Last reviewed 5 March 2019

Extreme heatwave events hit new highs last summer, impacting health, the environment and the economy. John Barwise reports.

Last year highlighted how the intensity of heatwaves is increasing due to global warming and climate change. The number of summer heatwaves has been rising since the 1950s. On the last day of August, the Met Office released its official national statistics and declared 2018 as the joint record holder, alongside 2006, 2003 and 1976, as the warmest UK summer since 1910 when data was first recorded. Of the four nations, England was clearly the warmest, with a provisional average temperature of 17.1°C for the whole country, beating the 17.01°C of 1976.

Summer temperature records were broken in the UK but also in parts of Canada and the USA, Central Europe, North Africa and Australia. At a global level, scientists at the National Oceanic and Atmospheric Administration recorded 2017 as the second hottest year since 1880. The five warmest years on record have all taken place since 2010.

In the August 2003 heatwave, temperatures reached 38.5°C in England. The Met Office predicts there is a risk that heatwaves of a similar intensity will occur every other year by the 2040s, as global average temperatures continue to rise.

But how does this impact on human health, the environment, and the economy? And what measures are in place to protect national infrastructures and deal with prolonged periods of intense heat in the future?

Heatwaves and climate change

The World Weather Attribution (WWA) initiative, which analyses the influence of climate change, says its link with extreme weather is clear. Using attribution analysis to assess data from several weather stations across northern Europe this summer, WWA scientists found that heatwaves are generally more than twice as probable because of human impacts on climate change.

Friederike Otto, from the University of Oxford who is part of the WWA team, thinks that what was once regarded as unusually warm will become commonplace. “The world is becoming warmer, and so heatwaves like this are becoming more common, so this is something that society can and should prepare for,” she said.

The WWA findings concur with the 2014 Intergovernmental Panel on Climate Change Fifth Assessment Report, which concluded that “It is likely that human influence has more than doubled the probability of occurrence of heatwaves in some locations.”

What is a heatwave?

Heatwaves happen when high pressure develops, mainly in summer. They are generally slow moving and can persist over an area for days or even weeks. They occur in the UK due to the location of the jet stream, which is usually to the north of the UK in the summer and allows high pressure to develop over area, resulting in persistent dry and settled weather.

The World Meteorological Organisation’s definition, which is commonly used by meteorologists in the UK, states that a heatwave occurs: “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.”

However, the Met Office says this definition is not necessarily appropriate for all regions and there is no official definition of what constitutes a heatwave in the UK, beyond a vague description of “periods of unusually hot weather, that place a toll on human health and activities”. The Met Office website outlines in general terms what a heatwave is, why they happen and their impact but does not address the increasing frequency of extreme heat events or how the threat has developed due to climate change.

Measuring the impact of heatwaves

For most of us, the long, hot summer of 2018 was a welcome respite from the usually unsettled weather conditions that tend to dampen the holiday period. The economy also seemed to hold up well during this period, with official figures showing GDP rising by 0.6% from May to July, driven largely by recovery in retail and the construction industry and growth in the service sector, especially the tourism industry.

But heatwaves bring their unique set of problems, often with chaotic and catastrophic consequences, posing a significant threat to human health, the environment and productivity. Last summer saw the first hosepipe ban in Northern Ireland for over two decades, as demand outstripped supply with no prospect of rain to replenish dwindling stocks.

The National Farmers Union described last summer’s heatwave as “tinderbox conditions”, reporting depleted yields for many crops and severely reduced grass growth, which resulted in shortages of feed for livestock and dairy farmers. Vegetables such as broccoli, cauliflower and salad crops were all affected by the heatwave, with fears that potato crops could also be limited.

Minette Batters, President of the National Farmers Union said: “This unprecedented spell of weather really should be a wakeup call for us all. It’s a timely reminder that we shouldn’t take food production for granted.” The situation across Europe was much the same, with many countries reporting poor crop yields and increased costs for animal feed. Germany’s farmers forecast a 22% reduction in grain production this year.


Wildfires across the UK were also a major concern this year, with almost 6000 acres of unique moorland damaged by the biggest wildfire Greater Manchester has ever seen. There were similar outbreaks in North Wales and the Scottish Highlands.

Wildlife was particularly badly hit, with the breeding sites of nesting birds such as oystercatchers and curlews destroyed. Reptiles such frogs, toads and lizards perished, which meant there was no food on the burned-out moorland for predators like the short-eared owl, kestrel and merlin.

In the rest of Europe, Greece suffered the worst wildfires for over a decade. There were fires too in Germany, Latvia, Poland, Portugal and Spain, which destroyed acres of croplands. Many people died. Forest fires in Sweden swept across the country reaching as far north as the Arctic Circle. Elsewhere, fires in Canada and the USA caused major damage to properties and destroyed crops.

The UK heatwave also triggered major disruption as intense heat caused roads to melt. Local authorities, such as Kirklees in West Yorkshire, deployed gritters in some areas spreading crushed rock dust in an attempt to create a non-stick layer between the surface and vehicles’ tyres. Heat damage to road surfaces in Oxfordshire alone cost an estimated £3.6 million to repair.

