As the UK enters its period of summer heat health alerts, Candice Howarth and Anna Beswick explain the role of this important early warning system in the context of insufficient preparedness for extreme heat.

The Heat Health Alert (HHA) system is an early warning system that issues alerts from yellow through to orange or red when high temperatures are likely to have an impact on people’s health and wellbeing. It is operated by the UK Health Security Agency (UKHSA) and the Met Office, who work together to monitor weather forecasts and assess the level of risk. Between 1 June and 30 September, individuals and organisations can receive heat health alerts if they register their details and heat–health planners are provided with regular weather–health horizon-scanning twice a week to support emergency planning.

The Met Office’s three-month outlook for June to August suggests the chance of a hot summer is “slightly higher than normal”, which “brings an increased likelihood of heatwaves and heat-related impacts”. If a heatwave or high temperatures that take us above certain temperature thresholds occur, then we could see an alert issued. The red alert, indicating the greatest risk, has so far been issued only once, on 19 July 2022, when the UK experienced temperatures over 40°C. Close to 3,000 heat-related deaths occurred that summer.

Our own research analysing England’s responses to the 2022 heatwaves concluded that the UK is not prepared for extreme heat. With projections indicating we are likely to see more heatwave events in future, early warning systems such as the HHA have an important role to play but there is also far more to be done.

Is heat risk increasing?

Due to climate change, heatwaves are increasing in severity and intensity across the world, impacting the built and natural environment, people and wildlife, and posing ever greater risks to health, wellbeing and productivity. Extreme heat events are here to stay, both in Britain and globally.

The UK’s average summer is expected to be around 1.5°C warmer by the 2050s compared with the 1981–2000 average and 10% drier. By 2100, temperatures exceeding 40°C could occur every 3.5 years under a high-emissions scenario.

But temperatures do not need to exceed 40°C or even 30°C before the impacts of heat are felt. Once the mercury registers 25°C, the number of heat-related deaths can increase by around 30% in England and 60% in Wales. And we know that the majority of heat-related deaths and health impacts are preventable using simple measures.

The UK experienced five heatwave periods over the summer of 2022, with a wide range of impacts including more excess heat-related deaths than in previous years and especially severe health impacts for at-risk groups such as the elderly and young children. On the day of the red alert, 19 July, a series of wildfires occurred, and the London Fire Brigade called it their busiest day since World War II.

How does heat affect us and why does this matter?

Heat risk is often referred to as a silent killer. It does not affect everyone equally and is compounded by and exacerbates health, social and economic inequalities. Over the past few months we have been hearing from people across London who are affected by extreme heat in their communities through a project in collaboration with Shade the UK, findings of which will be published later this summer. Informed by these local experiences and other research, we know that the impacts of heat risk are far-reaching:

  • Without adaptation and under a high-emissions scenario, heat-related deaths are estimated to increase by almost 166% in the 2030s (to 4,266 deaths per year). Heat exposure currently costs the economy an estimated £260–300 million per year, which could rise to £720–950 million per year by 2050.
  • 50% of existing homes in the UK require some form of intervention to address overheating risk in a 2°C or higher warming scenario. South- and west-facing properties, especially top-floor and ground-floor flats, are at high risk of overheating. It is important to address how the existing building stock will cope with the future impacts of heat.
  • Heat causes significant disruption to infrastructure including the railways, energy provision and telecoms – with knock-on impacts between different forms of infrastructure.
  • Heatwaves combined with periods of drought affect the ability of natural systems to provide essential ecosystem services such as water. This impacts crop production, with the potential to disrupt supply chains and affect food prices.

How prepared are we?

The UK is ill-prepared for heat risk. We need to develop comprehensive and multi-hazard strategies for emergency response, infrastructure resilience, environmental conservation, community safety, and long-term adaptation. The current policy response is weak and scattered. There is no national vision for addressing heat risk and no targets or mechanisms for measuring success, or indicators of preparedness against which to measure progress.

While the National Risk Register recognises that extreme heat has become more likely in the UK, the National Adaptation Programme, the strategic programme for addressing all aspects of climate adaptation, lacks a strong platform for addressing heat risk and does not include mechanisms for taking action. Instead, commitments focus on research and signposting to other policies as delivery mechanisms, many of which lack any detailed guidance or actions.

In our recent ‘Turning Up the heat’ report we called for government to develop a National Heat Risk Strategy for the UK, strengthen the National Adaptation Programme and build a new vision for leadership to address heat risk. This is based on our own analysis of responses to the 2022 heatwaves and ongoing work with the British Red Cross.

Our call to action supports many of the recommendations made by the Environmental Audit Committee (EAC) Heat Resilience and Sustainable Cooling inquiry to which we also submitted evidence. The Government’s response to that inquiry, published in April this year, recognised the growing threat but did not commit to new action to address major concerns such as overheating risk to existing homes or new investment to enhance green infrastructure to support cooling in urban areas. There remains a huge gap between the risk we face from heat and tangible action.

What further questions do we need to answer?

With the warmer months upon us, we are conducting work to consider questions relating to preparedness, response and resilience to heat. For example, how can we ensure early warning systems most effectively convey the severity of risk and are appropriately interpreted? The temperature threshold in the Heat Health Alert of less than 28ºC used for the ‘very low’ risk category for London (see Table 1; defined as “Little impact observed on health, healthcare services and social care provision”) is at odds with evidence that temperatures closer to 25ºC can lead to heat-related mortality. Levels of discomfort are felt by vulnerable people and others in overheated environments below the 28ºC threshold. This leads us to question if the alert system may be misinterpreted and could convey a false sense that there is low or no risk when a yellow alert is issued.

Source: UK Health Security Agency

Heat does not affect people equally, either in terms of direct impacts (and how circumstances and surrounding environment influence this) or in terms of people’s means to prepare, adapt and respond to heat events. We must explore the justice and equity issues that exist that make the impacts of and responses to heat complex.

We also need to align efforts to enhance adaptation to the impacts of heat with those that aim to reduce our emissions through mitigation. For example, some measures necessary to reducing carbon emissions may lead to unintended consequences for overheating if not properly designed, such as building insulation increasing airtightness without being accompanied by adequate ventilation. Understanding behaviour and designing interventions appropriately to support preparedness to extreme heat without leading to unnecessary increases in emissions, for example through the use of energy-intensive measures such as air conditioning, is also key.

It is hard to visualise the impacts of heat. We tend not to be exposed to images showing the widespread devastation a heat event can cause in the same way we might see for devastating floods. We are still having to convince the media not to use images of people having fun at the beach during a heatwave. How do we address this in a way that highlights the dangers of exposure to high temperatures, explains how seemingly healthy people can rapidly become vulnerable to heat and compels people to act to protect themselves?

A wider strategic focus is needed

The UK has an opportunity to adopt a forward-looking approach in its response to heat risk and ensure it is fully prepared for further heat events. The aim should be that no heat-related deaths occur in the UK. The Heat Health Alert system plays an important role in ensuring the nation is on alert and resources are deployed appropriately during the summer. But this will only be effective if it is part of a wider strategic focus that seeks to enhance our preparedness to overheating in the long term and not just confined to summer months.

The Grantham Research Institute is working with the British Red Cross to understand how to operationalise adaptation measures and inform emergency responses with local authorities to keep people safe during periods of extreme heat.

Keep in touch with the Grantham Research Institute at LSE
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