Hot nights due to climate change could increase death rate up to 60 per cent across world, study warns

The risk of death from excessively hot nights could increase nearly six-fold by the end of the century, according to a new study that explains how rising night-time temperatures due to climate change may disrupt the human body’s physiology.

Scientists, including those from the University of North Carolina (UNC) at Chapel Hill in the US, say disruption of sleep in people across the world brought on by climate change could lead to immune system damage and a higher risk of heart disease, chronic illnesses, inflammation, and mental health conditions.

The study, published last week in the journal The Lancet Planetary Health, found that the average intensity of hot night events would nearly double by 2090, from 20.4C (68.7F) to 39.7C (103.5F) across 28 cities.

Researchers say rising night-time temperatures would disrupt normal sleeping patterns and increase the burden of disease due to excessive heat.

“The risks of increasing temperature at night were frequently neglected,” study co-author Yuqiang Zhang from the Gillings School of Global Public Health at UNC Chapel Hill said.

Dr Zhang said such “hot night excess (HNE)” could become more frequent and rapid than changes in the daily mean temperatures.

“The frequency and mean intensity of hot nights would increase more than 30 per cent and 60 per cent by the 2100s, respectively, compared with less than 20% increase for the daily mean temperature,” he added.

The latest findings come on the back of a study published in May which found that the climate crisis could erode about 50-58 hours of sleep per person every year by 2099 due to altering ambient temperatures across the globe.

In the new research, scientists estimated the mortality due to excess heat in 28 cities in China, South Korea, and Japan between 1980 and 2015.

They then applied the projections to two climate change models that aligned with carbon-reduction scenarios adapted by the respective national governments.

Scientists found that between 2016 and 2100, the risk of death from excessively hot nights could increase nearly six-fold.

“From our study, we highlight that, in assessing the disease burden due to non-optimum temperature, governments and local policymakers should consider the extra health impacts of the disproportional intra-day temperature variations,” study corresponding author Haidong Kan from the Fudan University in China said.

“A more complete health risk assessment of future climate change can help policymakers for better resource allocation and priority setting,” Dr Kan added.

Scientists also found that regional differences in temperature accounted for many of the variances in nighttime temperature.

They say areas with the lowest average temperature are estimated to have the largest warming potential.

Researchers believe the findings may help craft better heatwave mitigation measures.

“Locally, heat during the night should be taken into account when designing the future heatwave warning system, especially for vulnerable populations and low-income communities who may not be able to afford the additional expense of air conditioning,” Dr Zhang explained.

“Also, stronger mitigation strategies, including global collaborations, should be considered to reduce future impacts of warming,” he added.

Citing a limitation of the study, researchers said they assessed data from only 28 cities in three East Asian countries, adding that the extrapolation of the results to other regions “should be cautious.”

Potential urban land-use expansion after future urbanisation may also amplify night-time heat exposure, they say.

Scientists are hoping to extend the analysis in future studies to other parts of the world to get a global picture of the potentially deadly nighttime heat on health.