The web of extreme heat: every consequence, system by system

How extreme heat ripples through 10 systems: 90 consequences and the links between them, each with its evidence.

Extreme heat: where every cycle starts

Extreme heat is where every cycle on this map starts, and it is no longer only weather. Climate change is already making Asia’s hottest days more frequent.

Summer 2026, June to August

• 1.5 billion+ people worldwide had at least 30 days of risky heat added by climate change.
• 117 million of them were in India, the most of any country, followed by China (94 million) and Indonesia (83 million).
• 2.8 billion people in Asia, 58% of its population, lived through at least 30 days of risky heat.

A risky heat day is hotter than 90% of the days recorded in that place from 1991 to 2020. Source: Climate Central, Risky heat added by climate change: June to August 2026. Today’s scores: Climate Shift Index map, Climate Central.

Nature and ecosystems

Heat dries land, burns forests, melts ice and warms the sea, wearing down the ecosystems that feed, water and shelter us.

Droughts

Higher temperatures speed up evaporation, so the same rain goes less far and dry spells turn into droughts.

Leads to: Wildfires (Parched land and vegetation burn more easily.); Water shortages (Rivers, wells and reservoirs fall.); Failing harvests (Crops fail without water.); Livestock losses (Less water and fodder for animals.); Wildlife moves into farms and villages (Animals leave parched forests in search of water and food.); City trees and parks die (Trees with no water or root space die in long dry spells.)

Sources: IPCC, AR6 Working Group I, Summary for Policymakers, 2021

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Wildfires

Hot, dry vegetation ignites more easily and burns longer, sending smoke far beyond the fire itself.

Leads to: Smoke, smog and ozone (Smoke travels hundreds of kilometres from the fire.); Glacier and snow melt (Soot settling on snow and ice darkens it, so it absorbs more sunlight and melts faster.); Extreme heat (Fires release carbon and strip away tree cover that shades and cools the land.)

Sources: UNEP and GRID-Arendal, 2022: Spreading like wildfire

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Forest dieback

Heat and drought stress trees until they stop growing, then die, turning forests from shade and carbon stores into fuel.

Leads to: Wildfires (Stressed and dying trees become fuel.); Biodiversity loss (Habitats disappear with the trees.); Wildlife moves into farms and villages (Dying forests offer less food and shelter, pushing animals out.)

Sources: Hammond et al., Nature Communications, 2022: a hotter-drought fingerprint for tree die-off

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Drying soils

Heat pulls moisture from the ground when crops and plants need it most.

Leads to: Failing harvests (Moisture vanishes just when crops need it most.); Extreme heat (Dry soil can’t cool itself by evaporation, so more of the sun’s energy becomes heat.)

Sources: Seneviratne et al., Earth-Science Reviews, 2010

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Glacier and snow melt

Mountain glaciers and snowpacks that feed rivers through the dry season are shrinking.

Leads to: Water shortages (Rivers fed by snow and ice run lower in the dry season.); Hydropower falls (Less meltwater reaches the dams.); Extreme heat (Melting snow and ice expose darker ground and water, which absorb more sunlight.); Glacial lake outburst floods (Meltwater pools behind unstable moraines.)

Sources: ICIMOD, 2023: glacier loss in the Hindu Kush Himalaya

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Glacial lake outburst floods

As glaciers retreat, meltwater pools behind loose rock and ice. When a bank gives way the lake can empty in hours. In October 2023 Sikkim’s South Lhonak lake burst after a frozen moraine collapsed into it; the flood breached the Teesta III dam, set off 45 landslides and cut the national highway. Climate change played a key role, and the lake can burst again.

Leads to: Roads, rails and runways strained (A burst lake sweeps away bridges and highways.); Hydropower falls (Floods breach dams and wreck power stations downstream.); Heat deaths (Floodwater arrives with little warning.)

Sources: ICIMOD, 2025: climate change played key role in the 2023 Sikkim lake outburst · Sattar et al., Science, 2025: the Sikkim flood of October 2023

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Marine heatwaves and coral bleaching

Ocean heatwaves bleach coral and drive fish away from the waters people depend on. The 2023–2025 global bleaching event, the worst on record, reached 84% of the world’s reefs in 82 countries and territories. In Malaysia more than half of all corals bleached in 2024.

Leads to: Fisheries decline (Fish move away from warming water, and dying reefs support fewer of them.)

Sources: NOAA and International Coral Reef Initiative, reported by Scientific American, 2025 · Earth Observatory of Singapore: field data from Asia’s coral reefs

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Biodiversity loss

Species that can’t move or adapt fast enough decline, weakening pollination, soils and fisheries.

Leads to: Failing harvests (Fewer pollinators and natural pest-eaters mean lower yields.)

Sources: IPCC, AR6 Working Group II fact sheet: biodiversity, 2022

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Wildlife moves into farms and villages

As water and forage dry up, animals leave forests for farms and villages. Crops are raided, people and animals are hurt, hunting for food rises, and closer contact raises the risk of diseases passing from animals to people. In Assam, villagers have grown paddy just for wild elephants, so the herds leave the main harvest alone.

Leads to: Failing harvests (Elephants, wild boar and other animals raid crops.); Infectious diseases spread (Closer contact between people, livestock and wild animals raises the risk of diseases crossing over.); Injuries and accidents rise (Encounters injure and kill people and animals.)

