Hospital admissions increase by when daily mean temperature rise over
Low-income families were proved to be more vulnerable, she said, explaining, “Families with more money can afford air-conditioning. Poor families can’t afford it.”
Under the weather
A clearer way of understanding how people break down under hot weather is explained by Richard Fielding, professor of the School of Public Health at the University of Hong Kong.
He explains that “wet-bulb” temperature is a useful way of sizing up the hazards of extreme heat on the human body. Wet-bulb temperature, as the name implies, involves wrapping a wet cloth around a thermometer bulb. The reading takes account of moisture in the air, which gives a more accurate index of the heat effect on the human body.
Fielding elucidates that while the normal core temperature is around 37 C, the temperature on skin surface is normally 2 C lower at 35 C.
The wet-bulb temperature at 35 C is about as much as the human body can stand. Above that it is impossible for the body to cool itself through sweat, the evaporation of which normally has a cooling effect. Heat becomes trapped inside the body. The temperature climbs. As the body absorbs more heat from the surrounding environment than it is capable of dissipating, hyperthermia sets in. Then come heat cramps, exhaustion and, at the worst, lethal heatstroke. For that reason the wet-bulb temperature of 35 C is sometimes referred to as the survivability threshold.
“When people get to a wet-bulb temperature of 35 C, if they can’t get out of that temperature they will die of heat stress after six hours, even if they are drinking a lot of water,” Fielding stressed.
In 2015, a severe heat wave with a wet-bulb temperature at 50 C — 15 C above the safety limit — swept India and Pakistan. More than 3,500 people died in the two regions where there was no air-conditioning and no relief from the heat even in public areas.
Hong Kong hasn’t seen days with the wet-bulb temperature over 35 C yet. However, given the trend toward increasing temperatures the future gives cause for concern. The HKO projects that the annual number of very hot and humid days in town, with a maximum wet-bulb temperature of 28.2 C or above, is expected to hit 96 days by the end of this century — compared to the current nine days — if greenhouse gas concentration continues to escalate.
The projection is calculated according to the formula of Representative Concentration Pathways (RCP). It’s an opaque-sounding term. Simply stated, it’s the calculation of the amount of solar radiation that penetrates the earth, related to the amount of heat reflected by the earth back into space. The calculation is recorded in terms of watts per square meter (W/m2). Climatologists predict a worst-case scenario, aka the RCP 8.5 scenario, in which extra heat of 8.5 W/m2 will be trapped in the earth, raising global temperatures 4.1-4.5 C above pre-industrial levels — that is if greenhouse emissions stay unchecked by 2100.
South Asia is especially susceptible to the onset of torrid conditions. It’s already one of the hottest regions of the planet. Between 2071 and 2100, an estimated 4 percent of the population in Pakistan, Nepal, India, Bangladesh and Sri Lanka will experience deadly, six-hour heat waves with wet-bulb temperatures exceeding 35 C at least once.
It is inevitable under the RCP 8.5 scenario as reported in the journal Science Advances earlier this year.
Young and old
The survivability threshold at 35 C applies to people already in good health. For children and the elderly, especially those who are poor, 35 C may already surpass the survivability limit. Temperatures of a few degrees below that can still be life-threatening.
Aggravating these circumstances is the well recognized fact that global warming is also associated with increased pollution. Copious residues from fossil fuels are pumped into the atmosphere, like ozone, sulfur dioxide and nitrogen dioxide. Increased warming over prolonged periods also causes plants to release more pollen into the atmosphere.
In the increasingly polluted air linked to climate change, children are the most vulnerable. They inhale more air in proportion to body weight than adults. As such, children ingest more pollutants with every breath. Their respiratory systems are still developing, thus they absorb a higher amount of toxic materials. Many of these toxins are retained in the body, depleting children’s health, said Chan.
As a result, asthmatic children are more likely to suffer more frequent attacks, while people with emphysema and bronchitis are more likely to suffer aggravated respiratory diseases.
In the case of infectious diseases, hot weather becomes a virulent breeding ground. In Hong Kong, the elderly aged 75 or above were found to be most vulnerable, with a 9.6-percent higher risk of hospitalization for contagious illnesses, relative to 3.7 percent for the youngest group (aged under 15).
Most elderly people have already developed chronic diseases like diabetes, high blood pressure and cardiovascular diseases, which have degraded their immune systems’ ability to withstand infectious diseases, Chan explained.
A torrid time
At his home, the little boy picked his way around the miniature flat and flopped down on the bottom mattress of the bunk bed which takes up two-thirds of the flat’s space.