Heat-Related Emergency Department Visits - United States, May-September 2023.

Unprecedented heat waves can affect all persons, but some are more sensitive to the effects of heat, including children and adults with underlying health conditions, pregnant women, and outdoor workers. Many regions of the United States experienced record-breaking high temperatures in 2023, with populations exposed to extremely high temperatures for prolonged periods. CDC examined emergency department (ED) visits associated with heat-related illness (HRI) from the National Syndromic Surveillance Program and compared daily HRI ED visit rates during the warm-season months (May-September) of 2023 with those during 2018-2022. In the 2023 warm-season months, daily HRI ED visit rates peaked in several regions and remained elevated for a prolonged duration. More males than females sought care in EDs for HRI, especially males aged 18-64 years. CDC issued multiple public health alerts using the Epidemic Information Exchange system to bring attention to increases in ED utilization for HRI. Deaths and illnesses associated with heat exposure are a continuing public health concern as climate change results in longer, hotter, and more frequent episodes of extreme heat. Near real-time monitoring of weather conditions and adverse health outcomes can guide public health practitioners' timing of risk communication and implementation of prevention measures associated with extreme heat.

Indoor Temperature and Energy Insecurity: Implications for Prenatal Health Disparities in Extreme Heat Events.

BACKGROUND: Extreme heat events are a major public health concern and are only expected to increase in intensity and severity as climate change continues to accelerate. Pregnant people are physiologically more vulnerable to the effects of extreme heat, and exposure can induce harm on both the pregnant person and the fetus. OBJECTIVES: This commentary argues that there is a need for greater epidemiological research on indoor heat exposure and energy insecurity as potential drivers of maternal and child environmental health disparities. DISCUSSION: While there is substantial evidence linking ambient (outdoor) high temperature to pregnancy-related outcomes, there is a lack of epidemiological evidence to date on pregnant people's exposure to high indoor temperature and adverse maternal and/or child health outcomes. Energy insecurity is disproportionately experienced by people with low incomes and/or people of color, and indoor temperature may play a role in shaping socioeconomic and racial/ethnic disparities in maternal and child health in the United States. Further research is needed to understand the relationship between indoor heat exposure, energy insecurity, and pregnancy outcomes in both parents and children and to inform potential policies and practices to enhance resilience and reduce maternal/child health disparities. https://doi.org/10.1289/EHP13706.

Extreme Heat and Pregnancy: A Content Analysis of Heat Health Risk Communication by US Public Health Agencies.

OBJECTIVES: Exposure to extreme heat events increases the risk for negative birth outcomes, including preterm birth. This study sought to determine the presence and content of web-based heat health information for pregnant people provided by federal, state, and local government public health websites. METHODS: This website content analysis consisted of 17 federal, 50 state, and 21 city websites, and noted which of 25 recognized pregnancy heat health data elements were included. Data for the analysis were collected from March 12, 2022, through March 16, 2022. RESULTS: The search identified 17 federal websites, 38 state websites, and 19 city websites with heat health information. Within these, only seven websites listed pregnant people as a vulnerable or at-risk population, and only six websites provided information related to heat health specifically for pregnancy. Of the 25 themes recognized as important for pregnancy risk during extreme heat exposure, only 11 were represented within these 6 websites. CONCLUSION: The presence of web-based pregnancy heat health information is infrequent and limited in content. Boosting web-based publication of extreme heat and pregnancy risks could mitigate negative maternal and child health outcomes.

Heat Exposure, Preterm Birth, and the Role of Greenness in Australia.

