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Heatwaves: adapting to climate change Contents

1The developing threat of heatwaves

1.As the climate change risks faced by the UK become clearer, adaptation is vital to reduce vulnerability to extreme and unpredictable weather events. We launched our inquiry in February 2018 to examine the risks heatwaves pose to health, wellbeing and productivity and to scrutinise the Government’s preparation for the emerging threat of heatwaves and high temperatures. This inquiry forms part of our ongoing scrutiny of the Government’s National Adaptation Programme and follows on from our predecessor’s inquiry into Flooding: Co-operation Across Government and hearing on Climate Change Adaptation.1 In future years we intend to look at other risks including invasive species, disease and food security. Since we launched our inquiry, the UK has experienced unseasonably hot weather in April, June and July 2018. We received 28 pieces of written evidence for this inquiry and conducted four hearings with climate change adaptation experts, meteorologists, experts on buildings, cities, water supply and infrastructure, national leaders for public health and healthcare, and Government Ministers. We also held a roundtable event with carers for the elderly, who are most vulnerable to heatwaves, to gain an understanding of frontline concerns. Additionally, we conducted a survey of teachers to understand how heatwaves affect the health and productivity of their students. We would like to thank all those who contributed to our inquiry.

What is a heatwave?

2.There is no official definition of what constitutes a heatwave in the UK, however they are generally understood to be periods of unusually hot weather, that place a toll on human health and activities.2 The World Meteorological Organisation’s definition is commonly used by meteorologists in the UK:

When the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5 °C, the normal period being 1961–1990.3

3.Dr Peter Stott, Science Fellow in Attribution at the Met Office Hadley Centre for Climate Science and Services explained that only some periods of unusually hot weather are classed as heatwaves. When asked about April’s period of hot weather, Dr Stott said:

We are calling that a hot spell. We had, as you well know, some very warm—anomalously warm—temperatures… It was 29.1 degrees, I think, on 19 April at St James’s Park. That was just below the all-time record for April temperatures, which was recorded at 29.4. These are extremely unusual temperatures for April, but when we think of heatwaves, then we are thinking of the hot season and we are thinking of temperatures, as I was referring to earlier, up in the 30s. So an extremely hot spell for April, but for the high summer, not what we use to trigger a heat watch system.4

4.The Met Office is commissioned by Public Health England to trigger heatwave alerts from June to September. Dr Stott explained how this time-limited commissioning agreement affects the definition of heatwaves:

A heatwave is, in terms of the Heat Health Watch Service, only during the hot season, from 1 June to 15 September, and therefore it is only when you reach these triggers that I have talked about. The reason we are calling the April weather a hot spell is because it did not reach those triggers and it was not in the hot summer season, but for the time of year, it was very anomalously warm for April.5

5.The Met Office is developing a UK specific definition of a heatwave and it is anticipated that this will be available by summer 2018.6 Dr Stott commented that the new definition would help the Met Office “communicate better to the general public when we have periods of warm weather and hot weather.”7

A hidden risk: the increasing frequency of heatwaves

6.The threat of heatwaves is developing rapidly. The number of extreme heatwave events in Europe has risen since 1950, and their intensity is increasing.8 Dr Stott’s attribution research found that carbon emissions from human activities have doubled the likelihood of severe heat events.9 He explained:

I worked on the Intergovernmental Panel on Climate Change and we have seen very clearly the evidence that has led us to conclude that human influence on the climate system is clear. But within the UK we have seen the general warming of temperatures, and with that, we have seen a warming of extreme temperatures.10

The 2014 Intergovernmental Panel on Climate Change Fifth Assessment Report concludes that “it is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in [greenhouse gas] concentrations and other anthropogenic forcings together.”11

7.The most severe heatwave of the twentieth century in the UK was the European heatwave of August 2003. The 10-day period of extreme heat is thought to be the warmest for up to 500 years. The highest temperature ever in the UK was recorded in Faversham in Kent reported a high of 38.5°C. The heatwave led to over 20,000 heat-related deaths across Europe, including 15,000 in France alone and 2,193 in the UK. A similarly intense heatwave occurred in July 2006 and there have been periods of unusually hot weather or heatwaves in July 2013, July 2015, July 2016, August 2016, September 2016, June 2017, April 2018 and June 2018. The increasing frequency of heatwaves above the daily minimum threshold since the 1960s is visualised in figure 1.