Sources: Abrahms et al., Nature Climate Change, 2023: climate change amplifies human–wildlife conflict · Mongabay India, 2023: Assam farmers grow paddy for wild elephants · Tamil Nadu State Planning Commission, Beating the Heat: Tamil Nadu Heat Mitigation Strategy, 2024

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Food and agriculture

Crops, animals, fisheries and the people who work them all have heat limits. Cross them and food gets scarcer and dearer.

Failing harvests

Heat during flowering and grain-filling cuts yields of staple crops, even when there is enough rain. Smallholders farming on rain alone, with no irrigation or savings to fall back on, are hit first.

Leads to: Food price spikes (Smaller harvests push up prices.); Farmers fall into debt (A failed season leaves farmers borrowing to eat and to replant.); Suicides rise (When heat ruins crops, farm incomes fall, and suicides rise in the growing season.)

Sources: Lobell, Sibley and Ortiz-Monasterio, Nature Climate Change, 2012 (wheat in India) · Peng et al., PNAS, 2004 (rice in the Philippines)

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Livestock losses

Heat-stressed animals eat less, produce less milk and eggs, fall ill and die.

Leads to: Hunger and malnutrition (Less milk, eggs and meat for families who rely on them.)

Sources: Eco-Business: climate stress is trampling productivity in India’s livestock sector

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Farmwork hours lost

Farm labourers work in the open sun. In the hottest hours, work becomes dangerous or impossible.

Leads to: Failing harvests (Fields go untended in the hottest hours.); Lost work hours and wages (Farm labourers lose daily wages.)

Sources: International Labour Organization, 2019: agriculture bears 60% of working hours lost to heat

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Pests and crop diseases spread

Warmer conditions let many pests and plant diseases breed faster and spread to new areas.

Leads to: Failing harvests (More pests and plant diseases mean more crops lost.)

Sources: Deutsch et al., Science, 2018, summarised by the University of Washington: crop losses to insect pests rise 10–25% per degree

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Fisheries decline

As waters warm and reefs die, fish move away or decline, and catches fall. Coastal and riverside families who live from fishing lose food and income together.

Leads to: Hunger and malnutrition (Coastal families lose a vital source of protein and income.)

Sources: Free et al., Science, 2019: warming has already cut fisheries productivity, by 15–35% in five regions including East Asian seas

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Food spoils faster

Without cool storage, more of every harvest rots between field and plate.

Leads to: Food price spikes (Losses after harvest push up prices.); Diarrhoea in young children (Food that spoils in the heat makes children ill.)

Sources: UNEP and FAO, 2022: Sustainable Food Cold Chains (526 million tonnes of food lost for lack of refrigeration)

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Food price spikes

Smaller harvests and losses push up prices, felt hardest by families who spend most of their income on food. A study with the European Central Bank found that hot extremes keep food inflation higher for about a year afterwards, and a 2025 study traced 16 food price shocks since 2022 to extreme weather.

Leads to: Hunger and malnutrition (The poorest spend most of their income on food.); Informal workers can’t stop work (Higher prices make it even harder to stop working.)

Sources: Carbon Brief, 2025: 16 times extreme weather drove higher food prices (on Kotz et al., Environmental Research Letters) · Inside Climate News, 2025: weather extremes are driving up food prices

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Hunger and malnutrition

When food costs more and incomes fall, families eat less and less well, and children suffer most.

Leads to: Learning suffers in hot classrooms (Hungry children struggle to learn.); Babies and young children at risk (Underfed babies and children have less reserve to survive heat and illness.)

Sources: Lancet Countdown 2024, summarised by Wellcome: heatwaves and droughts linked to 151 million more people facing food insecurity

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Farmers fall into debt

After a failed season, farmers borrow at high interest or sell livestock, land and seed to get by.

Leads to: Failing harvests (Indebted farmers cut back on seed, water and fertiliser, so the next harvest fails more easily.); Forced migration (When debts can’t be repaid, families leave the land to look for work.); Loan repayments slip (Failed harvests leave farm loans unpaid.)

Sources: Carleton, PNAS, 2017 · King’s College London, 2023: microfinance and climate shocks in Cambodia

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Water

Heat raises the demand for water just as it shrinks the supply, and lowers its quality.

Water shortages

Taps run dry and wells fall just as people, crops and animals need more water to cope with the heat.

Leads to: Longer trips to fetch water (Taps run dry, so someone has to fetch water.); Sanitation and hygiene fail (Without water, sanitation and hygiene fail.); Competition for water (Farms, cities and power plants compete for what is left.); Irrigation demand soars (Dry fields need more irrigation.); Power plants cut output (Power plants need cool water. When rivers run low or warm, they cut output.); City trees and parks die (When water runs short, watering trees and parks is cut first.); Buying water from tankers (When taps run dry, people buy water by the tanker.)

Sources: World Resources Institute: Day Zero lessons from Cape Town and Chennai

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Buying water from tankers

When the taps run dry, households buy water from private tankers, and prices jump as wells fail. Those beyond the pipes, often the poorest, pay the most or go without. In one Bengaluru informal settlement a family earning about Rs 6,000 a month paid around Rs 1,300 for water. When Chennai’s reservoirs ran dry in 2019, tankers could not reach most of its slums.

