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News and evidence

How sure are we?

A map of what the evidence shows firmly, what it suggests, and what nobody has measured yet. It ranks our knowledge, never any country, city or organisation.

Cycle by cycle

21 vicious cycles, 66 studies. 12 cycles rest on evidence that is still emerging; they come first. Each square is one study, coloured by its kind; select a cycle to see every study and the limits it states.

The energy-poverty trapEvidence emerging 1 study · 0 peer-reviewed · 0 from the region

People who can’t afford to cool fall ill. Illness brings debt, and debt puts cooling even further out of reach.

An older woman living alone

She has a fan but rations it to keep the electricity bill down. On a hot night she falls ill, the cost of care adds to what she owes, and next summer she can afford to run the fan even less.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: Who cannot afford to keep cool, measured directly rather than estimated?

See this cycle on the map

The displacement loopEvidence emerging A 2 studies · 0 peer-reviewed · 1 from the region

People forced to move often land in heat-trapping housing, fall ill, lose income, fall further behind, and are forced to move again.

A family newly arrived in the city

Pushed from their village by failed harvests, they rent a tin-roofed room that traps the heat. Illness costs them work, the rent falls behind, and they move again, to somewhere hotter and cheaper.

A composite, drawn from the evidence for this cycle. Not a real person.
  • Modelled or projected Groundswell Part II World Bank, 2021 · East Asia and the Pacific · Regional model
    Its limit: A worst-case scenario to 2050; covers all climate drivers, not heat alone.
  • Modelled or projected Groundswell Part 2: Acting on Internal Climate Migration World Bank, 2021 · Six world regions · Global model
    Its limit: A worst-case scenario to 2050; covers all climate drivers, not heat alone.

Open question: Does heat, on its own, push people to move within Asian countries, and where do they land?

See this cycle on the map

The protection-gap loopEvidence emerging AA 2 studies · 0 peer-reviewed · 2 from the region

As insurers retreat, public budgets absorb the losses, protection is cut, and the risk drives insurers further away.

A small business owner seeking insurance

After several bad years, insurers no longer cover heat losses for businesses like hers. When a heatwave hits, she turns to public relief, which strains the budget meant for protection.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: How large are uninsured losses from heat, and could money arranged in advance narrow the gap?

See this cycle on the map

The overwhelmed-clinic loopEvidence emerging A 2 studies · 2 peer-reviewed · 1 from the region

Heat illness floods clinics. Overwhelmed clinics treat people later, and more cases become severe.

A nurse at a primary health centre

On the hottest days the waiting room fills with people who are dizzy, vomiting or confused. With so many waiting, some are seen late, and by then their illness has become more serious.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: How much of the load on clinics in South and Southeast Asia during a heatwave is heat illness, and which early actions lower it?

See this cycle on the map

The lost-schooling loopEvidence emerging AA 4 studies · 1 peer-reviewed · 2 from the region

Children pulled out of school earn less as adults, and poorer families pull more children out of school.

A girl in her early teens

When heat closes her school for weeks and money is tight at home, she starts helping her mother instead. She falls behind, and each year it becomes harder for her family to send her back.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: How much learning do children lose in hot classrooms and heat closures in Asia?

See this cycle on the map

The reactive-spending loopEvidence emerging AAA 5 studies · 0 peer-reviewed · 3 from the region

Stretched budgets skimp on prevention. Emergencies multiply, and costly emergency response stretches budgets further.

A municipal budget officer

With money stretched, the cooling shelters and water points she planned are cut back. When the heatwave arrives, emergency spending takes even more of the budget, and prevention is cut again.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: Does money spent on prevention before summer reduce what is spent during heatwaves?

See this cycle on the map

The dying-green loopEvidence emerging A 3 studies · 3 peer-reviewed · 1 from the region

Heat and drought kill city trees. Without their shade the streets get hotter, and hotter streets kill more trees.

A neighbourhood gardener

She waters the street trees she planted years ago, but a hot, dry summer still kills some of them. Without their shade the pavement heats up, and the trees that remain struggle even more.

