As a teacher and presenter I know: the simpler you want to explain something, the better you should understand it. Anyone can explain something difficult in a complicated way. The trick is to see through what is essential and what you can leave out without losing sight of the core. Weather talk on TV should sound so simple that you won’t notice that I’ve been studying satellite images and weather model calculations all afternoon. That plan seems successful: many people think that I walk into the NOS at half past seven in the evening, put on a suit and then casually read a text from the autocue.
The blade of simplicity cuts both ways. The reader or viewer understands the message better if it is simple. And I also learn to understand the subject even better if I have to explain it simply. That’s why I was quite pleased when I was asked last month to write a short text about the greenhouse effect for a popular science book. In four hundred words, that’s about half of this column. That automatically makes you concise.
Exactly two hundred years
The greenhouse effect is a groundbreaking theory that is the foundation of everything we know about the climate. This year, by the way, is exactly two hundred years old: Joseph Fourier described it in 1824.
While writing that post, it dawned on me more clearly than ever that CO2 actually plays such a crucial role in the Earth’s climate by chance. The vibrational frequencies of a CO2molecule overlap exactly with the frequencies of the heat radiation that the Earth emits into space. Those two things have absolutely nothing to do with each other. But it is precisely this coincidental coincidence of frequencies that makes the greenhouse effect so decisive for the Earth’s climate.
I’ll explain.
On Earth we have a number of large reservoirs of carbon: soil and rocks, plants, the ocean and the atmosphere. In the carbon cycle, carbon moves continuously from one reservoir to another. Sometimes very quickly, think of trees that emit CO in the spring2 absorb from the atmosphere to grow. And sometimes very slowly, like peat that is compressed into coal over millions of years. In the atmosphere we mainly find carbon in the form of CO2 and methane (CH4). All processes in the carbon cycle influence how much of it is in the atmosphere.
From heat to vibration
Let CO2 can also be a greenhouse gas. Sunlight can reach the Earth’s surface without hindrance from greenhouse gases and be absorbed there into heat. The heat that the Earth then sends back to space is absorbed by greenhouse molecules. In short, greenhouse gases are transparent to sunlight, but opaque to heat. Since Max Planck we know that molecules can only vibrate at very specific, quantized frequencies. In the case of greenhouse gas molecules, exactly the frequencies of terrestrial heat radiation. This enables greenhouse gases to convert heat into vibration energy. Conversely, these gases can also stop vibrating and emit the heat again. They do this in all directions, including back to Earth. This way, some of the heat remains trapped in the atmosphere. The temperature on Earth therefore strongly depends on the amount of greenhouse gases.
Over the past tens of millions of years, the climate has been determined by extremely slow processes of the carbon cycle. Movements of tectonic plates created new mountains and changed ocean currents, slowly changing the carbon cycle in ocean and rocks. In a hundred million years we have essentially gone from a warm dinosaur world to an era with regular ice ages. However, since the discovery of fossil fuels, the carbon cycle has short-circuited. A million-year-old reservoir of carbon has been released into the atmosphere over the past century and a half – a geological blink of an eye. It is therefore not surprising that the current warming is entirely due to fossil fuels.
Boring and simple
All in all, the action of greenhouse gases is an extremely elegant theory that links the carbon cycle to the Earth’s climate. It can easily explain Earth’s climate on many time scales. It is also thanks to that elegance that the message from climate researchers has long been fatally boring and simple: stop burning fossil fuels to stop warming.
That message also remains valid at the end of the disaster year 2024, in which a record amount of fossil fuels was probably burned, one and a half degrees of warming was reached for the first time, a wind of climate disinterest started blowing at home and abroad, and hydrological cycle starts to spiral out of control. It is little consolation to think that the problem is not that Joseph Fourier and all those other scientists have not explained the greenhouse effect clearly enough. We understand it too well for that. I think the problem is that the laws of physics lose out to the power of the established order. I can’t explain it any simpler.
Peter Kuipers Munneke is a glaciologist at Utrecht University and weatherman at NOS