How hot is too hot? The study that warns of a new and surprising limit
Feeling hot already? Research shows that the body struggles to regulate its temperature under heat load conditions lower than previously thought. What does this mean for us in the Israeli summer?
The increase in heat loads is likely one of many that we will experience this summer. Does our body know how to adapt to this heat? It turns out the answer is complex. Research indicates that even temperature conditions that do not seem particularly extreme can burden the body to the point where it struggles to regulate itself. Against the backdrop of climate change, which increases heat and the potential for humidity in the air, heat waves are becoming an increasingly significant health challenge.
Not just temperature
We are used to assessing how hot it is using one index: temperature. But in fact, there is another index that greatly affects our feeling of heat, and that is humidity. Our body heats up as a result of internal physiological processes and also from the heat we absorb from the environment, explains Prof. Maya Negev from the School of Public Health at the University of Haifa and a member of the Climate Scientists Forum. We have two main means to cool the body. The first is the flow of blood to the skin to facilitate the body's release of heat, and the second is sweating. These are two very effective but limited mechanisms. That is, they cannot protect us in every situation. For example, the higher the humidity in the environment, the less effectively sweat evaporates, and the harder it is to get rid of heat, she explains.
As part of the study, subjects were exposed to controlled environmental conditions of heat and humidity. The heat and humidity were gradually increased to the point where the subjects' body temperature began to rise consistently — a sign that the body is no longer able to regulate heat under these conditions. The study was based on an index that combines temperature and humidity, which determines that in the range of 26–31 degrees Celsius, the body struggles to regulate heat.
Afterward, the research team checked what happened when the subjects stayed for a time in conditions slightly below the point where the body fails to regulate heat, and slightly above it. The results showed a sharp difference: below this point, the body still barely manages to maintain balance, but above it, the body temperature continues to rise without stopping — a situation that could lead to heat stroke within hours. That is, the study showed that there is a clear physiological limit to a person's ability to cope with heat load, and it is lower than previously estimated.
Negev explains that under heat load, heat stroke is indeed an extreme risk, but there are other health risks: an increase in mortality risk, especially in old age, an increase in the risk of heart attacks, and an increase in the risk of stroke. Those suffering from chronic diseases such as high blood pressure, diabetes, obesity, heart and kidney diseases are more sensitive. In addition, pregnant women, infants, and young children are more vulnerable. There are those who are affected and those who are affected more. In extreme heat in Israel, everyone is affected, but people living in poverty, people working outside, and in general the more vulnerable populations in society — they are more vulnerable and have fewer means to protect themselves. Climate change increases medical, economic, and social gaps, and a substantial part of what we must do is to reduce these gaps.
70 degrees at 11 a.m.
Negev explains that in the Middle East, and in Israel in particular, we are in a region that is at high risk compared to other regions of the world, in what is called a climate change hotspot. Already today we are exposed to high temperatures and high humidity in many areas of the country, and according to forecasts, this is expected to increase. Therefore, it is important to prepare for this, she says, adding that there are many ways to prepare for heat loads, especially in cities, where the problem is more severe. Buildings can be designed more efficiently and dependence on air conditioners can be reduced. An air conditioner does protect against heat, but it also emits heat outside — and when used excessively, it contributes to the warming of the environment. One can use an air conditioner more moderately so that it maintains health without over-cooling, explains Negev.
Other factors that increase heat load in cities are the cars themselves that emit heat, and the roads and parking lots that absorb radiation and heat up. Reducing car use alongside the development of public transport, walking paths, and bicycle paths can reduce the problem. In addition, shade plays a central role in the matter because in unshaded places like sidewalks and playgrounds, the temperature can reach 70 degrees as early as 11 a.m. The temperature we experience is affected not only by the air but also by the ground — and that we can regulate through shading, she explains.
The health system in Israel today has a great challenge, which is to prepare for climate change. The system is dealing with so many emergency challenges that it struggles to find time to address this issue as well. But there is no choice because if we do not prepare for this, later on, the load will be much greater, and it will not fall only on the health system. What characterizes climate change is that it affects all sectors. Therefore, this can be an opportunity for a paradigm shift and for thinking together about how our environment can be better and healthier, even as the climate changes, concludes Negev.
The article was prepared by Zavit — the news agency of the Israel Society of Ecology and Environmental Sciences.
