NEW YORK -- What would the world look like with 7 billion human beings in the mix, vying for resources? Pretty much what it looks like now.
That's because the planet is about to pass the 7 billion mark any day now. Or maybe it already has, according to academics at Columbia University.
Joel Cohen, a professor of populations at Columbia, briefed attendees here this week during an Earth Institute gathering on the subject. The conference was meant to celebrate, raise awareness and sound a few alarms regarding a U.N. estimate that the 7 billionth human is due to join the party Oct. 31.
To Cohen, whether the Earth will be able to sustain 7 billion humans, 9 billion or 10 billion will "depend on choices we and future generations make." He added that we may have already crested over 7 billion for the first time, though pinpointing an exact date on the threshold is next to impossible.
"The truth is we have never censused the entire Earth," Cohen said. "The U.S. Census, which costs billions, has an error of 1 to 2 percent."
What is clear is the Earth is poised to pass the mark, making it 12 years since we passed 6 billion in 1999 and 12 more years since 5 billion in 1987. More broadly, the 7 billionth addition to Homo sapiens represents a spurt of 4 billion people in five decades.
Cohen calls the phenomenon an "extreme explosion [that] ... has no precedent" in the history of human evolution. The growth rate prior to the mid-20th century was much slower and had effectively held steady for thousands of years until the 19th century's Industrial Revolution.
"That is an exceptional event and will probably never be repeated within human history," he said during a lecture here. "Not within the next few centuries, anyway."
'5 sub-Saharan Africans for every European'
Looking ahead, Cohen expects total fertility rates to drop almost everywhere by the end of the century. This pattern is already in evidence in Europe and the United States and eventually will trickle into less-developed nations as they raise their economic profile and education levels, he said.
Barring an apocalypse, Cohen predicts the Earth will hit 8 billion humans in another 12 years, then 9.3 billion by 2050 and 10.1 billion by 2100.
More remarkable than the numbers perhaps is how the demographics within that growth rate will shift. Cohen says that by 2100, the African continent will have overwhelmed a historic balance among continents, with "five sub-Saharan Africans for every European."
"You can only imagine that might have an impact geopolitically," he said.
The good news is that with the steady increase over the past half-century has come improved life expectancy to a global average of 70 years. The bad news is dwindling natural resources, food and water could mean 1 billion starving people across Africa and South Asia's "hunger belt" sooner than many think.
Whether the planet's supply of energy, water, food and other resources can handle the demand is an open question. Cohen says the Earth is finite, and fresh water in particular could be in short supply for about 10 percent of the planet by 2100.
The same dynamic is evident for agriculture, as farming already consumes about 40 percent of ice-free land. If that pattern continues to hold or increase, less forests to meet the demand for food could mean a corresponding uptick in carbon emissions worldwide.
Cities are likely to feel the brunt of the growth as humans continue their migration from rural areas to urban. Cohen says the small city (of about 1 million) is the future of urban life, and he feels civilization needs to do better at paying attention to their design.
"We are going to need to construct a city of a million people every five days for the next 40 years," he said.