How deadly is extreme heat?

Extreme heat is the deadliest weather-related hazard. An estimated 489,000 people die from heat-attributable causes per year globally (Gasparrini et al., Lancet Planetary Health 2017). The 2022 European heatwave alone caused approximately 61,672 excess deaths. Heat rarely appears on death certificates — it usually triggers fatal cardiovascular or respiratory events — so official heat death statistics dramatically undercount the true toll.

Who is most at risk from heat?

The most heat-vulnerable groups are: older adults (reduced physiological heat dissipation, often on diuretic or cardiovascular drugs); infants (high surface-area-to-volume ratio, cannot self-regulate); outdoor workers (sustained heat exposure without breaks); people with cardiovascular, respiratory or mental illness (impaired thermoregulation or reduced awareness of heat symptoms); people in poverty without air conditioning; and pregnant women (heat increases preterm birth risk).

Heat stroke is a medical emergency characterised by core body temperature above 40°C and central nervous system dysfunction — confusion, disorientation, seizures or coma. Classic heat stroke affects older adults during environmental heat without exertion; exertional heat stroke affects athletes and outdoor workers during intense activity. Treatment requires immediate, aggressive cooling (cold water immersion is most effective) and emergency medical care. Delayed treatment is fatal.

What is a Heat Action Plan?

A Heat Action Plan (HAP) is a coordinated government response plan for extreme heat events. Evidence-based components: heat warning systems with defined threshold temperatures triggering alerts; targeted outreach to vulnerable groups; cooling centres (air-conditioned public spaces); heat-proofing of healthcare facilities and nursing homes; training health and social workers to identify heat illness; and cross-agency coordination (health, emergency services, local government). Ahmedabad, India implemented the first comprehensive LMIC HAP in 2013 — reducing heat mortality by approximately 24%.

How does climate change affect heat risk?

Climate change is dramatically increasing extreme heat frequency, intensity and duration. Without emission reductions, the number of days per year exceeding dangerous heat thresholds will double or triple in many regions by 2050. The IPCC projects that at 2°C of warming, events currently occurring once every 50 years will occur once every 5 years. Heat extremes are one of the most immediate and certain health impacts of climate change.

What is the wet-bulb temperature limit?

The human body cools itself through sweating — but only if the sweat can evaporate. At high humidity, sweat evaporation is impaired. Above approximately 31°C wet-bulb temperature (combining temperature and humidity), sustained outdoor exposure is fatal even for healthy, acclimatised adults — the body cannot cool itself. Climate projections show that some regions (South Asia, Persian Gulf, West Africa) may exceed this threshold for extended periods within this century if emissions continue.

What is the urban heat island effect?

Cities are significantly hotter than surrounding areas — often 3-10°C warmer — because concrete, asphalt and buildings absorb and re-radiate heat; vegetation is scarce; and air conditioning adds waste heat. Urban heat islands amplify heatwave mortality in cities, where most people live. Adaptation strategies: urban greening (parks, street trees, green roofs); cool/reflective surfaces; white roofs and pavements; and passive cooling building design.

How does heat affect workers?

Heat is a major occupational hazard — particularly for agricultural, construction, mining and outdoor logistics workers. ILO estimates 2.4 billion workers face occupational heat stress and projects 2.2% of global working hours will be lost to heat by 2030 — equivalent to 80 million full-time jobs. Heat reduces productivity, causes errors and accidents, and kills through heat stroke. ILO standards on heat stress protection (rest breaks, hydration, shade, work scheduling) are systematically underimplemented.

What should individuals do in a heatwave?

Key protective measures: stay in cool or air-conditioned spaces; drink water regularly even without feeling thirsty; avoid outdoor activity during the hottest hours (11am-3pm); check on elderly neighbours and family members; recognise heat exhaustion (weakness, dizziness, heavy sweating) and cool the person immediately; call emergency services for heat stroke (confusion, hot/dry skin, loss of consciousness). Never leave people (especially children or older adults) in parked cars.

What is the Lancet Countdown on Climate and Health?

The Lancet Countdown is an annual scientific collaboration between over 40 academic institutions and UN agencies tracking indicators across five domains: climate change impacts on health; human vulnerability and health adaptation; mitigation and health; economics and finance; and public and political engagement. Its annual reports track heat exposure, heat mortality, dengue risk, wildfire, food security and other climate-health indicators. The 2023 report found that 2022 was the most dangerous year ever recorded for heat-related health risks.

How does GMJ News cover heat and health?

