Intended for healthcare professionals


Threats to human health multiply amid record global temperatures

BMJ 2023; 382 doi: (Published 07 August 2023) Cite this as: BMJ 2023;382:p1819
  1. Owen Dyer
  1. Montreal

The past week saw the world’s first heat related nationwide shutdown as Iran’s government declared two midweek days to be public holidays, urging elderly people and those with health conditions to stay indoors as temperatures in some southern towns hit 51°C.

In the United States, meanwhile, burn wards in Phoenix, Arizona, were full as the asphalt reached temperatures of 82°C. Asphalt and concrete burns accounted for half of the burn patients in the intensive care unit, said Kevin Foster, director of the Arizona Burn Center. He told the news channel CNN that people who fell and struggled to rise quickly had “really serious injuries” that were comparable to those seen in house fires. Paramedics have sustained burnt knees while attending to patients. Other patients had been scalded by water from garden hoses.

At the quadrennial World Scout Jamboree on South Korea’s southwest coast, where 43 000 scouts camped out in a blistering heatwave, 807 people sought medical treatment in the first two days, and UK and US scouts retreated to hotels over the weekend. The organisers tried to continue but ended the event early on Monday 7 August after learning that the campsite lay in the likely path of typhoon Khanun.

South Korea has recorded 16 heat related deaths this year, and at least 40 people died last month from floods and landslides triggered by extreme weather. But research suggests that such figures vastly understate the true health burden of extreme heat, as deaths attributed to other health conditions also climb during heatwaves only to be collated at a later date, if at all.

A study published last month in Nature Medicine estimated that Europe saw 61 672 (95% confidence interval 37 643 to 86 807) heat related deaths in summer 2022, which until this year was the hottest European summer on record. Women died at a rate 56% higher than men, the study found, and excess deaths were highest in Greece, Italy, and Spain.1

Catalyst of disease

Extreme heat worsens almost the entire spectrum of human disease, research has found. Cardiovascular mortality,2 acute kidney related emergency visits,3 exacerbations of chronic obstructive pulmonary disease,4 suicides,5 and hospital admissions for dementia6 all become more common in the presence of extreme heat.

High temperatures also bring a spike in preterm births and low birth weights,78 and some studies have found greater frequency of congenital anomalies during heatwaves.9

An additional threat is the smoke released by wildfires. And of 375 viral, bacterial, fungal, and parasitic diseases confronted by humanity worldwide, more than half have been aggravated by climactic hazards, a review in Nature Climate Change found.10

In the US tickborne diseases have spread northwards, and this year public health authorities have recorded the first locally acquired malaria cases since 2003. Dengue fever has gained a foothold in southern France, brought by the quickly spreading Asian tiger mosquito. Widespread flooding has also helped mosquitoes breed more quickly in Bangladesh, which is currently experiencing its worst ever dengue outbreak.

Workers struggle

The punishing summer has led to calls for better working conditions. But in Texas such calls were rejected by the state’s Republican dominated legislature, which voted to strike down city ordinances that allowed cooling breaks to workers in Austin and Dallas.

Qatar, which earned global criticism over workers’ deaths in the preparations for last year’s football World Cup, recently adopted worker heat guidelines which, on paper at least, are the world’s most protective. But Qatar’s experience also highlights the difficulty of quantifying workers’ heat related deaths when employers would often rather attribute them to other causes.

A study of Nepali migrant workers’ deaths in Qatar found that while only 15% of deaths in the 25-35 age group would normally be from cardiovascular causes, such causes were listed on the death certificates of 22% of those who died during the cool season and 58% of those who died in the hot season.11

Less noticed than acute deaths is a hidden burden of kidney disease among chronically dehydrated workers. In Nepal and Indonesia nephrologists have reported that about 10% of their patients are now young men working in the Gulf region. Many will need lifelong dialysis.

Winter heatwave

Perhaps the most alarming heatwave was the one that settled over Argentina, Bolivia, Chile, Uruguay, and southern Brazil in the middle of the southern winter. It was Chile’s 10th heatwave of 2023 as temperatures around the country brushed 39°C. The heat reached high into the mountains, which have had torrential rain instead of snow. With little snow to melt, farmers face a summer of dry rivers as the El Niño meteorological phenomenon, which this year is adding to the human induced warming effect, will continue to strengthen through 2023.

The crisis offers a window into a future in which adequate food and water can no longer be guaranteed. In Uruguay’s capital, Montevideo, tap water is no longer drinkable because authorities have had to refill the reservoir with brackish water from the River Plate estuary.

Similar conditions in Pakistan last year ruined the harvest, triggering the country’s worst economic crisis in decades. “What happened in Pakistan will not stay in Pakistan,” the country’s prime minister, Shehbaz Sharif, told the UN General Assembly. “Unless the leaders of the world come together to act and act now on an agreed common agenda, there will be no Earth to fight wars over. Nature will be fighting back. And for that, humanity is no match at all.”