A heatwave in May set monthly temperature records across Europe; a heatwave in June became the hottest ever observed in western Europe. Now, in July, yet another heatwave is developing. Just 50 years ago, the June heatwave would have been virtually impossible. But global warming is making heatwaves more frequent, longer and more intense.

Worldwide, heat is the deadliest type of weather, killing more than each year. The number will increase, since even if we reached net zero tomorrow, the carbon dioxide we have already emitted will keep raising temperatures.

鈥淭his is just the start,鈥� says at University College London. 鈥淭hings are unfolding in a very, very major way now, because this isn鈥檛 just about it [being] too hot in London, and the long-term effects are going to be savage.鈥�

Outside the tropics, the time of the year in which temperatures above 32掳颁 occur has lengthened by 12 days in the past half-century. In Europe, the fastest-warming continent, the season of strong heat stress now starts on average in June and continues until almost September. Sometimes, like this year, it starts in May.

That increases people鈥檚 exposure to hot days and heatwaves. Parts of North America, Europe, South America and Africa now experience up to 50 more days of strong heat stress compared with the 1970s.

鈥淚f you鈥檝e got heatwaves that last longer, and then you鈥檝e got more heatwaves, people are going to be in that raised physiological state for longer,鈥� says Neil Maxwell at the University of Brighton, UK. 鈥淭hat can lead to greater inflammatory marker responses, and that ultimately puts a greater stress upon individuals.鈥�

Strong heat stress almost never occurred at night before 1998. But now, nighttime temperatures in western Europe and other places are increasing at of global warming as a whole.

A drop in body temperature triggers sleep. If the environment is too hot, it is harder to fall asleep, as well as to enter a state of deep sleep. And loss of sleep over several nights in a row can hinder reaction time and boost anxiety and stress.

鈥淚f you don鈥檛 get cooling periods at night, which we define in this country as less than 20掳颁 at night, sustained temperatures without cooling have worse impacts,鈥� says Montgomery.

The hottest summer ever seen led to apocalyptic scenes in Europe in 2022. Wildfires broke out in France, Portugal and Spain. Italy鈥檚 longest river, the Po, ran dry in places, and wrecks of Nazi ships full of explosives were discovered as the Danube fell to record lows. In the UK, temperatures exceeded 40掳颁 (104掳F) for the first time.

More than 60,000 people died because of these baking temperatures. The highest mortality rates were in Mediterranean countries, which had some of the biggest temperature anomalies, with temperatures reaching higher than 40掳颁 in Italy, Greece and Spain. These countries also have some of the , whose bodies aren鈥檛 as resilient to heat and who are more likely to have chronic illnesses.

鈥淵ou also get inflammatory responses from heat, so heat exposure in itself triggers all sorts of bad biology in your body, basically, that is directly harmful鈥� and in particular in people with diseases,鈥� says Montgomery.

The frequency of a heat stress day followed by a tropical night of at least 20掳颁 has increased 73 per cent in Europe since the 1970s. These are called 鈥渃ompound events鈥� because the body isn鈥檛 able to cool down and recover at night, compounding the heat stress.

Europe has also seen prolonged periods of heat stress become more common. And Africa is now almost three times more likely to suffer hot spells lasting three-quarters of the year or more.

Leaders like US President Donald Trump have made pledges to plant millions of trees while increasing CO2 emissions. But in the case of urban heat, trees can make a big difference. They create areas of shade, and they also draw moisture from the soil, which then evaporates from their leaves, cooling the environment. Neighbourhoods with tree canopies can be as much as than similar places.

But although many cities have started planting trees to deal with heat, a recent found that many still have swathes of territory below the 30 per cent canopy cover that can reduce dangerous heat island effects. More than 90 per cent of the buildings in Paris and London fall below this threshold.

贰耻谤辞辫别鈥檚 most extreme heatwave so far may have killed between 17,000 and 25,000 people, according to an early estimate based on past deaths from heat in the region.

鈥淭hese numbers are preliminary,鈥� says at Indiana University. 鈥淏ut they highlight the need for rapid adaptation investments to avoid these impacts in the future.鈥�

Callahan鈥檚 estimate is based on . 鈥淲e鈥檙e taking data on temperature and mortality across Europe, and we are correlating how high temperatures relate to excess mortality rates,鈥� says Callahan. 鈥淲e then use that relationship to infer how a given heatwave affects mortality over a region like Europe.鈥�

Callahan鈥檚 conclusion is that the heatwave in Europe from 22 to 28 June 2026 killed approximately 20,390 people, including 5210 in France, 4543 in Germany, 3163 in Spain, 2709 in Italy and 862 in the UK. These numbers are much higher than the direct counts announced so far, but this isn鈥檛 surprising because it takes time for data on deaths to be collected and analysed.

