Why UK heatwaves are not good news as they become more frequent, longer and hotter

By ITV News Multimedia Producer Suzanne Elliott

The sun is not always a guarantee during a British summer and its appearance is invariably greeted with much excitement and gleeful 'hotter than Mallorca' headlines.

But where once a British 'heatwave' was shorthand for 'not raining', increasingly hot spells are becoming hotter and more dangerous, scientists warn.

This week a health warning was issued amid rising temperatures that could top 40°C in the coming days.

Here scientists explain why record-breaking temperatures are no longer something to celebrate.

What are heatwaves?

Heatwaves are caused by weather patterns that produce persistent high pressure, cloud-free conditions and dry continental winds during summer.

For a hot spell to be deemed a heatwave in the UK, the temperature threshold - which differs by area - has to be met or exceeded for at least three consecutive days.

The temperature threshold varies by county, ranging from 25°C to 28°C.

Will heatwaves become more common in the UK?

Scientists say, yes, they will. In fact, there's a chance 'heatwave' will simply be 'summer' in a few years' time as climate change increasingly alters the UK's weather towards a more Mediterranean climate.

Dr Michael Byrne, lecturer in earth and environmental sciences at the University of St Andrews, said: “The current heatwave is a dangerous reminder of the accelerating impacts of global warming.

"With London expected to feel like Barcelona by 2050, the UK is braced for more frequent and severe heatwaves over coming years."

Are heatwaves dangerous?

They can be. While extreme cold is the biggest weather killer of people in the UK at the moment, heatwaves, as they grow in intensity, are likely to become more dangerous, Professor Hannah Cloke, a natural hazards researcher at the University of Reading warned.

“This current hot spell in the UK is forecast to intensify over the coming days.

"While there is still some uncertainty in the forecasts for a week from now, the indications are that there is a small chance that we will hit record maximum temperatures in the UK, with highs close to 40°C," she said. 

“This is a dangerous level of heat on its own. We should remember that heat is most dangerous when it is persistent over several days, especially for those who cannot escape it or gain respite at night time."

Dr Friederike Otto, senior lecturer in climate science at the Grantham Institute for Climate Change at Imperial College London, agrees that the hot weather is "no reason to cheer", describing heatwaves as "by far the deadliest extremes in Europe".

"In 2020, in the UK alone more than 2,500 people died because of hot days – and those were less hot and less frequent than what we are already seeing this year,” she said.

Studies by the University of Reading's Department of Meteorology found heat-related deaths would likely rise if the current trajectory of climate change continues.

How prepared is the UK for increasingly hotter weather?

Not very is the general consensus, as many sweltering in their homes and offices will have noticed this week. And the rising cost of living will undoubtedly make conditions even more uncomfortable as people reduce their use of air-conditioning or fans amid rising electricity bills. But the problem is a long-term one, with scientists saying the UK will need a complete rethink of its infrastructure as temperatures soar.

New building regulations have come into force recently in the UK that aim to reduce overheating risks in homes. But the new regulations will take years to have an impact and older housing stock remains inadequate in temperatures of 30°C plus.

Dr Michael Byrne, lecturer in earth and environmental sciences at the University of St Andrews, said the UK was "UK is woefully under-prepared" to deal with the impact of climate change on the weather. “We urgently need to overhaul UK infrastructure to keep us cool and healthy in a rapidly warming world," he said.

"There is clearly a short-term link with the rising costs of heating or cooling our homes. But there is a much more significant long-term link with poorly designed buildings and infrastructure, that only carefully co-ordinated, far-sighted planning can overcome," Prof Cloke said.Is climate change behind heatwaves?

Heatwaves are not new, but their intensity and frequency continue to alarm climate scientists.

Heatwaves are made more intense and frequent mainly because overall temperatures are higher due to global warming, and so, when weather systems such as summer high pressure occur, the heat they bring is amplified.Heatwaves are extreme weather events but the latest research from the Intergovernmental Panel on Climate Change (IPCC) shows that climate change is making these events more likely. Heatwaves like the one the UK saw in 2018 are now 30 times more likely to occur than before the industrial revolution due to an increase of carbon dioxide in our atmosphere.

Dr Otto said the climate crisis is a "game changer" when it comes to heatwaves and had "already turned what would once have called exceptional heat into very frequent summer conditions".

"Every heatwave we experience today has been made hotter because of the fossil fuels we have burned over the last decades in particular," she said.

Richard Allan, professor of Climate Science at the University of Reading, said: "Climate change is intensifying these heatwaves as greenhouse gas increases raise temperatures and a warmer, more thirsty atmosphere dries out the soil so that more of the sun’s energy is available to heat the ground rather than evaporating water."

Professor Nigel Arnell an analyst at the University of Reading said modelling had shown the UK was "highly likely" to get more and longer heatwaves in the future due to climate change.

He added the number of heat-health alerts and heat-stress - when the body's ability to control its internal temperature starts to fail - days would also rise.