Leads to: Deepening inequality (The poorest pay the most for each litre, or go without.); Sanitation and hygiene fail (Costly water means less for washing and toilets.)

Sources: Citizen Matters: water access a daily struggle for Bengaluru’s slum dwellers · World Resources Institute: responding to Day Zero equitably, Cape Town and Chennai

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Water quality falls

Warm, low water breeds algae and bacteria and concentrates pollution.

Leads to: Infectious diseases spread (Contaminated water spreads disease.); Diarrhoea in young children (Warm, low water lets bacteria multiply.)

Sources: Review in International Journal of Environmental Research and Public Health, 2022: cyanobacteria gain the advantage above 20 °C

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Irrigation demand soars

Hot, dry fields need far more water to keep crops alive.

Leads to: Groundwater over-pumped (Farmers pump harder and deeper to keep crops alive.)

Sources: Rodell, Velicogna and Famiglietti, Nature, 2009

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Groundwater over-pumped

Farmers and cities pump deeper and harder, draining aquifers faster than rain can refill them.

Leads to: Water shortages (Aquifers fall and wells run dry.)

Sources: Rodell, Velicogna and Famiglietti, Nature, 2009

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Competition for water

Farms, cities, industry and power plants all compete for a shrinking supply.

Leads to: Conflict over water and land (Scarce water becomes a source of conflict.)

Sources: World Resources Institute, 2018: 40% of India’s thermal power plants are in water-scarce areas

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Longer trips to fetch water

Where taps fail, someone has to walk further, for longer, in the heat, to bring water home.

Leads to: Care burden falls on women and girls (Fetching water falls mostly on women and girls.); Children pulled out of school (Girls miss school to fetch water.); Violence against women rises (Longer trips for water, often alone, expose women and girls to harassment and assault.); Risks in pregnancy (Carrying water far in the heat adds strain to a pregnancy.)

Sources: UNICEF, 2016: women and girls spend 200 million hours a day collecting water

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Sanitation and hygiene fail

Without enough water, toilets, handwashing and cleaning suffer.

Leads to: Infectious diseases spread (Poor hygiene spreads diarrhoea and other infections.); Babies and young children at risk (Diarrhoea from unsafe water is most dangerous for the youngest children.); Diarrhoea in young children (Without clean water and handwashing, children catch diarrhoea more easily.)

Sources: ACAPS, 2017: Sindh heatwave briefing (more use of unprotected water sources)

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Energy

Heat drives up demand for cooling while cutting the ability of power plants and grids to supply it.

Cooling demand peaks

As temperatures climb, so does the demand for fans and air conditioning, pushing electricity use to new peaks.

Leads to: Power cuts and grid stress (Peak demand pushes grids to the limit.); Emissions from cooling rise (Most cooling still runs on fossil-fuelled power.); Urban heat islands (Air conditioners pump heat outdoors, warming the streets around them.); Can’t afford to keep cool (Higher bills push poor households into energy poverty.)

Sources: International Energy Agency, 2018: The Future of Cooling · International Energy Agency: The Future of Cooling in Southeast Asia

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Power cuts and grid stress

Peak demand and heat-stressed lines and transformers push grids to the edge. Outages switch off cooling when it matters most.

Leads to: Diesel generators run longer (Outages drive those who can afford it to diesel.); Cold chains break (Without power, fridges for food and vaccines fail.); Health systems overwhelmed (Hospitals and clinics lose cooling and equipment when the power fails.); Water shortages (Without power, pumps and treatment plants stop.); Phone and data networks fail (Phone masts and networks fail when the power does.); Small businesses close (Shops and workshops lose power and stock.)

Sources: World Bank estimate, reported by AFP via The Manila Times, 2023: Vietnam’s heat-driven power crisis

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Power plants cut output

Coal, gas and nuclear plants need cool water. When rivers run low or warm, they have to produce less.

Leads to: Power cuts and grid stress (Plants cut output just when demand peaks.)

Sources: World Resources Institute, 2018

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Hydropower falls

Low rivers and reservoirs mean less electricity from dams.

Leads to: Power cuts and grid stress (Low reservoirs mean less electricity.)

Sources: World Bank estimate, reported by AFP via The Manila Times, 2023: Vietnam’s reservoirs ran low

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Diesel generators run longer

When the grid fails, homes, shops and hospitals that can afford it switch to diesel.

Leads to: Emissions from cooling rise (Diesel adds still more emissions.); Smoke, smog and ozone (Generators fill streets with fumes.)

Sources: IFC, 2019: The Dirty Footprint of the Broken Grid (20–30 million back-up generator sites)

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Emissions from cooling rise

Most cooling still runs on fossil-fuelled power and refrigerants that warm the planet.

Leads to: Extreme heat (Emissions add to the warming that drives demand for cooling.)

Sources: International Energy Agency, 2018: The Future of Cooling

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Can’t afford to keep cool

For the poorest households, fans, cooling and electricity bills are out of reach.

Leads to: Heatstroke and heat exhaustion (With no way to cool down at home, heat builds up in the body.)

Sources: Sustainable Energy for All, 2023: Chilling Prospects

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Cold chains break

Without reliable power, fridges for food, medicines and vaccines fail.

Leads to: Food spoils faster (Food rots without refrigeration.); Infectious diseases spread (Spoiled vaccines leave people unprotected.)

