenix alone reported 602 heat-related deaths in 2024—25% of the country’s heat-related deaths that year. The trend of increasingly dangerous extreme heat has continued into 2025. In the last week of July, over 200 million Americans were issued an extreme heat warning.

At the same time, the electric grid is experiencing increasing strain. According to the North American Electric Reliability Corporation, much of the Midwest, New England, and the South-Central United States (particularly Texas and Louisiana) face an elevated risk of power shortages during periods of extreme heat due to the rapid increase in demand from air conditioning use. From 2014 to 2023, the United States experienced a 60% increase in heat-related power outages compared to the period between 2000 and 2009.   

 

Air Conditioning Isn’t the Silver Bullet

As temperatures continue to rise and the grid struggles to keep pace with new demand, the question now is not whether cooling is essential, but how to best go about cooling our homes, schools, workplaces, and other buildings. Air-conditioning (AC) units, systems designed to control the temperature of an enclosed space (such as window air conditioners or heat pumps), are a life-saving technology, but they require a significant amount of energy. AC accounted for 3.2% of global greenhouse gas emissions and 7% of electricity use worldwide in 2022. And the shares are substantially larger in the United States. Based on data provided by the U.S. Energy Information Administration, about 14.3% of U.S. electricity consumption went toward powering air conditioning in homes, commercial buildings, and factories.* Since fossil fuels represent 60% of U.S. utility-scale electricity generation, air conditioning is responsible for up to 8.6% of greenhouse gas emissions from U.S. power plants. As the number of domestic AC units is projected to reach approximately 542 million by 2050 (up from 380 million in 2017), the risk of worsening emissions through more fossil fuel electricity production is stark. 

Many existing air conditioning units also contribute to climate change more directly. Most air conditioning and other cooling systems use hydrofluorocarbons (HFCs) as refrigerants. HFCs have 675 times the global warming potential (GWP) of carbon dioxide (CO2), making them a much more potent greenhouse gas. Leaky AC units release HFCs into the atmosphere, as do improperly discarded units. Such leaks are estimated to represent about 0.5% of total annual greenhouse gas emissions.

In addition to contributing to global emissions, AC units also make the outside air hotter. ACs work by transferring heat from the interior of a building to the surrounding outside environment. Cities most acutely feel the impacts of the added heat, as it exacerbates the urban heat island effect. An Arizona State University study of Phoenix found that nighttime AC usage increased air temperatures by more than 1.8°F for some locations, creating a positive feedback loop of AC demand. 

Beyond its climate concerns, AC also poses accessibility concerns. The average household electric bill over the summer of 2025 is expected to be $178 per month, presenting a significant financial challenge to many American families. These costs are felt most significantly by Black and Hispanic households, which are more likely to report avoiding AC use for financial reasons or not having a functioning AC system at all. In addition to Black and Hispanic households, Asian households are also likely to report not having AC in their homes. In northern states, particularly Alaska, Washington, Montana, and Vermont, many homes lack AC entirely—a legacy of historically mild summers. However, this legacy is no longer reflective of these regions’ current climatic conditions, which include more frequent heatwaves and hot weather days. For example, Alaska declared its first-ever heat advisory on June 15, 2025. 

As the demand for cooling grows, so does the opportunity to rethink how we meet it. Across the United States, policymakers, scientists, and architects are turning to passive cooling and sustainable mechanical cooling as mainstream alternatives to AC.  

A comparison of passive cooling and sustainable mechanical cooling. 

 

What is Passive Cooling?

Passive cooling refers to building technologies or features that lower indoor temperatures without the need for mechanical systems such as AC. Instead of directly generating cold air, passive cooling reduces the overall need for cooling by controlling how heat enters, moves through, and exits buildings. These cooling techniques have existed for centuries, particularly in historically hot and arid regions in North America and worldwide.

How Does Passive Cooling Work?

Passive cooling works through three key mechanisms: heat control (blocking heat before it enters), heat reduction (cooling the surrounding environment), and heat removal (releasing built-up heat).

Heat control focuses on preventing or slowing heat from entering buildings. For example, reflective roofing materials repel sunlight rather than absorb it, while exterior shading devices like overhangs or trees block sunlight from reaching buildings’ windows and walls. Building orientation can also play an important role in reducing sun exposure. For instance, in northern latitudes, elongating and orienting a house along an east-west axis minimizes solar gain—the increase in heat due to solar radiation—by reducing window and wall exposure where solar gains are greatest in the summer. Additionally, dense materials such as concrete or brick have high thermal mass, slowly absorbing heat, delaying its release indoors, and helping stabilize indoor temperatures during the hottest parts of the day.

Heat reduction lowers the temperature of the air and surfaces around a building, which reduces the amount of heat available to be transferred indoors. Strategies such as green roofs, urban tree canopies, and shaded courtyards help cool through shading, evapotranspiration, and, in some cases, better air circulation. In dry climates, adding features such as fountains and water-retaining surfaces helps with evaporative cooling.

