Inequality in the availability of residential air conditioning across 115 US metropolitan areas

Declining urban density attenuates rising population exposure to surface heat extremes

In the past two decades, global cities have experienced a decline in urban population density, marked by urban land expansion outpacing population growth. The impact of this trend on urban population exposure to surface urban heat island (SUHI) has not been fully examined by considering the intra-city spatial variations in both population distribution and surface temperature. In this study, we examine the temporal trends of population-weighted SUHI extremes (as a proxy for spatial heat exposure) in the 1,000 largest global cities using high-resolution data from 2003 to 2020. Our findings reveal that cities with declining population densities experience a slower increase in population-weighted SUHI extremes compared to the rise in the area-average values, by approximately 0.5 ± 0.04 K per decade for every 1,000 persons/km2/year decrease in density (R2 = 0.71; P < 0.01). Conversely, cities undergoing densification face greater challenges in mitigating rising heat exposure. We further show that vegetation changes have a moderate association with changes in population-weighted heat exposure (R2 = 0.56), whereas variations in surface albedo exhibit a negligible relationship (R2 = 0.03). These results underscore the need for strategic urban planning to balance the benefits of densification with the imperative of reducing heat exposure risks. Urban greening efforts may offer some mitigation potential, while albedo-based interventions require further investigation to assess their effectiveness at scale. As cities worldwide pursue sustainability and economic growth through increasing density, it is critical to integrate heat exposure consideration into urban planning to enhance climate resilience.

How Climate Change Is Impacting Allergic Rhinitis: A Scoping Review

OBJECTIVE

The impact of climate change on health has become an increasingly widespread global health concern. This impact is especially relevant in the field of Otolaryngology; global warming has been shown to affect inflammatory upper airway disease, specifically allergic rhinitis (AR). This study aims to characterize the effect of climate change on the epidemiology of AR in adult and pediatric populations globally.

DATA SOURCES

In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, a literature search was performed across four databases. Inclusion criteria were: (1) published in English, (2) published between 2000 and 2023, (3) reported on the current epidemiological state of AR, (4) described factors related to climate change, and (5) observed global warming affecting allergy season and AR symptoms.

REVIEW METHODS

Two reviewers screened articles and performed full-text reviews.

RESULTS

Of the 502 articles assessed, 30 studies were eligible for inclusion. Sixteen studies reported longer pollen seasons and/or higher pollen concentrations related to climate change, with two projecting total pollen emissions to increase by 16-40% and pollen season length to increase by 19 days in North America. Four studies reported an increase in AR-related healthcare usage; low-income residents were most impacted by increased usage. Two studies identified that healthcare professionals want more education on climate change.

CONCLUSION

Our scoping review highlights how climate change is altering pollen seasons and concentrations, AR disease prevalence, allergy sensitization, and AR symptom severity. Health professionals have expressed an understanding of climate change's impact on health and a desire for further education.

LEVEL OF EVIDENCE

N/A.

Heat Waves and Early Birth: Exploring Vulnerability by Individual- and Area-Level Factors

Extreme heat has been linked to many health outcomes, including preterm and early term birth. We examine associations between acute heat wave exposure and risk of preterm (PTB) (28-36 weeks) or early term (ETB) (37-38 weeks) birth, stratified by individual-level and area-level factors. Daily ambient mean temperature was linked to maternal residence in state vital records for preterm and early term births in California, Florida, Georgia, Kansas, Nevada, New Jersey, North Carolina, and Oregon between 1990 and 2017. Heat waves were identified during the four-day exposure window preceding birth using the 97.5th percentile mean temperature for zip code tabulation areas (ZCTA). We used a time-stratified case-crossover design, restricted to the warm season (May through September) and stratified by maternal age, maternal education, ZCTA-level impervious land cover or social deprivation index. We pooled estimated odds ratios across states using inverse-variance weighting. The PTB and ETB analyses included up to 945,836 and 2,966,661 cases, respectively. Heat-related ETB risk was consistently highest among women <25 years of age, women with ≤high school education, and women living in areas of higher social deprivation and impervious land cover. PTB associations were also elevated in these subgroups, but positive associations were also observed among older, more educated mothers, and in areas with less social deprivation. Across all subgroups and outcomes, the change in odds associated with heat waves ranged from no increase to a 7.9% increase. Heat-related early term birth risk is enhanced among subgroups associated with socioeconomic disadvantage, but patterns of vulnerability were less consistent for preterm birth.