Fig. 1: Average number of days above the minimum and maximum heat thresholds per year. Source: National Centre for Atmospheric Science at the University of Reading

8.Heatwaves are projected to become more frequent in the future. The Met Office note in its written evidence that extreme temperature events in Europe are now 10 times more likely than they were in the early 2000s. By the 2040s, heatwaves as severe as 2003 could occur every other year.12 Heatwaves are also expected to intensify because of the contribution of human activities to the atmospheric concentration of greenhouse gases and other pollutants. Met Office research has estimated that human influence has at least doubled the risk of a heatwave exceeding the mean summer temperature threshold.13

9.However, despite strong evidence of the developing threat of heatwaves, there is a lack of public awareness of the risk. Kathryn Brown, Head of Adaptation at the Committee on Climate Change outlined the public misconception about heatwaves and rising temperatures:

Some of the statistics we have collected from research that DEFRA has done, which was based on a study of public awareness of different types of weather events and whether they had changed over the course of the last 10, 15 years and whether they would change in the future [found that] only 10% of people thought temperatures had increased over the last 20 years, whereas we know that they have, and only 29% thought that the climate was going to get warmer in the future. More people from that study thought it was going to get colder rather than hotter… we think that is fairly compelling evidence that this is a fairly hidden risk.14

Impact of heatwaves on human health

10.Heatwaves are associated with increased excess mortality. Excess mortality refers to deaths that otherwise would not have occurred under normal circumstances. In the 2003 heatwave excess mortality was 17% across England and Wales, and 40% in London.15 Heat-related deaths begin to increase when temperatures go above 25°C.16 Public Health England observed a linear relationship between temperature rises above 25°C and mortality, and that in England in 2006 there were “an estimated 75 extra deaths per week for each degree of increase in temperature.”17 The Director of Health Protection and Medical Director at Public Health England, Professor Cosford told us that there is a higher rate of heat-health illness and mortality in the first two or three days of a heatwave. Professor Cosford explained that this is partly due to acclimatisation and deaths tend to fall through the course of a heatwave.18

11.Climate Adapt Europe also note the importance of acclimatisation:

Heatwaves, among the various health hazards imposed by climate change, strike particularly hard in regions where the population is neither accustomed to high temperatures nor does expect them.19

For instance, although the population in India is accustomed to a very warm climate, a slight increase in recent summer temperatures coupled with more frequent heatwaves has led to an increase in heat-related deaths. A similar number of people each year now die from heat in India as they do in the UK, demonstrating the health effects of only a small change in normal regional temperatures.20

12.In the 2003 heatwave, there were 2,193 excess deaths across the UK between the 4th - 13th August. The main causes of death during a heatwave are respiratory and cardiovascular disease. When air temperatures are high, the body keeps cool through sweating. This places strain on the heart, which can be fatal for those with underlying heart conditions. Those with thermoregulatory problems (the body’s temperature control mechanism) are particularly vulnerable to overheating, meaning that women experiencing the menopause were most at risk. High temperatures are also linked with increased air pollution, as high levels of ozone are formed rapidly in strong sunlight and there is an increased concentration of fine particles in hot, still air conditions. This poor air quality can exacerbate pre-existing or underlying respiratory conditions. There is also an emerging understanding of the impacts of heatwaves on mental health. Public Health England note that higher rates of suicide have been observed in previous UK heatwaves.21

13.Heatwaves also cause specific heat-related illnesses such as heat cramps, heat rash, heat oedema (swelling, usually in the ankles), heat syncope (dizziness and fainting due to dehydration), and heat exhaustion which can lead to potentially fatal heatstroke. Recognising the early signs of heatstroke can avoid unnecessary death.

Box 1: Spotting the signs of heatstroke

Heatstroke is caused when the body’s thermoregulatory mechanism fails. Heatstroke can result in cell death, organ failure, brain damage or death. Initial symptoms indicate heat exhaustion, which usually gets better if addressed quickly. The symptoms are:

  • Headache
  • Dizziness and confusion
  • Loss of appetite and feeling sick
  • Excessive sweating and pale, clammy skin
  • Cramps in the arms, legs and stomach
  • Fast breathing or pulse
  • Temperature of 38° or above
  • Intense thirst

To help the person cool down you should move them to a cool place and get them to lie down and raise their feet slightly. You should get them to drink plenty of water and cool their skin by spraying or sponging them with cool water, fanning them and placing cold packs on their armpits or neck.

