South-east Asia and other tropical areas in the world look set to become hotter in the future, and one should be aware of the risks and take precautions.

If you were outside on March 24 and felt a bit dizzy, there was a reason for that. It was the hottest day of the year so far in Singapore, with the mercury soaring to 36.3 deg C in Choa Chu Kang.

Don’t expect things to cool down. Singapore’s weatherman says 2024 could be even warmer than 2023 and the hot season is just upon us. For example, in May 2023, Singapore recorded its highest maximum daily temperature – 37 deg C, equalling a record set in April 1983.

In neighbouring Malaysia, a heatwave alert has been declared in several areas in all states except Terengganu. At least one person is reported to have died from heatstroke.

Singapore and Malaysia are victims of global warming, with South-east Asia and other parts of the planet’s steamy tropical belt set to become hotter. As such, it is vital to be more aware of the risks of heat exposure and to take precautions if going outside.

Heat plus high humidity is stressful for the body, which needs to maintain a steady temperature. Sweating is a key way for the body to cool down. But if it is too humid, the sweat cannot evaporate fast enough and the body will struggle to get rid of the excess heat.

Prolonged exposure outdoors can lead to headaches, confusion, dehydration and muscle cramps. Unless treated quickly, which includes having a cool drink and seeking respite in the shade or indoors under an air-conditioner, this can lead to more serious complications.

Outdoor workers are especially at risk, but so is anyone spending time outdoors for prolonged periods, especially when exercising, or living in poorly insulated homes without air-conditioning.

So, how bad is the heat stress risk in Singapore?

According to Professor Marcus Ong, a senior consultant at Singapore General Hospital, there is little clinical data on the number and prevalence of heat-related illnesses in Singapore.

In 2023, he looked at heat-related injuries in Singapore based on patient records from 2008 to 2020. What he found was surprising. Data on the 426 recorded cases showed two-thirds involved adults, mostly male, between 18 and 39 years old. Many were exercising when they fell ill, mainly during the weekend and in December, usually one of the cooler months.

Of the total recorded cases, 14 per cent were sent to the intensive care unit and two patients, both seniors, died, said Prof Ong, who is also director of Duke-NUS Medical School’s Health Services and Systems Research programme.

Singapore is fortunate with its excellent healthcare, prevalence of air-conditioning and shading. Geography also helps, as Singapore is a small island, surrounded by the sea. These factors likely limit the incidence of severe heat stress.

But the risks facing people in the Republic and elsewhere in the tropics will likely mount in the future, researchers say. Global warming will push the human body towards its physiological limits in coping with heat stress.

The world has warmed about 1.2 deg C on average since pre-industrial times, and clearing forests (which have a cooling effect on the environment) and building bigger cities (which trap heat) are only making things worse.

An additional 1 deg C of warming from now will mean about 800 million people in the tropics will live in areas where heavy work should be limited for over half the time in a year, according to research published in Cell Press journal One Earth in March 2024.

The peer-reviewed study said more than a billion outdoor workers live in the tropics, where nearly a fifth of all hours in the year are already hot and humid enough to exceed recommended safety thresholds for strenuous outdoor labour.

Many workers already face rising heat-related illnesses such as heatstroke and chronic kidney disease.

The study defined the tropics as the region within 30 degrees north and south of the Equator. The authors studied data from various sources, including the latest weather statistics and climate models, and reviewed existing scientific literature on heat impacts on workers.

For outdoor workers, life-saving strategies include regular rest breaks with cooling drinks, wearing breathable clothing and shifting work hours outside the hottest parts of the day.

But for this to happen, laws need to be passed and enforced, which is often a problem in poorer nations. And millions of people work in informal or unregulated sectors, further limiting their chances of avoiding deadly heat stress.

The authors of the research said existing studies rarely delved into solutions, which means workers’ adaptations to heat remain understudied. There is also a lack of knowledge about how humid heat impacts specific populations and occupational groups in the tropics. “Furthermore, there is limited research on whether existing guidelines are applicable in all occupational settings in the tropics,” it said.

Heat stress and fertility

A separate study by researchers from the NUS Yong Loo Lin School of Medicine found that exposure to extreme heat caused a drop in the quality of sperm in men in Singapore.

They examined sperm samples from 818 men stored at the National University Hospital’s andrology section. The researchers found that those who were exposed to extreme heat during the three months prior to providing semen samples had a 46 per cent higher risk of low sperm count, and a 40 per cent increased risk of low sperm concentration.

The findings were more pronounced for men aged between 25 and 35, who tend to be at the stage of entering fatherhood, said research fellow Samuel Gunther, one of the researchers in the team. In another data gap, he said the links between extreme heat and fertility have not been well studied in tropical countries such as Singapore.

For humanity and economies to keep thriving in the tropics, there needs to be much greater awareness of the risks from heat exposure – and the huge costs in lost productivity and healthcare.

It also means better weather warning services and paying attention to them.

One example is Singapore’s heat stress advisory service, which was released in July 2023. The heat stress level is like a traffic signal – low (green), moderate (amber) and high (red). It is available on the myENV app and at, and there are clear guidelines for how to respond to the different levels.

The reasons for greater precaution are obvious. The Government’s Third National Climate Change Study, released in January 2024, projected that the daily average temperature in the Republic could rise by up to 5 deg C by the end of the century if global greenhouse gas emissions keep growing rapidly. And days with high heat stress will significantly increase as well.

Deep cuts to planet-warming greenhouse gas emissions can reduce the risks in the future. But with temperatures already at dangerous levels, the way we play and work outdoors needs to change and so, too, the design of our cities to increase shading and cooler green spaces.

It is time to heed the warning signs or risk the tropics becoming too hot to handle.