Climate change is no longer a future health threat for developing countries, it is a present one. The 2025 Lancet Countdown on Health and Climate Change, produced with the World Health Organization (WHO), finds that twelve of its twenty key indicators tracking climate-related health threats have reached record levels. Heat-related mortality now averages 546,000 deaths a year, a 23% increase since the 1990s. In 2024, the average person was exposed to 16 days of dangerous heat that would not have occurred without human-caused warming, with the largest increases concentrated in Africa, Asia and small island developing states.
While the 74 lowest-income countries emit only one-tenth of global greenhouse gases, they have experienced around eight times as many natural disasters in the past decade as in the 1980s. Already fragile health systems are not equipped for that burden, and warming will not pause while their systems catch up. Mitigation remains the durable answer, as every fraction of a degree of climate change avoided saves lives, but the present burdens mean that adaptation is also essential. The harder question is how to adapt well in contexts where resources, infrastructure, and political bandwidth remain constrained.
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A threat multiplier across the health system
The WHO describes climate change as a “threat multiplier” that undermines the basic ingredients of good health: clean air, safe water, adequate food and resilient shelter, to name a few. Heat increases physiological stress and reduces productivity; floods destroy clinics and contaminate water; droughts drive malnutrition; warmer, wetter conditions extend the range of vector-borne diseases. As Dr. Vidhya Venugopal of the Sri Ramachandra Institute of Higher Education & Research puts it, “heat exposure produces a spectrum of harm, ranging from discomfort and physiological strain, to higher risk of accidents, lower sleep quality, respiratory issues, worse organ functioning, all the way to potentially fatal heat stroke.”
What makes developing countries particularly vulnerable is not just exposure but its combination with weak adaptive capacity. Poor people, particularly outdoor workers and urban slum dwellers, often have insufficient access to water and cooling, breathe polluted air all day, and sleep in informal settlements with tin roofs and cement walls that absorb the day’s heat, leaving little chance of recovery. The vulnerability is also most critical much earlier than commonly assumed. Wameq A. Raza, Senior Health Economist at the World Bank, explains that “a lot of a person’s lifelong health is determined between the time of conception and age 2. Exposure to extreme heat in that period is significantly predictive of the probability of stunting [growth] and many other health issues.” Climate change is thus not just an acute mortality risk, but a quiet contributor to lifelong health problems.
Extreme heat: the slow, ongoing emergency
“In many places, heat exposure is chronic. It’s ongoing, even between the extreme weather events,” says Dr. Gloria Maimela, CEO of the Foundation for Professional Development (FDP) in South Africa. Increasingly, what matters is not just air temperature but the combination of heat and humidity. Raza explains that “wet-bulb temperatures, which measure heat and humidity together, are rising even faster than just temperatures, and these hot-humid conditions put the greatest strain on the body.”
In her previous research, Maimela focused on a group that receives little attention in development circles: pregnant women. “Especially in LMICs, heat exposure can lead to adverse pregnancy outcomes, including preterm labour and preeclampsia,” she explains. The interventions she describes sound modest but matter: cool sheds where people can access water and fans, white paint on hospital roofs to lower indoor temperatures, umbrella hats for women walking long distances to clinics. The point is that effective adaptation in these settings does not have to be high-tech.
There is an economic case for adaptation, too. Professor Jason Kai Wei Lee, who directs the Heat Resilience and Performance Centre at the National University of Singapore, observes that “the C-suite used to think that heat adaptation is basically welfare and reduces profits. Now the data shows that it’s not just altruism, it’s good for business. If you reduce heat strain among workers, they will work more effectively.” The macro figures support him: the Lancet Countdown estimates heat exposure cost the world 640 billion potential labour hours in 2024, with productivity losses worth roughly USD 1.1 trillion. Raza’s research arrives at a similarly stark national-level figure, finding that, “Bangladesh loses well over a billion PPP dollars every year from heat-related productivity losses alone, without even including longer-term impacts”.
When good intentions meet local realities
Even well-designed adaptation interventions can backfire when they do not consider the conditions of those they are meant to help. Lee describes an example from Manila: “Schools were closed to prevent children from being exposed to extreme heat, which at first sounds sensible. But you are assuming they have cooling options at home, which is just not true for the most vulnerable. Someone must then take care of these children, usually the mother, so she has to stay home, which threatens her job and could cause the family to lose money. You have to be careful about your policies’ unintended consequences.”
Early warning systems face a similar gap between design and reality. Venugopal observes that “heat action plans are rolled out by every government, but they don’t reach everybody. They need to reach the people working in the field, or as street vendors, or sorting garbage, but they actually reach the smartphones of people sitting in air-conditioned offices. We should show them on big display boards in every village, or on the evening TV, using pictures and simple messages so that less literate people can understand them.”
Natural disasters and the cost of compounding shocks
Climate-related disasters have surged fivefold over the past fifty years, and according to the World Meteorological Organization, over 91% of disaster-related deaths have occurred in developing countries. Health system effects such as damaged clinics, broken supply chains, displaced populations, and the spread of waterborne and vector-borne diseases compound the immediate toll. Seonmi Choi, Senior Advisor for Climate and Environment at The Global Fund, gave the example of Cyclone Freddy, the longest-lasting tropical cyclone on record, which in 2023 destroyed hundreds of health facilities in southern Africa that countries often lacked the resources to rebuild and exacerbated the spread of cholera, malaria, and other climate-sensitive diseases.
Climate-resilient infrastructure is thus more essential than ever, and it requires building for the future. Carla Ricchetti, Global Sector Lead for MedTech & Climate and Health Nexus at the International Finance Corporation(IFC), explains that “IFC developed a tool called Building Resilience Index to assess building’s exposure and resilience to climate and natural hazards, including floods, earthquakes, and extreme weather events. It helps identifyvulnerabilities and measures to strengthen any building’s ability to withstand disruptions and maintain operations. For critical infrastructure such as hospitals, this helps ensure essential services remain available when communities need them most.” Cold chains are another critical component of resilient healthcare systems: “Effective temperature-controlled storage and transport of medicines and vaccines help preserve their quality and availability, especially in remote and underserved areas where access to reliable electricity may be limited.” Adaptation in health, in short, cannot be separated from disaster preparedness, supply-chain hardening and the financing of resilient infrastructure.
Designing adaptation for the conditions it will face
Two themes run through every conversation with practitioners. The first is that adaptation must be tailored to local contexts and capacities. “It’s not enough to tell people to have cool roofs inside their houses, because not many people can afford that,” Maimela argues. “Just installing AC everywhere is too expensive and also a maladaptive response, because you’re increasing greenhouse gas emissions further.” Similarly, Ricchetti highlights that “In low- and medium-income markets, innovation is not just about adopting the most advanced technology, but about ensuring solutions are affordable, practical, and easy to use. We work on expanding access to diagnostic tools and technologies that are cost-effective, portable, and require minimal specialized training. Technologies like rapid diagnostic tests, portable ultrasound and telehealth platforms can play a critical role during health emergencies and climate-related disasters, helping healthcare providers reach affected communities and deliver essential diagnostic services where they are needed most.”
The second is that policy gaps are often less about ideas and more about implementation. Experts highlight that many solutions already exist, but often, the political will or capacity is insufficient to implement them at the required scale. Which brings the conversation back to money: Only about 0.5% of multilateral climate funding currently goes to projects that explicitly address human health, and just 5% of climate adaptation funding is committed to health. Most governments now have national health adaptation plans, but those need to be refined and funded. Mitigation will eventually decide how bad this gets. Adaptation, well-designed and well-funded, will decide how many people survive in the meantime.
