Know the health risks of extreme heat – 02/08/2023 – Environment

Hottest month ever recorded in history, July was marked by heat waves that hit millions of people, especially in the northern hemisphere. In addition to temperatures exceeding 50°C in China and exceeding 43°C in the US city of Phoenix, there have also been records of heat-related deaths.

This is due to the way the body reacts to high temperatures, which affects the cardiovascular, respiratory and renal systems. To try to cool the body, the heart pumps more blood, absorbing internal heat and moving it towards the skin to be dissipated into the environment in the form of sweat.

“So obviously your heart has to beat faster,” explains Daniel Vecellio, a climate and health researcher at George Mason University (USA). Since pumping more blood requires more oxygen, you also need to breathe more.

These measures make the body sweat and, with that, lower the internal temperature. But if the water that is being eliminated by sweat is not replaced (with the consumption of liquids) this can lead to a lack of hydration. “Which can be a big problem when you’re talking about kidney problems. So there are a lot of ways that heat affects health during hot flashes. And that’s before you even talk about heatstroke — which happens at a later stage,” he says. The specialist.

Heat stroke is the most serious type of heat-related illness and occurs when the body is no longer able to keep cool, with body temperatures that can exceed 41°C. Symptoms include mental confusion, loss of consciousness and seizures.

The effects of extreme heat tend to be strongest among those who already have cardiopulmonary disease and other at-risk groups. “Besides them, the elderly have difficulty in thermoregulation [ou seja, de manter a temperatura corporal] both when they are cold and hot, just like the children”, says Beatriz Oliveira, researcher at Fiocruz Piauí.

In 2022, the annual Lancet Countdown report pointed out that the mortality of people over 65 years related to heat increased by 68% between the periods 2000-2004 and 2017-2021, a situation aggravated by the Covid-19 pandemic.

Heat stress and climate change

This increase has to do with a warmer planet. Earlier this month, research published in the journal Nature Medicine estimated that more than 61,000 people died of heat in Europe last summer. The number is close to that recorded in one of the worst heat waves in the region, in 2003, when 70,000 people died.

“From a European perspective, the summer of 2003 was the first really, really hot summer,” explains Samantha Burgess, deputy director of the Climate Change Service at the European observatory Copernicus. “Two decades later, [os registros de] 2003 are significantly cooler than some of the heatwaves we’ve had this year and the summers of the past two years.”

She explains that it is necessary to wait until the end of August to know how 2023 compares with 2022 in terms of thermal stress on the continent. “But heat stress is here to stay as long as we have these high concentrations of greenhouse gases in the atmosphere.”

Heat waves are considered extreme weather events, in which very high temperatures are sustained over several days.

According to the IPCC (UN Intergovernmental Panel on Climate Change), these phenomena have already tripled compared to the period from 1850 to 1900 (when human carbon emissions began to climb). Global warming also increases the intensity of these events.

According to the research group WWA (World Weather Attribution), the heat waves that hit North America and Europe in July would have been “virtually impossible without climate change”.

“Heat waves are called the silent killers because they are by far the deadliest extreme summer events we have. for Climate Change and the Environment and one of the authors of the WWA report.

When the heat is too hot?

In addition to high temperatures, other factors influence the impact of heat on the body, such as the incidence of wind, solar radiation and humidity. A cool breeze or the protection of the shade of a tree, for example, help to reduce the feeling of heat.

In the case of air humidity, high levels make it difficult for the body to cool down. “The main physiological cooling mechanism we have is the evaporation of sweat from our skin. However, when it’s very, very humid and there’s already a lot of water vapor in the atmosphere, this reduces the ability for sweat to evaporate,” explains Vecellio .

A study conducted by the researcher showed that, among healthy and young men and women (between 18 and 34 years old), the heat begins to offer health risks when the temperature reaches 38°C in an environment with a humidity index of 60%. But with a humidity rate of 100%, the number drops to 31°C.

However, these numbers are not absolute. The scientist points out that even lower rates can overload the heart and other systems — especially in more vulnerable groups, such as the elderly or people with chronic diseases.

In addition, the study has limitations, such as the fact that it was conducted in Pennsylvania (where the population does not face temperatures as high as in tropical regions, for example) and that the laboratory used did not consider the incidence of solar radiation or wind.

In the Brazilian case, the Fiocruz researcher states that there are regional differences both in mortality and in hospital admissions related to heat.

“[Quem reside] in the South region tends to have smaller limits [de resistência ao calor] than who resides in the North and Midwest regions of the country, for example”, says Beatriz Oliveira.

“Sometimes we say ‘We have a heat wave in Brazil, but we don’t see that many elderly people dying, as we see in Europe’. This is because our sensitivity to risk is lower, because we are used to some effects of heat . Because we live in a tropical country, we end up not assimilating [o calor da forma] like in Europe.”

She explains that, in addition to being physiological, adapting to heat can be behavioral: avoiding being outside during the hottest hours of the day, wearing lighter clothes, drinking more water or making less physical effort.

There are also structural adaptations, such as the provision of breaks for workers who are exposed to the sun, the preparation of hospital services to deal with cases of thermal stress and access to air-conditioned environments —in the US and Europe, some cities offer centers cooling facilities, such as sports halls, where people can go to escape the heat.