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Beyond human endurance How climate change is making parts of the world too hot and humid to survive

Deadly heat waves have swept the globe and will continue to because of climate change.

The trends are prompting doomsday questions: Will parts of the world soon become too hot to live in? How will we survive?

When it comes to heat, the human body is remarkably resilient — it’s the humidity that makes it harder to cool down. And humidity, driven in part by climate change, is increasing.

A measurement of the combination of heat and humidity is called a “wet-bulb temperature,” which is determined by wrapping a completely wet wick around the bulb of a thermometer. Scientists are using this metric to figure out which regions of the world may become too dangerous for humans.

A man flowing Over 500W of Electricity Conducts Through His Body: Superhuman Showdown.

The study, published in the journal Nature Climate Change, was carried out by Elfatih Eltahir, a professor of civil and environmental engineering at MIT, and Jeremy Pal of Loyola Marymount University. They conclude that conditions in the Persian Gulf region, including its shallow water and intense sun, make it “a specific regional hotspot where climate change, in absence of significant mitigation, is likely to severely impact human habitability in the future.”

Running high-resolution versions of standard climate models, Eltahir and Pal found that many major cities in the region could exceed a tipping point for human survival, even in shaded and well-ventilated spaces. Eltahir says this threshold “has, as far as we know...never been reported for any location on Earth.” That tipping point involves a measurement called the “wet-bulb temperature” that combines temperature and humidity, reflecting conditions the human body could maintain without artificial cooling. That threshold for survival for more than six unprotected hours is 35°C, or about 95°F, according to recently published research. (The equivalent number in the National Weather Service’s more commonly used “heat index” would be about 165°F.)

This limit was almost reached this summer, at the end of an extreme, weeklong heat wave in the region: On July 31, the wet-bulb temperature in Bandahr Mashrahr, Iran, hit 35°C — just a fraction below the threshold, for an hour or less. The severe danger to human health and life occurs when such temperatures are sustained for several hours, Eltahir says — which the models show would occur several times in a 30-year period toward the end of the century under the business-as-usual scenario used as a benchmark by the Intergovernmental Panel on Climate Change. The Persian Gulf region is especially vulnerable, the researchers say, because of a combination of low elevations, clear sky, water body that increases heat absorption, and the shallowness of the Persian Gulf itself, which produces high water temperatures that lead to strong evaporation and very high humidity. The models show that by the latter part of this century, major cities such as Doha, Qatar, Abu Dhabi, and Dubai in the United Arab Emirates, and Bandar Abbas, Iran, could exceed the 35°C threshold several times over a 30-year period. What’s more, Eltahir says, hot summer conditions that now occur once every 20 days or so “will characterize the usual summer day in the future.” While the other side of the Arabian Peninsula, adjacent to the Red Sea, would see less extreme heat, the projections show that dangerous extremes are also likely there, reaching wet-bulb temperatures of 32 to 34 °C. This could be a particular concern, the authors note, because the annual Hajj, or annual Islamic pilgrimage to Mecca — when as many as 2m pilgrims take part in rituals that include standing outdoors for a full day of prayer — sometimes occurs during these hot months.

While many in the Persian Gulf’s wealthier states might be able to adapt to new climate extremes, poorer areas, such as Yemen, might be less able to cope with such extremes, the authors say.

Christoph Schaer, a professor of atmospheric and climate science at ETH Zurich (Swiss Institute of Technology) who was not involved in this study, provided an independent commentary in the journal, writing that while deadly heat waves have occurred recently in Chicago, Russia, and Europe, in these cases infants and the elderly were most affected. The new study, Schaer writes, “concerns another category of heat waves — one that may be fatal to everybody affected, even to young and fit individuals under shaded and well-ventilated outdoor conditions.”

Schaer writes that “the new study shows that the threats to human health may be much more severe than previously thought, and may materialise already in the current century.” He added: “I think the study is of great importance, since it indicates where heat waves could get worst if climate change proceeds.”

Image on top from the Nature Climate Change study

A term we rarely hear about, the wet-bulb temperature reflects not only heat, but also how much water is in the air. The higher that number is, the harder it is for sweat to evaporate and for bodies to cool down.

At a certain threshold of heat and humidity, “it’s no longer possible to be able to sweat fast enough to prevent overheating,” said Radley Horton a professor at Columbia University’s Lamont-Doherty Earth Observatory.

Within this century, parts of the Middle East, in particular the Persian Gulf region, could be hit with unprecedented events of deadly heat as a result of climate change, according to a study of high-resolution climate models, published Monday. Generally, Jeddah, the Red Sea port city in Western Saudi Arabia and Mecca in the mountains to the south, have more moderate temperatures than in the east coast but I was in Jeddah on 30 June 1995 for the hottest day in 20 years — 48°Celsius (118°Fahrenheit) and higher when humidity is accounted for. In more recent times Jeddah has been hit by extreme flooding and on 22 June 2010 the temperature rose to 52°C (126°F) — the record heat was accompanied by a sandstorm, which triggered power plant blackouts.

Scientists have found that Mexico and Central America, the Persian Gulf, India, Pakistan and Southeast Asia are all careening toward this threshold before the end of the century.

