Climate Change, COVID-19, and the End of Excess Mortality Extreme Heat in France since 2003

Abstract

The unprecedented heat wave of 2003 caught European citizens and health officials unaware, leaving devastating mortality in its wake. Since then, a changing climate has made extreme heat events a regular summer occurrence. How have European policies and tactics adapted to the new normal of regular extremes? What have been the ongoing health consequences of excess heat, and how did the COVID-19 pandemic affect vulnerability to high heat? This research note argues that the normalizing of extreme events and the staggering effects of the pandemic have changed patterns of mortality and have rendered a critical epidemiological tool—excess death calculations—largely useless in their wake.

Resumen

La ola de calor sin precedentes de 2003 sorprendió a ciudadanos europeos y funcionarios de salud, dejando una devastadora mortalidad a su paso. Desde entonces, un clima cambiante ha hecho que los eventos de calor extremo sean una ocurrencia regular en verano. ¿Cómo se han adaptado las políticas y tácticas europeas a la nueva normalidad de los extremos regulares? ¿Cuáles han sido las consecuencias para la salud producidas por el exceso de calor y cómo afectó la pandemia de Covid-19 a la vulnerabilidad al calor extremo? Esta nota de investigación sostiene que la normalización de eventos extremos y los efectos de la pandemia han cambiado los patrones de mortalidad y han vuelto inútil una herramienta epidemiológica crítica: los cálculos de muertes excesivas.

초록

2003년 전례 없는 폭염이 유럽 시민과 보건 당국을 놀라게 했고, 엄청난 수의 사망자가 발생했다. 그 이후로 기후 변화로 인해 극심한 폭염이 여름철에 정기적으로 발생하고 있다. 유럽의 정책과 전략은 주기적으로 발생하는 이상 기후의 새로운 정상성에 어떻게 적응해 왔을까? 폭염으로 인한 건강 영향이 계속되는 와중에, 코로나19 팬데믹은 폭염에 대한 취약성에 어떤 영향을 미쳤을까? 본 연구 노트는 극단적인 날씨가 정상화되는 것과 팬데믹의 엄청난 영향으로 인해 사망률 패턴이 바뀌었고, 그 로 인해 중요한 역학 분석 도구였던 초과 사망 계산이 대체로 의미없게 되었다고 주장한다.

Abstract

The unprecedented heat wave of 2003 caught European citizens and health officials unaware, leaving devastating mortality in its wake. Since then, a changing climate has made extreme heat events a regular summer occurrence. How have European policies and tactics adapted to the new normal of regular extremes? What have been the ongoing health consequences of excess heat, and how did the COVID-19 pandemic affect vulnerability to high heat? This research note argues that the normalizing of extreme events and the staggering effects of the pandemic have changed patterns of mortality and have rendered a critical epidemiological tool—excess death calculations—largely useless in their wake.

Resumen

La ola de calor sin pre ce dentes de 2003 sorprendió a ciudadanos europeos y funcionarios de salud, dejando una devastadora mortalidad a su paso. Desde entonces, un clima cambiante ha hecho que los eventos de calor extremo sean una ocurrencia regular en verano. ¿Cómo se han adaptado las políticas y tácticas europeas a la nueva normalidad de los extremos regulares? ¿Cuáles han sido las consecuencias para la salud producidas por el exceso de calor y cómo afectó la pandemia de Covid-19 a la vulnerabilidad al calor extremo? Esta nota de investigación sostiene que la normalización de eventos extremos y los efectos de la pandemia han cambiado los patrones de mortalidad y han vuelto inútil una herramienta epidemiológica crítica: los cálculos de muertes excesivas.

초록

2003년 전례 없는 폭염이 유럽 시민과 보건 당국을 놀라게 했고, 엄청난 수의 사망자가 발생했다. 그 이후로 기후 변화로 인해 극심한 폭염이 여름철에 정기적으로 발생하고 있다. 유럽의 정책과 전략은 주기적으로 발생하는 이상 기후의 새로운 정상성에 어떻게 적응해 왔을까? 폭염으로 인한 건강 영향이 계속되는 와중에, 코로나19 팬데믹은 폭염에 대한 취약성에 어떤 영향을 미쳤을까? 본 연구 노트는 극단적인 날씨가 정상화되는 것과 팬데믹의 엄청난 영향으로 인해 사망률 패턴이 바뀌었고, 그 로 인해 중요한 역학 분석 도구였던 초과 사망 계산이 대체로 의미없게 되었다고 주장한다.