鈥淭his figure is a modelled estimate rather than a final count, and it will be some months before the true toll is confirmed, in part because heat rarely appears on a death certificate,鈥� says at the University of Warwick in the UK.

For instance, on 28 June, the head of the World Health Organization, Tedros Adhanom Ghebreyesus, said so far. This number is largely based on reporting around 1000 more deaths in the country than expected from 24 to 26 June.

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However, that statement made it clear that this number is based on a computerised death certificate system that is far from complete. It records 80 per cent of hospital deaths, 45 per cent of deaths in long-term care facilities and 25 per cent of deaths at home. 鈥淢ortality will consequently be higher than these initial figures suggest,鈥� the statement said.

Even so, other experts think Callahan may have overestimated the numbers. 鈥淭wenty-thousand for a single week seems very large,鈥� says at the University of Bristol in the UK. 鈥淲e鈥檇 have to look into details of the modelling to be more sure.鈥�

While Callahan鈥檚 method is sound, the main issue is that he used data from 2015 to 2019 to calculate the relationship between heat and deaths, says at Pozna艅 University of Medical Sciences in Poland. People may now be less vulnerable due to ongoing adaptations, such as increased access to air conditioning, . Walkowiak鈥檚 back-of-the-envelope calculation is that if this is taken into account, the actual number of deaths would be around 15,000.

Callahan is sticking to his guns. 鈥淲e don鈥檛 have very strong evidence that the relationship between temperature and mortality dramatically changed over time,鈥� he says. 鈥淪o it鈥檚 not obvious it鈥檚 different now than it was 10 years ago.鈥�

鈥淚n general, we find that our sort of broader statistical estimates give higher numbers than direct reporting on the ground, because that direct reporting can often miss people who die from heat where it鈥檚 not obvious that heat was the cause,鈥� he says.

On the flip side, Walkowiak says that Callahan hasn鈥檛 taken into account the fact that heatwaves of the same temperature are more deadly in early summer than in late summer. 鈥淚n late summer, part of the especially vulnerable population is already long gone,鈥� he says.

Mitchell also says the kind of approach used by Callahan also counts only the immediate deaths. There can be longer-term impacts, such as more deaths from domestic violence, suicides and kidney failure. 鈥淭he impacts of heat on health vary a lot across timescales,鈥� he says.

What matters most is avoiding further deaths as the planet warms further and heat becomes more extreme, says Nunes. 鈥淭he signal is clear: heat is now the deadliest weather hazard we face, and the majority of these deaths are preventable,鈥� she says. 鈥淲e can now forecast these events with considerable accuracy; what we have not done is build the systems, across health, housing, social care and transport, for example, that translate an accurate forecast into actual protection. Adaptation is not keeping pace with the risk.鈥�

I鈥檓 finding the heatwave hitting Europe really scary. It鈥檚 bad enough in itself, with many records being broken, especially for the higher nighttime temperatures that make it so much harder to cope. But I just keep thinking, 鈥淚f it鈥檚 like this now, what鈥檚 it going to be like in 10, 20 or 30 years鈥� time?鈥�

The answer, of course, is hotter and hotter and hotter. In the UK, national weather service the Met Office has just warned that, by 2056, there could be , with some places hitting 45掳颁 (113掳F). In just 30 years! I鈥檝e seen at least one piece asking 鈥渋s this the new normal?鈥� about the current heatwave, but we鈥檙e never going to have normal in our lifetimes again 鈥� just ever more extreme heat.

It鈥檚 possible to get through even worse heatwaves than this if all your infrastructure and systems are geared up to cope. But the UK is very much not prepared. The air conditioning in New 女生小视频鈥檚 office, for instance, is failing to keep up with the heat as I write 鈥� and lots of people have to endure this hot weather without any air conditioning at all. In a sign of the times, a meeting on adapting to extreme heat 鈥� part of London Climate Action Week 鈥� got .

Climate scientists are continually warning of the need to prepare for hotter heatwaves, worse droughts, more flooding and rising seas. During heatwaves like this one, they might even get a little media coverage. But then the weather cools, the news agenda moves on and nothing is ever done.

That鈥檚 not just my view 鈥� it鈥檚 the official verdict of the UK鈥檚 Climate Change Committee, which advises the UK government. 鈥淎daptation progress is either too slow, has stalled, or is heading in the wrong direction,鈥� it said in last year. Everyone seems to assume this green and pleasant land is going to remain green and pleasant, but it won鈥檛. We鈥檙e heading towards catastrophe, but never looking up.

There are many aspects of this that frighten me. Firstly, emissions are still rising, so the fundamental cause of the problem is getting worse. True, it鈥檚 not getting worse as fast as it was, but we are currently , and possibly even more.

