History of research The phenomenon was first investigated and described by
Luke Howard in the 1810s, although he was not the one to name the phenomenon. A description of the very first report of the UHI by Luke Howard said that the urban center of London was warmer at night than the surrounding countryside by . Investigations of the urban atmosphere continued throughout the nineteenth century. Between the 1920s and the 1940s, researchers in the emerging field of local climatology or
microscale meteorology in Europe, Mexico, India, Japan, and the United States pursued new methods to understand the phenomenon. In 1929, Albert Peppler used the term in a German publication believed to be the first instance of an equivalent to urban heat island: (which is
urban heat island in German). Between 1990 and 2000, about 30 studies were published annually; by 2010, that number had increased to 100, and by 2015, it was more than 300. Leonard O. Myrup published the first comprehensive numerical treatment to predict the effects of the urban heat island (UHI) in 1969. While the general impacts of urban heat inequity depend on the city studied, negative effects typically act on historically marginalized communities. ethnicity and socioeconomic status. This raises the possibility of health impacts from UHIs being an
environmental justice issue. Studies have shown that
communities of color in the United States have been disproportionately affected by UHI. There is a correlation between neighborhood income and tree canopy cover. Low-income neighborhoods tend to have significantly fewer trees than neighborhoods with higher incomes. Researchers hypothesized that less-well-off neighborhoods do not have the financial resources to plant and maintain trees.
Affluent neighborhoods can afford more trees, on "both public and private property". One reason for this discrepancy is that wealthier homeowners and communities can afford more land, which can be kept open as
green space, whereas poorer housing often takes the form of
rentals, where landowners try to maximize their
profit by putting as much housing
density as possible on their land. On a global scale, there are discrepancies in the effects of UHIs in different regions of the world. While overall heat exposure is increasing worldwide, its effects have increased faster in the Global South in recent decades, per a study by Professor Kanging Huang and colleagues. The disproportionate impact of UHIs on the Global South exacerbates already occurring environmental injustices. Because many countries in the equator are naturally hot and humid, these areas are particularly susceptible to the effects of UHIs. One World Bank study has found a 7.0° disparity between the hottest and coolest neighborhoods in Bandung, Indonesia. .
The US experience There is a correlation in the U.S. between ethnicity and exposure to UHIs. Within most U.S. cities, people of color are more likely to live in areas of high Surface Urban Heat Island Intensity than white people in the same cities. According to a study by climatologist Angel Hsu and colleagues, "the average person of color lives in a
census tract with higher SUHI intensity than non-Hispanic whites in all but 6 of the 175 largest urbanized areas" in the U.S. A 2023 policy brief further found that historically redlined and low‑income Black neighborhoods—already burdened by urban heat—also experience clusters of violent crime, amplifying intersecting vulnerabilities in these communities. Economic status also plays a role in the human effects on UHIs. Not only are people of lower economic classes more likely to live in UHIs, but they are also less likely to be able to afford commodities such as air conditioning. Like the correlation between SUHI intensity and ethnicity, a similar pattern can be seen when comparing households under the poverty line against those with an income more than double the poverty line. Researchers have also noted that the spread of
impervious surfaces, such as concrete, tar, and asphalt, is correlated with neighborhoods of low socioeconomic status across various U.S. cities and states. The presence of these materials serves as a predictor of "intra-urban variation in temperature".
Redlining, Urban Heat Exposure, and Health Inequity in U.S. cities Redlining worked as a housing policy created and put to use in the 1930s, under the Roosevelt Administration, by the Home Owners' Loan Corporation (HOLC). This policy, when implemented, categorized neighborhoods by perceived investment risk. Notably, areas with higher populations of minorities and low-income residents were discriminated against using this policy, often labeled as hazardous and outlined in red on HOLC maps. This significantly restricted not only access to housing loans but also led to long-term divestment from these communities. A study analyzing 108 U.S. cities found that formerly redlined neighborhoods are, on average, 2.6 °C (4.7 °F) hotter than non-redlined areas, and as the authors noted, this was largely due to a lack of tree canopy and the increased presence of heat-absorbent surfaces like asphalt and other dark clustered infrastructure. In cities like Durham, Fresno, and Pittsburgh, "D" graded areas have substantially lower tree coverage compared to wealthier, "A" graded neighborhoods, which are also predominantly white. Similarly, Phoenix, Arizona, a rapidly warming city, also shows high surface temperatures in formerly redlined communities reaching up to 10-15 °F (5.6–8.3 °C) higher than other neighborhoods. In addition to higher temperatures, these neighborhoods also experience higher levels of air pollution due to their proximity to highways and industrial zones, a characterization of previously redlined areas. Cities like Los Angeles experienced freeway construction in the 1950s that routed interstates through redlined areas, including neighborhoods like Boyle Heights and South Los Angeles. These areas have since experienced much higher concentrations of vehicular emissions such as diesel exhaust and fine particulate matter (PM2.5), which are also closely associated with higher risks of respiratory illness, cardiovascular disease, and birth defects. On an international scale, research has also suggested that urban air pollution, like that of vehicular emissions, may directly intensify the urban heat island effect. In China, an urban haze effect, essentially a miniature greenhouse layer which prevents outgoing thermal radiation from escaping dense urban areas, was found to contribute as much as 0.7 °C of additional nighttime warming. This conclusion underscores the critical consequences of urban heat islands, especially in previously redlined communities driven by both local development and broader atmospheric processes. In response to these disparities, some cities have begun to introduce urban greening programs and reflective "cool pavement" initiatives to help mitigate the urban heat island effect in historically disadvantaged communities. These efforts are part of an ongoing push toward not only climate justice but also aims to redress the legacy of redlining, a policy driven by environmental racism.
Chief heat officers Beginning in the 2020s, a number of cities and local governments began creating Chief Heat Officer positions to organize and manage work counteracting the urban heat island effect. They lead efforts to try to mitigate the increasing effects of
climate change by increasing shade, providing for
cooling centers, planting trees, and coordinating anti-heat work. Early heat officer positions were created in
Los Angeles,
Miami-Dade County,
Melbourne,
Athens, and
Freetown. The initiative to create the positions was organized by the
Atlantic Council's
Adrienne Arsht-
Rockefeller Foundation Resilience Center.
Eleni Myrivili is the current
United Nations Human Settlements Programme's chief heat officer and the
City of Athens Chief Resilience Officer. == Examples ==