A new study has revealed people can tolerate far less heat than previously estimated highlighting the need to address the effects of climate change on human health.
The study from the University of Ottawa’s Human and Environmental Physiology Research Unit found many regions may soon experience heat and humidity levels that exceed safe limits for humans.
In South Africa researchers have warned climate change is projected to lead to warmer temperatures, especially in Southern Africa, where the warming is predicted to be 2°C higher than the global increase.
The health department has long been mindful of the impact, warning of the health risks that climate change would aggravate over the next few decades, including heat stress, vector-borne diseases such as malaria, dengue fever and yellow fever, extreme weather events, air pollution, communicable diseases such as HIV/Aids, TB and cholera, and non-communicable diseases.
Led by Dr Robert Meade and Dr Glen Kenny, the study was based on thermal-step protocols during which 12 volunteers were exposed to various heat and humidity conditions to identify the point at which thermoregulation becomes impossible.
Our research provided important data supporting recent suggestions that the conditions under which humans can effectively regulate their body temperature are actually much lower than earlier models suggested
— Dr Glen Kenny, University of Ottawa’s Human and Environmental Physiology Research Unit
“Our research provided important data supporting recent suggestions that the conditions under which humans can effectively regulate their body temperature are actually much lower than earlier models suggested,” said Kenny.
“This is critical information as we face increasing global temperatures.”
The participants were subjected to extreme conditions, 42°C with 57% humidity, representing a humidity index of about 62°C.
“The results were clear. The participants' core temperature streamed upwards unabated, and many participants were unable to finish the nine-hour exposure.”
Meade said the data provided the first direct validation of thermal step protocols, which have been used to estimate upper limits for thermoregulation for nearly 50 years.
“Our findings are especially timely, given estimated limits for thermoregulation are being increasingly incorporated into large-scale climate modelling. They also underscore the physiological strain experienced during prolonged exposure to extreme heat, which is becoming more common due to climate change.”
The researchers believe as cities prepare for hotter summers, understanding these limits can help guide health policies and public safety measures.
When it comes to South Africa, the South African Medical Research Council (SAMRC) found in its own study that infants, the elderly, people living with disabilities, pregnant women, outdoor workers and those who are on chronic medications are people most vulnerable to death as a result of exposure to extreme heat.
The research draws a correlation between the way in which the biological, environmental, medical, socio-behavioural and geographical effects of extreme heat exposure have had an adverse impact on morbidity and mortality in the most vulnerable communities in Africa.
Drawn from evidence from 1992 to 2019, and published in 2022, the research aimed to provide a synthesis of Africa-informed evidence on the effects of extreme heat on morbidity and mortality on the continent.
“The majority of studies on the relationship between extreme heat exposure and morbidity and mortality have been carried out in high-income countries,” said Dr Caradee Wright, a chief specialist scientist at the SAMRC’s Environment and Health Research Unit (EHRU).
Wright said there are major gaps in knowledge about the effects of heatwaves on health outcomes among different subgroups in low and middle-income countries and the few existing studies that address this topic for Africa largely focus on other continents and include selected African countries only as an add-on.
Complementing Wright’s research on the impact of extreme heat on mortality and morbidity in Africa, the EHRU conducted a study specific to heat resilience and coping mechanisms related to indoor and outdoor temperatures among 406 households in Limpopo province, where temperatures rose to above 40°C outdoors and 36°C indoors.
The study, published in the South African Journal of Psychology, found most people perceived their homes to be too hot when temperatures were high outdoors and relied on recommended heat-health actions such as sitting outdoors in the shade or opening windows to try to keep cool.
It is essential that outdoor workers and their employers are trained to recognise the symptoms of heat illnesses and effects
— Dr Caradee Wright, chief specialist scientist at SAMRC’s Environment and Health Research Unit
“Resilience to heatwaves as a result of climate change requires more than personal action. In light of climate threats and climate-related disaster risks facing South Africa, an all-encompassing approach, including education campaigns, climate-proofed housing, access to basic services, and financial considerations that will help support resilient coping among South Africans is urgently required,” said Wright.
According to the study, preparedness and resilience are key as South African temperatures are expected to become warmer than the projected global average.
Some parts of the country will experience drying and other parts will become wetter, and there aren’t any certainties as to how much exactly and where temperatures will reach extremes such as heatwaves.
Though there is no universally accepted definition of a heatwave, they are typically described as a consecutive period of hot days with temperatures above a given threshold. They are not based on a health outcome, specifically to avoid morbidity or mortality from heat extreme.
Wright said heat affected the human body by reducing its ability to regulate its temperature and keep cool by sweating.
As the body becomes too hot, a person may experience heat cramps, heat exhaustion, heat stroke and even hyperthermia. Irritability, lack of concentration, headaches and loss of ability to do skilled tasks or heavy work may also occur.
“People vulnerable to heat either lack the ability to self-regulate their internal ‘thermostat’, or are faced with excess heat exposure, as is the case for people working outdoors.
“It is essential that outdoor workers and their employers are trained to recognise the symptoms of heat illnesses and effects.”
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