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The change in global climate is causing an increase in frequency, duration and magnitude of extreme heat events, including heatwaves. UK climate observations show a rise in annual mean and peak temperatures, with maximum temperatures rising at a faster pace than mean temperatures. Two main definitions describe heat events:  

  • Heatwaves are defined by the Met Office as periods of at least three consecutive days in which a temperature threshold is met or exceeded. Thresholds differ between counties, reflecting regional differences in climate. There is no universal definition of a heatwave. 
  • Heat periods are defined by the UK Health Security Agency (UKHSA) as at least one day with an amber Heat-Health alert in at least one region and/or the mean Central England Temperature being at least 20 °C. The Office for National Statistics (ONS) and UKHSA use heat periods to report heat mortality statistics on excess heat-deaths. 

Heat and heatwaves pose a threat to public health. In summer 2022, an estimated 2,985 deaths were associated with the five heat periods in England. Without further adaptation to heat, this number is projected to increase further. 

The impact of heat on health varies across the population. Vulnerability factors render individuals more sensitive to negative heat impacts, increase their heat exposure, or impair their ability to adapt to heat. Some vulnerabilities commonly overlap, with some groups having multiple contributory risks arising from their physiology, social and environmental determinants. 


  • The frequency, duration and intensity of extreme heat and heatwaves in the UK has been increasing. Five heat periods of extreme heat were recorded in England in 2022, and temperatures exceeded 40 °C for the first time. 
  • Heat impacts the body and can lead to illness and death. In summer 2022 2,985 deaths in England were associated with heat periods. 
  • The number of heat-related deaths is projected to further increase, as the climate continues to change, and the population grows and ages. 
  • The impact of heat on health varies across the population. Vulnerability factors include advanced age, physical and mental health conditions and pregnancy; environmental factors such as living in urban areas, housing conditions and occupational setting; and sociodemographic factors such as homelessness, poverty, low educational attainment and being an immigrant. 
  • The Adverse Weather and Health Plan, published by the UK Health Security Agency, constitutes the overarching policy framework responding to heat-health risks. The plan includes an impact-focused heat-health alert system. 
  • Stakeholders from the academic, healthcare and charity sectors stress the importance of a joint policy response, including building regulations, urban planning, healthcare, public communication and research. 


  • Members of the POST Board* 
  • Tom Addison, The Physiological Society*
  • Leo Bryant, The British Red Cross* 
  • James Creswick, WHO European Centre for Environment and Health, WHO Regional Office for Europe 
  • Extreme Events and Health Protection Team, Centre for Climate and Health Security, UK Health Security Agency 
  • Dr Fai Fung, Met Office, University of Bristol 
  • Dr Jo Garrett, University of Exeter 
  • Dr Oliver Gibson, Brunel University 
  • Dr Anya Gopfert, Faculty of Public Health 
  • Professor Shakoor Hajat, London School of Hygiene and Tropical Medicine* 
  • Professor George Havenith, Loughborough University* 
  • Dr Clare Heaviside, University College London 
  • Dr Candice Howarth, Grantham Research Institute on Climate Change and the Environment, London School of Economics* 
  • Dr Vladimir Kendrovski, World Health Organisation European Centre for Environment and Health, World Health Organisation Regional Office for Europe 
  • Dr Sari Kovats, London School of Hygiene and Tropical Medicine* 
  • Professor Prashant Kumar, University of Surrey* 
  • Dr Emma Lawrance, Climate Cares Centre, Imperial College London* 
  • Jenny Lippiatt, Age UK* 
  • Andrew Mackenzie, The Physiological Society*
  • Dr Irene Mussio, Leeds University 
  • Dr Emer O’Connell, Greater London Authority 
  • Dr Charles Ogunbode, University of Nottingham* 
  • Professor David Ormandy, University of Warwick 
  • Shania Pande, The Physiological Society*
  • Dr Chengzhi Peng, University of Sheffield* 
  • Adeline Siffert, The British Red Cross 
  • The Physiological Society*
  • Dr Rhiannon Thompson, Imperial College London 
  • Dr Ben Wheeler, University of Exeter* 

 *denotes people and organisations who acted as external reviewers of the briefing. 


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