A new global climate study has revealed that nighttime heat is rising fast in cities around the world, and African communities, especially women and the poor, are getting hit the hardest.
The study showed that minimum nighttime temperatures have been rising much more rapidly during oppressively hot weather than daytime average highs in 83 percent of major global cities analyzed, with some cities experiencing increases up to 12 times faster.
The study by Climate Resilience for All, titled “Extreme Heat and the Shrinking Diurnal Range: A Global Evaluation of Oppressive Air Mass Character and Frequency,” analyzed weather data over a 30-year period from 1994 to 2024 across 100 major global cities.
The analysis was released at the COP30 Local Leaders Forum in Rio de Janeiro, Brazil, a gathering of global mayors focused on climate action.
The study found that 13 out of 15 African cities are experiencing higher nighttime temperatures in moist tropical weather, while 10 out of 14 African cities are experiencing higher nighttime temperatures in dry tropical weather.
Nighttime temperatures in African cities are rising fastest in Agadir, Morocco, where they are rising at a rate of 1°C every 5.6 years during dry tropical weather, and in Cairo, Egypt, where they are rising 1°C every 16.8 years during moist tropical weather.
African cities experiencing decreases between daytime and nighttime temperatures during moist tropical weather include Upington, South Africa; Bamako, Mali; Abidjan, Cote d’Ivoire; Cairo, Egypt; Agadir, Morocco; Mombasa, Kenya; Espargos, Cape Verde; Brazzaville, Congo; Dakar, Senegal; Algiers, Algeria; Cotonou, Benin; Luxor, Egypt; and Reunion, Reunion Island.
During dry tropical weather, cities seeing similar decreases include Agadir, Morocco; Cairo, Egypt; Luxor, Egypt; Espargos, Cape Verde; Cape Town, South Africa; Niamey, Chad; Dakar, Senegal; Mombasa, Kenya; Brazzaville, Congo; and Reunion, Reunion Island.
The study also found that summertime moist tropical weather patterns have increased close to or over 49 percent in Africa and have grown by 37 percent globally over the 30-year study period.
Cities in Africa average an increase of one moist tropical day every 2.5 years, while dry tropical weather patterns have grown by 14 percent over the same period, with cities averaging an increase of one dry tropical day every 3.4 years.
Larry Kalkstein, climatologist and Chief Heat Science Advisor at Climate Resilience for All, said the analysis revealed how rapidly nighttime heat has been rising within the most dangerous air masses.
“Before this analysis, we did not know how rapidly nighttime heat has been rising within the most dangerous air masses. It is critical for us to understand how the heat of summer—that sends people to the emergency room—is shifting, and what we are overlooking when we talk about it,” Kalkstein said.
Mayor Yvonne Aki-Sawyerr of Freetown, Sierra Leone, said the study reflects the lived reality of cities in the global south.
“This study reflects the lived reality of so many cities in the global south. Most of our residents lack access to cooling, and women market traders facing extreme heat all day return to homes that are dangerously hot at night,” Aki-Sawyerr said.
She added that as Freetown implements its heat action plan, the study sounds the alarm on the hidden threat of nighttime temperatures.
Kathy Baughman McLeod, CEO of Climate Resilience for All, said the research uncovers a critical blind spot in understanding extreme heat.
“We want this analysis to mobilize city and health leaders to urgently broaden their view of what is a 24-hour heat crisis. This research uncovers a critical blind spot in our understanding of extreme heat,” McLeod said.
High nighttime temperatures prevent the human body from cooling down, increasing risks of heat exhaustion, dehydration, and cardiovascular stress.
When sleep is disrupted by heat, the body loses its ability to recover from daytime exposure, heightening the danger of illness and death, especially for older adults, women, and those living in poorly ventilated housing.
The study urges health officials and policymakers to integrate these changing patterns into their work and ramp up regionally targeted heat warning systems that account for the growing probability of multi-day, high-intensity events that offer little nocturnal relief.
Heat warning systems are currently focused on high daytime temperatures and minimizing the impact of overnight temperatures, according to the researchers.
Climate Resilience for All is a global adaptation organization dedicated to protecting the health, income, and dignity of women on the frontlines of extreme heat.