Impact of Heat on Respiratory Hospitalizations among Older Adults in 120 Large U.S. Urban Areas

Rationale: Extreme heat exposure is a well-known cause of mortality among older adults. However, the impacts of exposure on respiratory morbidity across U.S. cities and population subgroups are not well understood. Objectives: A nationwide study was conducted to determine the impact of high heat on respiratory disease hospitalizations among older adults (≥65 yr of age) living in the 120 largest U.S. cities between 2000 and 2017. Methods: Daily rates of inpatient respiratory hospitalizations were examined with respect to variations in ZIP code-level daily mean temperature or heat index. For each city, we estimated cumulative associations (lag days 0-6) between warm-season heat (June to September) and cause-specific respiratory hospitalizations using time-stratified conditional quasi-Poisson regression with distributed lag nonlinear models. We estimated nationwide associations using multivariate meta-regression and updated city-specific associations via best linear unbiased prediction. With stratified models, we explored effect modification by age, sex, and race (Black or White). Results are reported as percentage change in hospitalizations at high temperatures (95th percentile) compared with median temperatures for each outcome, demographic group, and metropolitan area. Results: We identified 3,275,033 respiratory hospitalizations among Medicare beneficiaries across 120 large U.S. cites between 2000 and 2017. Nationwide, 7-day cumulative associations at high temperatures resulted in a 1.2% (95% confidence interval, 0.4-2.0%) increase in hospitalizations for primary diagnoses of all-cause respiratory disease, driven primarily by increases in respiratory tract infections (1.8% [95% confidence interval, 0.6-3.0%]) and chronic respiratory diseases and/or respiratory failure (1.2% [95% confidence interval, 0.0-2.4%]). Stronger associations were observed when exposure was defined using the heat index instead of mean temperature. Across the 120 cities, we observed considerable geographic variation in the relative risk of heat-related respiratory hospitalizations, and we observed disproportionate burdens of heat-related respiratory hospitalizations among the oldest beneficiaries (≥85 yr of age) and among Black beneficiaries living in South Atlantic cities. During the 18-year study period, there were an estimated 11,710 excess respiratory hospitalizations due to heat exposure. Conclusions: Results suggest that high temperature and humidity contribute to exacerbation of respiratory tract infections and chronic lung diseases among older adults. Geographic variation in heat-related hospitalization rates suggests that contextual factors largely account for disproportionate burdens, and area-level influences should be further investigated in multicity studies.

Emergency department visits in California associated with wildfire PM2.5: differing risk across individuals and communities

The threats to human health from wildfires and wildfire smoke (WFS) in the United States (US) are increasing due to continued climate change. A growing body of literature has documented important adverse health effects of WFS exposure, but there is insufficient evidence regarding how risk related to WFS exposure varies across individual or community level characteristics. To address this evidence gap, we utilized a large nationwide database of healthcare utilization claims for emergency department (ED) visits in California across multiple wildfire seasons (May through November, 2012-2019) and quantified the health impacts of fine particulate matter <2.5 μm (PM2.5) air pollution attributable to WFS, overall and among subgroups of the population. We aggregated daily counts of ED visits to the level of the Zip Code Tabulation Area (ZCTA) and used a time-stratified case-crossover design and distributed lag non-linear models to estimate the association between WFS and relative risk of ED visits. We further assessed how the association with WFS varied across subgroups defined by age, race, social vulnerability, and residential air conditioning (AC) prevalence. Over a 7 day period, PM2.5 from WFS was associated with elevated risk of ED visits for all causes (1.04% (0.32%, 1.71%)), non-accidental causes (2.93% (2.16%, 3.70%)), and respiratory disease (15.17% (12.86%, 17.52%)), but not with ED visits for cardiovascular diseases (1.06% (-1.88%, 4.08%)). Analysis across subgroups revealed potential differences in susceptibility by age, race, and AC prevalence, but not across subgroups defined by ZCTA-level Social Vulnerability Index scores. These results suggest that PM2.5 from WFS is associated with higher rates of all cause, non-accidental, and respiratory ED visits with important heterogeneity across certain subgroups. Notably, lower availability of residential AC was associated with higher health risks related to wildfire activity.