Importance: Preterm birth (PTB) is associated with adverse health outcomes. The outcomes of heat exposure during pregnancy and the moderating association of greenness with PTB remain understudied. Objective: To investigate associations between heat exposure, greenness, and PTB, as well as interactions between these factors. Design, Setting, and Participants: Included in this cohort study were births occurring in Sydney, New South Wales, Australia, between 2000 and 2020, retrieved from New South Wales Midwives Data Collection. Participants with incomplete or missing data on their residential address or those who resided outside of New South Wales during their pregnancy were excluded. Data were analyzed from March to October 2023. Exposures: Greenness measured using normalized difference vegetation index (NDVI) and tree cover derived from satellite images. Daily extreme heat and nighttime extreme heat were defined as above the 95th percentile of community- and trimester-specific daily mean temperatures and nighttime temperatures. Main Outcomes and Measures: Logistic regression models estimated the independent association of extreme heat with PTB, adjusting for individual- and area-level covariates, season of conception, and long-term trend. An interaction term between extreme heat exposure and greenness was included to explore potential modification. With a significant interaction observed, the number of preventable heat-associated PTBs that were associated with greenness was estimated. Results: A total of 1 225 722 births (median [IQR] age, 39 [38-40] weeks; 631 005 male [51.5%]) were included in the analysis, including 63 144 PTBs (median [IQR] age, 35 [34-36] weeks; 34 822 male [55.1%]). Compared with those without heat exposure, exposure to daily extreme heat and nighttime extreme heat in the third trimester was associated with increased risks of PTB, with an adjusted odds ratio (OR) of 1.61 (95% CI, 1.55-1.67) and 1.51 (95% CI, 1.46-1.56]), respectively (PTB rates: exposed, 4615 of 61 338 [7.5%] vs unexposed, 56 440 of 1 162 295 [4.9%] for daily extreme heat and 4332 of 61 337 [7.1%] vs 56 723 of 1 162 296 [4.9%] for nighttime extreme heat). Disparities in associations between extreme heat exposure and PTB were observed, with lower odds of PTB among pregnant individuals residing in greener areas. The associations between extreme heat exposure and PTB could be mitigated significantly by higher greenness. Improving NDVI and tree cover could reduce daily extreme heat-associated PTB by 13.7% (95% CI, 2.3%-15.1%) and 20.9% (95% CI, 5.8%-31.5%), respectively. For nighttime extreme heat-associated PTB, reductions were 13.0% (0.2%-15.4%) and 17.2% (4.1%-27.0%), respectively. Conclusions and Relevance: Results of this large birth cohort study suggest that extreme heat exposure was adversely associated with PTB, with greenness playing a moderating role. Increasing greenness levels in residential communities could prevent heat-associated PTBs. These findings emphasize the importance of integrating heat mitigation strategies and improving green space in urban planning and public health interventions.

Health risks from extreme heat in China: Evidence from health insurance.

Global warming has accentuated the effects of extreme heat on health. Health insurance, functioning as a risk management tool, has the potential to alleviate these impacts. Consequently, this paper investigates the correlation between extreme heat events and the demand for health insurance in China. Using data from the China Health and Nutrition Survey, we have observed a substantial increase in the likelihood of residents purchasing health insurance during extreme heat events. To be specific, for every extra day of extreme heat events annually, there is a 0.3% increase in the probability of purchasing health insurance. This effect is not uniform across different demographic groups. It is particularly pronounced among middle-aged and elderly individuals, rural residents, those with lower educational levels, higher income brackets, and individuals residing in underprivileged areas with limited access to green spaces and healthcare facilities. Furthermore, our study indicates that the increased frequency of extreme heat events not only impacts individuals' physical health but also triggers negative emotions, which in turn drive risk-averse behavior related to health insurance purchases. These findings carry substantial policy implications for mitigating the economic consequences of climate change.

Modification of the PM2.5- and extreme heat-mortality relationships by historical redlining: a case-crossover study in thirteen U.S. states.

BACKGROUND: Redlining has been associated with worse health outcomes and various environmental disparities, separately, but little is known of the interaction between these two factors, if any. We aimed to estimate whether living in a historically-redlined area modifies the effects of exposures to ambient PM2.5 and extreme heat on mortality by non-external causes. METHODS: We merged 8,884,733 adult mortality records from thirteen state departments of public health with scanned and georeferenced Home Owners Loan Corporation (HOLC) maps from the University of Richmond, daily average PM2.5 from a sophisticated prediction model on a 1-km grid, and daily temperature and vapor pressure from the Daymet V4 1-km grid. A case-crossover approach was used to assess modification of the effects of ambient PM2.5 and extreme heat exposures by redlining and control for all fixed and slow-varying factors by design. Multiple moving averages of PM2.5 and duration-aware analyses of extreme heat were used to assess the most vulnerable time windows. RESULTS: We found significant statistical interactions between living in a redlined area and exposures to both ambient PM2.5 and extreme heat. Individuals who lived in redlined areas had an interaction odds ratio for mortality of 1.0093 (95% confidence interval [CI]: 1.0084, 1.0101) for each 10 µg m-3 increase in same-day ambient PM2.5 compared to individuals who did not live in redlined areas. For extreme heat, the interaction odds ratio was 1.0218 (95% CI 1.0031, 1.0408). CONCLUSIONS: Living in areas that were historically-redlined in the 1930's increases the effects of exposures to both PM2.5 and extreme heat on mortality by non-external causes, suggesting that interventions to reduce environmental health disparities can be more effective by also considering the social context of an area and how to reduce disparities there. Further study is required to ascertain the specific pathways through which this effect modification operates and to develop interventions that can contribute to health equity for individuals living in these areas.

