Humanity hits the eight billion mark

"The milestone is an occasion to celebrate diversity and advancements while considering humanity's shared responsibility for the planet," UN Secretary-General Antonio Guterres said in a statement.

The UN attributes the growth to human development, with people living longer thanks to improvements in public health, nutrition, personal hygiene and medicine.

It is also the result of higher fertility rates, particularly in the world's poorest countries -- most of which are in sub-Saharan Africa -- putting their development goals at risk.

- How many is too many? -
Population growth has also magnified the environmental impacts of economic development.

But while some worry that eight billion humans is too many for planet Earth, most experts say the bigger problem is the overconsumption of resources by the wealthiest people.