Cooling Down Earth’s Cities
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- 7 min read
How Climate-Smart Architecture Is Making Urban Heat More Bearable—Naturally
With recent record-breaking summer heatwaves, spiking urban temperatures have become a major concern for cities tackling climate change. Densely populated areas are warming far faster than their rural and suburban surroundings, creating dangerous “urban heat islands” that threaten public health, increase energy consumption, and disproportionately impact city-dwellers with lower incomes.
Meanwhile, designing buildings to protect occupants from climate extremes—while managing energy demand—has become increasingly complex, and especially challenging in the developing world.
“Closing the skills and capacity gap in those markets is one of the most important levers the sector has,” Hanane Hafraoui, GlobalABC lead programme manager at the United Nations Environment Programme (UNEP), told The Earth & I.
Climate adaptation now goes further than just planting more trees. Professor Mat Santamouris has spent more than four decades developing a powerful combination of climate-smart solutions. These are aimed at designing cities and buildings to stay cool naturally, entice investors, and consider the well-being of citizens from lower-income brackets.
“Architectural adaptation to climate change is increasingly focused on enhancing thermal comfort, minimizing energy consumption, and improving urban resilience,” Santamouris, professor of high-performance architecture at the University of New South Wales in Australia, told The Earth & I.
Keeping Cool in a Changing Climate
According to UNEP’s Global Status Report for Buildings and Construction 2025-2026, demand for cooling in buildings has grown by 70% since 2015, driven by rising temperatures, urbanization, and population growth in tropical regions.
UNEP’s Global Cooling Watch 2025 recommends minimizing cooling loads by using low-energy cooling, maximizing air conditioning and other equipment efficiency, and then phasing down high-emission refrigerants.
Building designers are responding with an increased focus on reducing heat through external shading systems, reflective surfaces, improved insulation, natural ventilation, and enhanced daylight management.
Using Climate-Adaptive Tools in Urban Areas
Santamouris’ research suggests there are practical ways to lower city temperatures by several degrees while dramatically reducing cooling energy demand and heat-related illness.
Santamouris’ research suggests there are practical ways to lower city temperatures by several degrees while dramatically reducing cooling energy demand and heat-related illness.
For instance, in Athens, Santamouris engaged in one of the world’s largest applications of cool pavements in urban areas. As part of the Flisvos project, which remains operational today, the research team installed 4,500 m² of reflective pavement in one of the capital’s urban parks.
The researchers found that using cool paving materials can reduce peak ambient temperatures on a typical summer day by up to 1.9 kelvins (K)—or 3.42 degrees Fahrenheit—the unit used to measure thermodynamic temperature. Furthermore, applying cooling pavement dropped the surface temperature by 12 K (21.6 degrees Fahrenheit) and considerably improved comfort conditions.
Meanwhile, in another project in Riyadh, Saudi Arabia, Santamouris and his team applied climate-responsive design to help cool the capital.
Riyadh presented a steep challenge due to its very high summer temperatures, intense solar radiation, low humidity, and limited vegetation. “These conditions exacerbate the urban heat island effect while also restricting the effectiveness of some conventional cooling strategies that rely on water or extensive greenery,” said Santamouris.
The project team applied radiative coolers—specialized surfaces that radiate and/or dissipate heat—and cool materials, combined with greenery, across more than 3,000 buildings to measure the materials’ climate impact.
Their application resulted in a drop in peak ambient temperature of up to 4.5 °C (8.1 degrees Fahrenheit). Furthermore, they found that progressive urban heat strategies improved energy conservation by up to 16%, while applying heat mitigation and energy adaptation technologies lowered cooling demand by up to 35%.
They found that progressive urban heat strategies improved energy conservation by up to 16%, while applying heat mitigation and energy adaptation technologies lowered cooling demand by up to 35%.
As part of the Riyadh project, researchers selected super-cool materials (SCMs), namely those for roof covering. By reflecting nearly all incident sunlight and absorbing minimal heat, these SCMs delivered a solar reflectance close to 96% and an emissivity in the atmospheric window close to 90%.
Riyadh’s rapid urbanization, large expanses of heat-absorbing surfaces, and need to develop both water-efficient and economically feasible solutions under harsh climatic conditions presented additional hurdles. Thus, Riyadh is an ideal case study for testing innovative heat mitigation technologies and strategies at scale, the researchers said in their January 2024 article in Nature.
Using ‘Passive’ Cooling for Indoors
In India, Ashok B. Lall Architects has teamed up with UNEP and the Tata Steel Foundation to redevelop 44 homes in the Pragati Vihar community using passive cooling design, circular materials, and reduced concrete. They have achieved a 35% reduction in cooling loads (the rate at which energy must be extracted from a space to keep its air temperature constant) and a 16% reduction in embodied carbon per unit area (the carbon footprint of a building's materials from extraction through manufacturing and transportation—per a unit of area, typically measured in kilograms of carbon dioxide equivalent (kg CO₂e) per square meter (m²)).
