Is the hot weather that dangerous?

Nicolas Ozery

Table of Contents:How many people were affected? Is this reliable data?What directly causes people to die during a heat wave?Who else is threatened by the heat?Do people get sick more often with non-fatal illnesses in heat, too?What temperature is dangerous? When do heat-related deaths begin to rise?+25°C is too much in London, but too little in Bangkok? Why?Can future heat waves be prevented or predicted?Since the forecasts are powerless, how can we protect ourselves from the heat?

In July 2022 abnormally high temperatures were established in Europe. In Spain, the thermometer readings in the shade reached +45 degrees Celsius, in Portugal +47, and British meteorologists updated the historical highs of temperature in London. Extreme heat wave was also observed in India. The temperature records are accompanied by alarming news of hundreds of people killed by the heat wave.

How many people were affected? Is this reliable data?

The Spanish Carlos III Health Institute reported that from July 10 to 15, 2022 about 360 people died because of the heat. On July 16 the Portuguese Ministry of Health reported that in the previous seven days the number of victims of the disaster was at least 659 people. These data were published by news agencies without details, but we can assume that these are deaths directly related to the heat.

At the same time, we know from demographic studies that the deaths that doctors have immediately linked to the heat are only a small fraction of the deaths that are actually provoked by extreme weather phenomena. To be sure of this, it is enough to trace the dynamics of excess mortality in the days immediately following a heat wave: it increases significantly in the next 10-20 days.

A global statistical analysis of the relationship between temperature and mortality indicates that about 0.42% of deaths on the planet are due to heat in one way or another. Yet medical statistics, according to current estimates, account for only one in fifty of these deaths.

What directly causes people to die during a heat wave?

The most obvious immediate cause of death is heat stroke. In this case, the body cannot cope with cooling, resulting in seizures, swelling of the brain, ineffective heart function, difficulty breathing, kidney and liver damage (usually reversible).

Heat stroke is one of the leading causes of death in young athletes. And the main one for people who work at elevated temperatures (e.g., miners or glass factory workers) in their first days in a new place.

In heat stroke, help must be given within half an hour, otherwise the prognosis is quite bad - up to 80% of people die without help.

Who else is threatened by the heat?

In addition to people who are directly threatened by heat stroke, people die more often in heat waves:In addition to people who are directly threatened by heat stroke, people die more often in heat waves:

Do people get sick more often with non-fatal illnesses in heat, too?

Yes. For example, people are more likely to seek mental health emergencies (including exacerbations of already diagnosed disorders).

Hot, sunny days increase ozone levels in the air, which can harm the respiratory system and exacerbate pre-existing conditions, especially asthma.

Some reports indicate that heat causes babies to be born prematurely and weigh less than normal.

Over time, rising temperatures are expected to cause infectious agents (and their vectors) that are prevalent in the south to appear in more northern regions. For example, dengue will spread to Great Britain, a disease now predominantly found in Southeast Asia, Africa, Central and South America.

Finally, people sleep worse because of the high temperatures.

What temperature is dangerous? When do heat-related deaths begin to rise?

There is no specific temperature marker: the fact is that mortality from heat begins to rise much earlier than the maximum temperature to which a person can physiologically adapt.

It is estimated that even a healthy person cannot survive a long (more than six hours) stay in a room where the temperature of a wet thermometer exceeds 35 degrees Celsius (an ordinary thermometer, if the humidity is less than 100%, will show a temperature significantly higher). There are places on the planet where the temperature often rises much higher, but people still live there. The point is that the heat there is usually not combined with high humidity, which allows a person to cool down through perspiration.

But the temperature at which more people than usual begin to die varies in different parts of the world. In Tokyo and Madrid, for example, people on average normally tolerate average daily temperatures up to 30 degrees Celsius, while in London excess mortality begins to rise sharply already after 22-23 degrees Celsius.

The situation is similar with the cold: in Sao Paulo, for example, people begin to die more often when the temperature drops below +15 degrees, and in Toronto temperatures down to -20 have no effect on mortality at all.

+25°C is too much in London, but too little in Bangkok? Why?

It's all about adaptation: both purely physiological and related to the infrastructure of life - air conditioning, housing, and so on.

First of all, up to a certain point, a person can adapt. Residents of places where the heat is a frequent phenomenon certainly tolerate such temperatures easier. On average it takes a week or two to get used to the heat, and ideally one should get used to it by gradually increasing the "dose" (the risk of negative impact on health is especially high at the beginning of the heat). The essence of acclimatization is that a person begins to sweat more as the air temperature rises and he loses less electrolytes with sweat. The heart rate decreases. This allows you to cool down faster and not overload your cardiovascular system.

If after acclimatization a person has not been in the heat for a week or more, adaptation is gradually lost and the body needs to be trained again.

Second, many social measures are known to prevent high mortality rates. It is not uncommon for people who simply did not have the money to install air conditioning or pay their energy bills to die because of the heat, or for those who have to work outside, or else have no means of livelihood, to die.

In different countries the authorities try to help such people. In some countries there are requirements for employers to provide special working conditions at high temperatures.

Somewhere, people from at-risk groups are sought out by the police to help them if necessary. But it is good if the potential victims of the abnormal heat check up on their relatives or even just acquaintances: social isolation is one of the risk factors for the development of heat stroke.

Finally, somewhere through the media and government websites are trying to get the word out to parents about how not to forget their children in the car, and tips for coaches and athletes on how to prevent heatstroke in practice.

Can future heat waves be prevented or predicted?

It is impossible to predict. Heat waves are a weather phenomenon, and it is impossible to predict the weather over a long period of time. Nevertheless, it is safe to say that due to climate change, the probability of extreme weather events has increased significantly compared to the norm of the 20th century.

There are papers attempting to estimate not only this probability, but also to calculate the contribution of climate change to the excess mortality associated with heat waves. According to such estimates, about one-third of all heat-related deaths occurring during the warm period of the year are a direct result of warming.

The same distinction between weather and climate applies to the question of whether heat waves can be prevented rather than predicted. Each particular wave cannot be prevented, but the level of humanity's greenhouse gas emissions directly affects the overall global temperature and, therefore, the frequency of extreme events.

Since the forecasts are powerless, how can we protect ourselves from the heat?

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