Soon it will have been 7 years since I became a vegetarian. Although I had grown increasingly sensitive to animal suffering over time, it was the flu that made me a vegetarian. Yes, the flu. A really bad flu. While it kept me home for less time than COVID did, it was far worse. And it wasn’t just me: even Vincent, one of my colleagues—tough and healthy—stayed home for a couple of days. Me? I suffered for 3 weeks, coming close to asking my cat for the last rites. Okay, I exaggerate. I had a bad flu for a week (muscle pain, headache, fever), then a week of the “man flu,” and then a third week where I just stayed at home. I think I described that third week as the “CNRS flu,” though maybe someone else came up with that.

Now, I’ve heard of cases where people, after being sick—maybe even from the flu—can no longer digest meat. That’s not what happened to me. In my case, it was a second-order effect: the flu produced boredom, and boredom made me a vegetarian. By the second week, at the latest by the third, I had watched every documentary in the world about cats. Twice. Some, like Kedi, more often than that. I was forced to find something else to occupy my time, so I decided to try to understand the deal with climate change. Now, I can’t claim to understand the physics of it, but it was clear to me that it was going to be a real problem—and that we were causing it.

Here’s Climate Physics 101, possibly worth something close to an F, but bear with me. Heat arrives on Earth from the sun as radiation with a given wavelength. It heats the Earth, which also radiates heat. The amount of heat radiated by the Earth depends on its temperature, and over time, an equilibrium is reached where the same amount of heat is radiated out as is radiated in. But there’s something else at play. Certain gases absorb radiation at specific wavelengths, and the wavelength of the radiation coming from the sun differs from that leaving the Earth. Some gases, like CO₂, ignore incoming radiation but absorb outgoing radiation. In other words, it’s harder for heat to escape the Earth, much like a blanket makes it harder for your body to lose heat to the surrounding space. This effect—the greenhouse effect—makes the Earth warmer, which is a good thing. Without it, the average temperature of the Earth would be -18°C.

The strength of the greenhouse effect depends on the concentration of greenhouse gases in the atmosphere. The issue is that we’re increasing their concentration. Since the Industrial Revolution, the concentration of CO₂—one of the principal greenhouse gases—has increased by 50%, compared to what had been a stable concentration for much longer than all of recorded history. We’ve made the blanket thicker, and we’re still adding layers. These gases also decay, meaning the blanket naturally gets thinner, but this happens very slowly. Each CO₂ molecule remains in the atmosphere for something like 400 years. We’ve been adding layers to the blanket much faster than they’re removed, so for all practical purposes, the addition of those layers is irreversible.

There’s another thing. When you put on a blanket, it takes a while to feel warm. Similarly, when you close a window, it takes time for the room to heat up. We’ve already increased the greenhouse effect, but we’re not yet feeling the full effects of that increase. But since the blanket is here to stay, we’re certain to feel them. When people say it’s impossible to meet the 1.5°C objective, they mean that the concentration of greenhouse gases in the atmosphere is already such that we’ve reached a level guaranteeing a temperature 1.5°C higher than the pre-industrial average.

All of this is a brutal simplification—remember, I advertised it as an F in Climate Physics 101. There are countless models, and I’m no climate scientist, but the basic science has been well-established for 150 years. There’s clear consensus about what’s happening.

What the models are less clear about is the specific effects of temperature increases. They agree on what the likely effects will be, but not on how likely they are. Some effects might pull in different directions. For example, in Europe, we must consider the possibility of temperatures rising much more than the global average, or the possibility of temperatures dropping significantly because the AMOC (not the Gulf Stream, which is driven by Earth’s rotation, but another such current in the Atlantic) might weaken or stop. Different models assign different probabilities to these events. In short, while we’re certain the climate will change—the blanket is here and isn’t going anywhere—we don’t know exactly what the effects will be.