When successive and unprecedented heat waves struck Western and Central Europe in the summer of 2003, they caught hospitals, public health officials, and vulnerable populations off guard, leaving an estimated 70,000 dead in their wake. June and July brought heat waves that killed more than 3,000 in France, 7,000 in Spain, and 9,000 in Italy. But these were merely a prelude to the devastation of August's heat wave. The August event brought enervating temperatures that lasted for more than two weeks, killing nearly 15,000 in France alone (Robine et al. 2008). A political crisis compounded the staggering mortality, with repeated hearings in the French National Assembly and Senate demanding to know how the nation with what the World Health Organization called the world's best public health system in 2000 could experience such a catastrophe just three years later (World Health Organization 2000).

Officials could scarcely have guessed that the summer of 2003 foreshadowed the European experience of climate change in the early twenty-first century. Summers have continued to bring record-breaking temperatures and significantly elevated death rates to the continent—and France in particular—with extreme heat becoming one of the gravest health threats in a changing climate (Goodell 2023; Pascal et al. 2019). This research note explores what has happened in the two decades since 2003 as extreme summers have become a new norm. With a focus on France, it provides a brief review of what happened in 2003, examines the state response to the crisis, and outlines patterns of summer mortality over the past twenty years. I also argue that a changing climate has also broken one of the most useful epidemiological tools for measuring the toll of extreme heat, as constant increases in mortality have rendered excess death measurements ineffective. An epidemiological team at France's main public health agency has proposed a new model for tracking heat-related deaths that records overlapping high temperatures and high mortality instead of measuring deaths against a shifting baseline. The resulting data are a stark illustration of the rising death toll of extreme heat in an era of increasing temperatures. Finally, the article explores the overlapping mortality effects of extreme heat and the COVID-19 pandemic. As awful as climate-linked mortality might seem, the new model for capturing heat-related deaths and the effects of the pandemic indicate that the numbers are far worse than they appear.

The 2003 Crisis and Its Aftermath

Temperatures began to rise across Europe at the beginning of August 2003 as an anticyclone established itself over much of the continent.¹ A high-pressure system that stills the air and eliminates cloud cover, an anticyclone creates a clear path for the sun to heat the Earth's surface. In Paris, daytime highs exceeded 100°F, and nighttime lows only dipped to the low 70s. Stone buildings retained heat, and interiors in unairconditioned apartments, especially those on upper floors, remained well over 100°F. Along with temperatures, mortality started to rise in early August. Despite exponentially increasing deaths, the public health system was slow to respond for a number of reasons. The heat wave coincided with France's traditional August vacation period, meaning that high-ranking officials in the relevant ministries were away from their offices, breaking down normal lines of communication. Many private practitioners were also away, and hospitals were understaffed. Even journalists were away from their posts, as early August is traditionally a slow news period.

The earliest deaths that health authorities identified as heat-related were easy to write off as anomalies. They affected a handful of workers in outdoor industries such as paving and roofing, where exposures to heat were far higher than they were for the general public; people who had psychiatric conditions or substance-use disorders; or people over the age of seventy-five with existing health conditions. In addition, many of these deaths had yet to become known, as they happened behind closed apartment doors. Only when neighbors noticed the smell of death pervading their buildings, or maggots or body fluids dropping through shared ventilation ducts—in some cases weeks after the death had taken place—were officials able to note these deaths.

By the weekend of 9–10 August, public funeral directors and hospital emergency room physicians sounded the alarm. They noted an explosion in the death rate, especially among older people and those with serious health conditions. Mortality continued to skyrocket, with nearly 2,200 excess deaths in France on 12 August alone; by 20 August, well after temperatures had dropped back to normal, deaths ascribed to the heat reached 14,802. These deaths were anything but evenly distributed. Over 80 percent of excess mortality took place among those who were seventy-five or older, and nearly 60 percent of all excess mortality took place among women seventy-five or older (Hémon and Jougla 2003). Other factors that produced significant vulnerability were socioeconomic status and geography: those most affected tended to be poor and lived in cities rather than the countryside or suburbs. For example, periurban Paris contains about 18 percent of France's population, but it experienced fully a third of the country's excess deaths.

