How much vacancy is left for the Earth in the 21st century? (Picture: Ella Byworth for Metro.co.uk)

The year 1900 was a very different time.

We didn’t have smartphones, most of us didn’t have cars and we didn’t traverse the globe in aeroplanes.

Back in 1900 there were around 1.65 billion people living on Earth. As we welcomed in the year 2000, the population had ballooned to 6.1 billion.

In the 19 years since, it is predicted that a further 1.5bn people have come into the world – an increase nearly as large as the entire global population in 1900.


‘The rate of growth is totally unprecedented,’ explains David Coleman, professor of demography at the Oxford Institute Of Population Ageing.

And the population is still growing: we are predicted to reach 10 billion by 2060, according to United Nations estimates.



At that point, we’ll have 20 people living per square kilometre, including all the areas on our planet that are currently considered uninhabitable.

Is that too full?

It’s a hot debate but some experts think focusing purely on the number of people isn’t the best way to answer the question:

‘It’s not the number of people that drives environmental degradation or drives increasing greenhouse gas emissions,’ David Satterthwaite, senior fellow at the International Institute for Environment and Development, tells Metro.co.uk.

‘It’s the number of consumers and their consumption level.’

Though the number of ‘people’ and ‘consumers’ are not growing at equal rates, with some continents growing quicker than others.

While Africa is booming, much of Europe has slow or no population growth.

‘Europe’s population share is shrinking,’ Prof Coleman says.

‘It used to be around a quarter of the world’s total in 1900 and is now scheduled to end up at about 6% or 7% at the end of the [21st] century.’

European consumers are major greenhouse gas emitters, while countries in Africa, as well as India and China, are less so.

‘The average Chinese consumer has a carbon footprint of two tonnes of CO2 equivalent per year,’ says Diana Ivanova, of the Sustainability Research Institute at the School of Earth and Environment, University Of Leeds.

‘An average consumer in the US would have a carbon footprint of around 20 tonnes.’

‘The average world consumer has a carbon footprint of about 3.5-4 tonnes CO2 equivalent.

‘Context matters – and the individual consumption behaviours do, too.’

Much of the rapid growth in population across Africa and India has been due to a lack of contraception and good sexual health services.

‘If good sexual, reproductive and health services were universally available to all, this would help bring down population because it would eliminate so many unwanted pregnancies,’ says Dr Satterthwaite.

Yet like a scale, improved sexual health awareness in Africa and India could be counteracted by an increase in consumption in China – which has managed to control population growth through its one-child policy.

Rather than such a draconian measure – banning the right to choose the size of your own family – an educational campaign can help check the world’s ballooning population.



‘If you invest in girls’ education and family planning, you see quite fast change in the decisions made about how many children a family have,’ says Ivanova.

Early indications are that such educational programmes are working.

Though the world’s population is growing, it’s growing slower than it has in the last half-century.

The growth of the global population peaked around 1970 at 2.1% a year.

It’s currently around half that level – thanks to things like the contraceptive pill, increasing awareness of the impact of quick population growth on our environment and better education about sexual health and how to feed a family.

And things are slowing down further.

The United Nations (UN) estimates population growth will halve again, to around 0.5% by the middle of this century and will reach 0.1% annual growth by 2100.

Even that growth is seen as problematic.

‘Even a catastrophic mass mortality event of 2 billion deaths over a hypothetical 5-year window in the mid-21st century would still yield around 8.5 billion people by 2100,’ a 2014 study argued.

‘Africa and South Asia will experience the greatest human pressures on future ecosystems.

‘Humanity’s large demographic momentum means that there are no easy policy levers to change the size of the human population substantially over coming decades, short of extreme and rapid reductions in female fertility; it will take centuries, and the long-term target remains unclear.’

Perhaps Australian environmentalist Paul Gilding has put it most starkly:

‘The Earth is full,’ he has said.

‘It’s full of us, it’s full of our stuff, full of our waste, full of our demands.


‘Yes, we are a brilliant and creative species, but we’ve created a little too much stuff — so much that our economy is now bigger than its host, our planet…

‘To keep operating at our current level, we need 50% more Earth than we’ve got.’

He compares his view of what governments must do to a company responding to a bankruptcy threat when change ‘that seemed impossible’ just gets done.

He calls for immediate action.

And he is not alone in this view:

‘I don’t see any benefit in adding yet more people to a population of 7.5 billion which is in some cases growing faster or at least as fast as economic growth,’ says Prof Coleman.

He points towards Yemen, the first country in the world likely to run out of the water needed to quench the thirst of its population.

Yemen could be a bellwether of the future problems to come: water shortages are becoming commonplace in the west of the United States and the Rockies, exacerbated by poor consumption patterns by farmers and grape growers.

‘People are resourceful and will do their best to manage, but it’s going to be difficult in some areas,’ Prof Coleman says.

While almost all our governments have signed up to UN climate change targets and leaders try and solve the problem of continued growth in population and consumption, it will take more than governments to solve the problem.

‘We have all been sold this idea that through consumption we would become happier individuals,’ says Ivanova.


‘If I could wish for something, it would be for people to become more aware of their own needs and to satisfy them in a way that would be more thoughtful of the environment around them.’

If this doesn’t happen, an increased population will lead to increased consumption which will result in greater greenhouse gas emissions.

The impact on an already-warming world could make some places uninhabitable – ironically, the places seeing the greatest population growth.

‘More and more people will find it more difficult to live there,’ says Prof Coleman.

‘It’s highly plausible that we may have people taking the entirely rational decision to leave places that are going to become increasingly difficult to sustain.’

Prof Andrew D. Hwang, of the College of the Holy Cross, worked out that data shows the Earth can support one-fifth of its present population, 1.5bn people, if everyone wants the current standard of living in the US.

If that’s true, then there are two options:

Earth’s carrying capacity is overstretched so infant death and disease spike because of a shortage of resources and the population falls What the current standard living is in the US and similar economies change remarkably and people live more cleanly

As a guide, an adult needs less than five litres of water daily biologically.

In 2010, an adult in the US used an average of 4,000 litres-per-person-per-day.

If it’s not the number of people, but the number of consumers, that means the earth is ‘too full’ then it depends on which number you read as to whether we’re nearly full, already full or past the point of no return.

The Future Of Everything This piece is part of Metro.co.uk's series The Future Of Everything. From OBEs to CEOs, professors to futurologists, economists to social theorists, politicians to multi-award winning academics, we think we had the future covered, away from the doom-mongering or easy Minority Report references. Every week, we explained what's likely (or not likely) to happen. Talk to us using the hashtag #futureofeverything. Though the series is no longer weekly, if you think we might have missed something vital to the future, get in touch: hey@metro.co.uk or Alex.Hudson@metro.co.uk Read every Future Of Everything story