Sources: UNEP and FAO, 2022: Sustainable Food Cold Chains

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Cities and infrastructure

Concrete, crowding and ageing infrastructure turn cities into amplifiers of heat.

Urban heat islands

Dense surfaces, little shade and waste heat keep city cores several degrees hotter than their surroundings, especially at night. This is the urban heat island effect.

Leads to: Cooling demand peaks (A hotter city needs even more cooling.); Sleepless hot nights (Cities hold their heat overnight.); City trees and parks die (Hotter streets stress trees further; many city species are already past their heat limits.)

Sources: Cooling Singapore, citing Chow and Roth, 2006 · Tamil Nadu State Planning Commission, 2024

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Homes that trap heat

Tin roofs, poor ventilation and crowded rooms can make homes hotter inside than out, leaving nowhere safe to rest. Thin roofs cool slowly, so the worst comes at night: in low-income homes measured across South Asia, tin-roofed houses stayed warmer indoors than the outdoor air.

Leads to: Heatstroke and heat exhaustion (With no cool place to recover, heat builds up day after day.); Deepening inequality (Hot homes cost sleep, health and earnings, so the gap widens.); Sleepless hot nights (Rooms stay hot all night.); Violence against women rises (Crowded, hot homes may raise tension inside them.)

Sources: Frontiers in Built Environment, 2022: Ahmedabad informal settlements up to 7.6 °C hotter · Tasgaonkar et al., Scientific Data, 2022: indoor heat in low-income homes in South Asia

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Roads, rails and runways strained

Rails buckle, roads soften and hot, thin air means planes need longer runways or must carry less.

Leads to: Transport disrupted (Buckled rails and softened roads slow everything down.); Public budgets strained (Repairs drain public budgets.)

Sources: Coffel, Thompson and Horton, Climatic Change, 2017, via NASA: rising temperatures and aircraft take-off · Network Rail: buckled rails in summer heat

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Transport disrupted

Speed limits, cancellations and breakdowns slow the movement of people and goods.

Leads to: Supply chains disrupted (Goods stop moving.)

Sources: Network Rail: heat speed restrictions · World Bank estimate, reported by AFP via The Manila Times, 2023

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Smoke, smog and ozone

Heat speeds up the chemistry that forms ground-level ozone, and still, hot air traps pollution and smoke.

Leads to: Breathing problems worsen (Ozone and smoke inflame the lungs.)

Sources: Air Quality News, 2026: heatwaves drive dangerous ozone pollution across India (npj Clean Air study)

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Streets and parks unusable

Markets, streets and parks become too hot to use in the middle of the day.

Leads to: Small businesses close (Street trade and markets empty out.); Older people isolated at home (People stay indoors and alone.); Customers stay home (When streets are too hot to walk, shoppers stay away.)

Sources: Greenpeace India and National Hawkers Federation, 2024 · WIEGO and HomeNet Thailand, 2025

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City trees and parks die

Heat, drought and missing upkeep kill street trees and parks just when their shade is needed. Across 164 cities, 56% of urban tree and shrub species already face temperatures beyond those in their natural range, and in hot cities such as New Delhi and Singapore every species studied is at risk.

Leads to: Urban heat islands (Fewer trees means less shade and less evaporative cooling, so streets heat up.)

Sources: Esperon-Rodriguez et al., Nature Climate Change, 2022: climate change increases global risk to urban forests · Hansen et al., chapter 10 in Nature-Based Solutions for Cities, 2023: more than 500 of 870 new trees died in a Berlin park

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Green space follows wealth

Trees and parks cluster in better-off neighbourhoods, which can pay for them and for the upkeep that keeps them alive, so poorer districts stay hotter.

Leads to: Urban heat islands (Neighbourhoods with little green run hotter.); Greening pushes people out (When greening finally reaches the least green, cheapest districts as a property upgrade, without protection for tenants, rents rise.)

Sources: Wolch, Byrne and Newell, Landscape and Urban Planning, 2014: making cities “just green enough” · Hansen et al., chapter 10 in Nature-Based Solutions for Cities, 2023: tree survival tracks municipal budgets in Santiago

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Phone and data networks fail

Overheating equipment and power cuts take down phone masts, networks and data centres.

Leads to: Emergency services stretched (Warnings and calls for help don’t get through.); Help can’t reach remote places (Without a phone signal, heat warnings may not reach the last village.)

Sources: Asia News Network, 2026: Bangladesh’s mobile signals weaken as blackouts spread

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Health

The human body has limits. Heat strains the heart, kidneys, lungs and mind, and the services built to care for them.

Heat deaths

Extreme heat kills, often quietly, through failing hearts, kidneys and lungs. Europe’s 2003 heatwave alone is estimated to have caused more than 70,000 deaths.

Leads to: Heat deaths under-recorded (Most heat deaths are recorded as heart, kidney or lung failure.); Deepening inequality (Families lose breadwinners and carers.)

Sources: Robine et al., Comptes Rendus Biologies, 2008: death toll exceeded 70,000 in Europe in summer 2003

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Heatstroke and heat exhaustion

When the body can no longer cool itself, heat exhaustion can tip into heatstroke: a medical emergency that can kill. India’s suspected heatstroke cases rose more than tenfold in two summers, from 4,481 in 2022 to over 48,000 in 2024. Humid heat is the most dangerous: when the wet-bulb temperature is high, sweat stops cooling the body.

