Temperatures are rising in the United Kingdom, leading to dangerously hot days and longer warm spells - and thousands of deaths in recent summers.
The summer of 2022 saw temperatures surpass 40°C for the first time on record in the UK, and new national records set in England, Scotland, and Wales, according to the UK Health Security Agency's Health Effects of Climate Change report. Overall, the most recent decade has been the nation's warmest since records began.
What's more, as the climate continues to warm, the dangers posed by extreme heat could rise even more dramatically across the UK and around the world.
Since the late 1800s, human-caused climate change has warmed the Earth's average temperature by around 1 degree Celsius. That might not sound like much, but a relatively small warming of the average temperature has resulted in a large jump in extreme heat.
Is there a link between climate change and extreme heat?
A record number of days with 'extreme heat stress' - that is a 'feels-like' temperature of more than 46°C - were recorded across Europe in 2023, according to satellite data analysed by Europe's Copernicus Climate Change Service. And it's all due to climate change, affirms the State of the UK Climate report released in summer 2023.
As the Intergovernmental Panel on Climate Change has stated, "it is unequivocal that human influence has warmed the atmosphere, ocean and land". An analysis from the U.S.-based research group Climate Central shows that the fingerprints of climate change were all over that year's unusually hot summer, globally. Over 6.5 billion people - 81% of the global population - experienced at least one hot day in July 2023 that was at least three times more likely because of climate change. Of those, at least 2 billion people saw climate-induced high temperatures on every single July 2023 day.
Heatwaves were seen in nearly every corner of the globe in July 2023, and climate change made them more likely according to World Weather Attribution, a research group based in the U.K.
"Without human induced climate change these heat events would however have been extremely rare", states a World Weather Attribution report. "Maximum heat like in July 2023 would have been virtually impossible to occur in the US/Mexico region and Southern Europe if humans had not warmed the planet by burning fossil fuels".
What can we expect from extreme heat in the future?
Our recent past is merely a precursor to a hotter future. Met Office climate predictions suggest that all areas of the UK will be warmer by the end of the 21st century, with hotter and drier summers also becoming more common.
Exactly how hot could things get? It depends on how quickly the world can meet emissions reduction goals. The UK Climate Resilience Programme report projected that under a high emissions scenario (a 4°C rise in average global temperature), the number of extremely hot days in the UK could increase four-fold, jumping up from around 10 days per year today to 37 days. But with a 2°C global temperature increase, the number of days exceeding 25°C would be more like 18 days annually.
Whatever the exact increase in temperature will be, therefore, depends entirely on the success of decarbonisation efforts. In any case, however, temperatures in the UK will likely continue to rise until at least mid-century. And any increase in extreme heat will in turn come with consequences, most notably to human health.
A Scientific Reports study concludes: "It's the sustained nature of heatwaves that impose more devastating impacts than extreme temperatures on a single day. Excessive human morbidity and mortality rates are clearly associated with sustained extreme temperatures".
The UK Health Security Agency report chapter on temperature change looked at the future relationship between heat and mortality. In a high-emissions scenario, models indicate UK heat-related deaths could increase by one and a half times in the 2030s and by 12 times by 2070, with the elderly and children most at risk. Meanwhile, workplaces may get less safe and productive as increases in heat and humidity push the limits of human tolerance, making it difficult for workers to stay cool. Outdoor workers will be at heightened risk of heat-related illnesses and fatalities. People in cities will be more vulnerable to urban heat island effects. London, for instance, is associated with a higher risk of heat-related effects than surrounding rural areas.
Hotter days also evaporate more moisture from the ground, drying out vegetation and leading to losses in agriculture.
What can we do?
There's a lot that can still be done now to minimise the impacts - some of which are already underway.
For example in 2023 the UK implemented its new impact-based Heat-Health Alerts system to keep residents informed about dangerously hot weather and provide them with links to resources and guidance. Buildings can also be designed or updated to keep inhabitants cooler, from relatively simple solutions like external shutters and draught-reduction measures to installing 'cool' roofs that reflect sunlight rather than absorbing it.
Communities can get more creative in mitigating heat, too. The BBC reports such novel approaches as deploying lorries normally used for salting winter roads to instead prevent heat damage to roads with sand or stone dust; reflecting sunlight from London's Hammersmith Bridge by wrapping its chains in foil; and giving frozen lollies to zoo animals, to name a few.
Remember, the damage and impact can be better contained if the global community takes swift climate action. So broadly speaking, the most important step is to invest in aggressive measures to reduce carbon pollution and other heat-trapping gases.
But because some of the projected heating is already inevitable, we will also have to adapt to a warmer world, for example by planting shade trees and ensuring people have access to cooling centres. Such actions would also help protect people's lives.