Let’s apply some common sense. About 20,000–25,000 years ago, glaciers covered most of the UK and a huge part of the contiguous US. The average temperature of the Earth was 4.5°C colder than it is now, and since then, the temperature has remained more or less constant, with small variations—until now.

This means that, on geological timescales, the Earth’s temperature has always fluctuated, and the increase caused by human emissions isn’t huge in itself. From that perspective, the most remarkable thing is the speed of change. Still, I wouldn’t be surprised if someone told me that volcanic activity once had a similarly rapid effect. The Earth is about 4.5 billion years old, and not many people think in those terms. Homo sapiens appeared about 300,000 years ago. Even on that scale, our species has endured temperature changes greater than what we’re causing now. But most people don’t think in those terms because we tend to see our grandparents’ childhood as ancient history and our children’s grandchildren as the distant future. This means that 10,000 years—let alone the time since the last ice age—is a scale we can’t truly comprehend. And why 10,000 years? Because that’s roughly when agriculture began. All of human history we can vaguely relate to—everything we’ve ever heard of humans doing beyond a few cave paintings and flint axes—has happened during a time of relatively constant climate. Now, we’re changing it, and we’re doing it fast. To be precise, we’ve ensured it will change fast, and the only thing we can do now is decide whether we’ll continue to make this change worse or not. This change won’t happen overnight, but we—and definitely our kids—will see it. The timescale here is decades, not millennia.

What the effects will be is unclear, especially when looking at specific regions. The system is complex, and in Europe, it could rain more, or less, or in much more concentrated bursts. It could get much hotter or much colder. Different models say different things. Part of the issue is the existence of “tipping points.” As I understand it, some changes, once they happen, trigger others, like a chain reaction. For example, ice masses apparently have a critical size below which they’re doomed to melt. There are enormous amounts of greenhouse gases frozen in the permafrost, which could be released into the air rapidly. So, no one really knows what the effects will be, but all models agree they’ll be dramatic.

Dramatic like what? Like London having the same weather as Barcelona in 30 years? That would indeed be dramatic. First, 30 years isn’t much for a tree, so maybe we should start thinking about what will grow in Sussex. But the problem is that trees and plants are adapted to specific temperatures and weather patterns, as well as the number of daylight hours. That won’t change: the climate could become as hot as you like, and the winter nights of the Arctic could become tropical, but night it would still be. So, it’s not that the Barcelona lifestyle will move to London. No one knows exactly what the disruption will be, but it will be enormous. By the end of the century—when my daughter will be about the age my mother is now—global agricultural production is expected to decrease by 20–50%. That’s a big range, but even a 20% decrease would be dramatic.

Does this mean we’re screwed? Well, not in geological terms. It’s less clear in terms of the survival of our species, and maybe not for you personally (if you’re going to die soon enough). But our kids are definitely in trouble. Some more, some less, but it’ll be a bit like a lottery, and on average, people will be in trouble. Even if you’re lucky and local changes cancel out, you’ll still feel it because those who aren’t so lucky won’t take it with a stiff upper lip. In the 1930s, the Dust Bowl in the Midwest had effects as dramatic as the Great Depression and led millions to abandon everything and emigrate to luckier places. Right now, they’re considering evacuating Tehran due to a lack of drinking water caused by years of drought. Imagine that happening in LA, Algeria, Seville, or Barcelona. It seems unimaginable that this could happen in Barcelona, but COVID also seemed unimaginable in Barcelona when it was happening in Wuhan. So, if we live a few more decades, we’re in trouble. And our kids definitely will be. We’ve condemned them to that.

