"Plenty of food, but one billion people go hungry. Lavish lifestyles for a few, but poverty for too many others," UN Secretary-General Ban Ki-moon said at a press conference marking the occasion.
With two babies born every second, the world's population is skyrocketing, adding to existing challenges.
Despite the rapidly growing population, people today live longer and the child mortality rate is lower. But this does not necessarily mean people will lead better lives.
In 1999, then UN chief Kofi Annan welcomed the sixth billion human in a hospital in Bosnia, but the once-celebrated baby boy is now living in extreme poverty.
What about "Baby Seven Billion"? He is born to a world of contradiction and inequality.
Apart from strongly encouraging birth control in less-developed countries, we must also find solutions to the problems caused by population growth: an energy shortage, gender inequality, and an ageing population.
The world has made rapid technological advances. But, while most of us in Hong Kong have the latest gadgets and indulge in online entertainment, millions of others do not have that access to information.
Similarly, it is not surprising to find a lot of people with big bellies in the United States, while many Africans face starvation.
The world has not been equal for a long time and there is no easy solution unless the superpowers are willing to take concrete action instead of making empty promises.
No matter what the world is like when it welcomes another billion inhabitants, the birth of the seven billionth baby is a golden opportunity for us to think about what kind of future we want to give the next generation.
Hopefully, it's not a world of fear.