We only have one earth, so we will have to share it and we have to share it with more and more people. Will there be room for everyone? The demographer Thomas Malthus expressed his concerns at the beginning of the nineteenth century. “The power of population is indefinitely greater than the power of the earth to produce subsistence for man.”

That is obviously true: together, two people can produce more than two people, and those offspring can produce more offspring, etc, creating a snowball effect until there are too many people and we are forced to fight each other to the death to obtain food. That is the future as Malthus saw it. The good news is that he had a limited view of the word “indefinitely”. Even in his day, people could limit the number of children they had and that has become even easier now. And it appears that once people have reached a certain standard of prosperity, they tend to limit the number of their offspring.

Consequently, the global population’s rate of growth is slowing down. According to the United Nations, the earth will have 9.6 billion inhabitants by 2050. However, the number of Europeans will actually be lower than it is now: in the next forty years, the population will increase less than it has done in the past forty years, both in relative and absolute terms.

So far, so good. Humanity as a whole is now more prosperous and more peaceful than it was forty years ago, despite all the growth. So, will there be room for those extra 2.6 billion? And will everyone have enough to eat?

In the science journal Ecological Economics, environment scientist Ingrid Odegard from the Delft advisory agency CE and her Leiden colleague Ester van der Voet have calculated what will be needed in the way of food in 2050. “I calculated it for a number of different scenarios, including ones in which there are more than 9.6 billion people”, Odegard explains. “I researched what was needed for various types of food as best I could. Food is used in certain proportions in a dietary pattern, so I multiplied the different dietary patterns with the number of people.” This produces a rough estimate of how much food will be necessary to feed the world.

Odegard and Van der Voet’s model takes three necessities into account: agricultural land, water and fertilizers. We don’t have an unlimited amount of fertile agricultural land here on earth, and we want to leave part of that as it is for nature conservation areas. We have plenty of water – seen from outer space, our planet seems to be practically made of water. The problem is that only a tiny amount is suitable for agricultural purposes. Fertilizers are things like nitrogen, phosphor and potassium: plants can’t grow without them and without plants, there wouldn’t be any animals, or people for that matter.

Forty per cent more people does not necessarily mean that we need forty per cent more of whatever to feed them. In 2005, twice as much wheat was produced per square metre than in 1968 as a result of better varieties, better agricultural technology and better artificial fertilizers. The same applies to other crops. If we hadn’t managed to produce bigger crops, we would need more than twice as much agricultural land as we had back then. And we don’t have that much land, not even if we chop down all the forests on the planet.

In their model, the researchers have allowed plenty of scope for the fact that production may rise even more, as Odegard adds: “The yields in developing countries can still grow by a huge amount – in fact, they will have to.”

Well, that’s the good news. The bad news is that if all those 9.6 billion people eat like the average Westerner does, we will be facing a tremendous problem. We would be polluting far more water and we would need two to three times as much agricultural land.

Another issue involves the minerals for artificial fertilizers: we can get nitrogen from the air, but potassium and phosphor need to be mined. Depending on the actual 2050 scenario, we will have nearly depleted our stocks of extractable minerals. Van der Voet continues: “We could manage potassium, as it’s available in abundance. But I predict problems with phosphor. According to our model, it should last until the year 2150. That’s startlingly soon: phosphor is essential to humans. It’s high time we considered what to do when the easily extractable phosphor runs out.”

The hardest cut in our food will be meat: instead of eating plants, we give them to animals and then eat the animals, which is, by definition, not very efficient. “Sometimes people act as if this is just hippie talk”, Odegard sighs. “Though it’s very simple to calculate.” When asked, neither researcher admits to being a vegetarian.

We can feed humanity in 2050, but only if that humanity is willing to eat far less meat than most Westerners do now. “Such a lot can be done for the environment if we manage food more efficiently”, laments Van der Voet, “But that’s no-go area – it’s politically sensitive. Nonetheless, we can’t go back to agriculture without artificial fertilizers either: the land just wouldn’t produce enough. Not by an order of magnitude. We really wouldn’t be able to feed the global population.”