If their symptoms do not improve within 30 minutes or if their temperature has risen above 40°C, they are confused, unresponsive, lose consciousness or have a seizure they could have heatstroke. Seek emergency medical help by calling 999 immediately.

Source: https://www.nhs.uk/conditions/heat-exhaustion-heatstroke/ and https://assets.publishing.service.gov.uk government/uploads/system/uploads/attachment_data/file/201150/Heatwave_plan_2013_-_Making_the_case_Accessible_updated.pdf

14.Some people are particularly vulnerable to health effects of heat. During the 2003 heatwave, excess mortality in people over the age of 75 increased by 22%, a greater increase than any other age group. In London, 59% more people over 75 died during the heatwave.22 Age UK notes that:

While knowledge of the negative effects that exposure to cold weather has on older people is well known and communicated, the same cannot be said of the damaging effects of prolonged exposure to heat.23

Older people living in care or nursing homes are also at particular risk. A study of mortality in Southern England during the 2003 heatwave found that deaths in nursing homes increased by 42%. Around one quarter of all heat-related deaths occurred in care homes, although the study notes that this is likely to be an underestimate as some residents may have been admitted to hospital shortly before death.24

15.Social isolation is also a factor in heatwave mortality, so older people living alone and homeless people are at increased risk. Research has found that during the 2003 European heatwave, 92% of those who died in Paris lived alone.25 Those with chronic illnesses such as diabetes, heart conditions or respiratory disease are also at risk, as well as people with disabilities, infants and those living in urban areas and overheated buildings. Women are also more likely to die from heat-related illness. The reasons for this are unclear, although research suggests that thermoregulatory problems related to the menopause could be partly to blame.26 Children cannot control their body temperature as efficiently as adults during hot weather because they do not sweat as much and are therefore at an increased risk of ill health.

Heatwave Plan for England

16.To protect public health, Public Health England provides guidance on how to stay safe during a heatwave and issues advanced warning of heatwaves through a heat-health watch alert system. The Heatwave Plan for England was first published in 2004 as a response to the significant excess mortality during the 2003 European heatwave, and has been published annually ever since.27 The Plan relates specifically to England and is intended to be a template for more focused local heatwave plans produced by Directors of Public Health. An independent review of the effectiveness of the Heatwave Plan for reducing heat related illness and mortality is currently underway, with findings expected in November 2018.

17.The Plan recommends a series of steps for NHS, local authorities, social care services, other public agencies and professionals working with vulnerable people to reduce the risks to health from prolonged exposure to heat. A series of accompanying guides for health and social care professionals, care home staff and teachers are also published. “Beat the Heat” leaflets and guidance also outline simple steps to keep cool and prevent buildings from overheating.28

18.The guidance provided to individuals and health and social professionals is clear and informative, however in the main part of the Plan and the accompanying guides there is no explanation of how the threat of heatwaves is developing.29 This is concerning as general public opinion is that heatwaves have not increased over their lifetimes.30 The Committee on Climate Change noted in its 2014 and 2015 Progress Reports to Parliament that there is low awareness amongst the general public about how risks from heat are changing, and that this could lead to a lack of motivation to introduce adaptation measures such as shading for buildings.31 Written evidence from the Grantham Institute for Climate Change and the Environment states:

… there is little evidence that the Government is increasing activities to communicate the rising risk of heatwaves, or to monitor public awareness. No government department or agency has lead responsibility to communicate to the public about climate change impacts on extreme weather.32

19.Dr Stott from the Met Office Hadley Centre for Climate Change was not able to point us in the direction of a list of previous UK heatwaves, citing the lack of a heatwave definition as an obstacle.33 The Met Office has a webpage outlining in general terms what a heatwave is, why they happen and their impact, but there is no mention of the increasing frequency of extreme heat events or how the threat has developed due to climate change.34 The Minister for Public Health and Primary Care, Steve Brine MP, recognised that the public do not currently take the public health threat of heatwaves seriously:

