Heat resilience, cooling access and mortality: a way forward
There is vast inequity at the heart of the global heat crisis. The regions where this is most acute, including Sub-Saharan Africa, South Asia, parts of Latin America and South East Asia, are also those where the context-specific data and tools to measure and respond to heat mortality are least likely to exist.
But incomplete evidence is not a reason to wait. Many of the interventions that reduce heat deaths are the same interventions that reduce energy poverty, improve housing and build community resilience, making the case for action on health grounds and on the broader development agenda.
A hierarchy of responses
Reducing heat mortality requires layered responses, and the foundation should not be an emergency reaction but a fundamental shift in how heat is governed: heat mortality should not be treated as a crisis, but rather a recurring and predictable risk that is anticipated and financed for in advance. This calls for political will at every level, from grassroots community organizations and local government through to national policy and international finance, and is underpinned by poverty alleviation, social safety nets and energy access as structural enablers. Where people lack income, secure housing, reliable electricity and the social safety nets that provide support when heat events strike, every other tier of the cooling hierarchy becomes harder to access and harder to sustain.
Heat action plans, early warning systems and healthcare infrastructure that can function under thermal stress are essential components of this governance foundation. Around 60 percent of Africa's population has no access to any heat early warning system, and in much of the Global South heat continues to be treated as an exceptional event rather than a seasonal certainty that deserves standing investment. Changing that framing, and the financing that follows it, is a strong foundation for everything else.
The first physical layer of heat action plans should be passive and nature-based cooling. Architectural shading, cross-ventilation, thermally massive materials, reflective surfaces, urban tree canopy, green spaces and cooling centres reduce the heat load that mechanical solutions must manage, lower energy demand on fragile grids, and reduce the operating costs that make mechanical cooling unaffordable for many. Passive solutions are most effective when they meet the needs of their communities by drawing on indigenous and vernacular building traditions that encode generations of knowledge about thermal comfort in specific climates. Much of the building stock that will exist in 2050 is being constructed now, in fast-urbanizing countries with weak or absent building energy codes; and the window to design passive features at low cost is open but not for long. For the hundreds of millions of people in informal settlements where codes offer no protection, slum upgrading is an equivalent pathway, with evidence from Rio de Janeiro showing that upgrading programmes reduced heatwave mortality by 3.9-5.5 percent in affected areas.
Electricity access enables the next level of cooling. Where passive measures need supplementing, fans and evaporative coolers provide an affordable next step, effective across the vast majority of conditions in the Global South. When temperature and humidity combine beyond critical thresholds, air conditioning (AC) can become necessary for survival. Yet the countries projected to face the largest increases in heat mortality by 2050 are also those with the lowest projected AC ownership and the weakest electricity infrastructure to support it.
But energy access matters in a broader sense than simply enabling mechanical cooling. Reliable, affordable electricity drives income generation through productive use: powering small businesses, refrigeration, lighting and digital connectivity that raise household incomes and expand the range of adaptive options available to families. A household with reliable electricity is better placed to retrofit a roof, purchase a fan, or receive a heat warning than an unconnected household. Closing the electricity access gap is therefore not only a prerequisite for fans and AC, it is a driver of income growth, social resilience and poverty alleviation that makes every tier of the cooling hierarchy more accessible. Social safety nets, including cash transfers, community health worker networks and welfare cheque systems, play a parallel role: they reach the people most likely to fall through the gaps of infrastructure-based responses, particularly the elderly living alone, informal workers with no paid sick leave and households too poor to act on warnings even when they receive them.
Act on what we know, build what we need
Better mortality measurement is a medium- to long-term endeavour, but identifying who is most at risk does not have to wait. Heat vulnerability assessments, combining data on exposure, sensitivity and adaptive capacity, can direct cooling investment, target welfare outreach and guide urban policy even where mortality data are absent. Where mortality evidence does exist in comparable contexts, it should be used to validate these tools, ensuring that indicators reflect local drivers of heat mortality rather than assumptions imported from elsewhere.
Some evidence priorities stand out for longer-term heat mortality surveillance. Verbal autopsy instruments, currently the primary tool for capturing mortality data where registration is absent, are not designed to capture heat as a contributing factor, but this is addressable. Asking about time outdoors, sleep disruption, housing conditions and hydration makes heat attribution more feasible than relying on standard cause-of-death categories alone, and developing instruments that systematically incorporate these questions is a tractable and relatively near-term research priority. Community-based reporting offers a practical complement where formal systems are weak. Civil registration and vital statistics systems are the deeper foundation, and while strengthening them is essential, this is a long-term governmental and public health priority that extends well beyond heat and climate adaptation alone; the case for investment rests on its broader returns across all causes of death. The heat mortality evidence base has also been built largely at high-income institutions, and expanding it requires sustained investment in regional research networks and in-country epidemiological capacity, generating evidence grounded in the climates, disease burdens, and social conditions of the populations most affected.
The path forward connects better evidence to better action: stronger registration systems generate data for attribution; better attribution validates vulnerability assessments; better assessments direct cooling investment toward those most at risk. Crucially, the more granular that attribution becomes, the more precisely it can guide intervention choices. Understanding not just that heat kills, but which combinations of factors drive mortality in a given population, whether that is unreliable electricity, inadequate housing, social isolation or occupational exposure, makes it possible to identify which interventions will have the greatest impact in that specific context. A community where mortality is concentrated among outdoor workers in inadequate housing points toward different priorities than one where elderly residents living alone are most at risk. Better evidence does not just tell us where the problem is, it tells us what to do about it. The goal is not measurement for its own sake; it is ensuring that the people most exposed to heat, those living without reliable electricity, in inadequate housing and in cities warming faster than the global average, are visible enough to be reached, and that the interventions most likely to protect them, in their specific circumstances, are deployed at the scale and speed the problem demands.
