A new global study released at COP30 in Brazil warns that nighttime temperatures are rising sharply in cities worldwide — including Mombasa — posing serious health and environmental risks. The research shows that Mombasa’s nights are getting hotter during both humid and dry tropical conditions, leaving residents with little relief from daytime heat. Experts are urging urgent local action to adapt city planning and health systems to the new reality of “24-hour heat.”
MOMBASA, Kenya, Nov 8, 2025 — Mombasa has been listed among African cities experiencing a dangerous rise in nighttime temperatures linked to climate change, according to a new global study released at the COP30 Local Leaders Forum in Rio de Janeiro, Brazil.
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”, analysed weather data from 100 major cities over a 30-year period, revealing that minimum nighttime temperatures are rising up to 12 times faster than daytime highs in some regions.
According to the analysis, Mombasa is among the cities where the gap between daytime highs and nighttime lows is narrowing during both moist tropical (hot and humid) and dry tropical (hot and dry) weather patterns — conditions that scientists warn are most dangerous for human health.
“High nighttime temperatures prevent the body from cooling down, increasing risks of heat exhaustion, dehydration, and cardiovascular stress,” the report notes, adding that sleep disruption due to heat makes recovery from daytime exposure difficult.
In Africa, 13 out of 15 cities are experiencing higher nighttime temperatures during moist tropical conditions, while 10 out of 14 are affected during dry tropical weather. The trend has been most severe in cities like Agadir, Morocco, and Cairo, Egypt, but also extends to coastal hubs like Mombasa, Kenya, and Dakar, Senegal.
Local impact and urgent action
Environmental experts say the findings have serious implications for Mombasa, a low-lying coastal city already grappling with sea level rise, heatwaves, and high humidity levels.
“Nighttime heat is a silent killer — especially in informal settlements where ventilation is poor and cooling is unaffordable,” said an environment activist, local climate and Maji na Ufanisi Coast Regional Director Khamisa Maalim Zajjah. “We must integrate nighttime heat risks into urban planning and public health strategies.”
The study calls on city and health leaders to develop regionally tailored heat warning systems that take into account the increasing likelihood of multi-day, high-intensity heat events with little nighttime relief.
COP30 delegates emphasized that many cities in the Global South, including Mombasa, lack adequate infrastructure to protect residents from rising temperatures — a challenge compounded by rapid urbanisation and poverty.
“This research uncovers a critical blind spot in our understanding of extreme heat,” said Kathy Baughman McLeod, Climate Resilience for All, CEO. “We want this analysis to mobilise leaders to see heat as a 24-hour crisis.”