A composite, drawn from the evidence for this cycle. Not a real person.
  • Peer-reviewed Climate change increases global risk to urban forests Esperon-Rodriguez et al., Nature Climate Change, 2022 · 164 cities in 78 countries · 3,129 species
    Its limit: Compares climate to each species’ natural range; trees can survive outside it with care.
  • Peer-reviewed Planning and maintaining nature-based solutions: Berlin, Jakarta, Melbourne and Santiago Hansen et al., chapter 10 in Nature-Based Solutions for Cities, 2023 · Berlin, Jakarta, Melbourne and Santiago · Four city cases
    Its limit: The tree figures are from Berlin; Asian evidence on tree loss in heat is thinner.
  • Peer-reviewed 50 Grades of Shade Middel et al., Bulletin of the American Meteorological Society · Tempe, United States · Street-level measurements
    Its limit: A desert city; humid cities gain less from shade alone, though shade still cuts radiant heat.

Open question: Which street trees in humid Asian cities survive repeated heatwaves, and what care keeps them alive?

See this cycle on the map

The medical-debt trapEvidence emerging AAA 3 studies · 1 peer-reviewed · 3 from the region

Treatment costs push families into debt. Debt removes any option to rest, and working through the heat brings more illness.

A family caring for a sick father

Treatment for heat illness costs more than they had saved, so they borrow. Repaying the loan means everyone works longer hours through the hot months, and someone else falls ill.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: How often does heat illness lead households to borrow, and how much?

See this cycle on the map

The green-displacement loopEvidence emerging A 4 studies · 4 peer-reviewed · 1 from the region

Green space follows wealth. When greening reaches poorer districts without protection, rents rise, residents are pushed into hotter housing, and the gap grows.

A tenant near a new city park

The new park brings shade and cooler evenings to her street. It also brings higher rents, and she moves to a hotter part of the city with fewer trees than the one she left.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: When Asian cities add parks and trees, do rents rise and do residents move?

See this cycle on the map

The heat credit squeezeEvidence emerging AAAA 6 studies · 1 peer-reviewed · 4 from the region

Heat empties shops and small firms miss repayments. Banks tighten credit, so firms can’t afford to adapt, and the next heatwave hits harder.

The owner of a small corner shop

In a long heatwave, customers stay indoors and sales fall, so she misses a loan repayment. The lender is more cautious next time, and she cannot borrow to buy a cooler or shade for the shop.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: How do small firms and their lenders in Asia respond when a heatwave empties streets and shops?

See this cycle on the map

The invisible-deaths loopEvidence emerging AAAAA 5 studies · 0 peer-reviewed · 5 from the region

Heat deaths go uncounted, so heat protection goes unfunded, so more people die uncounted.

A district health officer

She knows that heat played a part in many deaths this summer, but few were recorded that way. With so few counted, it is hard to make the case for next year’s heat budget.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: How many heat deaths go uncounted, and which ways of counting close the gap?

See this cycle on the map

The farm-debt loopEvidence emerging AAA 3 studies · 3 peer-reviewed · 3 from the region

A failed harvest pushes farmers into debt. Debt leaves less for seed, water and fertiliser, so the next harvest fails more easily.

A wheat farmer before the harvest

A heatwave at the wrong moment shrinks the grain, and the harvest does not cover what he borrowed. With the loan still open, he buys less seed and fertiliser, and the next crop is more fragile.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: When heat cuts a harvest, how often does debt follow, and what helps farmers recover?

See this cycle on the map

The global cooling loopWell established A 2 studies · 0 peer-reviewed · 1 from the region

Cooling powered by fossil fuels adds to the warming that makes us need more cooling.

A shop owner in a fast-growing city

The summers feel longer, so she buys a second air conditioner for the shop. It keeps her customers comfortable, and the power that runs it adds a little more to the warming that made her buy it.

