How much human life can planet Earth sustain?

How much human life can planet Earth sustain? It’s a question scientists have been struggling with for hundreds of years. They have yet to agree on an answer.
Thomas Malthus kicked off the debate in the early nineteenth century when he predicted imminent doom for the human race. He believed that the population of the earth was increasing at a geometric rate, while food production was increasing only at an arithmetic rate. Human population would soon outstrip their own ability to produce food, and there would be a catastrophe by the mid-nineteenth century.

We’re still here, so that obviously didn’t happen. Technology allowed humans to produce far more food than Malthus anticipated. Even though Malthus was wrong, his ideas remain influential. The carrying capacity of the earth is a hotly contested subject. Many believe that we are at or near our capacity already. Others believe the earth can support far more people. It’s far too complicated to truly determine what the real limit is. And even if we could, the “real” limit would be meaningless without proper context.

The main context is lifestyle. Our planet can support many more people if we are living in near-starvation mode and consuming as little energy as possible, than if we are all living at North American levels of consumption. Practical considerations also matter. If we were all living in starvation mode, would we be able to survive, or would we be at war with one another, killing each other off so we can eat more food?
Distribution of resources has always been unequal, and continues to be an issue now and in the future.

Ignoring these considerations, can we reach some sort of estimate?
Important factors that determine how many people the earth can sustain include food, drinking water, and energy. Let’s look at each of these areas in more detail.

Food

The earth currently produces 2,264 million metric tons of cereals, which is the staple food of the world. If each person consumes 2,000 calories per day, 2,264 million metric tons of cereal will support a little bit over 10 billion people. Currently, around half of all arable land in the world is producing crops. If we clear-cut all the forests and jungles, we could double our theoretical food production. These calculations assume all we eat is cereal though. Most people want to eat more than just rice, bread and pasta. Vegetables and fruits are also produced on arable land. Most of this produces a higher calorie per area yield than cereals. But what about meat? Currently about one third of cereals produced in the world go towards feeding animals for meat production.
Meat production is very inefficient in terms of land use. The more meat is eaten, the less people the land can support.

Water

It’s hard to say much about water other than that we are in dire need.
There are 1,385 cubic kilometers on earth. Most of this water is salt water, and not suitable for human consumption. Most of the fresh water available…is locked inside polar ice caps. Only 0.26% of all water is available for human consumption. Most of this water is in clouds or in the ground though. Only 0.014% of water on the earth is actually available for drinking. Problem? Yes! There are already severe water shortages in Africa and parts of Asia. North Americans use 1,280 cubic meters of water annually. Africans use 186. If there isn’t enough water, such as is the case in many countries, disease and malnutrition are the result. This is already happening, and will continue to spread as population continues to increase. Water also affects food in a big way, as 70% of water used by humans irrigates crops.

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