We offer for your consideration modern and ancient architectural solutions: smart windows, green spaces and special buildings.
Windows that can be darkened at the touch of a button are already reducing the need for air conditioning. Global energy demand continues to rise as cities grow, technology advances, and industry expands. Buildings account for about 30% to 40% of the total—even more than industry or transportation. This is largely due to heating, cooling, and ventilation systems, with air conditioning being particularly energy-intensive.
Windows are a big part of the problem. They allow heat to escape in winter and enter in summer, causing thermal systems to use more energy and increase emissions. The challenge is to control this heat transfer without sacrificing the transparency of windows and the amount of daylight they let in, which is essential for people’s well-being and productivity.
Most modern versions of smart windows on the market are what are known as electrochromic (EC), meaning they work by applying electricity to layers of particles or crystals inside the glass when you press a button. This causes a reversible molecular transformation that makes the window either opaque or dark, depending on the product. This blocks most of the infrared light that makes rooms uncomfortably warm. This dramatically reduces the need for air conditioning in hot countries, keeping around 60%-70% of the heat outside during peak temperatures. They can also reduce heat loss from rooms by around 40% in cold weather.
These windows have been selling quite well for both commercial and residential properties for a number of years now, with the total global market value estimated at US$6.6bn (£5.2bn) in 2023. However, they do have some important limitations. Although the windows do not use much energy, they only work with a power source. This can be difficult in remote locations or areas with unreliable electricity. And to the extent that renewable options from the grid are not available, users will need to install an alternative, such as solar panels, to make these windows carbon neutral.
In many cases – although there are exceptions – you can only switch between full restriction and full transparency. This means you lose the benefits of having windows in hot weather, and the rooms will likely need artificial light. And as mentioned earlier, EC windows are great at keeping out heat in hot countries, but they are a little more limited in colder climates.
Smart Windows. Live Science
One alternative that at least eliminates the need for electricity is known as photochromic. These use a layer of either tiny silver halide crystals or compounds known as naphthopyrans, both of which react to increased levels of ultraviolet (UV) light, causing the glass to tint in brighter conditions. This is the same material used in light-sensitive sunglasses.
Compared to EC windows, they have the added benefit of creating a barrier to UV light. UV light is not only carcinogenic, but it also damages everything from furniture and paintings to EC coatings.
However, photochromic windows are very expensive, at least if they use silver. They are very sensitive to weather, which can reduce their reliability in cloudy or rainy weather. They also do not block infrared light as well and do not have manual controls, so they are more useful for privacy than for regulating the temperature of a room.
Many argue that the more promising type of smart window for the future is a third, known as thermochromic, which means they use a coating of particles that react to temperature instead of light. Again, this means no electricity is needed.
They are much cheaper than photochromic windows, still block UV light, and can potentially match EC windows for infrared blocking. They can also gradually darken as the outside temperature rises, meaning you can have clearer windows than on/off EC products.
But while thermochromic glass already exists, it can’t yet be used for windows. That’s because the vanadium dioxide layers in current versions only fully reflect infrared radiation at temperatures around 67°C, which is much higher than even the world’s hottest temperatures.
Many researchers around the world are looking at ways to improve thermochromic glass. This includes our project at the University of Exeter’s Institute for Environment and Sustainability, which is partly involved in testing other coatings to try to find one that effectively reduces infrared radiation at more realistic external temperatures.
Uniquely, we are also looking at combining this with several other types of capabilities that may currently exist in other varieties of thermochromic glass, beyond those that can reflect infrared light. These include the ability to make windows more useful in cold climates, allowing them to act as an insulator at low temperatures so that rooms do not lose their heat to the outside, as well as storing energy so that it can be used to heat rooms.
It’s hard to predict the exact time frame, but perhaps within five or ten years, similar research should bring to market smart windows that are just as useful in cold countries — both day and night. This is the key to widespread adoption of a single type of window across the globe.
This should have a significant impact not only on air conditioning requirements, but also on heating and radiator needs. I would imagine that installing five smart windows in an apartment in a colder country would allow owners to reduce the number of radiators from, say, five to two. And beyond buildings, these technologies could be used in aircraft and cars.
At the same time, there is every reason to believe that the EC window market continues to grow. According to one forecast , it should increase by almost another US$4 billion, or about 60%, by 2028. With the right combination of research success and policy support in both developed and developing countries, the next generation of smart windows should be able to move forward and make a major contribution to the carbon emissions of buildings in a decade or two.