The other thing that is important to say is that there is a public education exercise that I think we need to do here through Public Health England because, in terms of heatwave advice, heat alerts tend to be seen as barbecue alerts, as opposed to there being a risk. I think the public are quite well trained for cold weather alerts being about a risk, but of course there is also a great risk in heat alerts and public education is important there to look out for the person next door who is elderly and vulnerable and lives on their own.35

20.Despite multiple science-based predictions of the increasing severity of heatwave risk in the UK, the Government does not provide clear information for the public on the developing threat of heatwaves. There is no commonly accepted definition of a heatwave in the UK. The Heatwave Plan does not make it clear that extreme heat events have become more frequent or that severe heatwaves are projected to be common by the 2040s. The Met Office webpage on heatwaves also does not mention that climate change will make extreme heat events more frequent and intense. There is a public misconception that heatwaves have become less frequent over recent years, which could lead to lack of motivation to take the threat of heatwaves seriously. The Government should launch a Minister-led public information campaign on the developing threat of heatwaves and their significant impact on human health and activities. Public Health England should update the Heatwave Plan for England with evidence of the increasing frequency of heatwaves. The Met Office should detail this risk on its website.

Heat-health watch alert system

21.To provide advanced warning of heatwaves, Public Health England operates a heat-health watch alert system as part of the Heatwave Plan for England, provided by the Met Office. The Met Office publishes the current alert status on its website, however it clarifies that is a “service is for health professionals, contingency planners and emergency responders” and alerts no longer appear as a banner on its website, making it more difficult for the public to find information about the current heatwave level.36

22.Public Health England commissions the Met Office to issue heatwave alerts from 1st June to 15th September each year. Heatwave alerts are issued when temperatures reach a certain set of thresholds. These thresholds vary across the country according to local weather conditions.37 The alerts trigger a series of responses from local authorities, the NHS, Public Health England and government. The alerts are cascaded down through Public Health England and NHS networks. We heard frustration that the heat-health alert system only runs from June to September. An NHS Trust Resilience Manager commented:

Can I ask why it starts on 1 June, though? We have experienced some really hot Aprils in the previous years and some very cold Julys? If we are working towards a co-ordinated response, then some trusts will invoke their plan earlier than 1 June, because they have to. To get those messages out earlier than Public Health England does, normally before 1 June, would possibly benefit going forward.38

23.The Director for Health Protection and Medical Director from Public Health England, Professor Cosford told us that higher levels of illness and health problems occur in the first heatwave of a season.39 However, he assured us that a heatwave alert would still be triggered outside the heatwave season:

We are concerned about a heatwave whenever it occurs. Although the routine system is in play between certain dates, as you suggest, that does not prevent the heatwave plan being implemented whenever it is required. We would still alert through our systems and NHS England would alert through its systems at whatever time of year.40

24.Professor Davies, Member of the Adaptation Sub-Committee, told us that the most deaths occur during warm periods not classed as heatwaves and that the greatest burden of heat-related mortality falls outside the heatwave period.41 Professor Cosford also explained that heat-related deaths begin to occur before alert thresholds are reached:

Although our thresholds for heatwave plans are roughly 30°C, it looks as if actually the mortality begins to increase when temperatures get into the late 20s.42

This is concerning given that during the unseasonably hot spell during April 2018, no heatwave alert was issued by the Met Office or Public Health England. Temperatures reached 24.1°C during the 2018 marathon, making it officially the hottest London marathon on record.

25.We heard that Public Health England plan to combine the Heatwave Plan and the corresponding Cold Weather Plan into one single adverse weather plan as part of the forthcoming National Adaptation Programme.43 This should mean that the public can be alerted to unseasonable “heatwaves” in the same way as summer heatwaves.

26.Most deaths occur during warm periods not classed as heatwaves and the greatest burden of heat-related mortality falls outside the official heatwave period. The time limited nature of the heat-health watch alert service means that the public are not necessarily alerted to unseasonal spells of very high temperatures. We only received an informal assurance that Public Health England would instruct the Met Office to issue a heat-health alert outside the usual June to September period. Furthermore, excess deaths start occurring at 25°C, but heatwave alert thresholds are roughly 30°C, meaning that the public are not alerted about some dangerous hot spells. We support the Government’s plan to create a single adverse weather plan and strongly recommend that alerting systems run throughout the year, especially targeted to those who are likely to suffer before heatwave temperature thresholds are reached.