“Humid heat risks are grossly underestimated today and will increase dramatically in the future,” Horton said. “As locations around the world experience previously rare or unprecedented extremes with increasing frequency, we run the risk that our previous messaging about extreme heat risk — already woefully inadequate — will fall further short of the mark.”

You might think that being closer to the beach would be a great way to catch that ocean breeze and cool off. But Horton said proximity to water in extreme conditions could make things worse. As warming temperatures cause the water to evaporate, it adds humidity to the air.

“If you’re sitting in a city along the Persian Gulf, the sea breeze could be a deadly breeze,” he said.

To better understand why these places are becoming too hot and humid for humans to endure, you have to first understand how the body cools itself.

As the sun heats up the air, the ground, objects and people, the human body will react in an effort to cool itself.

The skin sweats. Evaporation of this water cools the body — as long as the surrounding humidity levels allow the evaporation to take place.

If the hot air is too humid, that heat exchange is blocked and the body loses its primary means of cooling itself.

The wet-bulb temperature that marks the upper limit of what the human body can handle is 95 degrees Fahrenheit (35 Celsius). But any temperatures above 86 degrees Fahrenheit (30 Celsius) can be dangerous and deadly. Horton and other scientists noted in a 2020 paper that these temperatures are occurring with increasing frequency in parts of the world. To put things in perspective, the highest wet-bulb temperature ever recorded in the Washington region, known for its muggy, unbearable summers, was 87.2 degrees (30.7 Celsius).

“Extreme humid heat overall has more than doubled in frequency since 1979,” the study’s authors wrote.

These conditions are reaching that deadly threshold in places like South Asia and the Middle East and could regularly cross it by 2075, scientists say.

Horton and his colleagues found parts of the United Arab Emirates and Pakistan have each passed the 95 degree mark for one or two hours more than three times since 1987.

On the coast of the Gulf of California, in the Mexican state of Sonora, scientists are also seeing a “very significant” increase in wet-bulb and air temperatures, said Tereza Cavazos, a senior researcher in the department of physical oceanography at the Ensenada Center for Scientific Research and Higher Education.

During the summer, parts of the gulf can reach temperatures of 86 to 87.8 degrees Fahrenheit (30 to 31 degrees Celsius), which causes the water to evaporate more quickly. The combination of warmer waters and increasing heat trends in Sonora are causing the wet-bulb temperatures to reach dangerous levels.

“Just increasing 1 or 2 degrees Celsius can be the tipping point for changing the impact,” Cavazos said.

The blistering heat is resulting in difficult living conditions, especially for communities that lack resources to provide relief.

Why some will survive while others die

Even below these thresholds, cooling down is hard work on the body. The efforts to fight the effects of heat puts pressure on your heart and kidneys. With extreme heat, people’s organs can start to fail. If you have preexisting conditions, it’s even more likely.

As your body works to cool down, the heart works harder in an effort to pump blood up just below the surface of the skin, where it can get cooler.

The kidneys work harder to conserve your body’s water.

When your body temperature gets too high, it will ultimately cause your body’s proteins to break down, its enzymes to stop regulating your organs’ functions and your organs to start shutting down.

This is a heat stroke: Your body essentially cooks to the point where you have multi-organ failure.

In heat waves, many deaths are due to health problems exacerbated by the extreme conditions.

“It’s very clear during a heat wave, more people do die of heat stroke,” said Zachary Schlader, an associate professor at Indiana University Bloomington who focuses on thermal stress and the human body. But even more die of heart-related conditions. “The body responds [to heat] in such a way it could make the organ vulnerable.”

During heat waves there are some simple ways to take care of your body.

If you have air conditioning, the solution is simple: Go inside.

If you don’t have those resources, hydrate. Drinking water can ease the load on the heart, kidneys and other organs.

Take a break: Even moderate physical exertion such as walking greatly increases the heat your body’s muscles will generate.

Protecting yourself from such stress is inextricably tied to socioeconomic status and resources.

“The poorest people are the most vulnerable, and they are already suffering,” Cavazos said, noting that Sonora depends on farming, meaning a lot of people have to engage in physical labor in the dangerous heat.

In regions like the Persian Gulf, extreme heat is the new normal: Qatar has adapted so extensively to the blistering climate that it air-conditions the outdoors. But not everyone has access to outdoor air conditioning, including those building the facilities that have them. When the wealthy country began construction on venues to host the 2022 World Cup, it faced an uproar over its treatment of workers building the stadiums.

In 2019, the United Nations warned during the four hottest months of the year, outdoor labourers in Qatar were working under "significant occupational heat stress conditions.“

Qatar in May imposed regulations expanding the number of hours that prohibits outdoor labor from taking place to 10 a.m. and 3:30 p.m. during the hotter months of the year, while also outlawing any work if the wet-bulb temperature is more than approximately 89 degrees Fahrenheit.

Merely surviving in those conditions depends on your place in society and what that affords: access to air conditioning, insulated homes, jobs that don’t require extreme physical exertion under the sun and policies in place to protect you from dangerous conditions.

“As humans, we have learned to adapt,” Cavazos said. “The problem is the cost. Some will not survive.”


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