A composite, drawn from the evidence for this cycle. Not a real person.
  • Modelled or projected The Future of Cooling in Southeast Asia International Energy Agency, 2019 · Southeast Asia · Region-wide energy model
    Its limit: A projection to 2040 under stated policies, not a forecast; it changes with efficiency rules.
  • Modelled or projected The Future of Cooling International Energy Agency, 2018 · Global · Global energy model
    Its limit: A projection to 2050 that assumes current trends; better efficiency changes it.

See this cycle on the map

The dry-soil loopWell established 1 study · 1 peer-reviewed · 0 from the region

Heat dries the soil. Dry soil can’t cool itself, so the land heats up faster.

A farmer on rain-fed land

After weeks without rain, the soil in his fields cracks and the afternoons feel hotter than they used to. Without moisture to cool it, the ground bakes faster each day, and the next dry spell starts sooner.

A composite, drawn from the evidence for this cycle. Not a real person.

See this cycle on the map

The wildfire loopWell established A 2 studies · 0 peer-reviewed · 1 from the region

Heat dries forests into fuel. Fires release carbon and strip away the trees that cool the land.

A forest guard in the dry season

The undergrowth he walks through each morning is drier than it used to be. When a fire comes, it takes the trees that kept the valley cool, and the land beneath them dries out further.

A composite, drawn from the evidence for this cycle. Not a real person.

See this cycle on the map

The melting-ice loopWell established A 2 studies · 1 peer-reviewed · 1 from the region

Heat melts ice. Darker ground and water absorb more sunlight, and the melting speeds up.

A herder high in the mountains

The snowfield her family has used for generations shrinks a little each year. The bare rock that replaces it holds the sun’s heat, and the edge of the ice retreats faster than she remembers.

A composite, drawn from the evidence for this cycle. Not a real person.

See this cycle on the map

The energy–water loopWell established AA 2 studies · 0 peer-reviewed · 2 from the region

Water systems need power and power plants need water. In a heatwave, each failure deepens the other.

A water-pump operator on the city’s edge

During a heatwave the power fails, so the pumps stop and taps run dry. Meanwhile the power station upstream is short of water to cool itself, and the cuts come more often.

A composite, drawn from the evidence for this cycle. Not a real person.

See this cycle on the map

The cooling trapWell established AA 4 studies · 1 peer-reviewed · 2 from the region

Air conditioning heats the street, and a hotter city needs even more air conditioning.

A street vendor in a dense neighbourhood

Air conditioners hum above her stall, blowing their heat into the lane where she works. The hotter the lane gets, the more of them switch on, and the afternoon becomes harder to bear.

A composite, drawn from the evidence for this cycle. Not a real person.
  • Modelled or projected Excess heat from air conditioners causes higher nighttime temperatures Salamanca et al., Journal of Geophysical Research, 2014 (summary by Arizona State University) · Phoenix, United States · One city, simulated heatwave
    Its limit: A desert city outside Asia; the size of the effect in humid Asian cities is not measured here.
  • Modelled or projected The Future of Cooling International Energy Agency, 2018 · Global · Global energy model
    Its limit: A projection to 2050 that assumes current trends.
  • Official and agency Beating the Heat: Tamil Nadu Heat Mitigation Strategy Tamil Nadu State Planning Commission, 2024 · Chennai and Tamil Nadu, India · State-wide, satellite land surface temperature
    Its limit: Land surface temperature, not the air temperature people breathe; the two differ.
  • Peer-reviewed Cooling Singapore: digital urban climate twin Cooling Singapore, citing Chow and Roth, 2006 · Singapore · City-wide measurements
    Its limit: The 7 °C is a maximum on calm, clear nights, not a typical night.

See this cycle on the map

The groundwater loopWell established AA 2 studies · 1 peer-reviewed · 2 from the region

Dry fields need more water, so farmers pump harder, aquifers fall and the shortage deepens.

A smallholder with a borewell

As the fields dry, he pumps for longer each season. His neighbours do the same, the water table drops, and the well has to be dug deeper just to keep the crop alive.