Leads to: Heat deaths (Heatstroke kills if it is not treated quickly.); Health systems overwhelmed (Heat illness brings sudden surges of patients.); Lost work hours and wages (Illness means days off work, and for daily earners no work means no pay.); Medical costs and debt (Treatment and lost days are paid for out of pocket.)

Sources: Ministry of Health and Family Welfare, reply in India’s Rajya Sabha, 6 August 2024

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Kidney and heart strain

Sweating and dehydration make the heart work harder and can damage the kidneys, especially with repeated exposure.

Leads to: Heat deaths (Many heat deaths are heart and kidney failures.)

Sources: Kidney International Reports, 2023: heat stress and kidney health in Tamil Nadu salt-pan workers

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Breathing problems worsen

Ozone, smoke and hot air inflame airways and worsen asthma and lung disease.

Leads to: Heat deaths (Breathing problems turn fatal in the heat.)

Sources: Air Quality News, 2026: heat-driven ozone and health in India

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Risks in pregnancy

Each 1 °C rise in temperature raises the odds of preterm birth by about 5%, and a heatwave by about 16%; stillbirths rise by about 5% for each 1 °C, and the risks are largest for poorer women and at the youngest and oldest ages. Women who keep working outdoors or fetching water while pregnant carry the most risk: in a Tamil Nadu study of 800 pregnant women doing physical work, those with high workplace heat had about twice the risk of miscarriage. In Bangladesh, the extreme-heat days a pregnancy passes through rose from about 4 for births in 2018 to about 30 for births in 2024.

Leads to: Health systems overwhelmed (Complications add to the load on maternity care.); Babies and young children at risk (Babies born early or small are more fragile in the heat.); Mental health suffers (Heat in pregnancy adds stress and anxiety, known risks for the birth.)

Sources: Chersich et al., BMJ, 2020: systematic review and meta-analysis of 70 studies in 27 countries · Rekha et al., BJOG, 2023: occupational heat and pregnancy outcomes in 800 women workers, Tamil Nadu · Preprint, not yet peer reviewed: prenatal extreme heat and newborn deaths in Bangladesh, 2015–2025 (medRxiv, 2026) · WHO, UNICEF and UNFPA, 2023: Protecting maternal, newborn and child health from the impacts of climate change

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Babies and young children at risk

Babies and small children overheat and dehydrate faster than adults, and can’t say when they are struggling. Heat brings more diarrhoea, malnutrition and hospital visits for the youngest.

Leads to: Care burden falls on women and girls (Sick babies and children need someone at home to look after them, usually their mother.)

Sources: Lancet Countdown 2024, India data sheet: infants faced 7.7 heatwave days a year · WHO, UNICEF and UNFPA, 2023: Protecting maternal, newborn and child health from the impacts of climate change

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Diarrhoea in young children

Warmth lets bacteria multiply in water and food. Across 26 studies, each 1 °C rise in temperature was linked to about 7% more diarrhoea, a leading cause of death in young children. Repeated bouts leave children undernourished.

Leads to: Babies and young children at risk (Repeated diarrhoea leaves young children undernourished and weak.); Health systems overwhelmed (Sick children fill clinics in the hot months.)

Sources: Carlton et al., International Journal of Epidemiology, 2016: temperature and diarrhoeal disease, 26 studies

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Mental health suffers

Heat is linked to more anxiety, distress and suicide, and to worse outcomes for people living with mental illness. Heat in pregnancy adds stress and anxiety, known risks for the birth. In many countries, mental health services are far from meeting the need.

Leads to: Sleepless hot nights (Stress and anxiety make sleep even harder.); Violence and crime rise (Frayed tempers spill over into violence.); Suicides rise (Distress that goes without support can end in self-harm.)

Sources: Thompson et al., The Lancet Planetary Health, 2023, summarised by Imperial College London · WHO, 2022: Mental health and climate change, policy brief · WHO, UNICEF and UNFPA, 2023: Protecting maternal, newborn and child health from the impacts of climate change

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Suicides rise

In India, where one fifth of the world’s suicides occur, a 1 °C rise in a day’s temperature above 20 °C in the growing season was linked to about 70 more suicides, as the same heat cut crop yields. Warming over 30 years is estimated to account for 59,300 suicides. The findings have been debated.

Sources: Carleton, PNAS, 2017: crop-damaging temperatures increase suicide rates in India

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Sleepless hot nights

When nights stay hot, the body has less chance to recover from the day, so the next day can start already depleted.

Leads to: Mental health suffers (Poor sleep wears down mood and the ability to cope.); Heatstroke and heat exhaustion (Without cool nights, the body starts each day already overheated.)

Sources: Minor et al., One Earth, 2022: rising temperatures erode human sleep

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Infectious diseases spread

Warmth helps the mosquitoes that carry dengue breed and bite, and dirty water and spoiled food spread illness. Bangladesh had its worst dengue year on record in 2023: by 30 October, WHO counted 267,680 cases and 1,333 deaths, with the surge starting unusually early.

Leads to: Health systems overwhelmed (Outbreaks add to the caseload.)

Sources: WHO Bangladesh, Dengue Situation Report 10, 30 October 2023 · WHO Disease Outbreak News: dengue in Bangladesh, August 2023

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Injuries and accidents rise

Heat strain can unsteady balance and slow reactions, especially in heavy work in humid heat, so the risk of accidents at work, on the road and at home rises. How much depends on how hot the body gets, the task and the person: at milder strain, some studies find no loss in thinking at all.