But what we can still do is stop making the situation worse—stop piling unremovable blankets onto an already overheated bed. We can also prepare. Some people are preparing. Elon Musk dreams of Mars, and others prepare refuges for themselves in New Zealand. I can’t do that, and I assume you can’t either. For what it’s worth, I try to improve my house so that if winters get colder or summers hotter, it’ll be more comfortable. I plant trees in the garden to create a more protected environment, but we all agree that this is just peanuts. However, what I really try to protect is my future self-image in front of my daughter. At some point, the shit is going to hit the fan so hard that people in her generation will justly consider us the scum of the Earth, thinking that out of obvious selfishness, we screwed everything up for them. I expect to see this happen in my lifetime. My absolute priority is to do what I can to avoid her thinking that I always told her I loved her very much while knowing what kind of mess I was leaving her to deal with—and without doing anything about it. You might find this overly dramatic, but think about how 20-something Germans in the 1960s must have viewed their parents. I’m sure my daughter will find enough reasons to think I’m a bit of a shit, but I definitely don’t want to add to that list the idea that I ignored climate change out of pure convenience.

At a personal level—and this is all most of us can do—there isn’t much we can change. We can’t alter global distribution channels, how electricity is produced, how hospitals operate, or where steel mills get their energy. This means that simply living in a Western society already results in far higher emissions than we should produce to avoid worsening the problem. All the emission reductions we’re seeing are just slowing the rate at which we’re making things worse. To stop making it worse altogether, far more dramatic reductions would be needed. In France, the baseline for emissions is about 5 tons of CO₂ per person per year, but a sustainable level would be 2 tons. However, the actual emissions per person in France are around 10 tons (only half are physically emitted within France; the rest come from imports). This means that about half of our emissions are due to things under our direct control: how we travel, how we heat our homes, our diet, and the products we consume.

Just because these levers are up to us doesn’t mean acting on them is easy or cheap—there’s a reason people live the way they do. But they are up to us. Traveling from Rennes to Rome by plane is faster and cheaper than taking the train, but it’s up to me to choose. The idea of flying to Oaxaca or Banff for a conference sounds great and would surely be scientifically profitable, but the flight alone emits 2 tons of CO₂—my entire sustainable budget. It’s up to you to decide if it’s worth it. Making your house more energy-efficient costs money, but it’s up to you whether to spend that money on vacations instead. If your job requires you to fly across the Atlantic once a month, it’s up to you to look for a different job, even if it pays less or has less prestige. I’m not saying it’s easy or cheap to reduce your emissions, but it’s up to you. The upside is that if you do, besides doing the right thing, your kids, nieces, nephews, or whoever might end up thinking, “He/She is a bit of a shit, but at least they tried.” When I think of my daughter, that’s upside enough for me.

When I understood this—thanks to flu-induced boredom—I looked at what I could change about how I lived. Until then, I ate a lot of meat, but I became a vegetarian (which reduces diet-related emissions by about half, or 1–1.5 tons of CO₂ per year). I also decided to drastically reduce how much I fly, limiting myself to one flight within Europe per year (when going to Helsinki, the alternative is spending 3 days traveling each way) and one flight outside Europe every few years. I’ve spent money on better windows and try to buy more durable goods. All of this comes at a cost: fewer conferences, more hours stranded in train stations, and boy, do I miss burgers. But it also comes with advantages beyond feeling like I can look at myself in the mirror. For example, I’ve learned to cook a wide variety of vegetarian dishes. I might not have burgers, but I probably eat more varied food than most people—and certainly more than I did before. In a way, dealing with the limitations of refusing certain ingredients—like not driving or insisting on traveling by train—can be empowering. I miss burgers, but once you learn to live without them, the world of dals is much wider and more interesting than that of bœuf bourguignon.

I could claim that what made me a vegetarian was the desire to be seen in a good light by my daughter, but that sounds a bit pathetic as a conversation starter. Saying I’m a vegetarian because of the boredom caused by the flu is better, but who wants to talk about boredom? So, my line is that I’m a vegetarian because I had a really bad flu. It’s at least a fractional truth, and it has the virtue of piquing people’s curiosity, probably expecting some slightly terrible medical story. Little do they know about the terribly boring rant that follows. Little did you know, if you’re the lost soul reading this and haven’t heard me talk about it before.