Health in a world of extreme heat

The heat waves and forest fires that swept southern Europe and the United States this summer have been traumatic and fatal. In the Pacific Northwest alone, 600 additional deaths have been reported. According to the Sixth Assessment Report of Working Group I of the Intergovernmental Panel on Climate Change, which summarizes the latest scientific evidence on climate change, global temperature is expected to reach or exceed 1.5 ° C on average over the next 20 years. The report predicts that these record temperatures will persist more frequently, more intensely, and longer due to man-made climate change. What the health consequences of a hotter climate are and how to deal with extreme heat will be two of the defining questions of this decade and are covered in several articles in this issue of The Lancet.

A two-part modeling study by Katrin Burkart and colleagues from the Global Burden of Diseases, Injuries, and Risk Factors Study is the first comprehensive analysis of the global cause-specific temperature-related death burden. Analysis of data from 65 million deaths and temperature estimates in nine countries shows that extreme heat and cold are linked to 17 causes of death – mainly cardiovascular or metabolic diseases, but also suicide and various types of injuries. The authors estimate that 1.7 million deaths worldwide were due to extreme heat and cold in 2019 (356,000 were due to heat). Although there are uncertainties surrounding these global estimates, the study shows the importance of temperature as a global health risk factor and provides valuable data to help policymakers and others plan interventions. The latest insights into how heat directly affects the human body (making you ill through dehydration or cardiovascular stress) and heat-prone environments are showcased in The Lancets Heat and Health Series, led by Kristie Ebi, Ollie Jay and Anthony Capon. The series also looks at effective prevention and response measures in the event of heat extremes. Two major lessons can be distilled.

First, more sustainable and affordable cooling measures are needed that do not increase greenhouse gas emissions or exacerbate existing inequalities. For example, despite the immediate health benefits of air conditioning and its global spread, it is an unsustainable solution to extreme heat that contributes to air pollution, greenhouse gas emissions and an increased urban heat island effect. In addition, air conditioning is often unaffordable for those most at risk from extreme heat, adding to inequality and penalizing those who are often least likely to contribute to climate change. Evidence-based strategies that focus on cooling the individual, such as the use of battery-powered fans, rather than just cooling the surrounding air, must be a priority.

Second, there may be benefits in putting health at the center of multisectoral policy and planning that goes beyond simply reducing heat-related stress. Since extreme heat has a greater impact on people’s health in urban environments, green spaces are crucial for cooling in cities, but they also have additional benefits: They reduce exposure to air and noise pollution, reduce stress, and provide a framework for social Interaction and physical activity and sequester carbon.

To reduce the effects of extreme heat on individuals and vulnerable populations, some governments have adopted national or local heat health action plans. However, the plans are very variable and the implementation inconsistent. Many healthcare institutions are unprepared. If their physical infrastructure fails due to overheating, the ability to treat extreme heat patients could be compromised when it is most needed. All countries, local communities and institutions must adopt effective heat health action plans tailored to local conditions.

Such action plans provide measures to adapt to extreme heat, but do not address the root cause of heat extremes – greenhouse gas emissions. Minimizing the effects of temperature on health requires both prevention and adaptation to a changing climate – two of the main goals of COP26, which will take place in Glasgow, UK from October 31 to November 12, will tackle the climate crisis will translate into decisive action and effective action. The meeting’s leaders need to provide transformative regulatory frameworks, guidelines and investments to ensure sustainable mitigation and adaptation to climate change. The publications released today make a strong scientific argument that the health dimensions of heat can no longer be overlooked.

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Published: August 21, 2021



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  • Ollie Jay: Manage Heat, Improve Health
    • “Our work is all about driving multidisciplinary efforts to find solutions to complex health problems arising from the effects of heat stress, all in the context of increasing extreme weather events as a result of climate change,” explains Ollie Jay, professor of Heat and Health in the Faculty of Medicine and Health, University of Sydney, Australia. Jay is also director of the Thermal Ergonomics Laboratory at the Sydney Heat and Health Research Center. “We have a rich research environment with many opportunities to work in broad areas of science, industry, and in our collaboration with many Australian sports organizations to develop policies and systems that reduce the effects of extreme heat on health,” he says.

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  • Estimating the Cause-Specific Relative Risks of Sub-Optimal Temperature on Daily Mortality: A Two-Part Modeling Approach Applied to the Global Burden of Disease Study
    • Acute exposure to heat and cold can increase or decrease the risk of death for various causes of death. Although cold effects dominate in most regions, locations with high prevailing temperatures can have significant heat effects that go far beyond the exposure caused by the cold. In particular, a high exposure to external causes of death contributed to the strong effects of heat, but cardiovascular and metabolic diseases could also make a significant contribution. Changes in both exposure and the composition of the causes of death resulted in changes in risk over time.

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  • Hot Weather and Heat Extremes: Health Risks
    • Hot environmental conditions and the associated heat stress can increase mortality and morbidity, increase negative pregnancy outcomes and negatively affect mental health. High heat stress can also reduce physical work capacity and motor-cognitive performance with consequences for productivity and increase the risk of work-related health problems. Almost half of the world’s population and more than 1 billion workers are exposed to episodes of heat, and around a third of all workers exposed have negative health effects.

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  • Reducing the health effects of hot weather and heat extremes: from personal cooling strategies to green cities
    • Heat extremes (i.e. heat waves) are already having serious effects on human health, with age, poverty and chronic illness emerging as aggravating factors. As the global community struggles with even hotter weather conditions in the future as a result of global climate change, there is an urgent need to better understand the most effective prevention and response measures that can be implemented, particularly in resource-poor environments. In this article in the series, we describe how future reliance on air conditioning is unsustainable and continues to marginalize the communities most vulnerable to the heat.

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