https://unherd.com/2022/01/how-long-can-humans-survive/
BY TOM CHIVERS – UnHerd’s Science Editor. His second book, How to Read Numbers, is out now.
How long can humans survive? This time of plenty won’t last for ever
Excerpt: We are currently living in a time of whalefall, suggests the scientist Vaclav Smil in his new book, How the World Really Works. …
The demand for material – for energy and nutrients – is greater than it has ever been. The world’s population has exploded: in 1800, there were about 1 billion humans. In 1950, there were 2.5 billion. Now there are 7.7 billion. In my parents’ lifetime, the number of humans alive has trebled. But amazingly, the amount of material available to each of them has increased even more, and that is in large part because of our use of fossil fuels.
In 1800, almost all the energy used globally was in the form of human and animal muscles, for mechanical work, or plant matter, burned for heat and light. Coal, the first widely used fossil fuel, was just starting to be used in steam engines in the UK, but it was negligible overall. By 1900, fossil fuels were the source for half our energy. By 2000, they were the source of 87%.
And as a result, our lives have been transformed. The amount of energy available to the world has increased 1,500-fold. That is only part of the story, though: increased energy efficiency means that the gain in useful energy is more like 3,500 times. And even though the world’s population has gone up many times, “an average inhabitant of the Earth nowadays has at their disposal nearly 700 times more useful energy than their ancestors had at the beginning of the 19th century”.
But most of us don’t realise how that energy is actually used. A large percentage, for instance, is used to create four materials which are the building blocks of modern society – materials which are so ubiquitous that we barely notice them, even as we depend on them.
Smil identifies these four basic pillars of human civilisation as steel, cement, plastic and ammonia. Producing them takes enormous amounts of fossil fuels. It takes, for instance, 25 gigajoules of energy to produce one ton of steel, roughly twice the amount of energy used by the average UK household per year. In 2019, the world used 1.8 billion tons of steel; its production is responsible for about 8% of the world’s total carbon emissions. But we can’t do without it: the frameworks of our cities are built of it; the pipes we send our water and gas through, too. Our cars, our transporter ships, our knives and cooking pots. Our machines for making all these things. Cement and plastic are similarly vital, and are responsible for comparable amounts of our total carbon output. We can’t do without them, and there’s no easy carbon-free alternative way of making them.
And then there’s ammonia, which rarely features in any conversation about cutting carbon emissions. Ammonia is a nitrogen atom ringed by four hydrogen atoms. Our atmosphere is 80% nitrogen by mass, but plants – which need it for growth – can’t easily take it out of the air. Instead they need to gather it from the soil. Bacteria that live in the roots of some plants can “fix” it into the soil; animal wastes like manure have relatively high nitrogen content. But those methods can only support a certain amount of growth.
In the beginning of the 20th century, a German chemist called Fritz Haber invented a process for getting nitrogen out of the air by making ammonia. It requires huge amounts of energy, and hydrogen, usually taken from natural gas. We now spread hundreds of millions of tons of ammonia on our fields — about 50% of the total nitrogen going into food production comes from it. Smil quotes an author, writing in 1971: “industrial man no longer eats potatoes made from solar energy; now he eats potatoes partly made of oil.”
This means the world is able to eat. The share of the global population that is underfed has plummeted, even as the actual population has ballooned – about 65% of people could not get enough to eat in 1950, compared to about 9% in 2019. So, “in 1950 the world was able to supply adequate food to about 890 million people,” as Smil puts it: “but by 2019 that had risen to just over 7 billion”. That is not entirely down to ammonia, but ammonia is a large part of the story. If fertiliser were removed, perhaps half the world’s population would starve.
Agriculture, then, depends on the whalefall: the glut of energy provided by fossil fuels. Our deep reliance on fossil fuels, to create materials most of us don’t appreciate we need, is unnerving. Especially when Smil points out that much of the world — notably, sub-Saharan Africa — lives on well below average levels of energy use. Africa uses just 5% of the world’s total ammonia supplies, despite having almost 25% of the population. About 40% of the world — 3.1 billion people — has a per capita energy supply “no higher than the rate achieved in both Germany and France in 1860”. “In order to approach the threshold of a dignified standard of living,” writes Smil, “those 3.1 billion people will need at least to double — but preferably triple — their per capita energy use.”