When the official report announced in late September that nearly 15,000 had died from the heat, the state took action to try to prevent another heat disaster. At the national level, the health ministry developed the Plan Canicule or "extreme heat plan" to issue alerts and ensure proper staffing of hospitals (Bosch 2004; Haut conseil de la santé publique 2014). The alert system entailed close temperature monitoring throughout the summer, with specific thresholds for national or regional alerts and intervention. At the intervention threshold, activation plans for nursing homes, hospitals, police and fire departments, and volunteer networks would go into effect. The ministry provided funding for nursing homes to install air conditioning in at least one room per establishment to allow for cooling during extreme heat emergencies. At the municipal level, officials created phone networks so that those who perceived themselves as vulnerable to heat stroke could register with the city. As temperatures rose, social workers would call those on the registry to ensure their safety. While these efforts represented an improvement on the heat defense infrastructure that had been in place in 2003, they had crucial weaknesses. Air conditioning nursing homes did little to protect older people who lived independently—a significant majority of those who died in 2003. Alert systems could not reach poorer citizens who had no access to media or phones. As I explain below, self-perception of vulnerability is low, therefore disincentivizing voluntary registration with municipal protective networks.

The Legacy of 2003

The devastation of August 2003 generated a broad awareness of the dangers of climate change not only for small islands threatened by rising sea levels but also for major urban centers in the industrialized world (San Marco 2018). The shocking mortality of the heat wave and predictions that future summers would bring "more intense, more frequent, and longer lasting heat waves" to Europe (Meehl and Tebaldi 2004: 994) brought wide support for the Plan Canicule and new initiatives for sustainable development. In 2007, Paris Mayor Bertrand Delanoë launched a bike share program along with significant investment in bicycle infrastructure in the city to reduce emissions. His successor, Anne Hidalgo, built extensively on these initiatives, creating car-free zones in central Paris beginning in 2024 and introducing legislation to ban gas-powered autos from the city entirely beginning in 2030. In 2015, the National Assembly passed a law mandating the installation of green roofs or solar panels on all new commercial construction. The droughts of 2022 and 2023, which dried rivers such as the Loire and led to the shutdown of several nuclear facilities for want of water for cooling, have only cemented concern about a changing climate (Horowitz 2022). Around the country, bars, schools, and libraries have begun to host fresques du climat or "climate fresks," in which participants learn about climate change through information cards on topics such as the carbon chain and then post the cards on the wall to create educational "frescoes" (climatefresk.org; Méheut 2023).

It is therefore somewhat surprising to see how murky knowledge about the threats of extreme heat remains in France. A 2019 study led by Karine Laaidi at Santé publique France (SPF, France's national public health agency) on behaviors and knowledge about heat risk yielded disturbing results. According to an extensive survey, only 12 percent of French citizens consider themselves vulnerable to extreme heat, despite 40 percent claiming to have suffered during the major heat waves of summer 2015. Nine of ten French people rightly see those over age sixty-five as at risk, and two of three see babies under age two as vulnerable. Yet fewer than 20 percent see patients with chronic illness—a major risk group for heat stroke and dehydration—as vulnerable, and only 2 percent and 1 percent, respectively, see workers with high heat exposure and people living in isolation as at risk (Laaidi et al. 2019). This is jarring, as exposed workers are often the first to die during extreme heat events, and social isolation is the greatest single predictor of death from extreme heat (Keller 2015).

The study noted other troubling findings. Of those surveyed, only 38 percent thought that heat stroke could be fatal, and 7 percent considered it no threat at all. Nearly one in five of those over sixty-five did not know that drinking water could prevent dehydration. Less than half of respondents knew that cooling residences could prevent the damaging effects of heat. While almost all parent respondents recognized the importance of protecting small children from heat, less than half opened their children's windows at night to allow cool air into their bedrooms.² The study noted the positive finding that a majority of those over sixty-five reported being visited by family during heat events, but also noted that fewer than 7 percent of those over sixty-five had contact from government employees, and only 4 percent registered with protective municipal telephone networks—perhaps a function of low awareness of personal vulnerability to extreme heat.