Builders knew how to stay cool in hot, dry climates thousands of years ago. It’s time to bring that knowledge back. Modern buildings tend to take electricity and air conditioning for granted. They often have glass facades and windows that can’t be opened. And when the power goes out for days during a heat wave, as it did in the Houston area in July 2024 after Hurricane Beryl, these buildings can become unbearable.
But civilizations have known for millennia how to provide humans with shelter in hot, dry climates. Research suggests that as global temperatures rise, dangerously hot summers like those in 2023 and 2024 will become more common, and severe storms could lead to more power outages. To prepare for an even hotter future, today’s planners could learn from the past.
Each of these ancient cultures boasts lessons in staying cool in hot, dry climates that modern designers can learn from today.
Some architects are already using them to improve designs. For example, buildings in the northern hemisphere can be oriented to maximize southern exposure. South-facing windows, combined with shading devices, can help reduce solar radiation in the summer but provide solar heating in the winter. Rainwater harvesting and its use to irrigate gardens and landscapes can help reduce water consumption, adapt to drier conditions, and make cities more resilient.
Retrofitting modern cities and their glass towers to better control heat is no easy task, but there are techniques that can be adapted to new designs for better living in hotter, drier climates and for less reliance on constant summer air conditioning. These ancient civilizations can teach us how.
Archaeologists studying the ruins of Mesopotamian cities describe how Sumerian buildings used thick walls and small windows that could minimize heat gain and keep interiors cool.
The Sumerians built their walls and roofs from materials such as adobe or clay, which could absorb heat during the day and release it at night.
They also built buildings right next to each other, which reduced the number of walls exposed to intense solar radiation. Small courtyards provided light and ventilation. Narrow streets provided shade throughout the day and allowed pedestrians to move comfortably around the city.
The ancient Egyptians also used materials that could help get rid of excess heat. Palaces were made of stone and had courtyards. Residential buildings were made of clay bricks.
Many people also adopted a nomadic lifestyle inside their buildings to escape the heat, using rooftop terraces, which were cooler at night, as sleeping quarters.
To cool buildings, Egyptians developed a unique technology called mulqaf, which consists of tall openings in the walls facing the prevailing winds. These openings act like scoops to capture the wind and direct it downwards to help cool the building. The incoming wind creates air circulation that helps to expel heat through other openings.
The mulqaf principle can also be scaled up to cool larger spaces. Known as a wind catcher, it is currently used in buildings in the Middle East and Central Asia, making them comfortable without air conditioning, even during very hot periods.
Civilizations on other continents and at other times have developed similar strategies for living in hot, dry climates, while also developing their own unique solutions.
The Pueblo people of what is now the American Southwest used small windows, materials such as mud brick and stone, and designed buildings with shared walls to minimize heat gain.
The Mesa Verde pueblo cliff dwellings provided protection from the elements and, due to their orientation, from direct sunlight in the summer. Andreas F. Borchert, CC BY-SA
They also understood the importance of solar orientation. Ancient Puebloans built entire communities under the shelter of south-facing cliffs. This orientation kept their buildings shaded and cool in the summer, but still allowed sunlight and radiated heat to stay warm in the winter.
Their descendants adopted a similar orientation and different urban planning strategies, and adobe houses remain common in the American Southwest.
Modern water management is also rarely designed for dry climates. Stormwater infrastructure is designed to move rainfall runoff away from the city as quickly as possible. Yet those same cities must deliver water to people and gardens, sometimes from distant sources.
In the eighth century, Muslim caliphates in the arid lands of northern Africa and southern Spain designed their buildings using rainwater harvesting techniques to capture water. Rainwater runoff was collected across the roof and channeled into cisterns. The slope of the roof and the floor of the courtyard channeled the water so that it could be used to irrigate the green landscapes of their courtyards.
The landscape design of the Cordoba Mosque, Spain, was designed to direct rainwater to where it is needed for irrigation. Adriana Zuniga/Live Science
Modern Mendoza, Argentina, uses this approach to irrigate the plants and trees that line the city’s magnificent streets.
Maya and Teotihuacan: Collecting Rainwater for Later Use. On a city-wide scale, people also collected and stored rainwater to survive the dry season.
The ancient city of Teotihuacan in Xochicalco and many Mayan cities in what is now Mexico and Central America used their pyramids, plazas, and aqueducts to channel rainwater into large cisterns for future use. Plants were often used to purify the water.
Large cisterns like this one at Xochicalco, a Teotihuacan community in what is now Mexico, were used to collect and store rainwater. Adriana Zuniga/Live Science
Today, scientists are studying ways to store good quality rainwater in India and other countries. Rainwater harvesting and green infrastructure are now recognized as effective strategies for making cities more resilient.
