AS we reported last weekend, researchers at Singapore’s Nanyang Technological University (NTU) recently conducted a successful experiment with so-called cool paint, demonstrating that it could help to relieve a phenomenon known as the “urban heat island” (UHI) effect, a serious and dangerous problem for people in cities. While the NTU scientists’ work is still experimental, its initial results show that there likely is a simple solution to UHI, one that should be adopted here on a large scale.
UHI is a manmade climate effect in which the ambient temperature in urbanized areas is several degrees warmer than in the surrounding countryside. This happens because concrete, asphalt and metal absorb and re-radiate solar heat. It exists in every city in the world but is particularly dangerous in cities in tropical climates, such as Metro Manila and other urban areas in the Philippines and elsewhere across Southeast Asia. According to a 2023 World Bank report on UHI, Southeast Asian cities are, on average, between 1 and 2 degrees Celsius warmer than their neighboring rural areas. However, the Philippines, Malaysia and Indonesia suffer much more severe UHI, regularly experiencing urban temperatures that are up to 5.9 degrees C warmer in their cities.
And, of course, as Earth’s climate steadily warms up due to greenhouse gas emissions, the UHI problem is growing steadily worse. By 2050, the number of “heat wave” days per year in Southeast Asian cities — days with a dangerous heat index above 40 degrees C — is expected to double.
There are grave consequences to the UHI effect, as the same World Bank report explains. There are about 100,000 deaths annually across Southeast Asia linked to heat, either directly due to heat stroke, heat exhaustion or dehydration, or due to heat aggravating other health conditions. These health risks disproportionately affect the poor, the elderly and young children, the World Bank found.
Extreme heat places additional demand on water and electricity supplies and has a clear negative impact on economic productivity; it is estimated that heat will result in an average GDP decline of 1.4 and 1.7 percent by 2050, and for the worst-affected urban areas, as much as 11 percent. High temperatures are also associated with risks to public safety, including more fires, car accidents and higher crime rates.
The most effective way to moderate urban temperatures is to increase green spaces within the city. However, while this is certainly preferable, it may not always be feasible or practical. A simple technical solution such as “cool paint” is an accessible alternative.
The concept is not new, and there are already many types of paint commercially available that are advertised as heat-reducing. Even painting roofs and walls with white or light-colored paint can help, but the positive effect is modest, measured in fractions of a degree, rather than the 1.5 to 2 degrees achieved in the Singapore experiment. Ordinary paint only blocks part of the solar radiation, so surfaces still absorb heat that is re-radiated into the surroundings, mostly at night. Plus, there is another drawback to white or pale shades of paint, in that they reflect light.
The NTU researchers did not provide many details of the exact formula of their “cool paint” in their public announcement of the results, probably for proprietary reasons, but a bit of further research reveals that it most likely contained the compound barium sulfate. Barium sulfate crystals reflect as much as 98 percent of visible and infrared solar radiation, preventing the underlying surface from absorbing any heat. As an added benefit, barium sulfate crystals scatter rather than reflect incoming light so that even a pure white surface is not blinding to look at.
Naturally, there is a trade-off; paint fortified with barium sulfate or similar compounds is significantly more expensive than ordinary paint. However, the prevented costs of heightened health risks, risks to public safety, reduced productivity and the general degradation of the quality of life in sweltering urban heat islands more than justify the investment. Government should consider taking the lead in demonstrating the efficacy of “cool paint,” perhaps by using it for school buildings, health centers and other facilities.