A major new report from HERA launched today at London Climate Action Week, reveals that extreme heat is emerging as one of the most underestimated threats to economic development worldwide, hammering city economies, overwhelming health systems, and falling hardest on women working on the frontlines of a hotter world.
The report, Counting the Cost of Heat: The Case for Urgent Solutions for Cities, draws on global and regional evidence and grounds it in detailed economic modelling of four cities chosen for their sharply different climates and heat profiles: Ahmedabad in India, Bangkok in Thailand, Monterrey in Mexico, and Freetown in Sierra Leone.
Across the four modelled cities, heat already drains as much as 4 to 8 per cent of city GDP in an average year and claims more than 1,000 lives. At the global level, informal sector women who bear a disproportionate burden lose an estimated US$57 billion in earnings each year to extreme heat (which represents 4-11 per cent of their wages). Without targeted action, those impacts are projected to intensify three- to fivefold by 2050, driven by climate change, rapid urbanisation, and ageing populations.
“Extreme heat is draining growth, health, and equality, not a distant climate risk,” said Kathy Baughman McLeod, CEO of HERA. “The evidence in this report is unambiguous. Heat is taking a major toll on the women most exposed and least able to escape it, and it is quietly scarring the economies of cities that can least afford the loss. But the same evidence shows us the way out. The solutions exist, they are affordable, and they work.”
Heat is hammering women’s health and livelihoods
The report makes clear that the burden of extreme heat is not shared evenly. Women, especially the estimated 740 million who work in the informal sector globally, face the highest exposure and the least protection.
Key findings include:
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Informal sector women in every region but the US and Europe lose an estimated US$57 billion in earnings each year to extreme heat. Many women workers make as little as US$3 per day.
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Heat accounts for a larger share of women’s mortality than men’s, up to 20 per cent, driven by a combination of physiological factors and the social and economic conditions that increase women’s exposure and reduce their capacity to adapt.
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The damage ripples outward. Women reinvest up to 90 per cent of their income back into their families and communities, so when heat cuts their earnings, spending on children’s education, nutrition, and healthcare falls with it. In Bangkok, extreme heat reduces women’s annual spending on their children by US$500.
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These individual losses do not stay individual. In Bangkok, heat-driven productivity losses reduce the city’s GDP by an average of 4 per cent a year, the equivalent of the city government’s entire budget, and as much as 8 per cent in an unusually hot year. In Freetown, extreme heat raises the average household debt-to-income ratio by 3 per cent annually, crowding out investment in education and entrepreneurship.
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In Monterrey alone, heat-related pre-term births are expected to more than triple over the next 25 years.
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In the cities analyzed, women suffer heat-driven annual productivity losses ranging from about 3 per cent in Monterrey to 11 per cent in Bangkok. Because they already earn less than men – from 66 per cent less in Freetown to 4 per cent less in Bangkok – even modest productivity losses translate into a greater proportional hit to household income, leaving fewer resources to fall back on.
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Across the cities in this analysis, working women are consistently more likely than working men to be employed informally, reaching as high as 91 per cent of employed women in Freetown (compared to 83 per cent of employed men
The danger does not end when the sun goes down
The report highlights that rising nighttime temperatures, which in many cities are climbing faster than daytime highs, are a critical and often overlooked driver of illness and death. Hot nights deny the body any respite, and together with compound heatwaves they account for 85 per cent of heat-related mortality. The risk falls hardest on lower-income residents living in homes built from heat-trapping materials like corrugated iron and tin, a reality sharply felt in Freetown.
Affordable solutions that pay for themselves
Despite the scale of the threat, the report’s central message is one of opportunity. A representative portfolio of low-cost interventions, including Heat Response Plans, urban green space, cool roofs, labour protections, and heat insurance, could reduce heat-related mortality by more than 36 per cent by 2050 in the cities analysed.
Crucially, these measures deliver exceptional value for money:
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Heat Response Plans generate returns of between 12 and 90 times their cost, making them among the most cost-effective public health investments available.
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Cool roofs lower indoor temperatures by 2 to 7°C (3.6 to 12.6°F) from the day they are installed, protecting the low-income households at greatest indoor risk.
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Heat-related income loss insurance, designed for the poorest informal workers who fall outside formal protections, could reduce informal sector women’s earnings losses by over 40 per cent by 2050.
The report stresses that these returns depend on inclusive design. Standard heat responses too often miss the people who need them most: early warning systems rely on phone ownership and literacy, cooling centres assume mobility and free time, and labour protections rarely reach the unregulated informal sector. Tailoring interventions to account for this protects the most exposed residents and maximises the return on every dollar spent.
“We cannot keep designing heat responses as though everyone experiences heat the same way,” said Baughman McLeod. “When solutions are built with women in the informal sector, not just for them, they save more lives and protect more income per dollar than any blanket approach. That is the case for action, and it is a case decision-makers, employers, and investors can no longer afford to ignore.”
A global tool for practitioners
The report is paired with HERA’s first-of-its-kind tool, designed to help policymakers, practitioners, and development partners understand the impacts of extreme heat and evaluate the case for adaptation.
The tool is global: it lets users see how heat affects mortality and economic output in 11,408 cities across 190 countries, well beyond the four featured in the report, and explore how these impacts could evolve through 2050. Users can also compare the costs and benefits of different adaptation measures to find those with the greatest returns and access practical frameworks for explaining how heat affects people and economies.
The report draws on the most comprehensive evidence to date of heat’s impacts on women, integrating climate projections, health and labour productivity modelling, gender-disaggregated economic analysis, and qualitative evidence from informal women workers, alongside city-specific case studies of those most affected, from how heat disrupts their sleep to how it spoils the wares they sell.
This analysis closes by setting out four urgent priorities: developing sustainable financing models, building deeper partnerships across sectors and levels of government, investing in better evidence on women-centred heat impacts, and closing the awareness gap through heat literacy. The case for action is clear, the document concludes, and the window for building heat resilience is narrowing.
About HERA
HERA (Heat Resilience Action) is a global adaptation NGO dedicated to protecting the health, income, and dignity of women on the frontlines of extreme heat. HERA partners with local organisations, bringing expertise, capacity, and resources to co-design and deliver practical, scalable solutions for a hotter world.
Learn more at www.heranow.org.
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