A composite, drawn from the evidence for this cycle. Not a real person.
  • Modelled or projected Groundwater extraction may drown mega-delta Minderhoud et al., Environmental Research Communications, 2020 · Mekong delta, Vietnam · Delta-wide model
    Its limit: Sinking rates vary across the delta; the top rate is not everywhere.
  • Peer-reviewed Satellite-based estimates of groundwater depletion in India Rodell, Velicogna and Famiglietti, Nature, 2009 · Rajasthan, Punjab and Haryana, India · Three states, 2002–2008
    Its limit: An older period; it measures water lost, not the heat link itself.

See this cycle on the map

The poverty–heat trapWell established AAA 6 studies · 1 peer-reviewed · 3 from the region

People who can’t afford to stop working fall ill. Illness costs income, and lost income makes stopping even less affordable.

A day-wage construction worker

He knows the midday sun is dangerous, but stopping means losing a day’s pay. When the heat makes him ill, he loses several days instead, and the next week he cannot afford to rest at all.

A composite, drawn from the evidence for this cycle. Not a real person.

Open question: Which protections lower heat risks in pregnancy in South and Southeast Asia: rest and lighter work, cooler homes, antenatal advice, or cash that lets women stop work?

See this cycle on the map

The sleepless-nights loopWell established AAA 5 studies · 2 peer-reviewed · 3 from the region

Hot nights wreck sleep. Poor sleep frays mental health, and stress makes sleep harder still.

A garment worker on night shifts

Her room never cools down, even after midnight, so she sleeps in short, restless stretches. Tired and anxious, she finds sleep harder to come by, and each night feels longer than the last.

A composite, drawn from the evidence for this cycle. Not a real person.

See this cycle on the map

Stronger evidence, little funding traced

For each action that breaks cycles: on the left, how many solutions in our library have been measured in a study or independently evaluated; on the right, how many pieces of funding we traced. Our funding trace covers public announcements, mostly investment in businesses; public budgets, which pay for much of this work, are not in it. So a short bar on the right means we have not traced funding, not that none exists.

Measured or evaluated solutionsActionPieces of funding traced
29Cool by design5
28Affordable cooling for the poorest4
27Cool, affordable housing4
14Clean, efficient cooling40
8Keep city trees aliveStronger evidence, little funding traced1
8Heat action plans3
7Keep water in the soilStronger evidence, little funding traced0
7Green, cool citiesStronger evidence, little funding traced1
6Heat-safe workStronger evidence, little funding traced0
6Green without pushing people outStronger evidence, little funding traced1
5Dedicated heat budgetsStronger evidence, little funding traced0
5Cool nights and support8
3Cooling centres and check-insStronger evidence, little funding traced0
3Heat-ready health services33
2Income protection in heatwaves2
2Anticipatory action5
1Smart irrigation and groundwater rules0
1Social protection floors0
1Count every heat death3
1Keep children in school4
1Heat-smart lending5
1Crop insurance and fair credit17
0Free care for heat illness0
0Shared risk pools2
0Backup power for water8

Not shown, because our library has no solution or funding for them yet: Deep emission cuts, Cut black carbon, Fire-smart landscapes, Power that doesn’t need water, Heat-safe pregnancy and newborn care, Mental health in heat plans, Violence prevention in heat planning, Safe water and rehydration for young children. The solutions library · Follow the money

Questions nobody has answered yet

A learning agenda, drawn from the limits the studies above state about themselves. Each question is sized so that one well-designed study could move it. The suggested approach and scale are ours, offered for discussion; researchers and funders closer to each place will know better.

Five of these questions, on pregnancy, newborns, children, mental health and violence against women, are set out with their evidence in a citable brief: Heat and the health of mothers, children and minds.

  1. The overwhelmed-clinic loop · Uncertain

    How much of the load on clinics in South and Southeast Asia during a heatwave is heat illness, and which early actions lower it?

    What we have
    A global health assessment that does not give Asia’s share, and one before-and-after evaluation in Ahmedabad where other changes may explain part of the effect. The studies
    What could answer it (our suggestion)
    Compare clinic records across hot seasons in cities with and without early-warning plans.
    Scale
    Two or three cities, two seasons

  2. The invisible-deaths loop · Uncertain

    How many heat deaths go uncounted, and which ways of counting close the gap?