The impact of extreme heat on older regional and rural Australians: A systematic review.

INTRODUCTION: Extreme heat causes a major health burden, especially for older Australians. OBJECTIVE: To assess the impact of extreme heat on older regional and rural Australians, including clinical presentations, social implications, and health-seeking behaviours and adaptations. DESIGN: A systematic review and narrative synthesis. FINDINGS: Ten articles were included in the review with research on this topic limited. Extreme heat causes an increase in mortality and ambulance dispatches for older rural Australians. Social connectedness is negatively affected by extreme heat due to cancellation of events and individuals becoming housebound. Air conditioning is the main cooling mechanism used, although cost is a major concern. Despite this, older rural populations display a depth of knowledge regarding practical behavioural responses to adapt to extreme heat. Studies show older rural Australians do not consider extreme heat to be a threat to health. DISCUSSION: Further research needs to examine the role extreme heat may play in contributing to experiences of loneliness. Air conditioning cannot be the ultimate solution in responding to extreme heat due to cost and increased carbon emissions. The low-risk perception of extreme heat for older rural people may inform effective heat health warnings and effective use of primary health care in heat-health education. Listening to First Nations knowledge in dealing with heat may provide a powerful mechanism in which to protect health. CONCLUSION: The extensive health effects of extreme heat highlights the necessity of further research and strengthening of services in preparation for an ageing rural population enduring climate change.

Extreme Heat Vulnerability Among Older Adults: A Multilevel Risk Index for Portland, Oregon.

BACKGROUND AND OBJECTIVES: Extreme heat is an environmental health equity concern disproportionately affecting low-income older adults and people of color. Exposure factors, such as living in rental housing and lack of air conditioning, and sensitivity factors, such as chronic disease and social isolation, increase mortality risk among older adults. Older persons face multiple barriers to adaptive heat mitigation, particularly those living in historically temperate climates. This study measures two heat vulnerability indices to identify areas and individuals most vulnerable to extreme heat and discusses opportunities to mitigate vulnerability among older adults. RESEARCH DESIGN AND METHODS: We constructed two heat vulnerability indices for the Portland, OR, metropolitan area: one using area scale proxy measures extracted from existing regional data and another at the individual scale using survey data collected following the 2021 Pacific Northwest Heat Dome event. These indices were analyzed using principal component analysis and Geographic Information Systems. RESULTS: Results indicate that the spatial distribution of areas and individuals vulnerable to extreme heat are quite different. The only area found among the most vulnerable on both indices has the largest agglomeration of age- and income-restricted rental housing in the metropolitan area. DISCUSSION AND IMPLICATIONS: Due to spatial variations in heat-related risk at the individual and area scales, measures addressing heat risk should not be spatially uniform. By focusing resources on older adult individuals and areas in particular need of assistance, heat risk management policies can be both highly efficient and cost effective.

Body Core Temperature After Foot Immersion and Neck Cooling in Older Adults Exposed to Extreme Heat.

This randomized study evaluates the hypothesis that foot immersion in cool water alone or with supplemental neck cooling mitigates increases in core temperature in older adults exposed to environmental conditions simulating deadly heat waves in North America.

Heatstroke presentations to urban hospitals during BC's extreme heat event: lessons for the future.