The temporal change of heat exposure and adaptation capacity in Chinese adults from 1994 to 2023

Background

Studies have found decreased heat effect and increased minimum mortality temperature (MMT) during the past decades. However, it is unclear whether heat exposure or temperature adaptation play an important role in this change.

Methods

This is a cross-sectional study. Data were collected from 3,094 respondents aged 31-64 years old based on online questionnaire. The Cochran-Armitage test for trend and Cochran-Mantel-Haenszel (CMH) test were used for the difference between three decades. The Chi square test was employed to compare the difference between different demographic subgroups during 2014-2023. Multivariate logistic regression model was used to analyze the risk factors of air conditioner ownership.

Results

Most respondents (94.6%) thought ambient temperature had been increasing, and 57.0% people thought climate change impacted their health. Long duration outdoors work (≥4 h) decreased from 36.01, 30.93 to 24.53% (Z = -9.80, p < 0.01) and bicycling/walking decreased from 62.3, 27.9, to 9.7% (CMH value = 156.40, p < 0.01) significantly during the last three decades. Temperature adaptation capacity increased with air conditioner ownership rates increasing from 25.40, 57.63 to 81.51% at home (Z = -44.35, p < 0.01) and from 22.24, 57.47 to 80.51% in the office/school (Z = -45.95, p < 0.01), and the older adult, women, people with low income, outdoor work, low education, and people from northern China had lower air conditioner ownership rates. The frequency of air conditioner usage when felt hot also escalated significantly both at home (from 42.6%, 54.9, to 63.4%, CMH value = 156.40, p < 0.0001) and in the office/school (from 61.8, 63.1 to 72.7%, CMH value = 65.29, p < 0.0001) during the same periods.

Conclusion

Our study found that most people perceived climate change and changed behaviors to adapt to heat. Heat exposure significantly decreased and temperature adaptation capacity significantly increased during the last decades. The findings implied that heat-related health risk and burden driven by global warming may not increase in the future.

More extremely hot days, more heat exposure and fewer cooling options for people of color in Connecticut, U.S

It is well-documented that people of color in the U.S. are disproportionately exposed to extreme urban heat. However, most studies have focused on large cities for one point in time, and less is known about how heat exposure changes over time in smaller cities. Here, we present a study of the changing nature of urban heat exposure and cooling strategies for ten cities in Connecticut in the U.S. Our results show that people of color experience more heat exposure and fewer adaptation strategies. They experienced higher overall temperatures, more extremely hot days, and larger increases in heat exposure. Also, they have lower air conditioning ownership rates and lower tree cover. Taken together, the results indicate that people of color are not only exposed to higher temperatures but also disproportionately exposed to increasing temperatures over time. With lower heat adaptation capacity, people of color are more vulnerable to increasing urban heat.

Ambient smoke exposure and indoor air quality in eastern Massachusetts during the 2023 wildfire season

Widespread North American wildfires in 2023 led to exposure to ambient wildfire smoke outside of traditionally wildfire-prone regions. The objective was to evaluate levels of indoor air pollutants in relation to ambient wildfire smoke exposure in eastern Massachusetts. Using a real-time multipollutant sensor system in five Boston area households, this study assessed indoor fine particulate matter (PM2.5), nitrogen dioxide (NO2), and total volatile organic compound concentrations (TVOC) two days before and during days of hazardous wildfire smoke exposure (smoke days). The relationship between ambient PM2.5 from regulatory monitors and indoor PM2.5 before and during smoke days was investigated by mixed effects linear regression. During smoke days and the preceding non-smoke days, median indoor PM2.5 was 9.9 µg/m3 and 3.5 µg/m3 (p < 0.001), respectively; median NO2 was 20.5 ppb and 18.4 ppb (p = 0.11); median TVOC was 6,715 µg/m3 and 5,361 µg/m3 (p = 0.35). A 1% increase in ambient PM2.5 was associated with a 0.93% increase in indoor PM2.5 on smoke days (95% CI, 0.54%-1.32%) and a 0.34% increase on non-smoke days (95% CI, 0.17%-0.66%), though interaction testing of smoke day status was not statistically significant (p = 0.14). In Northeastern US homes, indoor PM2.5 increased significantly during ambient wildfire smoke exposure, which may reflect increased infiltration and increased indoor particle-generating activities during smoke days.Implications: This study reports on household exposure to wildfire smoke in eastern Massachusetts, finding that indoor PM2.5 more than doubled compared to preceding non-smoke days, while indoor NO2 and TVOC did not significantly rise. Though the generalizability of this study is limited by the small number of homes studied, the findings suggest that more investigation is needed to understand indoor air pollution during future wildfire smoke exposure in regions not traditionally wildfire-prone and to inform mitigation efforts.