    What we have
    Official counts that rise partly because reporting improves, and part-season counts that show the gap but not the true toll. The studies
    What could answer it (our suggestion)
    Compare excess deaths with recorded heat deaths in a few districts, and test simple reporting changes.
    Scale
    A few districts, one or two seasons

  3. The reactive-spending loop · Uncertain

    Does money spent on prevention before summer reduce what is spent during heatwaves?

    What we have
    One modelled estimate for Bangkok, multi-hazard estimates, and a review of heat plans as they stood in 2023. The studies
    What could answer it (our suggestion)
    Track what a city spends before and during heatwaves over several seasons, with its health and work outcomes.
    Scale
    One or two cities, three seasons

  4. The medical-debt trap · Uncertain

    How often does heat illness lead households to borrow, and how much?

    What we have
    Studies of household debt that do not measure heat’s part, and an older national survey of all medicine costs. The studies
    What could answer it (our suggestion)
    Follow households through a hot season with a short monthly survey of illness, costs and loans.
    Scale
    Two countries, one season

  5. The heat credit squeeze · Uncertain

    How do small firms and their lenders in Asia respond when a heatwave empties streets and shops?

    What we have
    Evidence from rich economies and from Mexico, an industry statement naming heat among several causes, and one self-reported survey of vendors in Delhi. The studies
    What could answer it (our suggestion)
    With willing lenders, compare microfinance repayments against daily heat records.
    Scale
    Two or three lenders, two seasons

  6. The energy-poverty trap · Uncertain

    Who cannot afford to keep cool, measured directly rather than estimated?

    What we have
    A global model that estimates the risk of lacking cooling from income, power and heat data. The studies
    What could answer it (our suggestion)
    Add a few cooling questions to an existing national household survey.
    Scale
    One country, one survey round

  7. The lost-schooling loop · Uncertain

    How much learning do children lose in hot classrooms and heat closures in Asia?

    What we have
    Strong evidence from schools in the United States, and counts of closures in Asia that measure days lost rather than learning lost. The studies
    What could answer it (our suggestion)
    Compare learning results with classroom temperatures over a school year.
    Scale
    One country, one school year

  8. The farm-debt loop · Uncertain

    When heat cuts a harvest, how often does debt follow, and what helps farmers recover?

    What we have
    A debated national association, and studies from single sites or single crops. The studies
    What could answer it (our suggestion)
    Follow farm households across seasons, linking heat to yields, loans and recovery.
    Scale
    Two regions, three seasons

  9. The green-displacement loop · Uncertain

    When Asian cities add parks and trees, do rents rise and do residents move?

    What we have
    A multi-city study with no Asian cities, mostly US reviews, and one qualitative study in Bangkok. The studies
    What could answer it (our suggestion)
    Track rents and who lives where around new green spaces, before and after.
    Scale
    Two cities, three years

  10. The dying-green loop · Uncertain

    Which street trees in humid Asian cities survive repeated heatwaves, and what care keeps them alive?

    What we have
    Tree-loss figures from Berlin, and a global comparison of species’ natural climate ranges. The studies
    What could answer it (our suggestion)
    Survey street-tree survival after each hot season, with watering and care records.
    Scale
    Two cities, three seasons

  11. The displacement loop · Uncertain

    Does heat, on its own, push people to move within Asian countries, and where do they land?

    What we have
    Worst-case scenarios to 2050 that cover every climate driver together, not heat alone. The studies
    What could answer it (our suggestion)
    Link existing migration surveys with local heat records.
    Scale
    One or two countries

  12. The protection-gap loop · Uncertain

    How large are uninsured losses from heat, and could money arranged in advance narrow the gap?

    What we have
    Figures for all natural catastrophes together, and a qualitative regional review. The studies
    What could answer it (our suggestion)
    Estimate uninsured heat losses for one sector in one country, and test a pre-arranged payout design.
    Scale
    One sector, one country

  13. The poverty–heat trap · Uncertain

    Which protections lower heat risks in pregnancy in South and Southeast Asia: rest and lighter work, cooler homes, antenatal advice, or cash that lets women stop work?

