Heat risk isn’t just about the highs: Large daily temperature swings can harm human health

Shengjie Liu, USC

This summer has highlighted how high temperatures can be deadly, but it’s not just extreme heat and cold that are concerning—daily temperature swings also pose significant health risks. Research indicates that larger-than-normal temperature variations can lead to increased asthma flare-ups, hospitalizations for respiratory and cardiovascular issues, and higher overall death rates. A study tracking data from 308 cities between 1972 and 2013 estimates that 2.5% of deaths during this period were linked to large daily temperature swings.

Daily temperature changes strain various bodily systems, especially in vulnerable populations like the very young and the elderly. To better understand this issue, we mapped daily temperature variations across the U.S. and found that these swings are more pronounced in areas affected by poverty and historical discrimination, disproportionately impacting racial minorities and low-income residents.

For instance, large night-to-day temperature swings are more common in the U.S. Southwest but can also vary significantly within short distances due to factors like the urban heat island effect. Coastal areas, such as Santa Monica, experience smaller temperature swings compared to inland regions like downtown Los Angeles, due to the moderating influence of the ocean. Similarly, green spaces and urban vegetation can help mitigate temperature swings.

Using NASA satellite data from 2000 to 2017 and U.S. Census Bureau demographic data, we analyzed how race, income, and age influence exposure to temperature variations. We found that racial and ethnic disparities were the most pronounced, followed by income differences, while age had the least impact.

In Rhode Island, for example, Hispanic and Black populations experienced average daily temperature swings of 31.2°F (17.3°C) in May, compared to 25.8°F (14.3°C) for white populations—a 5.4°F (3°C) difference. Low-income residents faced swings of 28.6°F (15.9°C), while high-income residents experienced 24.5°F (13.6°C)—a 4.1°F (2.3°C) difference. Age differences were minimal, at just 1.8°F (1°C).

Nationwide, significant racial and ethnic disparities in temperature swings were observed in 46 states, income disparities in 39 states, and age disparities in 15 states. Temperature swings were notably higher in western states, especially in late spring and summer.

These disparities in exposure to temperature swings underscore another facet of climate change inequality. Evidence suggests that these temperature swings are likely to widen further due to rising greenhouse gas emissions. Since the 1990s, research shows an increase in temperature swings after a period of global decline from the 1950s to the 1980s. Under the Intergovernmental Panel on Climate Change’s highest emissions scenario, temperature swings could increase by up to 2.9°F (1.6°C) by the century’s end.

To address these risks, it is crucial to cut greenhouse gas emissions and implement local measures to mitigate temperature swings. Enhancing tree cover, using reflective roofing materials, and supporting low-income and minority communities with cooling and heating resources are essential steps. These actions can help protect the most vulnerable populations from the health impacts of extreme temperature variations.

[Abridged]