BACKGROUND: Climate change is leading to more extreme heat events in temperate climates that typically have low levels of preparedness. Our objective was to describe the characteristics, treatments, and outcomes of adults presenting to hospitals with heatstroke during BC's 2021 heat dome. METHODS: We conducted a review of consecutive adults presenting to 7 hospitals in BC's Lower Mainland. We screened the triage records of all patients presenting between June 25th and 30th, 2021 for complaints related to heat, and reviewed the full records of those who met heatstroke criteria. Our primary outcome was in-hospital mortality. We used Mann-Whitney U tests and logistic regression to investigate associations between patient and treatment factors and mortality. RESULTS: Among 10,247 consecutive presentations to urban hospitals during the extreme heat event, 1.3% (139; 95% confidence intervals [CI] 1.1-1.6%) met criteria for heatstroke. Of heatstroke patients, 129 (90.6%) were triaged into the two highest acuity levels. Patients with heatstroke had a median age of 84.4 years, with 122 (87.8%) living alone, and 101 (84.2%) unable to activate 911 themselves. A minority (< 5, < 3.6%) of patients presented within 48 h of the onset of extreme heat. Most patients (107, 77.0%) required admission, and 11.5% (16) died in hospital. Hypotension on presentation was associated with mortality (odds ratio [OR] 5.3). INTERPRETATION: Heatstroke patients were unable to activate 911 themselves, and most presented with a 48-h delay. This delay may represent a critical window of opportunity for pre-hospital and hospital systems to prepare for the influx of high-acuity resource-intensive patients.

RéSUMé: CONTEXTE: Les changements climatiques entraînent une augmentation des épisodes de chaleur extrême dans les climats tempérés qui ont généralement de faibles niveaux de préparation. Notre objectif était de décrire les caractéristiques, les traitements et les résultats des adultes présentant un coup de chaleur à l'hôpital pendant le dôme de chaleur de 2021 en Colombie-Britannique. MéTHODES: Nous avons effectué un examen des adultes consécutifs qui se sont présentés dans sept hôpitaux du Lower Mainland de la Colombie-Britannique. Nous avons examiné les dossiers de triage de tous les patients qui se sont présentés entre le 25 et le 30 juin 2021 pour les plaintes liées à la chaleur et examiné les dossiers complets de ceux qui répondaient aux critères de coup de chaleur. Notre principal résultat était la mortalité à l'hôpital. Nous avons utilisé les tests de Mann-Whitney U et la régression logistique pour étudier les associations entre le patient et les facteurs de traitement et la mortalité. RéSULTATS: Parmi les 10247 présentations consécutives aux hôpitaux urbains pendant l'événement de chaleur extrême, 1,3 % (139; intervalles de confiance [IC] à 95 %) répondaient aux critères de coup de chaleur. Parmi les patients ayant subi un coup de chaleur, 129 (90,6 %) ont été classés dans les deux niveaux d'acuité les plus élevés. Les patients atteints d'un coup de chaleur avaient un âge médian de 84,4 ans, 122 (87,8 %) vivant seuls et 101 (84,2 %) incapables d'activer le 911 eux-mêmes. Une minorité (< 5, < 3,6 %) de patients se sont présentés dans les 48 heures suivant l'apparition de la chaleur extrême. La plupart des patients (107, 77,0 %) ont dû être admis et 11,5 % (16) sont décédés à l'hôpital. L'hypotension au moment de la présentation était associée à la mortalité (rapport de cotes [RC] 5.3). INTERPRéTATION: Les patients atteints d'un coup de chaleur n'ont pas pu activer le 911 eux-mêmes, et la plupart se sont présentés avec un délai de 48 heures. Ce délai peut représenter une fenêtre critique d'opportunité pour les systèmes préhospitaliers et hospitaliers de se préparer à l'afflux de patients à forte intensité de ressources.

Drivers of the time-varying heat-cold-mortality association in Spain: A longitudinal observational study.

BACKGROUND: A number of studies have reported reductions in mortality risk due to heat and cold over time. However, questions remain about the drivers of these adaptation processes to ambient temperatures. We aimed to analyse the demographic and socioeconomic drivers of the downward trends in vulnerability to heat- and cold-related mortality observed in Spain during recent decades (1980-2018). METHODS: We collected data on all-cause mortality, temperature and relevant contextual indicators for 48 provinces in mainland Spain and the Balearic Islands between Jan 1, 1980, and Dec 31, 2018. Fourteen contextual indicators were analysed representing ageing, isolation, urbanicity, heating, air conditioning (AC), house antiquity and ownership, education, life expectancy, macroeconomics, socioeconomics, and health investment. The statistical analysis was separately performed for the range of months mostly causing heat- (June-September) and cold- (October-May) related mortality. We first applied a quasi-Poisson generalised linear regression in combination with distributed lag non-linear models (DLNM) to estimate province-specific temperature-mortality associations for different periods, and then we fitted univariable and multivariable multilevel spatiotemporal meta-regression models to evaluate the effect modification of the contextual characteristics on heat- and cold-related mortality risks over time. FINDINGS: The average annual mean temperature has risen at an average rate of 0·36 °C per decade in Spain over 1980-2012, although the increase in temperature has been more pronounced in summer (0·40 °C per decade in June-September) than during the rest of the year (0·33 °C per decade). This warming has been observed, however, in parallel with a progressive reduction in the mortality risk associated to both hot and cold temperatures. We found independent associations for AC with heat-related mortality, and heating with cold-related mortality. AC was responsible for about 28·6% (31·5%) of the decrease in deaths due to heat (extreme heat) between 1989 and 1993 and 2009-2013, and heating for about 38·3% (50·8%) of the reductions in deaths due to cold (extreme cold) temperatures. Ageing (ie, proportion of population over 64 years) attenuated the decrease in cold-related mortality. INTERPRETATION: AC and heating are effective societal adaptive measures to heat and cold temperatures. This evidence holds important implications for climate change health adaptation policies, and for the projections of climate change impacts on human health.

