The heat is on

| August 21, 2021

A two-part series on heat and health published in The Lancet and co-led by Professor Ollie Jay from the University of Sydney (Australia) and Professor Kristie Ebi from the University of Washington (USA) warns that heat-related morbidity and mortality will likely increase without investment in evidence-based research and risk-management strategies.

“As a result of human activity, it is inevitable that much of the planet’s population will in the future be at greater risk of exposure to extreme heat than they are today,” said Professor Ollie Jay, Professor of Heat and Health from the University of Sydney’s Faculty of Medicine and Health and Charles Perkins Centre.

“Amid stark projections about the increasing effects of climate change, urgent investment in research and measures to combat the risks of extreme heat is critical if society is to not only survive, but thrive, in a hotter future world.”

The series brings together academic experts from epidemiology, physiology, medicine, climate science, built environment and sustainable development with contributions from 15 authors from eight countries spanning four continents.

Prevention and planning

“Two strategic approaches are needed. One is climate change mitigation to reduce carbon emissions to alter the further warming of the planet. The other is identifying timely and effective prevention and response measures, particularly for low-resource settings,” said Professor Kristie Ebi, Professor of Global Health at the Centre of Health and the Global Environment at the University of Washington.

“With more than half of the global population projected to be exposed to weeks of dangerous heat every year by the end of this century, we need to find ways to cool people effectively and sustainably.”

“Failure to reduce greenhouse gas emissions and to develop and deploy heat action plans will mean a very different future awaits many people and communities around the world. Day-to-day summer activities– such as exercising and working outdoors – may change dramatically as increasing warming means people are at greater risk of exposure to intolerable heat far more often, particularly in tropical regions.”

Health risks of extreme heat

When exposed to extreme heat stress, the body’s ability to regulate its internal temperature can be overwhelmed, leading to heat stroke. In addition, physiological thermoregulatory responses that are engaged to protect body temperature induce other types of physiological strain and can lead to catastrophic cardiorespiratory events.

Effects from extreme heat are also associated with increased hospitalisations and emergency room visits, increased deaths from cardiorespiratory and other diseases, mental health issues, adverse pregnancy and birth outcomes, and increased healthcare costs.

Older people and other vulnerable people due to a limited behavioural adaptive capacity (e.g., isolated at home, poor mobility) are also more likely to experience the health effects of extreme heat.

Extreme heat also lessens worker productivity, especially among the more than 1 billion workers who are exposed to high heat on a regular basis. These workers often report reduced work output due to heat stress, many of whom are manual laborers who are unable to take rest breaks or other measure to lessen the effects of heat exposure.

“Extremely hot days or heat waves that were experienced approximately every 20 years will now be seen more frequently and could even occur every year by the end of this century if current greenhouse gas emissions continue unabated. These rising temperatures combined with a larger and older population, mean that even more people will be at risk for heat-related health effects,” said Professor Ebi.

Evidence-based and sustainable cooling strategies

The authors argue that the global community and policy makers should look beyond short-term solutions that might be convenient but do not promote long term resilience. Planning must also consider those that are most economically and clinically vulnerable to extreme heat.

While air conditioning is set to become the most widely adopted heat reduction strategy worldwide, Professor Jay says it is unaffordable for many, and is financially and environmentally costly, potentially leaving many defenceless during power outages.

They highlight accessible and effective cooling strategies at the individual, building, and urban and landscape level and recommend tailored approaches for specific settings where people may be particularly vulnerable to the effects of extreme heat including care homes, unplanned settlements, workplaces, schools, mass gatherings, refugee camps, and sports play.

In the Series, the  authors highlight actions individuals can take to cool themselves down and blunt other types of physiological strain that arise from regulating body temperature to combat health risks from extreme heat.

Effective and sustainable strategies include;

  • electric and misting fans
  • self-dousing with a water spray or sponge
  • wearing wet clothing
  • immersing feet in cold water
  • short breaks from physical activity
  • remaining well hydrated (the temperature of water consumed has little consequence)
  • modifying clothing or protective equipment to improve ventilation.

Adaptations to buildings can help cool indoor environments. These include external coatings to reflect heat away from buildings and green walls to reduce surface temperatures, improved insulation and glazing, and better ventilation through and around buildings.

Features of the urban environment and surrounding landscape also influence conditions in built-up areas. Lakes, large grasslands and parks, and shaded outdoor areas, as well as reducing pollution within cities, are important.

To protect populations, heat action plans, which include early warning and response systems and robust surveillance and monitoring, must include evidence-based cooling strategies.

“What’s clear is that the effectiveness of strategies depends on the setting in which they are implemented. We use the example in the paper that solutions for an older person in a high-rise apartment in New York will be very different to a young person in a garment factory in Bangladesh or an elite footballer competing in Qatar,” said Professor Jay.

“We are fortunate that advances in research and technology now allow physiologists to simulate human exposure to different heatwave scenarios in climate chambers, providing us with scientific evidence that can inform low cost and effective cooling strategies for different circumstances.”

“Integrating this evidence-based information into heat action plans that are robust, communicated well to the public, and informed by real-time surveillance will provide optimal health protection into the future. Currently many heat-health action plans are not supported by evidence, and this urgently needs to change – it will save lives.”

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