Hospi­tal ad­mis­sions in­crease by when daily mean tem­per­a­ture rise over

China Daily (Hong Kong) - - CRITICAL HK ISSUES -

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.

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