Identifying groups at-risk to extreme heat: Intersections of age, race/ethnicity, and socioeconomic status

Anthropogenic climate change has resulted in a significant rise in extreme heat events, exerting considerable but unequal impacts on morbidity and mortality. Numerous studies have identified inequities in heat exposure across different groups, but social identities have often been viewed in isolation from each other. Children (5 and under) and older adults (65 and older) also face elevated risks of heat-related health impacts. We employ an intersectional cross-classificatory approach to analyze the distribution of heat exposure between sociodemographic categories split into age groups in the contiguous US. We utilize high-resolution daily air temperature data to establish three census tract-level heat metrics (i.e., average summer temperature, heat waves, and heat island days). We pair those metrics with American Community Survey estimates on racial/ethnic, socioeconomic, and disability status by age to calculate population weighted mean exposures and absolute disparity metrics. Our findings indicate few substantive differences between age groups overall, but more substantial differences between sociodemographic categories within age groups, with children and older adults from socially marginalized backgrounds facing greater exposure than adults from similar backgrounds. When looking at sociodemographic differences by age, people of color of any age and older adults without health insurance emerge as the most exposed groups. This study identifies groups who are most exposed to extreme heat. Policy and program interventions aimed at reducing the impacts of heat should take these disparities in exposure into account to achieve health equity objectives.

Climate change and public health in California: A structured review of exposures, vulnerable populations, and adaptation measures

California faces several serious direct and indirect climate exposures that can adversely affect public health, some of which are already occurring. The public health burden now and in the future will depend on atmospheric greenhouse gas concentrations, underlying population vulnerabilities, and adaptation efforts. Here, we present a structured review of recent literature to examine the leading climate risks to public health in California, including extreme heat, extreme precipitation, wildfires, air pollution, and infectious diseases. Comparisons among different climate-health pathways are difficult due to inconsistencies in study design regarding spatial and temporal scales and health outcomes examined. We find, however, that the current public health burden likely affects thousands of Californians each year, depending on the exposure pathway and health outcome. Further, while more evidence exists for direct and indirect proximal health effects that are the focus of this review, distal pathways (e.g., impacts of drought on nutrition) are more uncertain but could add to this burden. We find that climate adaptation measures can provide significant health benefits, particularly in disadvantaged communities. We conclude with priority recommendations for future analyses and solution-driven policy actions.

Residential segregation and summertime air temperature across 13 northeastern U.S. states: Potential implications for energy burden

High ambient summertime temperatures are an increasing health concern with climate change. This is a particular concern for minoritized households in the United States, for which differential energy burden may compromise adaptive capacity to high temperatures. Our research question was: Do minoritized groups experience hotter summers than the area average, and do non-Hispanic white people experience cooler summers? Using a fine-scaled spatiotemporal air temperature model and U.S. census data, we examined local (within-county) differences in warm season cooling degree days (CDDs) by ethnoracial group as a proxy for local energy demand for space cooling across states of the northeast and mid-Atlantic U.S. in 2003-2019. Using state-specific regression models adjusted for year and county, we found that Black and Latino people consistently experienced more CDDs, non-Hispanic white people experienced fewer CDDs, and Asian populations showed mixed results. We also explored a concentration-based measure of residential segregation for each ethnoracial group as one possible pathway towards temperature disparities. We included the segregation measure as a smooth term in a regression model adjusted for county and year. The results were nonlinear, but higher concentrations of white people were associated with lower annual CDDs and higher concentrations of Latino people were associated with higher annual CDDs than the county average. Concentrations for Black and Asian people were nonmonotonic, sometimes with bowed associations. These findings suggest that present-day residential segregation, as modeled by spatially smoothed ethnoracial subgroup concentrations, may contribute to summertime air temperature disparities and influence adaptive capacity. We hope these findings can support place-based interventions, including targeting of energy insecurity relief programs.