Rising Temperatures, Increasing Threats

What is so dangerous about these misconceptions is that a changing climate has brought increasingly hot summers to Europe, contributing to rising death rates. As temperatures have gone up, so have deaths from all causes. Since 2010, annual deaths in France have steadily risen from an average of roughly 550,000 per year to roughly 675,000 in 2022 (Institut national d'études démographiques 2024). There are important overdetermining factors that influence this trend: the COVID-19 pandemic played a critical role in the death tolls of 2020–2022, and the aging of France's Baby Boomers has increased the population at risk of death from natural causes. Increasing summer heat has also played a part. A study led by environmental epidemiologist Mathilde Pascal (Pascal et al. 2019) noted dramatic increases in the number of officially designated departmental heat waves in France.³ In the decade from 1974 to 1983, French departments recorded 166 heat waves. The decade from 2004 to 2013 witnessed twice as many, and the three-year period 2014–2016 (where the study's data end) recorded a staggering 187: a trend that if extended over a decade would result in 623 departmental heat waves from 2014 to 2023.

Extreme heat has brought significant mortality. Just three years after the 2003 disaster, 2006 brought a deadly heat wave that lasted for much of July, killing some 2,100. Epidemiologists estimate that if similar weather had struck before 2003, it would likely have killed closer to 6,500, attributing the lower number to greater awareness of the dangers of heat (Pascal, Le Tertre, and Saoudi 2012); however, it is also critical to note that much of the vulnerable population had already died in 2003, thereby reducing the number of those at risk in 2006. Again in 2015, a brutally hot summer brought estimates ranging from 1,700 to 3,300 excess deaths and a 300 percent increase in emergency room visits (Institut de Veille Sanitaire 2015; Pascal et al. 2019; Ung et al. 2019). Each year from 2017 to 2020, a period that broke records for extreme temperatures, brought an average of 1,475 excess deaths (see figure 1). In 2022, when France experienced its second-hottest summer of the twenty-first century, the country counted some 7,000 excess deaths between June and September in a period in which the French endured 121 departmental heat waves (Santé publique France 2022).

Figure 1.

Excess deaths during heat waves in France, 2015-2022

(Source: Santé publique France.)

This is not just a French story: a recent study in the Lancet Planetary Health noted that a survey of 854 cities showed an average of 20,000 excess deaths per year due to extreme temperatures in Europe since 2000 (Masselot et al. 2023).

These high annual death tolls from extreme heat call the very notion of excess mortality into question. At its core, excess mortality is a metric that allows for measuring the magnitude of a severe health crisis. There are several ways to calculate it, but the one that demographers and epidemiologists have tended to use in France since 2003 subtracts average deaths for a given period over the three to five years preceding the one in question from observed deaths in the period under study. In 2003, the country observed 41,621 deaths during 1–20 August. Based on averages for the same period in 2000, 2001, and 2002, France should have anticipated about 26,819 deaths. The difference—14,802—emerged as the official toll of excess deaths from the August 2003 heat wave in an official report.

There are some real benefits to this kind of calculation. As the authors of the 2003 report noted, it is "simple and robust"; does not require sophisticated population estimates (assuming the relative stability of the population over a three-year period); and it allows for studying mortality by age, sex, department, and location of death, which are known factors for each of these years (Hémon and Jougla 2003: 21). There are also some disadvantages to the method. It assumes the population and death rates are relatively stable over three years. It is also overinclusive: for example, drownings and suicides climb significantly during heat waves, and these are included here, although one could argue they are only indirectly caused by the heat. But in the absence of any other major cause of death—for example, a cholera epidemic—it presents a clear snapshot of the death toll.

Yet successive summers of extreme heat with concomitant mortality introduce important problems with the excess death model. If epidemiologists measure excess deaths by comparing them to averages from preceding summers, what happens when those deaths happen every year, when they become part of background mortality that constitutes the slow violence of climate change (Nixon 2011)? They become less and less visible, because observed deaths are measured against an already elevated expected death toll. If heat deaths increase each year, then the point of reference also increases, meaning that excess deaths become an invisible part of the point of reference. This parallels what ecologists have called in other contexts a "shifting baseline syndrome," whereby the standards against which a phenomenon such as environmental degradation change incrementally over time (Pauly 1995; Olson 2002; Soga and Gaston 2018). For example, the desertification of the Sahel might not appear so dramatic if one were to compare the desert's reach in 2022 to its reach in 2020. Comparing it to its reach in 1980 would reveal a stark transformation. With a changing climate, excess mortality becomes the norm, a consistent, recurring effect of increasing death as a function of the regularity of extreme heat (Keller 2019). Much as the increasing intensity of heat has required meteorologists to add new colors to maps to show new temperature ranges, the consistency of excess deaths requires new epidemiological tools for measuring the heat's toll (Carrington 2013).