Drinking water, building an island from scratch, and creating an urban forest: three bold ways cities are already adapting to climate change. Climate change will fundamentally challenge the world’s urban centers. Three cities—San Diego, Milan, and Jakarta—offer lessons on how to adapt to a warming planet.
Milan’s marble facades and narrow stone-paved streets are elegant and timeless. But all that stone gives off heat and doesn’t soak up rain, and temperatures and flooding in this posh Italian city are only expected to rise in the coming decades.
In Jakarta, black floodwaters already rush into homes each winter along the Indonesian city’s many rivers. The water is filled with sewage and is a breeding ground for disease, but many people can’t afford to move. Climate change will soon cause much of Jakarta — and many other low-lying cities — to be below sea level.
And in arid San Diego, water is already seen as a precious commodity. As drought worsens in the coming years, protecting this resource will become even more important.
Human-caused climate change is transforming weather patterns and shifting ecosystems around the world. In some places, climate change means too much water; in others, it causes drought. Global action is needed to limit fossil fuel use, slow rising temperatures, and prevent the worst effects of human-caused climate change. But significant warming has already happened.
Cities will have to respond, and some are already taking bold steps. Milan is planting millions of trees. Indonesia is moving its capital. And San Diego is recycling wastewater back into city taps — one of the first major cities to do so.
Each of these three cities offers a climate adaptation action plan that could be useful to other places around the world. And while no single approach will be a panacea, each offers a hopeful vision of how we can learn to live and thrive on a warming planet.
In Milan, for example, the government is working to plant trees across the city rather than focusing on just the wealthiest areas. Like many cities, Milan is a “heat island,” with temperatures 7 to 14 degrees Fahrenheit (4 to 8 degrees Celsius) higher than surrounding rural areas. That’s because buildings, roads, and other infrastructure absorb and re-radiate heat from the sun better than forests and bodies of water. And climate modeling predicts that the situation will only get worse, with temperatures in the city rising by 4.1 degrees Fahrenheit (2.3 degrees Celsius) by 2050.
To combat this threat, the city launched a public-private partnership called ForestaMi — or Forest for Milan — that aims to plant 3 million trees and shrubs by 2030. As of 2024, more than 610,000 trees and shrubs have been planted. The tree-planting initiative is part of a larger climate plan that Milan hopes will help it keep local warming below 3.6 F (2 C) by 2050.
In the world of urban planning, planting trees is a popular strategy for mitigating climate change. Trees and other vegetation reduce temperatures by providing shade, absorbing and dissipating heat better than cobblestones and pavements, and releasing moisture into the air. Increasing tree canopies over European cities could save thousands of lives by mitigating the impact of urban heatwaves, according to a 2023 study in The Lancet.
But planting trees can have other benefits, too. Replacing pavements with soil can help cities soak up more rainwater and reduce flooding. That could prove important in Milan, which climate modeling predicts will see heavier rainfall in the coming decades.
But tree planting has its limits. In July 2023, Milan was hit by a sudden hailstorm that toppled 5,000 trees in just 15 minutes. While such storms are rare in Milan, Grandi noted, the city will face more river floods and droughts in the future, meaning it will need a mix of trees that can withstand such conditions.
Jakarta, a megacity about eight times the size of Milan, faces both a water shortage and a surplus. Rising sea levels are already a crisis in low-lying Jakarta, a marshy city crossed by 13 rivers.
Jakarta was built during the Dutch colonial era around a series of canals that never contained these rivers. Since 1990, Jakarta’s population has more than doubled, further straining the city’s infrastructure. Because Jakarta can’t provide its residents with enough running water, owners of both high-rise condominiums and informal shacks are digging illegal wells to pump out groundwater, Deden Rukmana, a professor and expert in Indonesian urban planning at Alabama A&M University, told Live Science.
Due to over-pumping, the city has become one of the fastest sinking areas in the world, with some areas sinking as much as 4 inches (10 centimeters) a year. Coastal flooding is forcing people to leave their homes, and at the current rate, it is estimated that 95% of the city’s coastal area will be underwater by 2050.
And the risks aren’t limited to the coast. The combined effects of rising sea levels and depleted groundwater will leave the entire city below sea level by 2100, the model predicts. Rising sea levels also mean saltwater will contaminate the city’s fresh water.
To buy time, Jakarta’s city planners are already building and shoring up seawalls and estuaries closer to the shore. As a next step, they plan to build a cluster of 17 islands in the shape of a giant bird. Together, the islands will create an 80-foot-tall (24-meter), 25-mile-wide (40-kilometer) seawall and an artificial lagoon that planners hope will help protect the city from tidal flooding.
