Last month the global population of humans hit seven billion; an extra billion people since 1999. Given that it took until 1804 to reach one billion, the recent upsurge would suggest serious problems in future. The immediate concern, however, isn’t actually space. Standing shoulder-to-shoulder, the entire world’s population could fit within the 1,300 square kilometres of Los Angeles.

If they were to live at the population density of New York City we would all only take up an area the size of Texas. Although this may seem a farfetched example, it’s worth noting that (as of 2008) the world’s population has shifted from mainly rural to more than 50 percent urban. By 2050, 70 percent will be living in built-up areas.

The problem is actually the ecological requirements to sustain that number of people. A 1995 report by the International Institute for Environment and Development pointed out that a city depends on a lot of land beyond its urban sprawl on which food is grown and where other essential materials exist, ranging from forests to absorb the carbon dioxide emissions to factories to produce materials.

For example, the land area required to supply London’s environmental needs is estimated to be 120 times the size of London itself. Calculating the overall carrying capacity for humans on Earth is more tricky as there are so many factors to consider — land, sanitation, medical facilities, environmental changes, access to drinkable water, supply of food, and so on. But according to the Global Footprint Network, humanity was using 40 percent more resources than the Earth can regenerate by 2006, so we are already well on the way to a global disaster if the current course is maintained.

What we don’t know is what might change that course in the future — for better or (even) worse. Take India as an example. According to the Population Reference Bureau (PRB), India will surpass China to become the world’s most populous country by 2050, with a headcount of almost 1.7 billion. But the PRB doesn’t factor in things that could slow India’s population growth in future. As the country develops and standards of living increase, the need to have so many children will fall.

In fact, the actual number of births per 1,000 people globally is falling already, with the current figure set at 23 by the PRB. In 1995 it was 31 and back in 1900 it was 40. It’s just that we’re not seeing the knock-on effect yet.

This means figures have been predicated on inherently inaccurate information . Back in India, the rates of malnutrition and poverty have declined from around 90 percent at the time of India’s independence, to less than 40 percent today. Even in the last decade the infant mortality rate has fallen from 65 per 1,000 to 48, so the need to have so many children is being slowly eradicated, but that takes time to filter through to everyone.

Already, wealthier Indians are having fewer children and increased literacy levels are also helping educate people about contraception. Currently, almost half of married women use contraception compared to just 13 percent in 1970. Other factors could affect the statisticians’ prediction of nine billion people by 2045.

Figures don’t take into account unquantifiable future events, such as pandemics thinning out the population. The Plague of Justinian in 541AD killed an estimated 25 million worldwide and caused Europe’s population to drop by around 50 percent. Black Death reduced the global population from 450 million to between 350 and 375 million in the 14th century. Even fairly recently, in 1918, the Spanish Flu pandemic infected one-in-four of the world’s population and killed around 100 million.

Mass contagions could occur at any time. And we’re certainly overdue another one. More positive unknowns could also affect future figures; a lesson we learn from the past. In the late 1800s, large urban centres were “drowning in horse manure”. With no obvious solution to this problem, people were making dire predictions. In 1894, The Times of London estimated that by 1950 every street in the city would be buried nine feet deep in horse manure. In Manhattan, the situation was even worse, but unbeknownst to the world, Henry Ford was inventing the automobile. By 1912, cars in New York outnumbered horses, and by 1917 horsedrawn streetcars stopped running.

Even so, measures could and should be taken today to avert disaster. The principle one is consumption, which is 32 times higher in the West than the developing world. Author and academic Jared Diamond notes that if everyone consumed at that same rate, consumption would rise elevenfold, the equivalent to a population of 72 billion people.

This, clearly, would be a total disaster. However, Westerners are hugely wasteful. If resources were to be created and consumed more sustainably (for example, sustainable logging and fishing), it would be a start. These good habits could then be shared with the rest of the world on an equal footing. At the moment we have no moral footing to tell the rest of the world how to behave.

Beyond that we must hope the Henry Ford of sustainability or Green technology is out there somewhere.

For Esquire Magazine