Rail tracks expanded and buckled on various parts of the UK rail network and trains were stopped from running over some sections due to searing heat, causing long delays and speed restrictions for passengers in many parts of the country. Rails in direct sunshine can be as much as 20°C hotter than air temperature and, because they are made from steel, they expand as they get hotter and buckle. To reduce buckling, Network Rail adjusted tension to allow rail expansion and painted the rails white to reflect heat in some hot spots.

Heatwaves and work output

Heatwaves have been linked to lower workplace productivity and worsening indoor air quality. Research from the National Institute of Occupational Safety and Health in the USA estimates that the productivity of the average British worker drops by 8% when the temperature edges above 26°C and falls further as the temperature rises.

Last summer, trade unions warned of intolerable working conditions for workers caused by extreme temperatures. While there is a legal minimum workplace temperature requirement of 16°C, there is no maximum temperature, merely a requirement that it is “reasonable”.

Heatwaves and health

Heatwaves can be particularly damaging to human health. In its Heatwave Plan for England, NHS England says the evidence about the risks to health from heatwaves is extensive and consistent from around the world. Excessive exposure to high temperatures can kill.

The main risks posed by a heatwave are dehydration from not having enough water, and heat exhaustion and heat strokes from overheating. Symptoms are worse for people who already have problems with their heart or breathing.

During the 2003 summer heatwave, there were more than 2000 excess deaths in England over the 10-day heatwave period in August, compared to the previous five years over the same period. The vast majority of these were among older people. Projections from the UK Climate Change Risk Assessment 2017, suggest heat-related deaths in the UK could more than double by the 2050s.

At-risk groups include older people, the very young and those whose health, housing or economic circumstances put them at greater risk of harm from very hot weather. People working outdoors or who are physically active are also at risk.

How prepared are we?

The Met Office predicts that heatwaves of a similar intensity to 2018 may occur every other year by the 2040s. And, while much effort has gone into dealing with the effects of excessive storm damage caused by climate change, there is growing concern that the UK is ill prepared to deal with heatwaves.

Earlier last year the Environmental Audit Committee (EAC) opened an inquiry entitled “Heatwaves: Adapting to Climate Change”, to assess the risks to health, wellbeing and economic productivity associated with heatwaves, and also to assess the level of UK resilience and Government actions to date.

Launching the inquiry, Mary Creagh MP, Chair of the EAC, said the inquiry would look at “whether the UK is prepared for higher temperatures, and what more the Government should be doing to protect people, businesses and digital infrastructure from rising temperatures”.

The inquiry took evidence from various Government departments, including health and social care, housing, Defra and a range of scientists and technical experts working on climate change and national infrastructures, such as rail networks, highways and buildings, which are integral part of economic productivity.

In its summary report, the EAC noted that while adaptation to heatwaves spans the remit of many Government departments, there was little evidence of cross-departmental action, describing the current situation as “a silo approach to policies for heatwave risk.”

Government ministers are unclear about whether Building Regulations should address the health aspects of overheating and the current lack of regulation to prevent overheating, means that new developments, which will be around for the next 70 years, will add to the growing number of buildings that overheat.

Impact on infrastructure

The committee also heard evidence of the effects heatwaves can have on critical national infrastructure such as transport, digital systems and water supply, which can affect economic output. Higher temperatures double the likelihood of service failure on railways.

Only 50% of England’s strategic road network is surfaced with the most heat resilient material and, according to the EAC inquiry, previous UK heatwaves led to very costly road repairs, particularly for local authorities. Lord Gardiner, Under Secretary of State for Rural Affairs and Biosecurity, told the inquiry he didn’t know what the cost implications are for local authorities, but added, “clearly in terms of readiness and preparedness, we need to be ensuring that the road network and the rail network can function and accommodate increasing temperatures, whatever that degree will be”.

The predicted increase in heatwaves is also expected to reduce the UK’s water supply by 4–7% in the coming years, and this will be exacerbated by the increasing demand for water during hot weather. Yet, according to the EAC report, the Government has: “weakened its water efficiency ambitions and continues to fail to introduce sustainable urban drainage systems, which bring multiple benefits.”

Heatwaves result in decreased workplace productivity, particularly for workers engaged in heavy outdoor manual labour or employees working in offices. Research on the economic consequences of heatwaves concluded that they brought significantly more cost to the economy than benefit. In 2010, approximately five million staff days were lost due to overheating above 26°C. Based on an average staff cost of £150 per day, this resulted in an economic loss of £770 million, the inquiry was told.

The growing risk to business productivity was highlighted in an earlier report published by the Climate Change Adaptation Sub-committee in 2017, which concluded that lower productivity is a major risk due to workplace overheating, loss of work days due to transport failures, significant costs to the healthcare sector and high maintenance costs for roads and public transport.

Time to take action

Last summer’s heatwave revealed the vulnerability of UK infrastructure and the consequent impacts on health, the environment and the economy as a whole.

The EAC inquiry also highlighted the lack over-arching strategy for heatwaves together with a lack of coordination between Government departments. If the Met Office projections are correct and heatwaves do happen every two years by 2050, we have a lot of catching up to do.