Sociodemographic Determinants of Extreme Heat and Ozone Risk Among Older Adults in 3 Sun Belt Cities

BACKGROUND

Vulnerable populations across the United States are frequently exposed to extreme heat, which is becoming more intense due to a combination of climate change and urban-induced warming. Extreme heat can be particularly detrimental to the health and well-being of older citizens when it is combined with ozone. Although population-based studies have demonstrated associations between ozone, extreme heat, and human health, few studies focused on the role of social and behavioral factors that increase indoor risk and exposure among older adults.

METHODS

We conducted a household survey that aimed to understand how older adults are affected by extreme heat and ozone pollution inside and outside of their homes across Houston, Phoenix, and Los Angeles. We examine contributing factors to the risk of self-reported health effects using a generalized linear mixed-effects regression model of telephone survey data of 909 older adults in 2017.

RESULTS

We found an increased occurrence of self-reported symptoms for extreme heat with preexisting respiratory health conditions and a lack of air conditioning access; self-reported ozone symptoms were more likely with preexisting respiratory health conditions. The risk of heat-related symptoms was slightly higher in Los Angeles than Houston and Phoenix. We found several demographic, housing, and behavioral characteristics that influenced the risk of heat- and ozone-related symptoms.

CONCLUSIONS

The increased risk among older adults based on specific social and behavioral factors identified in this study can inform public health policy and help cities tailor their heat and ozone response plans to the specific needs of this vulnerable population.

Climate change and health: rethinking public health messaging for wildfire smoke and extreme heat co-exposures

With the growing climate change crisis, public health agencies and practitioners must increasingly develop guidance documents addressing the public health risks and protective measures associated with multi-hazard events. Our Policy and Practice Review aims to assess current public health guidance and related messaging about co-exposure to wildfire smoke and extreme heat and recommend strengthened messaging to better protect people from these climate-sensitive hazards. We reviewed public health messaging published by governmental agencies between January 2013 and May 2023 in Canada and the United States. Publicly available resources were eligible if they discussed the co-occurrence of wildfire smoke and extreme heat and mentioned personal interventions (protective measures) to prevent exposure to either hazard. We reviewed local, regional, and national governmental agency messaging resources, such as online fact sheets and guidance documents. We assessed these resources according to four public health messaging themes, including (1) discussions around vulnerable groups and risk factors, (2) symptoms associated with these exposures, (3) health risks of each exposure individually, and (4) health risks from combined exposure. Additionally, we conducted a detailed assessment of current messaging about measures to mitigate exposure. We found 15 online public-facing resources that provided health messaging about co-exposure; however, only one discussed all four themes. We identified 21 distinct protective measures mentioned across the 15 resources. There is considerable variability and inconsistency regarding the types and level of detail across described protective measures. Of the identified 21 protective measures, nine may protect against both hazards simultaneously, suggesting opportunities to emphasize these particular messages to address both hazards together. More precise, complete, and coordinated public health messaging would protect against climate-sensitive health outcomes attributable to wildfire smoke and extreme heat co-exposures.

Indoor Air Sources of Outdoor Air Pollution: Health Consequences, Policy, and Recommendations: An Official American Thoracic Society Workshop Report

