By Bilkis Abdulraheem Lawal
A new global study has sounded the alarm on a growing but often overlooked threat, dangerously rising nighttime temperatures, which are increasing faster than daytime highs in most major cities worldwide.
The report, unveiled at the COP30 Local Leaders Forum in Rio de Janeiro, found that 83% of 100 global cities studied now experience sustained higher nighttime temperatures, making hot nights more frequent and oppressive.
Conducted by Climate Resilience for All (CRA), the study titled “Extreme Heat and the Shrinking Diurnal Range: A Global Evaluation of Oppressive Air Mass Character and Frequency” examined 30 years of weather data from 1994 to 2024. It focused on two forms of extreme heat, dry tropical (hot and dry) and moist tropical (hot and humid), which are considered most dangerous to human health.
Africa Among Hardest Hit
The findings show that 13 out of 15 African cities recorded rising nighttime temperatures during humid conditions, while 10 out of 14 showed the same trend during dry conditions.
Agadir in Morocco and Cairo in Egypt are experiencing the fastest nighttime warming, with temperatures climbing by 1°C every 5.6 years and 16.8 years respectively.
According to the researchers, this rise in overnight heat reduces the temperature difference between day and night, a phenomenon that prevents the human body from cooling down and increases the risk of heat exhaustion, dehydration, and heart strain.
“This is a wake-up call,” said climatologist and lead author Dr. Larry Kalkstein, Chief Heat Science Advisor at CRA. “Before this analysis, we didn’t realise how quickly nighttime heat was rising within the most dangerous air masses. This data shows that we must act fast to prevent heat-related illnesses and deaths.”
Human and Public Health Consequences
High nighttime heat disrupts sleep and prevents recovery from daytime exposure, worsening health risks, especially for older adults, women, and those in poorly ventilated homes. Yet, most existing heat warning systems only focus on daytime temperatures, the study noted.
In Africa, cities are also seeing more frequent hot weather days. Moist tropical weather patterns have risen by nearly 49%, while dry tropical conditions grew by 14% over three decades.
Mayor Yvonne Aki-Sawyerr of Freetown, Sierra Leone, said the research mirrors realities in African cities where many residents lack access to cooling or electricity.
“Women traders toil all day under the sun and return to unbearably hot homes at night,” she said. “This study highlights the hidden danger of nighttime heat and the urgent need for action.”
Call To Action
CRA’s Chief Executive Officer, Kathy Baughman McLeod, urged governments and city leaders to expand their definition of heat crises.
“We must see heat as a 24-hour emergency,” she said. “Our systems and policies must protect people from both scorching days and sleepless, dangerous nights.”
The study calls for health agencies and policymakers to upgrade early warning systems and include overnight heat in their planning.
About Climate Resilience for All (CRA):
CRA is a global adaptation non-profit dedicated to protecting women’s health, income, and dignity amid rising extreme heat. The group partners with local organisations to co-design and scale practical solutions for hotter, more vulnerable communities.
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