The heat wave that affects the northern hemisphere left until now, and only in Europe thousands of deceased. According to the World Health Organization (WHO) and taking only Spain and Portugal as of the beginning of this month, at least 1,700 people had died. In England and WalesHealth services put the excess deaths (meaning those that exceed the average number recorded each year) at over a thousand, when temperatures hit 40 degrees in late July. About half of the deceased were people over 80 years old.
The high temperatures, which are exceeded year after year, are regular visitors to the planet’s summers, climate crisis and global warming through. The question isHow long will the human body endure? According to scientific studies, the margin is not wide. A person’s body has a limit and withstands only up to a certain amount of heat and humidity combined.
A study published in the scientific journal Science Advances indicates that these limits are no longer the material of a dystopia and that have already been reachedand for this reason the specialists place great emphasis on the fact that it is it is essential to reduce greenhouse gas emissions as soon as possible that trap heat inside the planet and do not let it escape to the outside. In addition, you have to develop urgent policies that help vulnerable populations maintain bearable body temperatures.
What kills is the humidity
High temperatures cause the human body to produce sweatthat helps cool the skin as that moisture evaporates. But when the heat is accompanied by a very high humidity that evaporation process slows down and can even stop. The latter happens when what scientists call “wet bulb temperature”a measure that combines air temperature and humidity, reaches 35 degrees Celsius.
From the NASA Jet Propulsion LaboratoryColin Raymond and collaborators analyzed temperature data from more than 7,000 meteorological stations located in various parts of the world, starting in 1979. They thus found that extreme humid heat occurs twice as often today as it did four decades ago and that, in addition, the severity of heat is increasing.
Many places have reached wet bulb temperatures of 31 degrees C and higher. And several have recorded readings above the crucial 35-degree mark. Most of the areas where extremes of humid heat were detected are coastal areas located near warm bodies of water, which can provide abundant moisture, and are subject to very high ground temperatures. Others, particularly on the Indian subcontinent, are regions where monsoon winds introduce moisture-laden air.
The highest extremes were generally only sustained for an hour or two, so they are not yet necessarily reaching the limit of human tolerance. But such events will start to last longer and cover larger areas in a warmer future. Even much lower wet bulb temperatures can be deadly, especially for older adults, infants and children, and those with pre-existing conditions (such as cardiovascular, respiratory, or kidney disorders). In addition, there are common medications (such as beta-blockers, for example) that can affect the body’s ability to perspire.
“Although some heat and humidity shocks can be avoided through acclimatization and behavioral adaptation, there is an upper limit to survival under sustained exposure, even with idealized conditions of perfect health, total inactivity, complete shade, absence of clothing, and unlimited water,” the researchers explain in their paper. They add: “The normal internal human body temperature of 36.8° ± 0.5°C requires skin temperatures of around 35°C to maintain a gradient that directs heat outwards. Once the air (dry-bulb) temperature rises above this threshold, metabolic heat can only be removed through sweat-based latent cooling, and with a dry-bulb temperature above 35°C, this cooling mechanism loses its effectiveness completely.
Historic heat waves across much of Europe in 2003 and Russia in 2010 never had a wet bulb temperature above 28 degrees Celsius. However, during the one that followed in 2003, the excess of deaths in Europe (that is, those that exceeded the margins normally registered on average each year) was no less than 70,000 people.
hot cities
Another study, published in the prestigious Proceedings of the National Academy (PNAS)points out how cities are becoming virtually ovens for its inhabitants. “Increased exposure to extreme heat from both climate change and the urban heat island effect threatens rapidly growing urban settlements around the world,” warn Cascade Tuholske, Kelly Caylor and Chris Funk, from the University of California-. However, because we don’t know where urban population growth and extreme heat intersect, we have limited ability to reduce the impacts of urban extreme heat exposure.”
The researchers studied population and temperature data to measure urban exposure to extreme heat in 13,115 cities between 1983 and 2016. They found that urban exposure increased by nearly 200%, affecting 1.7 billion people globally. Total urban warming raised exposure rates 52% above population growth alone.
“However, spatially heterogeneous exposure patterns highlight the urgent need for locally tailored adaptations and early warning systems to reduce the harm of urban exposure to extreme heat in the planet’s diverse urban settlements,” they warn. As in the case of the work that analyzed the limits of heat and humidity, also in this case the scientists call for actions to urgently mitigate the global warming of the Earth, and urgent protective measures.
Those from California publish very specific data: “Using a maximum daily wet-bulb temperature threshold of 30°C, global exposure increased by almost 200% between 1983 and 2016. Total urban warming raised the annual increase in exposure by 52% compared to urban population growth alone. Exposure pathways increased for 46% of urban settlements, which together in 2016 comprised 23% of the planet’s population (1.7 billion people).”
On the other hand, Colin Raymond and team also found that some regions of the world will have to endure wet bulb temperatures above the 35 degree Celsius limit on a regular and frequent basis, if average terrestrial temperatures rise just 2.5 degrees Celsius above those in pre-industrial times. The world has already warmed about 1 degree above that level.
What preventive measures do scientists suggest taking? In addition to the essential curbing of the increase in global warming: changes in work schedules for those who have to work outdoors, special centers to shelter the elderly and babies, public health campaigns to not only warn the population when a heat wave, but also to understand that extreme heat can kill more people than cold or flooding.
