Preface
I began writing this back in June of this year. I planned to have it out by July because I couldn’t imagine a worse time than what I was experiencing then. Clearly, I was wrong. Until recently, the very end of August, could I actually continue writing in earnest because the heat was so constant that I couldn’t keep a coherent thought for more than a few minutes. Now that the worst of the heat is over in Europe, I’ve already noticed a shift in the way it is discussed online and in person. Something about heat seems to leave our memory as soon as it’s over, and so already the most dominant voices are those who claim to want the warm weather back. Hopefully, I can act as a reminder for all of you out there just how dire things can be as we begin to move into autumn in the Northern Hemisphere.
Intro
As I write this intro, I sit in the office, having finally recovered from the 10 minute bicycle ride from my home. I’ve been here for an hour. It is the week of the 22nd of June, 2026, and Europe is in the midst of a massive heatwave. The area I live tends to average around 20 C (68 F) at it’s highest for this time of year. We’ve been seeing temperatures of 34 C (93 F) for days at a time. On Friday evening, the Netherlands suffered a massive lightning storm. These heatwaves are becoming more common globally, with Europe warming faster than most of the rest of the world. So, what are their causes? Why does the weather sometimes become unbearably warm? Why does it hurt some places more than others? Why are they becoming more common? And what can we do about it, in the short and long term?
It is now one week later, the 29th of June, 2026, that I can start writing and researching again. The part of the heatwave that I was in has finally ended after taking an impromptu break over the week. Temperatures peaked around 38 C (100 F) with the only air conditioning I had available to me being my brief visits to one of the grocery stores. In the hours between Saturday night and Sunday morning, another storm hit the Netherlands, knocking over trees, massively disrupting transportation, and hitting a new record for amount of lightning strikes within 24 hours at 300,000.
There is something different about the heat this year, and it feels like a lot of other people feel that too. In my own life, my friends and acquaintances are beginning to talk about getting some form of air conditioning. I’m seeing more jokes and references online to human caused climate change. In the Netherlands, it has often felt more accurate to think of normal summer temperatures as oddities and even being chilly. Consider this a crash course into the most recent research of heatwaves and perhaps an explanation as to why things seem to be worse than they used to be.
What is a heatwave?
The exact circumstances of a heatwave can be hard to define in a general sense, because the usual climate where you live will change the definition. What would be a heatwave in Moscow may be a cool and comfortable day in Singapore, after all. In an effort to sum this all up, the European State of the Climate 2023 said that a heatwave was “a period of at least three consecutive days when both the daily surface air temperature minima and maxima are higher than the highest 5% of values for the day in question during the 1991–2020 reference period.” Essentially, a heatwave is a period of a few days where temperatures are warmer than are expected. More of a ‘you know it when you feel it’ situation.
Heatwaves on land aren’t the only kind to exist. It’s possible for the ocean to warm enough to be considered a heatwave, having knock-on effects across the ecosystem in and out of the water. I won’t get into this here for the sake of brevity. For one of the issues that comes from a marine heatwave, read my Burnt Coral feature.
What causes them?
As with any weather phenomena, it is difficult to pin any individual cause onto them. It can help to show what the major types of heatwave are: daytime, nighttime, and compound. During daytime heatwaves, temperatures increase during the day, but are able to cool down at night. For nighttime heatwaves, heat is unable to leave, sticking around well past sunset. Compound heatwaves, meanwhile, exhibit both a drastic increase in day temperatures and an inability to cool down at night.
In 2023, researchers were able to identify some major characteristics that explained why these different types acted so differently. For instance, daytime heatwaves happen in dry conditions with few clouds in the sky as more shortwave radiation reaches the surface, causing moisture in the ground to dry up. Nighttime heatwaves are much the opposite, with moisture in the ground and air holding onto heat for longer, as longwave radiation gets reflected back down from clouds. Compound heatwaves, despite being the most common type, are possibly the least understood of all of them. Not due to rarity, as these are the most common type, but rather because they are a combination of daytime and nighttime heatwaves, as their name implies.
Radiation can be a bit of a worrying term. In science, we use words like radiation to talk about anything that radiates. In this way, light is radiation, and is in fact the kind of radiation we are talking about. In this context, shortwave radiation refers to the light that comes from the sun, like UV or visible light. Longwave radiation refers to the infrared that is given off by the Earth as heat.
These compound heatwaves make categorisation difficult, as they exhibit many signs of both daytime and nighttime ones. Cloudlessness increasing heat during the day, humidity preventing a dip in temperature at night, longwave and shortwave radiation dominate at all times of day. This kind is particularly common in North America, Europe, India, and Australia.
How dangerous are they really?
It depends on where you are, who you are, and how much money you have. There are the risks associated with direct heat, of course, such as sunburn, heat exhaustion, dehydration, and heat stroke, but the biggest risks are often the secondary effects. This can be measured by looking at how many people died during that time period in the past, and using that to predict how many we would have expected to die in normal temperatures. The difference between that prediction and the actual number of deaths is roughly how many people died due to the effects of a heatwave. Using this method, the Dutch government found that the period of extreme heat in the Netherlands at the end of June 2026 killed nearly a thousand people. Of these, only a few were caused by the complications above, with most heat-related deaths being from those who were already vulnerable, such as the elderly or those experiencing poverty and a lack of resources.