Despite best efforts to control and reduce the amount of heat entering buildings, some heat will inevitably make its way inside. Heat removal strategies focus on getting that heat back outside. Natural ventilation uses naturally-occurring pressure differences between warm and cool air to carry warm air out and bring cool air in. In some parts of the world, traditional architectural features such as wind catchers and solar chimneys enhance natural airflow, increasing cooling.

 

Overview of passive cooling strategies. Information source: Song et. al. 

Turning Table Salt into Passive Cooling: Spotlight on the Lawrence Livermore National Laboratory

At the forefront of passive cooling research are passive daytime radiative cooling technologies, which extend beyond traditional passive cooling methods by directly manipulating how buildings store, transfer, and shed heat. Radiative cooling materials absorb and emit heat in the form of infrared radiation directly into space, taking advantage of Earth’s atmospheric window, whereby certain electromagnetic radiation wavelengths can pass directly through Earth’s atmosphere.  

Diagram showing how passive daytime radiative cooling (PDRC) works; materials reflect sunlight and radiate thermal energy of a specific wavelength through the atmospheric window, sending heat into space. 

A leading example of this next-generation technology comes from Lawrence Livermore National Laboratory, where researchers have developed salt-based radiative cooling panels. Researchers turned sodium chloride (table salt) and potassium chloride into a porous, aerogel-like structure, allowing the panels to reflect incoming sunlight while simultaneously allowing radiative heat from below to pass through them and escape. When tested, these panels cooled surfaces by up to 18°F below the surrounding air temperature, even on the hottest days. They also consistently outperformed a leading commercial cooling film. Based on their light weight, low-cost, and easy manufacturing process, these panels present a scalable solution that has the potential to be adopted across the country for everyday cooling applications, including rooftops, refrigeration, and power generation.   
 

What is Sustainable Mechanical Cooling?  

While passive design and emerging materials can minimize the need for mechanical cooling, most buildings will continue to rely on air conditioning in some form, particularly those in hot, humid climates. Spurred by the American Innovation and Manufacturing (AIM) Act of 2020 (within P.L. 116-260), a growing number of manufacturers and researchers are transitioning to sustainable mechanical cooling, which involves the replacement of high global warming potential (GWP) refrigerants with climate-friendly alternatives.  

Hydrofluoroolefins (HFOs) are one of the most promising classes of low-GWP refrigerants. According to the EPA, HFOs that would replace HFCs in ducted and rooftop systems are under development, and they are being introduced into larger commercial chillers across Europe and the United States. 

Contrast between high-warming HFCs and lower-warming impact HFOs.

Testing by the Oak Ridge National Laboratory shows the potential benefits of switching to HFOs. They found that the refrigerant blend R-448A (an HFO and HFC mixture) reduced energy use by 10 to 15% and GWP by 60% compared to traditional HFCs. Across Europe, Asia, and the United States, over 60,000 supermarkets and stores have converted their systems to R-448A, including large chains such as Walmart, Whole Foods Market, and 7-Eleven.

The private sector is playing a significant role in accelerating the shift away from HFCs. For instance, Honeywell’s Solstice line of refrigerants has become a fixture of the industry-wide shift toward low-GWP HFOs. In 2024, Honeywell and Bosch partnered to incorporate Solstice 454B into heat pumps. Honeywell asserts that using this refrigerant instead of traditional HFCs can decrease refrigerant greenhouse gas emissions by 78%. Other companies, including Multistack, Hisene, and the Dehumidifier Corporation of America, will be incorporating 454B into commercial chillers, home air conditioners, and industrial and commercial dehumidifiers. 

 

Cooler Solutions Ahead

Extreme heat is becoming a more common and severe challenge across the United States, increasing the need for effective cooling strategies. While air conditioning remains an important tool, it also presents environmental, economic, and accessibility challenges. Passive and sustainable mechanical cooling present a promising alternative, meeting cooling needs while reducing strain on the electric grid. Other options to make air conditioning more environmentally friendly include replacing fossil fuel power plants with renewable energy systems, and making AC units more energy efficient (consuming less electricity means releasing fewer greenhouse gas emissions!).

The federal government can play a role in turning down the heat for communities across the country by funding research, establishing resilience-based building standards, and empowering communities with financial and technical assistance. The Trump administration has recently made several cuts to federal programs that provided climate-related financial and technical assistance to states and communities, including the Hazard Mitigation Grant Program, Building Resilient Infrastructure and Communities, and American Climate Corps, and removed NOAA’s climate.gov, which hosted technical assistance resources.    

 

Author: Erin Parker

 

*According to the U.S. Energy Information Administration, homes represent 38.4% of total U.S. electricity consumption and use about 19% of their electricity to power their AC. That means 7.3% of all U.S. electricity is used to power residential AC units. The same calculation finds that 4.9% of all U.S. electricity is used to power AC in commercial buildings (35.4% of 14%) and 2.1% is used for AC in manufacturing plants (26% of 8%). Adding all three numbers indicates that 14.3% of all U.S. electricity is used for air conditioning.

 

Featured Image: Brett Sayles for Pexels