Another recent study directed by Pascal at SPF offers real insight into this problem and concludes by proposing a new model for how to assess heat's effects for mortality. The report focuses in particular on extreme heat deaths that occur outside of officially declared heat waves. A note on terminology is important: to be considered a heat wave, an extreme heat event necessitates temperatures above a predetermined threshold for at least three days (Pascal et al. 2023). The report notes high levels of elevated deaths in departments that have heat events that are either less intense than required for an official declaration, or with sufficiently high temperatures that last for fewer than three days. The report finds that a significant majority of heat deaths occur outside of designated heat waves (see figure 2). Using 1 June and 15 September as beginning and ending dates for the period of highest risk, Pascal's team found that between 2015 and 2022, 31,555 deaths were attributable to heat. Yet only "twenty-eight percent of these deaths were observed during periods defined as heat waves by the heat wave management plan" (Pascal et al. 2023: 1).

This finding is essential for gauging the effects of climate change for increased vulnerability. In an atmosphere of extreme heat, most deaths occur outside of officially declared heat waves, calling the very notion of a heat

Figure 2.

Heat deaths in France, 2015-2022: comparison of total deaths attributable to heat and those occurring during designated heat waves.

(Source: Pascal et al. 2023.)

"wave" into question. For all the attention paid to record-shattering temperatures, the consistent occurrence of steady, increased temperatures is what produces the greatest risk. These temperatures that are below the threshold, or that last for shorter durations, for meeting the criteria for official declarations of emergency pose lower risk than proper heat waves, but they occur at such frequency that they have a more profound effect on mortality. With consistently high heat, people are dying in significant numbers throughout the summer, further complicating the calculation of an excess mortality that has become a summer norm in France, as well as much of the rest of Europe. Much as the notion of a 500-year-flood has become a misleading label, considering the regularity with which such events are occurring in a changing climate, the idea of concentrated heat events has become less important than the incessant toll of dangerously high temperatures.

Pascal proposes a new model for measuring the mortality effect of heat, citing the imprecision of excess death measurements as a precipitating need. The model uses daily temperature data gathered from Méteo-France weather stations in each French department and compares it to all-cause mortality measured by the Institut national de la statistique et des études économiques (Insee, France's national census agency), plotting the coincidence of high heat and rising death tolls. It provides a spatial demonstration of the potential relationship between temperature and mortality, relying less on population variation from year to year or on official declarations of emergency and more on the regional and local overlapping of heat and death. Perhaps most important, it reveals that heat deaths are happening in dramatically higher numbers than excess mortality measures suggest (see figure 3):

Figure 3.

Measuring heat deaths, 2015-2022. Where the isolated excess mortality figures show a pattern of rising heat deaths, the Pascal model indicates the heat's toll is significantly higher.

(Sources: Santé publique France, Pascal et al. 2023.)

for example, where the excess death toll for 2022 was 2,816, Pascal's method shows a toll of 6,969.

Although this new model has significant advantages over measurements of excess mortality, it remains imperfect for several reasons. First, while it makes correlations between temperature and mortality visible in a way that excess death measurements no longer can, they are exactly that: correlations, not causal evidence. Second, as the 2003 disaster demonstrated, temperature and mortality are not necessarily proportional, because social factors are often more significant than absolute temperature in determining vulnerability or resilience. For example, Marseille recorded higher temperatures than Paris in 2003, but had an elevated death rate of only 25 percent, compared with Paris's 300 percent, in part due to better preparation for extreme weather (Hémon and Jougla 2003). Finally, weather stations cannot always identify urban heat islands, which have a profound effect for structuring risk in cities (Benmarhnia and Beaudeau 2018; Laaidi et al. 2012), nor do mortality data necessarily show social determinants of vulnerability to extreme heat (Cadot and Spira 2006; Keller 2015).

COVID-19, Extreme Heat, and the Invisibility of Risk

The arrival of SARS-COV-2 in Europe in 2020 greatly complicated the measurement of vulnerability to extreme heat. The same populations are at highest risk for dying from both causes: people over seventy-five years old, people with comorbidities, and people living in poverty. Yet the mitigation of risk in each case is strikingly different. While an important means of preventing COVID-19 infection is social distancing or self-isolation, isolation is one of the most important risk factors for dying of heat stroke or dehydration. Going to public air-conditioned spaces such as cinemas or grocery stores reduces the risk of extreme heat but increases the risk of catching an airborne virus. Moreover, as an SPF report (Santé publique France 2022: 6) noted, "the Covid-19 epidemic could exacerbate the vulnerability of certain populations to heat." Infection provokes a comorbid condition that increases the risk of dying from extreme heat, and fear of infection in a clinical environment could deter those at risk of heat stroke or dehydration from seeking medical attention.