1 Flooding: Co-operation across Government, Second report of session 2016–17, Environmental Audit Committee and Environmental Audit Committee, oral evidence, Climate Change Adaptation, Tuesday 14th March 2017, HC1023

2 Met Office (HTW0017) and Heatwaves and health: guidance on warning-system development, World Meteorological Organisation and World Health Organisation, 2015.

4 Q4

5 Q6

6 Met Office (HTW0017)

7 Q2

8 Met Office (HTW0017)

9 P Stott et al, Attribution of extreme weather and climate-related events, WIREs Climate Change, Volume 7 (January/February 2016)

11 https://www.ipcc.ch/pdf/assessment-report/ar5/syr/SYR_AR5_FINAL_full_wcover.pdf The 2014 IPCC report also notes “Changes in many extreme weather and climate events have been observed since about 1950. Some of these changes have been linked to human influences, including a decrease in cold temperature extremes, an increase in warm temperature extremes, an increase in extreme high sea levels and an increase in the number of heavy precipitation events in a number of regions.”

12 N, Chrsitidis et al, ‘Dramatically increasing chance of extremely hot summers since the 2003 European heatwave’, Nature Climate Change 5, 46 -50 (2015)

13 Q21 and Met Office (HTW0017)

14 Q9

15 R S Kovats et all, ‘The impact of the 2003 heat wave on mortality and hospital admissions in England’, Health Statistics Quarterly 29, Spring 2006, 6–8

20 Mean temperatures across India have risen by more than 0.5°C between 1960 to 2009, leading to an increase in the probability of severe heat events that affect health. Heatwaves in India killed 1,300 people in 2010, 1,500 in 2013 and 2,500 in 2015. O Mazidiyasni et al, ‘Increasing probability of mortality during Indian heat waves’, Science Advances, Vol. 3, no.6 (June 2007)

22 R S Kovats et al, ‘Mortality in southern England during the 2003 heatwave by place of death’, Health Statistics Quarterly 29, Spring 2006, 6–8

23 Age UK (HTW0021)

24 R S Kovats et al, ‘Mortality in southern England during the 2003 heatwave by place of death’, Health Statistics Quarterly 29, Spring 2006, 6–8

25 Q10, M Poumadere et al, The 2003 Heat Wave in France: Dangerous Climate Change Here and Now, Risk Analysis: an international journal, Volume 25, issue 6, 1483–1494

26 S Hajat et al, Heat-related and cold-related deaths in England and Wales: who is at risk?, Occup Environ Med 64, 2007, 93–100

27 https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/711503/Heatwave_plan_for_England_2018.pdf Public Health England took over operation and maintenance of the plan in 2014. The Plan is produced in partnership with NHS England, the Met Office and the Local Government Association.

29 “The Plan does not quantify the scale of the risk, nor does it indicate how this risk is changing in response to climate change.” Grantham Research Institute on Climate Change and the Environment (HTW0028)

30 Q9 and Grantham Research Institute on Climate Change and the Environment (HTW0028)

32 Grantham Research Institute on Climate Change and the Environment (HTW0028)

33 Q8

34 The Met Office states in its written evidence that “extreme summer temperature events in Europe, similar to that endured in 2003, are now 10 times more likely than they were in the early 2000s”: Met Office (HTW0017), https://www.metoffice.gov.uk/learning/temperature/heatwave

36 https://www.metoffice.gov.uk/public/weather/heat-health/#?tab=heatHealth

37 The summer period of June to September is known as Level 1 and individuals and organisations are encouraged to take preparation measures throughout this time. Level 2 is triggered as soon as there is a 60% chance of temperatures being high enough on two consecutive days to have an impact on health. Level 3 is triggered when a heatwave temperature threshold is met and level 4 is triggered when a heatwave is so severe that it is deemed a national emergency.

42 Q286 and Professor Davies from the Adaptation Sub-Committee of the Committee on Climate Change also expressed concern about excess mortality at lower temperatures (Q9).

43 Q49 and Q381




Published: 26 July 2018