    What we have
    A review of 70 studies in 27 countries, only seven of them low- or middle-income, and one cohort of 800 working women in Tamil Nadu; none tests what reduces the risk. The studies
    What could answer it (our suggestion)
    Add heat exposure and simple protections to antenatal records in a few districts, and compare outcomes across hot seasons.
    Scale
    Two or three districts, two to three years

  14. The overwhelmed-clinic loop · Uncertain

    How hot do labour wards and newborn units get in a heatwave, and what keeps them safe when the power fails?

    What we have
    A WHO, UNICEF and UNFPA call to action that names heat among the risks to mothers and newborns, and no measurements from facilities in the region that we have found. The studies
    What could answer it (our suggestion)
    Log indoor temperatures and power cuts in a sample of facilities through one hot season, alongside any cooling and back-up power they have.
    Scale
    Twenty to thirty facilities, one season

  15. The farm-debt loop · Uncertain

    Beyond farm households in India, how does heat affect self-harm and suicide across South and Southeast Asia, and does income support in bad seasons reduce it?

    What we have
    One national study of India over 47 years linking heat in the growing season to suicides through crop losses; little from cities or other countries. The studies
    What could answer it (our suggestion)
    Link daily temperatures with suicide and self-harm records where they exist, and study districts where crop insurance or cash reached households in bad years.
    Scale
    Two or three countries, existing records

  16. The poverty–heat trap · Uncertain

    Why is heat linked to more intimate partner violence in South Asia, and do income support, cooler homes or women’s groups weaken the link?

    What we have
    A cross-sectional study of 194,871 women in India, Nepal and Pakistan, using yearly temperatures; it shows an association, not the reasons for it. The studies
    What could answer it (our suggestion)
    Add heat and household strain questions to existing violence surveys, and compare places with and without seasonal income support.
    Scale
    Existing surveys, with a qualitative study in a few districts

  17. The poverty–heat trap · Uncertain

    How much does heat add to diarrhoea and undernutrition in young children in the region, and how much do safe water and oral rehydration offset it?

    What we have
    A review of 26 studies finding about 7% more diarrhoea per 1 °C, uneven across regions and with signs of publication bias. The studies
    What could answer it (our suggestion)
    Combine clinic records of child diarrhoea with temperature and water-supply data in a few towns over several seasons.
    Scale
    Three to five towns, three seasons

  18. The reactive-spending loop · Uncertain

    How do heat-health pilots in Southeast Asia keep their institutional footing once their first funding ends?

    What we have
    A funder’s own account of the region notes that successful pilots often lose their institutional footing once funding ends. The studies
    What could answer it (our suggestion)
    Follow a handful of heat-health pilots for two years after their first funding, recording who kept which part going and why.
    Scale
    Five to eight pilots, two years

Know of a study that answers one of these, or a better question? Tell us, and we will add it with credit.

The weekly evidence review

This map keeps growing. Each week, a harvest asks open research services for new studies on heat and health, passive cooling and heat finance in South and Southeast Asia: Europe PMC (which includes PubMed and preprints), Crossref (including SSRN, World Bank and ADB papers), arXiv, OpenAlex (including university repositories), the World Bank’s document library and WHO’s repository. Studies set in the region that report new data are queued, with their sample size, place, climate zone, effect size, unit cost and shortcomings copied from the abstract where the abstract states them.

Nothing reaches this map until a reviewer has read the study, written its finding in their own words, graded it and chosen the cycle it speaks to. The first reviewed studies will appear in their cycles above, marked as added in the weekly review. Studies that were queued but not added are not judged here: many are simply outside what this map covers.

How we graded

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How sure are we?

One thing worth sharing with a colleague

How sure we are, cycle by cycle: 66 studies graded by kind, where evidence looks stronger than the funding we traced, and 18 questions nobody has answered yet.

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