Since 2020 COVID-19 has likely been muddying heat-related mortality data. As fewer tests are reported and fewer deaths are counted, the pandemic is becoming less visible and its deaths are increasingly difficult to isolate from heat deaths in a warming climate. For example, a 2022 Insee report initially indicated that heat was "likely the origin of more than 11,000 excess deaths in France" in summer 2022 (Roucaute 2022).⁴ By contrast, Pascal et al.'s 2023 study, although remaining silent on estimates of COVID deaths, drew on temperature/mortality correlations to indicate that heat was the likeliest factor in 6,969 of these 11,000 deaths, while in its 2023 revision Insee makes no effort to disentangle mortality due to COVID versus heat (Insee 2023a, 2023b). The coincidence of the pandemic and major heat waves makes some overlap in mortality both inevitable and indiscernible.⁵

COVID-19 has played another, perhaps more significant role in obscuring the heat's toll in an era of climate change. A study in Nature Medicine noted that 2022 was the hottest summer on record in Europe (at the time of publication; 2023 has since surpassed it, raising further concerns about runaway climate change: see Schmidt 2024), producing an estimated more than 61,000 heat-related deaths—a staggering figure that shows a near return to the 70,000 dead of 2003 (Ballester et al. 2023). The influence of COVID-19 indicates that despite the lower figure, the 2022 toll represents a significantly higher effect than that of 2003. The Nature Medicine study did not control for COVID-19 deaths in its estimation of heat mortality. Although COVID-19 mortality had slowed by 2022, it had not stopped. Some of these deaths were likely attributable to the lingering effects of the pandemic. In addition, COVID-19 may well have had an indirect effect on mortality, as overburdened health systems suffered from simultaneous crisis, with patient care suffering as a consequence.

Far more important is the fact that people can only die once. As Pascal et al. (2023: 22) noted in the SPF report, before the onset of extreme heat in 2022, the pandemic "had reduced the number of people who were highly vulnerable to the heat, to the extent of masking the elevation of risk." Before summer 2022, COVID-19 had already killed two million Europeans, who were therefore no longer capable of dying from extreme heat. Given the overlap in vulnerability to the virus and extreme heat, this indicates that thousands more may well have died from 2022's excessive heat, but COVID-19 had already killed them. Heat killing 61,000 in a population in which the vulnerable population was already significantly reduced by a pandemic represents not a reduction in heat impact from the 70,000 deaths of 2003, but a likely escalation (Keller 2023).

Conclusion

The murderous August of 2003 has had a powerful legacy in France. The death toll signaled the risk of extreme heat in an era of climate change, placing environmental concerns squarely on the political agenda. It also initiated new approaches to heat waves as deadly threats. The French largely forgot the lessons of the deadly heat waves of 1976 and 1983, and many underestimate their vulnerability to the threats of high heat. But the sheer magnitude of 2003 launched a new era of state caution in the face of extreme heat, with officials and scientific experts establishing alert thresholds, action plans, and social interventions designed to facilitate adaptation to a new environment. The rapidity and intensity of climate change, along with successive and lethal heat events and the normalization of extreme heat, has rendered these efforts insufficient to slow the pace of a relentless summer death toll. The constancy of high heat and its ensuing mortality has forced a reconsideration of the tools that are capable of measuring their extent as their extremity has become routine. The Pascal team's new model for measuring the mortality effect of heat, though imperfect, represents an important new direction in assessing relative risk in an era of climate change. It avoids the pitfalls of excess death measurements while highlighting the dangers of persistent (yet not necessarily record-breaking) heat, forcing a reconsideration of the concept of a heat wave itself. The COVID-19 pandemic has only underscored the relative obsolescence of the excess mortality model for determining the effects of extreme heat. Given the clear correlations between anthropogenic climate and land use change and the emergence of new health threats (Lawler et al. 2021; Vidal 2023), the pandemic also offers a glimpse of a future that will likely witness multiple, coinciding crises that threaten to strain the human capacity to respond and that erode human resilience.