'Rise in night temperature may up your death risk 6-fold'

As night-time temperature climbs owing to climate change, so does your risk of death - nearly six-fold in the future - due to excessive heat that disrupts normal sleeping patterns, a new global study has warned.

Sweltering nights caused by climate change are predicted to increase the mortality rate worldwide by up to 60 per cent by the end of the century, according to researchers from China, South Korea, Japan, Germany and the US.

Ambient heat during the night may interrupt the normal physiology of sleep. Less sleep can lead to immune system damage and a higher risk of cardiovascular disease, chronic illnesses, inflammation and mental health conditions, said the study published in The Lancet Planetary Health.

"The risks of increasing temperature at night were frequently neglected," said study co-author Yuqiang Zhang, a climate scientist from the University of North Carolina at Chapel Hill in the US.

"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 per cent increase for the daily mean temperature," said Zhang from the department of environmental sciences and Engineering at the Gillings School.

Results show that the average intensity of hot night events will nearly double by 2090, from 20.4 degrees celsius to 39.7 degrees celsius across 28 cities in east Asia, increasing the burden of disease due to excessive heat disrupts standard sleeping patterns.

This is the first study to estimate the impact of hotter nights on climate change-related mortality risk.

The findings showed that the burden of mortality could be significantly higher than estimated by the average daily temperature increase, suggesting that warming from climate change could have a troubling impact, even under restrictions from the Paris Climate Agreement.

The team estimated the mortality due to excess heat in 28 cities in China, South Korea and Japan between 1980 and 2015 and applied it to two climate change modelling scenarios that aligned with carbon-reduction scenarios adapted by the respective national governments.

Through this model, the team estimated that between 2016 and 2100, the risk of death from excessively hot nights would increase nearly six-fold. This prediction is much higher than the mortality risk from daily average warming suggested by climate change models.

"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," said Haidong Kan, a professor at Fudan University in China. Since the study only included 28 cities from three countries, Zhang said that "extrapolation of these results to the whole East Asia region or other regions should be cautious".