Indoor sources of air pollution worsen indoor and outdoor air quality. Thus, identifying and reducing indoor pollutant sources would decrease both indoor and outdoor air pollution, benefit public health, and help address the climate crisis. As outdoor sources come under regulatory control, unregulated indoor sources become a rising percentage of the problem. This American Thoracic Society workshop was convened in 2022 to evaluate this increasing proportion of indoor contributions to outdoor air quality. The workshop was conducted by physicians and scientists, including atmospheric and aerosol scientists, environmental engineers, toxicologists, epidemiologists, regulatory policy experts, and pediatric and adult pulmonologists. Presentations and discussion sessions were centered on 1) the generation and migration of pollutants from indoors to outdoors, 2) the sources and circumstances representing the greatest threat, and 3) effective remedies to reduce the health burden of indoor sources of air pollution. The scope of the workshop was residential and commercial sources of indoor air pollution in the United States. Topics included wood burning, natural gas, cooking, evaporative volatile organic compounds, source apportionment, and regulatory policy. The workshop concluded that indoor sources of air pollution are significant contributors to outdoor air quality and that source control and filtration are the most effective measures to reduce indoor contributions to outdoor air. Interventions should prioritize environmental justice: Households of lower socioeconomic status have higher concentrations of indoor air pollutants from both indoor and outdoor sources. We identify research priorities, potential health benefits, and mitigation actions to consider (e.g., switching from natural gas to electric stoves and transitioning to scent-free consumer products). The workshop committee emphasizes the benefits of combustion-free homes and businesses and recommends economic, legislative, and education strategies aimed at achieving this goal.

Urban Versus Lake Impacts on Heat Stress and Its Disparities in a Shoreline City

Shoreline cities are influenced by both urban-scale processes and land-water interactions, with consequences on heat exposure and its disparities. Heat exposure studies over these cities have focused on air and skin temperature, even though moisture advection from water bodies can also modulate heat stress. Here, using an ensemble of model simulations covering Chicago, we find that Lake Michigan strongly reduces heat exposure (2.75°C reduction in maximum average air temperature in Chicago) and heat stress (maximum average wet bulb globe temperature reduced by 0.86°C) during the day, while urbanization enhances them at night (2.75 and 1.57°C increases in minimum average air and wet bulb globe temperature, respectively). We also demonstrate that urban and lake impacts on temperature (particularly skin temperature), including their extremes, and lake-to-land gradients, are stronger than the corresponding impacts on heat stress, partly due to humidity-related feedback. Likewise, environmental disparities across community areas in Chicago seen for skin temperature are much higher (1.29°C increase for maximum average values per $10,000 higher median income per capita) than disparities in air temperature (0.50°C increase) and wet bulb globe temperature (0.23°C increase). The results call for consistent use of physiologically relevant heat exposure metrics to accurately capture the public health implications of urbanization.

Urban heat island impacts on heat-related cardiovascular morbidity: A time series analysis of older adults in US metropolitan areas

Many United States (US) cities are experiencing urban heat islands (UHIs) and climate change-driven temperature increases. Extreme heat increases cardiovascular disease (CVD) risk, yet little is known about how this association varies with UHI intensity (UHII) within and between cities. We aimed to identify the urban populations most at-risk of and burdened by heat-related CVD morbidity in UHI-affected areas compared to unaffected areas. ZIP code-level daily counts of CVD hospitalizations among Medicare enrollees, aged 65-114, were obtained for 120 US metropolitan statistical areas (MSAs) between 2000 and 2017. Mean ambient temperature exposure was estimated by interpolating daily weather station observations. ZIP codes were classified as low and high UHII using the first and fourth quartiles of an existing surface UHII metric, weighted to each have 25% of all CVD hospitalizations. MSA-specific associations between ambient temperature and CVD hospitalization were estimated using quasi-Poisson regression with distributed lag non-linear models and pooled via multivariate meta-analyses. Across the US, extreme heat (MSA-specific 99th percentile, on average 28.6 °C) increased the risk of CVD hospitalization by 1.5% (95% CI: 0.4%, 2.6%), with considerable variation among MSAs. Extreme heat-related CVD hospitalization risk in high UHII areas (2.4% [95% CI: 0.4%, 4.3%]) exceeded that in low UHII areas (1.0% [95% CI: -0.8%, 2.8%]), with upwards of a 10% difference in some MSAs. During the 18-year study period, there were an estimated 37,028 (95% CI: 35,741, 37,988) heat-attributable CVD admissions. High UHII areas accounted for 35% of the total heat-related CVD burden, while low UHII areas accounted for 4%. High UHII disproportionately impacted already heat-vulnerable populations; females, individuals aged 75-114, and those with chronic conditions living in high UHII areas experienced the largest heat-related CVD impacts. Overall, extreme heat increased cardiovascular morbidity risk and burden in older urban populations, with UHIs exacerbating these impacts among those with existing vulnerabilities.