Hot nights could increase global mortality rate by 60 percent

Hotter nighttime temperatures will increase the global mortality rate by up to 60 percent in the coming decades, according to an international study led by UNC Chapel Hill. The experts report that the burden of disease will increase as normal sleeping patterns are disrupted by excessively hot nights.

Sleep disruption can lead to a cascade of dangerous health risks, ranging from immune system damage to a higher risk of heart disease, chronic illness, and mental health issues. 

The study is the first of its kind to estimate the impact of hotter nights on climate change-related mortality risk. The results show that the average intensity of hot nights will nearly double by 2090, from 68.7℉ to 103.5℉ across 28 cities in east Asia. With this in mind, the mortality rate will jump much higher than predicted based on average temperature increases alone. 

“The risks of increasing temperature at night were frequently neglected,” said study co-author Dr. Yuqiang Zhang. “However, in our study, we found that the occurrences of hot night excess (HNE) are projected to occur more rapidly than the daily mean temperature changes. The frequency and mean intensity of hot nights would increase more than 30% and 60% by the 2100s, respectively, compared with less than 20% increase for the daily mean temperature.”

The researchers analyzed the number of deaths associated with heat in 28 cities throughout China, South Korea and Japan between 1980 and 2015. By modeling this data with two future climate scenarios, the experts estimated that the risk of death from excessively hot nights would increase nearly six-fold between 2016 and 2100.

“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 study co-author Dr. Haidong Kan of Fudan University in China. “A more complete health risk assessment of future climate change can help policymakers for better resource allocation and priority setting.”

“To combat the health risk raised by the temperature increases from climate change, we should design efficient ways to help people adapt,” said Dr. Zhang. “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. Also, stronger mitigation strategies, including global collaborations, should be considered to reduce future impacts of warming.”

The study is published in the journal The Lancet Planetary Health.

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By Chrissy Sexton, Earth.com Staff Writer