Flooding has become a huge problem in Jakarta, where over-pumping has left the city one of the fastest-sinking regions in the world. Rising sea levels due to climate change will only make flooding worse. danikancil/Getty Images
But researchers warn that even a massive seawall won’t prevent flooding if overpumping continues to cause subsidence inland. Efforts to relocate water-guzzling industries and promote development in areas less prone to flooding help on that front, Rukmana said.
To stay above sea level, Indonesia’s main city will have to crack down on illegal wells and create alternative water sources, which could take years, Rukmana said. The city could also work to replenish aquifers, as Tokyo has done.
But there’s another move that could ease the pressure on Jakarta’s groundwater: mass relocation. In 2019, Indonesia announced plans to move its capital from Jakarta to a new city called Nusantara on the island of Borneo. The first government workers are expected to move there in September 2024.
Like similar relocations in Brazil and Nigeria, the project aims to move the colonial-era capital to a more central location in the country, Rukmana said.
“Without any intervention, people will still move to Jakarta,” Rukmana said. Nusantara won’t change that right away, but it could have an impact over time. When Nusantara is built, the goal is for 10,000 civil servants to move their jobs, he said.
Of course, relocations don’t always go to plan. In 1999, Malaysia moved the prime minister’s office from Kuala Lumpur to nearby Putrajaya, also because of water problems. Its population has increased to 100,000 in the past two decades, but that number is less than a fifth of the total it was supposed to be. Rukmana said building a new city from scratch is a big risk, but one that could pay off for Indonesia if it provides a new source of development for the country.
For now, Nusantara is mostly just cleared land. But planners envision a smart city built around public transportation, walkability, and electrification, with robust digital management tools — a far cry from the congested traffic, air pollution, and overcrowding of Jakarta.
Nusantara also has tree-planting goals that are perhaps even more ambitious than Milan’s. The new city will be located on land that was previously used for industrial agriculture; it aims to restore 204,000 acres (83,000 hectares) of rainforest. At the city’s current planting density, that would be the equivalent of tens of millions of trees.
But experts say the effort has so far fallen short of expectations, Mongabay reports. Non-native trees, such as eucalyptus, are being planted in place of native rainforest species, and a phased approach may be needed to account for the damaged soil in the area. For example, “pioneer” tree species may need to be planted first, followed by typical rainforest species to replicate natural forest processes.
While low-lying Jakarta struggles with flooding, arid San Diego faces drought. The California city, which gets less than 12 inches (30 cm) of rain a year, is expected to experience higher temperatures and less predictable rainfall as climate change worsens.
But San Diego is better off than many cities because its adaptation to the climate actually began decades ago. When California suffered a drought in 1990, San Diego’s water supplier, the Los Angeles Metropolitan Water District, temporarily cut the city’s water supply by half.
At that point, they began rolling out a low-flow toilet initiative to reduce household water use that inspired similar efforts across the country. Over the past 30 years, the city has pulled nearly every lever available to reduce demand. Low-flow toilets were followed by low-flow landscaping and water conservation partnerships with inland agricultural areas.
Since San Diego County began its conservation efforts, it has successfully cut its per capita water use in half and further reduced its reliance on water from Los Angeles. But conserving water alone is not enough.
A worker walks through the Claude “Bud” Lewis Carlsbad desalination plant near San Diego. The desalination plant is the largest in the country and one of the ways the city is trying to avoid a future drought. Allen J. Schaben/Getty Images
So the city built and raised dams to store more water and straightened canals to keep water from leaking out of the Colorado River along the way. It built pumps to move water north into San Diego County, partly to help with droughts.
And San Diego has also taken steps to bolster its local water supply. Because the city’s abundant seawater compensates for its lack of groundwater, San Diego has invested in the nation’s largest desalination plant, which now supplies about 10 percent of the region’s water.
After three decades of work and a couple of rainy winters, San Diego now has a water supply. It even plans to lease some of its Colorado River supply to nearby cities.
And facing the possibility of a more severe climate-induced drought, the city is still looking to do more. To do that, San Diego is once again looking to toilets for inspiration. Over the next decade, the city of San Diego and two suburbs plan to recycle wastewater back into city taps. It’s a new approach in California. It goes beyond graywater — the not-quite-drinkable water that’s used for landscaping. Instead, San Diego will send treated wastewater back into the city’s drinking water system.
That level of treatment may sound daunting, but when planners crunched the numbers, it was cheaper than other waste upgrades, Stevenson said. San Diego County expects 18 percent of its water to come from recycled water by 2045.