GMJ News covers Lancet Countdown annual reports, European heatwave mortality estimates, occupational heat stress, Heat Action Plan evidence and urban heat island adaptation. Georgia has experienced increasingly severe heatwaves — a direct public health concern for PHIG and the Georgian Medical Journal in the context of climate change adaptation planning.

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Heat and Health

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Extreme heat is one of the most lethal climate-related hazards: in 2022, the European heatwave caused an estimated 61,000 excess deaths, and globally an estimated 489,000 people die from heat stress annually — a figure that will rise dramatically as climate change makes heatwaves more frequent, intense and prolonged (WHO/Lancet Countdown). Heat disproportionately harms older adults, outdoor workers, pregnant women, infants and people with cardiovascular or respiratory disease. The WHO Operational Framework for Building Climate Resilient and Low Carbon Health Systems calls for national heat action plans (HAPs) as a life-saving infrastructure investment.

Key messages

Fastest-growing climate hazard

Extreme heat is now the deadliest weather-related hazard — causing an estimated 489,000 deaths annually (Gasparrini et al., Lancet Planet Health 2017). Climate change is making heatwaves more frequent, intense and prolonged in every region.

2022 European heatwave — 61,000 deaths

The 2022 European heatwave caused an estimated 61,672 excess deaths across Europe (Ballester et al., Nature Medicine 2023) — demonstrating that heat is a mass casualty event comparable to infectious disease outbreaks.

Disproportionate impacts

Heat disproportionately kills older adults (the primary victims), outdoor workers (agricultural, construction), pregnant women, infants, people with cardiovascular or respiratory disease, and people in poverty without access to cooling.

Heat Action Plans

National and city-level Heat Action Plans (HAPs) — identifying at-risk populations, setting alert thresholds, coordinating public information and cooling centre access — are WHO-endorsed, evidence-based life-saving infrastructure.

Urban heat islands

Cities are significantly hotter than surrounding rural areas — up to 10°C warmer — due to heat-absorbing surfaces, lack of vegetation and waste heat from buildings. Urban greening, cool surfaces and building codes are core adaptation strategies.

Occupational heat stress

Approximately 2.4 billion workers are exposed to occupational heat stress — with agricultural workers in LMICs facing the highest risk. ILO estimates that by 2030, 2.2% of total working hours will be lost to extreme heat — equivalent to 80 million full-time jobs.

Key statistics

489K

heat-attributable deaths/year (Lancet 2017)

Gasparrini et al.

61,672

excess deaths in 2022 European heatwave

Ballester et al. 2023

2.4B

workers exposed to occupational heat

ILO

2.2%

of working hours lost to heat by 2030

ILO 2019

10°C

hotter in cities vs rural areas (urban heat island)

WHO/UNEP

>40°C

physiological danger threshold (wet-bulb temperature)

WHO/research

Excess mortality attributed to heat in major European heatwaves — WHO/ECDC/Lancet

Source: Published excess mortality estimates for major heatwave events. 2022 is the most comprehensively studied.

Glossary of key terms

Wet-bulb temperature
WHO/researchThe temperature measured by a thermometer covered in a water-saturated cloth — combining temperature and humidity. Above approximately 31°C wet-bulb (equivalent to 35°C wet-bulb globe temperature, WBGT), the human body can no longer cool itself through sweating. Prolonged exposure is fatal even for healthy people.

Heat stroke
WHO/ClinicalA life-threatening emergency — core body temperature exceeding 40°C with central nervous system dysfunction (confusion, seizures, coma). Classic heat stroke (from environmental heat) primarily affects older adults; exertional heat stroke affects young athletes and outdoor workers. Requires immediate cooling.

Heat exhaustion
WHOA milder heat illness with weakness, dizziness, nausea, headache and heavy sweating — body temperature normal or mildly elevated (<40°C). Treated with cooling, rest and oral fluids. Can progress to heat stroke if untreated.

Urban heat island (UHI)
WHO/UNEPThe phenomenon where urban areas are significantly warmer than surrounding rural areas — due to heat-absorbing materials (concrete, asphalt), reduced vegetation, waste heat from buildings and vehicles, and reduced evapotranspiration. UHI increases heat mortality in cities.

Heat Action Plan (HAP)
WHOA coordinated plan for responding to extreme heat — typically including: heat alert thresholds and early warning systems; identification and outreach to at-risk groups; cooling centres; cooling strategies for health facilities; media communication; and inter-agency coordination. Evidence-based HAPs have saved thousands of lives.

Excess mortality
WHO/ECDCThe number of deaths above baseline expected levels — used to estimate heat-attributable deaths because heat rarely appears on death certificates. Calculated by comparing observed deaths during heatwaves against expected numbers from historical data.