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Even these alarming numbers are a little misleading because the oceans that cover most of the planet don鈥檛 warm as fast as the land. Average land temperatures are therefore going to go up by a lot more than the above numbers imply.

And what really matters to us is extreme weather, not the average. The projections for future extremes are already dire, and there are reasons to think that we鈥檙e in for extremes even greater than those currently projected for a given level of warming. For starters, heatwaves are already more extreme than projected in some parts of the world. One reason for this is that climate models may not be capturing how the dynamics of the jet streams change in a warmer world. Another is that regional models haven鈥檛 accounted for reductions in sunlight-blocking air pollution.

The next level beyond is how bad the knock-on effects of this extreme weather will be. These kinds of things are very difficult to project because so many complex systems are involved, but here, too, there is reason to think we are underestimating the impacts.

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For starters, we could see mass deaths even among young people as heatwaves get more extreme. Then there鈥檚 our ability to feed people, the basis of civilisation. There鈥檚 growing evidence that global warming is already hitting food production, pushing up prices and causing yet more deforestation as farmers try to compensate.

As ever more weather extremes hit the world at the same time, the economic impacts are going to get ever more serious, too. One 2024 study warned that the result could be the worst global financial crisis ever.

And I haven鈥檛 even mentioned the wild cards, such as the Amazon drying up or the Atlantic Meridional Overturning Circulation shutting down. One researcher I chatted with at a recent conference thinks a slowdown of this crucial current system around 12,000 years ago triggered extreme seasonality in places like Britain, with sweltering summers, but temperatures plummeting tens of degrees below freezing in winter.

The fact is, the world is changing fast and we need to change just about every aspect of our lives to adapt 鈥� our homes and offices, factories and schools, cars and trains, farms and gardens, and so on. But it鈥檚 not happening.聽 That鈥檚 why if you鈥檙e not scared witless by this heatwave, you should be.

With Europe in the grip of a mega heatwave and deaths already being reported, staying cool isn鈥檛 just about comfort 鈥� for many, it is a matter of life and death. Many people will be relying on fans rather than air conditioning, so it is important to be aware that, as it gets hotter, fans can flip from cooling you to warming you.

But how hot is too hot? The UK government warns , whereas the World Health Organization says . Some studies suggest even lower or . The reality is that there is no simple answer, as several factors are involved.

The key thing to know is that you become less good at sweating as you age, so fans will start to warm you at a lower temperature than is the case for younger people. However, you can compensate for this by spraying yourself with water or wetting your clothes.

The situation would be very simple if we didn鈥檛 sweat. Our skin temperature in the shade is typically between 35掳颁 and 37掳颁 (99掳F). If the air temperature is lower than our skin temperature, heat is transferred to the air, cooling us, but if it is higher, we gain heat from the air. Moving air over our skin with a fan speeds up this heat transfer, whichever way it is going.

Because of this, in the past, 35掳颁 was often said to be the point at which fans stop cooling us, says in the UK. But this number doesn鈥檛 take account of evaporative cooling.

The evaporation of water transfers lots of heat from our skin into the air, cooling us even when air temperatures exceed skin temperatures. But blowing air over our skin with a fan doesn鈥檛 necessarily cool us more if it鈥檚 too dry or too humid.

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When it is very dry, our sweat can evaporate as fast as we produce it. In this situation, turning on a fan won鈥檛 help, because evaporation cannot increase any further. Instead, the moving air will just transfer more heat to your skin. For instance, modelling and experiments show that at 15 per cent humidity and 45掳颁, turning on a fan will almost certainly .

But as the humidity rises, evaporation slows because there鈥檚 already lots of moisture in the air. Basically, if you are dripping with sweat, you are producing sweat faster than it can evaporate. In these conditions, a fan does help.

For instance, a fan can still cool you at up to 60 per cent humidity and 38掳颁. As the humidity gets even higher, however, evaporation will slow to a point when a fan stops helping.

鈥淪o it depends on the humidity in the air,鈥� says Havenith. 鈥淭hat鈥檚 why people often look at what kind of climate you have in different countries.鈥�

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The other big factor is age. As we age, our body temperature and skin temperature can fall. It also takes longer for us to start to sweat, and we produce less sweat. This means the temperature at which a fan will start warming us at a given humidity declines as we age.

In this situation, wearing wet clothes or spraying ourselves with water can help. This can also reduce sweating and thus reduce the risk of dehydration.

Many other factors also play a part, such as clothing and whether your body is adapted to high temperatures. The bottom line, however, is that if you live in a building that gets really hot, temperatures during this heatwave could well exceed the level at which fans will help, even if you鈥檙e spraying yourself with water.

鈥淎t that stage, you probably would have to leave your house and find a cooler place,鈥� says Havenith. 鈥淏ecause it鈥檚 a really bad situation.鈥