Leads to: Health systems overwhelmed (More casualties to treat.); Lost work hours and wages (Injured workers lose income.)

Sources: APN: high temperatures and work-related injuries in Guangzhou, China · Tan et al., Medicine & Science in Sports & Exercise, 2025: humid heat and balance in simulated construction work at height · Tan et al., Journal of Sport and Health Science, 2024: severe heat, brain temperature and executive function · A counterpoint: no loss of executive function or risk-taking at modest heat strain (≤38.5 °C), 28 adults, PubMed Central

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Health systems overwhelmed

Heatwaves bring surges of patients just as staff, power and supplies are under strain.

Leads to: Heatstroke and heat exhaustion (Overstretched services treat people later, and heat illness turns severe fast.)

Sources: Context, 2024: India’s hospitals adapt to killer heat

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Work and economy

Heat slows hands, closes businesses and squeezes the incomes of those with the least margin.

Lost work hours and wages

The International Labour Organization projects that heat stress could cut 2.2% of all working hours worldwide by 2030, the equivalent of 80 million full-time jobs.

Leads to: Informal workers can’t stop work (Lost income leaves even less margin, so the next heatwave has to be worked through too.); Deepening inequality (Lost earnings hurt most where there are no savings to fall back on.); Hunger and malnutrition (Less income means less food.); Violence against women rises (Lost income and stress at home raise the risk of violence against women.); Loan repayments slip (Lost wages make household and microfinance repayments harder.)

Sources: International Labour Organization, 2019: heat stress predicted to cost the equivalent of 80 million jobs

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Informal workers can’t stop work

Without paid leave, contracts or savings, stopping work means losing the day’s income. So people keep working through dangerous heat. About three in four Indian workers, some 380 million people, depend on heat-exposed work. Around 90% of India's workers, and 80% in urban Delhi, work informally.

Leads to: Heatstroke and heat exhaustion (Working through the hottest hours without shade, water or rest raises the risk of heat illness.); Injuries and accidents rise (Fatigue and heat cause accidents.); Care burden falls on women and girls (When workers fall ill, someone has to care for them, usually women.); Risks in pregnancy (Pregnant women who keep doing heavy work in the heat face more miscarriage and early birth.); Hot workplaces without toilets (Many women’s workplaces have no safe toilets.)

Sources: World Bank, 2022, reported by Down To Earth · NIUA Climate Centre for Cities, 2026: Heat Resilient Cities Framework, p. 8, citing WIEGO's statistical profile of informal workers in India

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Hot workplaces without toilets

Heat at work carries a hidden cost for women where there are no safe toilets. In a study of 312 women workers in India, heat exceeded safe limits for 71%; of those with poor or no toilets, 87% reported genitourinary problems, and about 1 in 10 showed heat strain and moderate dehydration.

Leads to: Kidney and heart strain (Dehydration at work strains the kidneys.)

Sources: Venugopal et al., Global Health Action, 2016: heat and inadequate sanitation for 312 women workers in India

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Migrant workers abroad

Millions from Nepal, Bangladesh and the Philippines build and serve in some of the world’s hottest places, and the money they send home holds families and economies together: about a quarter of Nepal’s GDP. Among Nepali workers in Qatar, cardiovascular deaths rose with the summer heat, and as many as 200 of 571 such deaths in 2009–2017 could have been prevented with heat protection.

Leads to: Heat deaths (Heat strain kills workers far from home.); Lost work hours and wages (When a worker falls ill or dies, the money home stops.)

Sources: Pradhan et al., Cardiology, 2019, summarised by ClimateCHIP: heat stress and cardiac deaths of Nepali workers in Qatar · World Bank: personal remittances received, % of GDP (Nepal)

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Productivity falls

Above a certain temperature, people work more slowly and make more mistakes, indoors and out. Across 2.7 million firms in 23 advanced economies, ten extra days above 35 °C cut a year’s labour productivity by 0.3%, and days above 40 °C did five times the damage. In humid, still air the loss roughly doubles.

Leads to: Lost work hours and wages (Slower work means lower output and pay.); Public budgets strained (Lower output means lower tax revenue.)

Sources: OECD Economics Department, Working Paper No. 1828, 2024

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Medical costs and debt

Treatment, medicines and lost days are often paid for out of pocket, pushing households into debt.

Leads to: Informal workers can’t stop work (Debt repayments remove any option to stop work in the heat.); Can’t afford to keep cool (Debt leaves nothing for electricity or cooling.)

Sources: Selvaraj, Farooqui and Karan, BMJ Open, 2018

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Small businesses close

Street vendors, workshops and shops lose customers, stock and power, and many shut for good.

Leads to: Lost work hours and wages (Closed businesses mean lost jobs.); Deepening inequality (Small firms lose the most in hot years while the largest firms gain, so heat widens the gap between them.); Loan repayments slip (Lost sales leave small firms short of cash to repay their loans.)

Sources: OECD Economics Department, Working Paper No. 1828, 2024 · Greenpeace India and National Hawkers Federation, 2024

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Supply chains disrupted

Heat slows factories, ports, roads and warehouses. The delays ripple through prices and jobs far away.

Leads to: Food price spikes (Delays and losses push up prices.)