All of these changes required political will. They also required significant resources: San Diego benefits from a stable population, ample funding, and effective governance systems that many cities around the world lack. And for San Diego, as for Milan, Jakarta, and Nusantara, one-shot projects will not be a panacea for the effects of climate change.
An international team of scientists from China, the UK and Spain studied the impact of green spaces on the health of city dwellers during extreme heat waves. The study was published in the scientific journal Environment International (EnvInt). The researchers analyzed how different types of vegetation affect the microclimate in Hong Kong. The experts used a new method to measure the average amount of green cover in the surrounding human habitat.
The findings suggest that urban greening strategies should focus on planting trees within walking distance of local residents, as well as adding other types of vegetation to certain areas. According to the researchers, forested areas within 1 km of residential areas significantly reduce the risk of death from heatstroke.
The analysis also found that small green spaces near residential buildings were less effective than larger greening strategies such as forest parks or parklands.
Representatives of the Japanese automaker Nissan have shown a new car paint that reflects sunlight and thus reduces the impact of thermal energy on the car body and interior. The company believes that their development will allow drivers to spend less energy on air conditioning systems, which will reduce the load on the power plant and increase the overall level of comfort.
On hot days, many drivers face an unpleasant situation, especially in southern countries, where the air temperature in summer can rise above 40°. We are talking about the strong heating of a car parked in direct sunlight. In this case, it heats up so much that touching the door handle can leave real burns.
The main threat of heating is harm to health. If you stay in a locked car for a short time in the heat without the air conditioner on, heat stroke is guaranteed. In addition, with strong heating, the risk of explosion of any containers containing liquids or gases under pressure increases – plastic bottles with highly carbonated drinks, lighters, aerosols. In extreme heat, unpleasant “glue” and “polymer” odors intensify in the interior of a car left in the sun. When heated, upholstery materials begin to actively emit toxic vapors, which in high concentrations are harmful to humans.
Many researchers have long been working on creating a car protective paint with a cooling effect that would help “cool” the car. Engineers from the Nissan research center have developed one of these coatings. The new paint uses the principle of “radiative cooling” and contains metamaterials that help reflect the sun’s rays more effectively.
The technology uses a special composite made up of two light-reactive types of particles with a special microstructure. The first type effectively reflects infrared radiation (near infrared), which causes surface temperatures to rise. The second type of particle creates “electromagnetic waves” that Nissan says counteract the sun’s rays and redirect energy from the car’s body back into the environment.
The cooling enamel is currently undergoing testing: it is being tested on Nissan NV100 vans operated by All Nippon Airways at Tokyo’s Haneda Airport. The first results are already in. The new paint has reduced the temperature of the car body surface by 12° and by five inside the cabin on hot days. According to experts, this has reduced the load on the air conditioning system and the power unit (due to less heating, the load on the power unit involved in the cooling process of the car is reduced).
As reported by the online publication Naked Science, the thickness of the paint coating developed by Nissan’s research center is approximately 120 microns, which is about 6 times thicker than the conventional car paint used in the modern automobile industry. Therefore, before launching the paint into mass production, Nissan needs to find a way to reduce its thickness while maintaining its effectiveness.
White roofs protect against overheating, but they can have a negative climate effect. Reflecting sunlight can protect a neighborhood from scorching temperatures, but surrounding areas can suffer as a result. A climate change adaptation strategy aimed at cooling cities may inadvertently make nearby areas hotter, according to a new study by Harvard University researchers.
This strategy, known as land-based radiation management, involves techniques such as painting roofs and sidewalks white to reflect sunlight and reduce heat absorption. While this effectively reduces temperatures in the area of application, it also disrupts weather patterns, reducing precipitation both inside and outside the area.
This creates a problem for the surrounding areas. Precipitation keeps the soil moist, and the evaporation of moisture cools the surrounding air. As precipitation decreases, evaporation decreases, which leads to higher temperatures. Within the white roof zone, the cooling effect of reflecting sunlight outweighs the warming caused by the decrease in soil moisture. However, the surrounding areas not only do not benefit from the reflective cooling, but they actually experience warming due to the lower precipitation. As a result, the outside areas heat up, and the heating effect there is approximately 1–4 times greater than the cooling effect in the white roof zone.
The researchers warn that if the method is used in high-income areas bordering low-income areas, it could worsen climate inequality.
However, if applied at the right scale, white roofs could still be beneficial. The authors suggest that when used in areas less than 1 kilometre in diameter, they are unlikely to affect precipitation and cause unintended warming. However, if used in areas greater than 10 kilometres in diameter, they are likely to cool a much larger area than they warm, potentially making the trade-off worthwhile.