Projected Change in the Burden of Excess Cardiovascular Deaths Associated With Extreme Heat by Midcentury (2036-2065) in the Contiguous United States.

BACKGROUND: Climate change is causing an increase in extreme heat. Individuals with cardiovascular disease are at high risk of heat-related adverse health effects. How the burden of extreme heat-associated cardiovascular deaths in the United States will change with the projected rise in extreme heat is unknown. METHODS: We obtained data on cardiovascular deaths among adults and the number of extreme heat days (maximum heat index ≥90 °F [32.2 °C]) in each county in the contiguous United States from 2008 to 2019. Based on representative concentration pathway trajectories that model greenhouse gas emissions and shared socioeconomic pathways (SSP) that model future socioeconomic scenarios and demographic projections, we obtained county-level projected numbers of extreme heat days and populations under 2 scenarios for the midcentury period 2036 to 2065: SSP2-4.5 (representing demographic projections from a "middle-of-the-road" socioeconomic scenario and an intermediate increase in emissions) and SSP5-8.5 (demographic projections in an economy based on "fossil-fueled development" and a large increase in emissions). The association of cardiovascular mortality with extreme heat was estimated with a Poisson fixed-effects model. Using estimates from this model, the projected number of excess cardiovascular deaths associated with extreme heat was calculated. RESULTS: Extreme heat was associated with 1651 (95% CI, 921-2381) excess cardiovascular deaths per year from 2008 to 2019. By midcentury, extreme heat is projected to be associated with 4320 (95% CI, 2369-6272) excess deaths annually, which is an increase of 162% (95% CI, 142-182) under SSP2-4.5, and 5491 (95% CI, 3011-7972) annual excess deaths, which is an increase of 233% (95% CI, 206-259) under SSP5-8.5. Elderly adults are projected to have a 3.5 (95% CI, 3.2-3.8) times greater increase in deaths in the SSP2-4.5 scenario compared with nonelderly adults. Non-Hispanic Black adults are projected to have a 4.6 (95% CI, 2.8-6.4) times greater increase compared with non-Hispanic White adults. The projected change in deaths was not statistically significantly different for other race and ethnicity groups or between men and women. CONCLUSIONS: By midcentury, extreme heat is projected to be associated with a significantly greater burden of excess cardiovascular deaths in the contiguous United States.

Projection of extreme heat- and cold-related mortality in Sweden based on the spatial synoptic classification.