Sources: World Bank estimate, reported by AFP via The Manila Times, 2023: factories hit by Vietnam’s power cuts

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Customers stay home

Heat empties markets and high streets in the hottest hours. Spending shifts to cooled malls and cooling products, while street vendors, small shops, restaurants and hotels lose sales.

Leads to: Small businesses close (Fewer customers mean lost sales and spoiled stock.)

Sources: Greenpeace India and National Hawkers Federation, 2024 · Orissa Post, 2024: heat cut showroom footfall

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Tourism shifts away

Visitors avoid places and seasons that become too hot, taking jobs and income with them.

Leads to: Lost work hours and wages (Fewer visitors, fewer jobs.)

Sources: Eco-Business, 2026: extreme heat reshapes travel in Asia (Booking.com survey) · Hong Kong Polytechnic University: climate change and tourism demand risks from extreme heat

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Education

Hot classrooms and closed schools cost children learning that shows up years later as lower skills and earnings.

Schools close in heatwaves

When classrooms become dangerous, schools shut, sometimes for weeks.

Leads to: Learning suffers in hot classrooms (Lost school days mean lost learning.); Care burden falls on women and girls (Children at home need someone to look after them.); Hunger and malnutrition (Children who rely on school meals go without them when schools shut.)

Sources: UNICEF, 2025: Learning interrupted

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Learning suffers in hot classrooms

Studies link hotter school days to measurably lower learning and exam results.

Leads to: Lower skills and earnings (Lost learning becomes lower earnings later.)

Sources: Park, Goodman, Hurwitz and Smith, American Economic Journal: Economic Policy, 2020

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Children pulled out of school

When families are squeezed, children, often girls, leave school to work, care or fetch water.

Leads to: Lower skills and earnings (Leaving school early limits a whole life’s options.)

Sources: Bakhtiar and Karim, IFPRI, 2025: extreme heat, schooling and child labour in rural Bangladesh

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Lower skills and earnings

Learning lost today becomes lower skills and lower earnings for a lifetime.

Leads to: Deepening inequality (Gaps in learning become gaps in income.)

Sources: Garg, Jagnani and Taraz, 2020, summarised by Ideas for India: temperature and human capital in India

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Society and security

Heat frays the social fabric: it isolates, displaces, divides and widens every existing gap.

Deepening inequality

Every impact lands hardest on those with the least protection, widening gaps in health, income and opportunity.

Leads to: Green space follows wealth (Better-off districts can pay for trees and parks, and for the upkeep that keeps them alive.); Children pulled out of school (Poorer households pull children out of school to work, care or fetch water.); Forced migration (When the gap becomes unbearable, people move.)

Sources: FAO, 2024: heat stress widens the income gap between rural women and men · Frontiers in Built Environment, 2022: Ahmedabad

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Care burden falls on women and girls

When people fall ill, schools close or water runs short, the extra caring and fetching usually falls on women and girls. In India, women already lose about 19% of their paid working hours to heat.

Leads to: Deepening inequality (Unpaid care pulls women and girls out of paid work and school.)

Sources: Climate Resilience for All, 2023, reported by Scientific American: women bear greater burdens from extreme heat

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Older people isolated at home

Older people living alone are among the most likely to die in a heatwave. Many victims of Chicago’s 1995 heatwave died alone at home.

Leads to: Heat deaths (Older people alone at home are among the most likely to die.)

Sources: Semenza et al., New England Journal of Medicine, 1996: heat-related deaths in the July 1995 Chicago heatwave

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Violence and crime rise

Hot days are linked to more aggression, domestic violence and violent crime.

Leads to: Social trust frays (Violence erodes trust.)

Sources: Burke, Hsiang and Miguel, Annual Review of Economics, 2015 (NBER working paper) · Zhu et al., JAMA Psychiatry, 2023

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Violence against women rises

Across 194,871 women in India, Nepal and Pakistan, each 1 °C rise in yearly temperature was linked to about 4.5% more intimate partner violence, with physical and sexual violence rising most. Under very high emissions it could rise about 21% by the 2090s, against about 6% if warming is held lowest. Lost income, stress and crowded hot homes may all play a part.

Leads to: Mental health suffers (Violence leaves lasting harm to mental health.); Deepening inequality (Violence keeps women out of work, decisions and public life.)

Sources: Zhu et al., JAMA Psychiatry, 2023: ambient temperature and intimate partner violence in India, Nepal and Pakistan

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Conflict over water and land

Where water and pasture shrink, disputes between communities can turn violent.

Leads to: Forced migration (Conflict forces people from their homes.); Refugee camps under tarpaulin (Conflict drives people into crowded camps.)

Sources: Mach et al., Nature, 2019, summarised by Stanford University

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Greening pushes people out

New parks and greening can raise rents and land prices until the poorer residents they were meant to cool are pushed out, often into hotter, more crowded housing. This is green gentrification. Across 28 North American and European cities, greening in the 1990s and 2000s was followed by gentrification in 17.

Leads to: Homes that trap heat (People pushed out often land in hotter, more crowded housing.)

Sources: Anguelovski et al., Nature Communications, 2022: green gentrification in European and North American cities · Bangkok: a master’s thesis on Pathumwananurak Park, built where the Rong Poon community lived

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Forced migration

When land, work and water fail, families may be forced to move, often into cities that are hotter still.

