The intensifying effects of climate change are disproportionately felt in urban areas, where the “urban heat island” effect exacerbates rising temperatures and poses a significant threat to public health. A growing body of research, including studies analyzing data from 2000 to 2019, demonstrates a clear link between non-optimal ambient temperatures – both extreme heat and cold – and increased mortality rates globally. This is particularly concerning as urban populations continue to expand, increasing exposure to these risks.
Recent analyses of global temperature and mortality data reveal that in 2019 alone, approximately 5.08 million deaths worldwide (9.43% of all deaths) were associated with non-optimal temperatures, according to a 2021 study published in The Lancet Planetary Health. While cold-related deaths accounted for the majority (8.52%), heat-related mortality is a growing concern, representing 0.91% of all deaths that year. The research underscores the urgent need for targeted interventions to mitigate the impact of rising temperatures in cities.
The urban heat island (UHI) effect, as described by researchers like Voogt and Oke in 2003, refers to the phenomenon where urban areas experience significantly warmer temperatures than their surrounding rural counterparts. This is primarily due to the prevalence of impervious surfaces like concrete and asphalt, which absorb and retain heat, coupled with reduced vegetation and altered wind patterns. Recent work by Du et al. (2023) highlights contrasting trends in surface and canopy urban heat islands, emphasizing the complex interplay of factors driving these temperature increases.
Global Disparities in Heat-Related Mortality
The burden of heat-related mortality is not evenly distributed across the globe. The Lancet study found that Asia accounted for over half (51.49%) of all excess deaths attributable to non-optimal temperatures. Eastern Europe experienced the highest heat-related excess death rate, while Sub-Saharan Africa faced the highest rates of cold-related deaths. These regional variations are linked to a complex interplay of factors, including climate, socioeconomic conditions and access to resources like air conditioning and healthcare. The World Bank’s Global Subnational Atlas of Poverty (October 2025) demonstrates the correlation between poverty and vulnerability to climate-related health risks.
Researchers are increasingly focused on understanding the specific characteristics of urban environments that contribute to the UHI effect. Guo et al. (2022) found that urban morphology – the shape and structure of buildings and streets – plays a significant role in influencing thermal environments. Li and Chen (2023) characterized variations in the surface urban heat island effect across 561 global cities, highlighting the importance of considering both daytime and nighttime temperatures.
Measuring and Predicting Heat Exposure
Accurately measuring and predicting heat exposure is crucial for effective public health interventions. Scientists are utilizing a range of metrics, including the Wet-Bulb Globe Temperature (WBGT), which takes into account temperature, humidity, wind speed, and solar radiation, to assess heat stress. Spangler, Liang, and Wellenius (2022) developed metrics for US counties, while Liu et al. (2025) created a dataset for daily maximum simplified WBGT covering 1940-2022. Kong and Huber (2025) have created a global, high-resolution dataset of projected heat stress metrics using CMIP6 climate models.
Advances in remote sensing technology are also playing a key role in monitoring urban heat islands. Yu et al. (2019) used remotely sensed data to analyze spatiotemporal patterns of heat islands in rapidly urbanizing areas of Southern China. Yu, Yang, Zhou, and Xiao (2025) have developed a Global UHE dataset, providing valuable data for researchers and policymakers.
Future Risks and Adaptation Strategies
Looking ahead, the risks associated with urban heat islands are projected to increase as global temperatures continue to rise and urban populations grow. Wang et al. (2023) predict a significant increase in future population exposure to heat waves. The Intergovernmental Panel on Climate Change (IPCC) AR6 report (2022) emphasizes the urgent need for adaptation measures to reduce the health impacts of climate change, including strategies to mitigate the UHI effect.
Effective adaptation strategies include increasing green spaces in urban areas, implementing cool roofs and pavements, improving building insulation, and developing early warning systems for heat waves. Chen et al. (2022) demonstrated the effectiveness of diurnal heat exposure risk mapping and governance zoning in Beijing, China. Meque et al. (2022) highlighted the importance of understanding the variability of heat-wave characteristics in southern Africa to inform targeted interventions.
The growing body of evidence linking urban heat islands to increased mortality underscores the critical need for proactive measures to protect vulnerable populations. Continued research, coupled with effective policy interventions, will be essential to building more resilient and sustainable cities in a warming world. Further investigation into the socioeconomic factors influencing vulnerability, as highlighted by the World Bank data, will be crucial for equitable adaptation strategies.
This research highlights a complex and evolving challenge. Continued monitoring of urban temperatures, coupled with robust public health initiatives, will be vital in mitigating the risks associated with the urban heat island effect. Share this article to raise awareness and encourage discussion about solutions for a hotter future.