BACKGROUND: Climate change is projected to result in increased heat events and decreased cold events. This will substantially impact human health, particularly when compounded with demographic change. This study employed the Spatial Synoptic Classification (SSC) to categorize daily weather into one of seven types. Here we estimated future mortality due to extremely hot and cold weather types under different climate change scenarios for one southern (Stockholm) and one northern (Jämtland) Swedish region. METHODS: Time-series Poisson regression with distributed lags was used to assess the relationship between extremely hot and cold weather events and daily deaths in the population above 65 years, with cumulative effects (6 days in summer, 28 days in winter), 1991 to 2014. A global climate model (MPI-M-MPI-ESM-LR) and two climate change scenarios (RCP 4.5 and 8.5) were used to project the occurrence of hot and cold days from 2031 to 2070. Place-specific projected mortality was calculated to derive attributable numbers and attributable fractions (AF) of heat- and cold-related deaths. RESULTS: In Stockholm, for the RCP 4.5 scenario, the mean number of annual deaths attributed to heat increased from 48.7 (CI 32.2-64.2; AF = 0.68%) in 2031-2040 to 90.2 (56.7-120.5; AF = 0.97%) in 2061-2070, respectively. For RCP 8.5, heat-related deaths increased more drastically from 52.1 (33.6-69.7; AF = 0.72%) to 126.4 (68.7-175.8; AF = 1.36%) between the first and the last decade. Cold-related deaths slightly increased over the projected period in both scenarios. In Jämtland, projections showed a small decrease in cold-related deaths but no change in heat-related mortality. CONCLUSIONS: In rural northern region of Sweden, a decrease of cold-related deaths represents the dominant trend. In urban southern locations, on the other hand, an increase of heat-related mortality is to be expected. With an increasing elderly population, heat-related mortality will outweigh cold-related mortality at least under the RCP 8.5 scenario, requiring societal adaptation measures.

"Mothers get really exhausted!" The lived experience of pregnancy in extreme heat: Qualitative findings from Kilifi, Kenya.

Heat exposure in pregnancy is associated with a range of adverse health and wellbeing outcomes, yet research on the lived experience of pregnancy in high temperatures is lacking. We conducted qualitative research in 2021 in two communities in rural Kilifi County, Kenya, a tropical savannah area currently experiencing severe drought. Pregnant and postpartum women, their male spouses and mothers-in-law, community health volunteers, and local health and environment stakeholders were interviewed or participated in focus group discussions. Pregnant women described symptoms that are classically regarded as heat exhaustion, including dizziness, fatigue, dehydration, insomnia, and irritability. They interpreted heat-related tachycardia as signalling hypertension and reported observing more miscarriages and preterm births in the heat. Pregnancy is conceptualised locally as a 'normal' state of being, and women continue to perform physically demanding household chores in the heat, even when pregnant. Women reported little support from family members to reduce their workload at this time, reflecting their relative lack of autonomy within the household, but also potentially the 'normalisation' of heat in these communities. Climate change risk reduction strategies for pregnant women in low-resource settings need to be cognisant of local household gender dynamics that constrain women's capacity to avoid heat exposures.

Spatio-temporal interpolation and delineation of extreme heat events in California between 2017 and 2021.

Robust spatio-temporal delineation of extreme climate events and accurate identification of areas that are impacted by an event is a prerequisite for identifying population-level and health-related risks. In prior research, attributes such as temperature and humidity have often been linearly assigned to the population of the study unit from the closest weather station. This could result in inaccurate event delineation and biased assessment of extreme heat exposure. We have developed a spatio-temporal model to dynamically delineate boundaries for Extreme Heat Events (EHE) across space and over time, using a relative measure of Apparent Temperature (AT). Our surface interpolation approach offers a higher spatio-temporal resolution compared to the standard nearest-station (NS) assignment method. We show that the proposed approach can provide at least 80.8 percent improvement in identification of areas and populations impacted by EHEs. This improvement in average adjusts the misclassification of about one million Californians per day of an extreme event, who would be either unidentified or misidentified under EHEs between 2017 and 2021.

Marine heatwaves are not a dominant driver of change in demersal fishes.

Marine heatwaves have been linked to negative ecological effects in recent decades1,2. If marine heatwaves regularly induce community reorganization and biomass collapses in fishes, the consequences could be catastrophic for ecosystems, fisheries and human communities3,4. However, the extent to which marine heatwaves have negative impacts on fish biomass or community composition, or even whether their effects can be distinguished from natural and sampling variability, remains unclear. We investigated the effects of 248 sea-bottom heatwaves from 1993 to 2019 on marine fishes by analysing 82,322 hauls (samples) from long-term scientific surveys of continental shelf ecosystems in North America and Europe spanning the subtropics to the Arctic. Here we show that the effects of marine heatwaves on fish biomass were often minimal and could not be distinguished from natural and sampling variability. Furthermore, marine heatwaves were not consistently associated with tropicalization (gain of warm-affiliated species) or deborealization (loss of cold-affiliated species) in these ecosystems. Although steep declines in biomass occasionally occurred after marine heatwaves, these were the exception, not the rule. Against the highly variable backdrop of ocean ecosystems, marine heatwaves have not driven biomass change or community turnover in fish communities that support many of the world's largest and most productive fisheries.