Leads to: Homes that trap heat (People forced to move often end up in crowded, poorly built housing that traps heat.); Violence against women rises (Displaced women and girls face higher risks of violence and exploitation.); Migrant workers abroad (Some leave the country to work in hotter places.)

Sources: World Bank, 2021: Groundswell Part II

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Refugee camps under tarpaulin

About a million Rohingya refugees live in the camps of Cox’s Bazar in shelters of bamboo and tarpaulin, which offer little protection from heat. When the April 2024 heatwave pushed temperatures past 40 °C, learning centres across the camps closed for several days.

Leads to: Homes that trap heat (Tarpaulin shelters trap heat, with no way to cool.); Schools close in heatwaves (Learning centres close when the heat peaks.)

Sources: UNICEF Bangladesh: rebuilding education for climate resilience in Cox’s Bazar · Amnesty International Australia: conditions in Cox’s Bazar · UNFPA: Cox’s Bazar

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Mass gatherings turn deadly

Crowds in open sun with little shade or water are deadly. During the 2024 Hajj, more than 1,300 pilgrims died in extreme heat.

Leads to: Heat deaths (Crowds in the open sun turn deadly.); Emergency services stretched (Mass casualties overwhelm responders.)

Sources: Saudi Ministry of Health figures, reported by Gulf News, 2024: 1,301 deaths during Hajj

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Social trust frays

Hot spells are linked to more conflict between groups, and unequal suffering and failing services can erode trust between neighbours and in institutions.

Leads to: Older people isolated at home (Weaker community ties leave more people alone.)

Sources: Burke, Hsiang and Miguel, Annual Review of Economics, 2015: heat raises conflict between groups

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Governance and finance

The institutions that decide who is protected, and who pays, are themselves strained by heat.

Emergency services stretched

Ambulances, fire crews and emergency rooms are swamped all at once.

Leads to: Heat deaths (When responders are stretched, help arrives too late.); Public budgets strained (Reacting after the fact costs far more than preparing.)

Sources: Times of India via India Environment Portal, 2018: 10,000 heat emergencies in 15 days in Ahmedabad

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Public budgets strained

Repairs, emergency response, lost tax revenue and relief payments all drain public money.

Leads to: Heat protection underfunded (Stretched budgets leave little for heat protection.)

Sources: Park and Rubinyi, World Bank, 2026: heat deaths in Bangkok cost more than its public health budget

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Insurance losses and retreat

Rising losses push premiums up and insurers out, leaving more people and businesses unprotected.

Leads to: Public budgets strained (When insurers retreat, governments carry the losses.); Small businesses close (Uninsured losses close small businesses.)

Sources: Swiss Re Institute sigma, reported by Global Reinsurance

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Heat deaths under-recorded

Heat is rarely written on death certificates. Most heat deaths are recorded as heart, kidney or lung failure. In India, heatwaves are declared on dry-air temperature from relatively few weather stations, which can miss humid heat where many informal workers live and work.

Leads to: Heat protection underfunded (What isn’t counted isn’t funded.)

Sources: Down To Earth, 2024: the miscalculation in India’s heatwave mortality data · NIUA Climate Centre for Cities, 2026: Heat Resilient Cities Framework, p. 10

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Heat protection underfunded

Warnings, cooling centres, outreach and heat-ready services get a small share of budgets compared with floods or storms.

Leads to: Heat deaths (Without warnings, cooling centres and outreach, more people die.); Emergency services stretched (Without prevention, emergencies multiply.); Health systems overwhelmed (Clinics aren’t prepared for heat.); Insurance losses and retreat (Unmanaged risk drives insurers away.)

Sources: Centre for Policy Research, 2023: assessment of 37 heat action plans

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Help can’t reach remote places

In remote villages, islands, hills and river settlements, the nearest clinic, cool shelter or reliable power can be hours away, and heat warnings often do not arrive.

Leads to: Heat deaths (When help is hours away, treatable heat illness turns fatal.); Heat deaths under-recorded (Deaths far from clinics are rarely recorded as heat deaths.)

Sources: Mercy Corps, 2025: extreme heat in Nepal, policy brief

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Loan repayments slip

When heat cuts sales, harvests or wages, small firms and households fall behind on loans, and lenders collect less.

Leads to: Borrowing costs rise (Lenders respond to missed repayments by charging more, asking for more collateral and lending less.)

Sources: Aguilar-Gomez et al., summarised in VoxEU, 2024 · Sa-Dhan, reported by Business Standard, 2024

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Borrowing costs rise

Lenders and rating agencies increasingly price climate risk into borrowing. After heat shocks, banks have charged small firms more, asked for more collateral and lent less.

Leads to: Public budgets strained (Higher borrowing costs leave less to spend.); Small businesses close (Dearer, scarcer credit leaves small firms unable to restock, cool their premises or ride out the next heatwave.)

Sources: Aguilar-Gomez et al., summarised in VoxEU, 2024

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Public services disrupted

Heat disrupts voting, courts and public offices. On the last day of India’s 2024 general election, Uttar Pradesh’s chief electoral officer said 33 polling staff had died of heat, and more died in Bihar and Odisha.

Leads to: Social trust frays (Disruption to public services can test public trust.)

Sources: AFP via Malay Mail, 2 June 2024 · Arab News, 2024: heatwave and election workers’ deaths

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