Before you read this: Take a guess! Ok… now read. Estimates for how many people the Earth can support range from 500 million to 1 trillion . This is not very helpful. However, most scientists believe it is 8 billion or fewer , which is close to today’s population of 7.7 billion . Scientists mostly agree that it is very unlikely to be more than 16 billion .
Why are the numbers so uncertain? Because the number depends on a few key things:
1) WHAT people eat. Different foods have very different impacts on the environment . For example, per gram of protein, on average peas use 2% as much land as lamb & mutton to produce . Cheese uses 22% as much land as lamb & mutton . If we eat less land-demanding food, we can feed more people. If everyone lived the lifestyle of the average American, we would need 5 planet Earths !
2) How much NATURAL LAND we convert to farmland. We could, in theory, grow food and build houses on every bit of available land. But we need some natural habitat to support us , for example, rainforests provide rain for surrounding land . Plus, many of us value wild plants and animals for what they are .
3) HOW we produce food. For many crops, yields per hectare are 3x higher in the UK than in some African countries . Bringing all countries ‘up to speed’ with farming methods could mean we can produce a lot more food ! Even in developed countries we are finding new, more efficient ways to produce food . For instance, black soldier fly larvae literally turn waste into protein and fat . It has recently been gaining popularity as animal feed  and could be used as food for humans too !
4) Future THREATS. Many scientists are worried that crop losses will increase with climate change, due to e.g. more severe droughts  and spread of pests and disease .
So: the true number of people Earth can sustainably support probably lies somewhere between 4 and 16 billion . One thing is for sure, we can’t support a growing population without changing what we eat, and how we produce it [12,13].
 Our calculations based on data S2 from Poore and Nemecek 2018: https://science.sciencemag.org/content/360/6392/987/tab-figures-data
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