Separately, in the nation of Niger, architects like Mariam Issoufou are creating buildings that draw on pre-colonial Sahelian construction principles, using compressed earth bricks, passive ventilation, and orientation for shade. The Hikma Community Complex in Dandaji, created by Issoufou, a professor at ETH Zurich, reportedly stays up to 15°C (59 degrees Fahrenheit) cooler than the outside air at peak summer temperatures, without air conditioning.
In an interview with the Holcim Foundation, Issoufou shared the importance of drawing on local climate-smart cooling traditions. “[Our] collaboration with local masons was crucial, as they shared their knowledge of traditional techniques and materials that could be adapted to improve the building's durability and weather resistance, such as mixing the mud with natural substances like salt, Arabic gum, and shea butter,” she said.
Santamouris applauds such innovation.
“It is possible to maintain acceptable comfort conditions and significantly reduce—sometimes even eliminate—the need for conventional air conditioning, thereby improving resilience to extreme heat while lowering energy consumption and greenhouse gas emissions,” Santamouris said.
“It is possible to maintain acceptable comfort conditions and significantly reduce—sometimes even eliminate—the need for conventional air conditioning.”
He added that using nature-based solutions, including green roofs, green walls, urban vegetation, and trees, contributes to passive cooling. “These strategies help lower ambient and surface temperatures, mitigate urban heat island effects, improve air quality, and enhance outdoor thermal comfort,” he said.
“One visible shift is the growing policy emphasis on passive design,” said Hafraoui. Approaches such as external shading, natural ventilation, cool or reflective roofing, and thermal mass reduce the heating or cooling load that a building places on mechanical systems, she explained.
More Cooling Materials in Development
In Senegal, UNEP and GlobalABC are supporting a pilot facility to produce insulation boards from Typha, a cattail-like plant that aggressively grows in—and even chokes—local waterways.
Working in partnership with the École Supérieure Polytechnique de Dakar, the collaboration aims to transform an invasive species into a commercially viable, low-carbon building material.
“Significant progress has also been achieved through the use of advanced cool materials and passive daytime radiative cooling (PDRC) technologies,” Santamouris said.
Prioritizing Progress in Low-Income Countries
Policy changes in different regions are shaping how architecture is designed to withstand heat.
For instance, California's 2025 Energy Code requires heat-reflecting “cool roofs” on new constructions.
Kenya's 2024 National Building Code now mandates passive cooling strategies as a baseline requirement for new buildings. UNEP is working with Kenya’s State Department for Public Works to further integrate green building principles into the National Building Code.
Kenya's 2024 National Building Code now mandates passive cooling strategies as a baseline requirement for new buildings.
Around 80% of the growth in global floor area between now and 2030 will occur in low-income countries. “The majority of new construction over the coming decades will happen in Africa and Asia,” said Hafraoui. These regions are both where climate extremes are most severe and where most of the new construction will take place.
GlobalABC’s Higher Education Institutions Action Group is aligning research priorities across regions, with a review paper due in 2026 mapping the most critical knowledge gaps. In India, UNEP is working with RMIT University and the Building Materials and Technology Promotion Council to train architects, policymakers, and developers to use climate-responsive design and sustainable materials in practice.
Yet, according to data from the UN’s Global Status Report for Buildings and Construction 2025-2026, the sector remains significantly off track. Buildings' energy intensity has improved by just 8.5% since 2015, roughly half the reduction needed to achieve net zero by 2050, with resilience considerations poorly embedded in the building codes of most countries.
“We want to see climate-responsive design become the baseline expectation everywhere,” said Hafraoui.
“It means recognizing that compelling, scalable answers are already being developed in many of the most climate-exposed parts of the world—in Senegal, India, Niger, and beyond—and that those solutions deserve to travel,” Hafraoui added.
Supporters are calling for embedding climate-responsive design in building codes, teaching it in architecture schools, and supporting it through long-term performance financing measures.
Future architecture is increasingly combining passive cooling, advanced materials, urban greening, and climate-informed design principles to ensure comfortable and sustainable living environments in a changing climate.
“The challenge is no longer a lack of solutions, but rather the speed and scale at which we implement them,” Santamouris concluded.
*Natasha Spencer-Jolliffe is a freelance journalist and editor. Over the past 10 years, Natasha has reported for a host of publications, exploring the wider world and industries from environmental, scientific, business, legal, and sociological perspectives. Natasha has also been interviewed as an insight provider for research institutes and conferences.
Editorial notes
Sources:
Interview with Hanane Hafraoui, GlobalABC Lead Programme Manager at UNEP
Interview with Mat Santamouris, Professor of High Performance Architecture at the University of New South Wales, Australia
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