Earlier this year, in May 2026, India experienced near record temperatures for a very long period of time. Official government figures often report only the number of deaths from direct heat related causes, such as heat stroke. However, estimates by researchers suggest that the excess deaths in India from a heatwave that lasts 5 days could reach over 30,000. It’s hard to quantify how many lost their lives as a result of this one because of the way figures are reported, so these estimates will have to do.
Are they getting worse, and is it because of global warming?
In science, we are taught to speak in terms of probabilities. We say whether something is likely caused by this, or how things might be related. In every article about heatwaves, there is essentially no doubt as to whether they are increasing and to the cause of the increase. Now, as I said before, the most common kind of heatwave, the compound heatwave, is also the least understood. It is also increasing in frequency, rather drastically. The second most common heatwave is the night heatwave. This used to be the third most common type, but at some point in the 90s overtook the daytime heatwaves in number and frequency. Although the share of heatwaves that are classified as daytime has gone down, the total number of them still went up. Heatwaves of all kinds are significantly more common than they were only two decades ago.
This is happening specifically because of our effect on the atmosphere, the greenhouse gases building up over the last few decades as a result of things like burning fossil fuels and industrial agriculture. Humanity is unequivocally causing these disasters and unless something drastic is done, they will continue to increase in frequency and severity.
Why haven’t I been told this before?
When you hear about a heatwave, it’s often associated with imagery of people outside and enjoying the sun. On a lake, at the beach, playing sports, and so on. An Australian study found that more than half of news reports used this framing when discussing the impacts of heatwaves, which makes the risks seem less severe. Another major source of messaging was the idea of ‘braving the heat’, or continuing to do strenuous activities during high temperatures, which almost makes doing something dangerous seem like a virtue.
One of the least reported aspects of heatwaves is the deaths that are caused, and even then the stories almost exclusively focus on heatstroke. Even still, it is shown as abstract figures, something that the viewer can distance themselves from. When you have seen this kind of reporting, it hasn’t stuck in your brain, not like the idea of relaxing or playing in the summer sun. I will reiterate my point that these are some of the deadliest events to regularly occur, and it is my belief that this style of reporting is dangerously irresponsible.
It is for this reason that this article doesn’t contain any typical summer imagery. These are natural disasters that have increased in severity in my own lifetime. Europe, when I first moved here, was cooler. I also scoffed at the need for air conditioning. I thought maybe in 20 years, it may be needed. And then 2019 gave a taste of what was to come, and every year since the amount of time I’ve spent languishing inside with a fan on me has increased, even as my heat tolerance has been forced to improve.
It is my opinion that journalists should end the practice of using fun imagery with heatwaves, and instead put more focus on practical steps that can be taken to avoid the heat, and keeping people aware of the dangers, particularly to vulnerable people.
What can I do?
Naturally, the ultimate way to help make sure these events happen less is to end global warming. Even if humans aren’t causing global warming (we are), it’s clear that the reason hundreds of thousands of people are dying every year is because the climate is warming up and greatly increasing the likelihood of extreme heat.
In 1953, the Netherlands experienced a devastating flood. It killed 1,836 people, and led to a massive investment in flood prevention in the country. The Netherlands built a flood barrier that cost 2.5 billion guilder, or about $2.9 billion in modern USD (which is, oddly enough, also € 2.5 billion at the time of writing this). In addition, the Delta Fund was created to keep the Netherlands safe from future flooding, with € 27.4 billion currently expected to be paid in to it. This is a good and responsible thing to do in response to a disaster, to prevent it from doing harm in the future. For disasters that have the potential to kill that many people every year in the Netherlands alone, a similar response should be enacted.
Until global warming is solved, the most important thing you can do is to keep yourself and others safe. If you are in a position to do so, get air conditioning. Our bodies require dryer air and cooler temperatures to manage the ways we naturally make heat, and air conditioners are our best technology in order to support that. If you do have air conditioning and know of vulnerable people who don’t, I would recommend offering them a place in your home for some time to give them a chance to recover from the heat.
Some cities will offer designated ‘cool areas’, places that have offered their premises in the case of extreme heat. See if you can find any in your city if the heat becomes too much for you, they can offer a brief respite. And finally, stay cool however you can. Keep an icepack in the freezer to put in bed with you at night. Put a damp hand towel in your fridge to cool yourself off with. Enjoy some ice cream. And most certainly stay in the shade and don’t let sunlight into your home.
Heatwaves will continue to be an issue, will continue to increase in severity, and will continue to increase in frequency. The best we can do right now is to protect yourself and your community while doing whatever is in your power to encourage large-scale change.
If you have any comments, questions, or criticisms, please don’t hesitate to leave a comment here, mention me on BlueSky, or get in contact with me via my email snippetsofscience@gmail.com. I endeavour to address everything I can and to make my work as factual and informative as possible.
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