Matthew Lloyd/Getty Images
One of the most remarkable events of modern times? Human population growth.
At the time of the First Dynasty in Egypt — around 3000 BC — global population was just 100 million, according to estimates. By the height of the Roman Empire and the birth of Christ, that number was perhaps 250 million. And in 1750, at the dawn of the industrial revolution, global population had risen to 750 million.
Now — thanks to antibiotics, improved sanitation, mechanized agriculture, vaccinations — it's 7,155 million, or 7.15 billion.
Current estimates suggest that global population will top out at 8.5 billion in 2030. The growth rate is already falling, due to women having less children. In 2012, the global fertility rate was 2.47 births per woman. That was a decrease from 2.50 in 2011, and 2.90 in 2006. The rate at which population growth will level off is 2.10, according to projections.
Of course, 8.5 billion people is still a huge number for the planet to support in the long run. Can the Earth do it? Some estimates say no, and some estimates say yes. Personally, I'd say a lot depends on technology. If humans can figure out a way to keep atmospheric dioxide levels close to pre-industrial levels, and transition to renewable energy to avoid over-reliance on finite resources like oil and goal, then we have a pretty good chance.