There is an argument that we currently have more people on Earth than ideal, but even if you accept that we have an overpopulation problem, the idea that a sudden reduction in the population would solve the problem is both absurd, dangerous and damaging.
The premise of the movie ‘Inferno’ is that a virus could randomly target and render infertile one in three humans as a means of population reduction. Inferno is a movie, and a suspense drama, not an actual plan. But if you do accept that the earth is overpopulated, what would be a real appropriate response, and why are ideas, such that containing in the movie, so damaging?
Understanding the problem.
To give some perspective, during the mid 20th century, the population on Earth was on a trajectory of doubling every 30 years. This means even a plan as drastic sterilising 1/3 of the population, or even for that matter, even killing 1/3 of the population, would simply undo around 10 years of growth.
The fact is: any overpopulation problem is about growth rate, not about numbers.
How many people is too many? Well if the growth rate was to continue at that late 20th century level, it doesn’t matter because whatever the number, it would be reached with exponential growth. Even if you believe we could have 200 people for each square centimetre of the earth, we would reach that level and be heading towards 1,000 in another 60 years. One day growth rate has the change. The population number is not so important as the growth rate, because no change in the current population number is significant in the long term compared, to a change in the growth rate.
Sudden change: a significant concern.
Anyone who suggests sudden change to fix ecological problems should be cautious. The earth has been through many changes, and life on earth has survived many changes. But when the change is too sudden, there is a mass extinction event. Radical change dangerous. A sudden change in the human population, would have far reaching change impact and kill off even more species, but would fix nothing as the required fix is to return to historic rates of population growth.
The ideal solution is already in place, the challenge is to not disturb the change.
If you have ever seen someone try to steer a boat for the first time, you will have seen have they try to steer and as nothing immediate happens, they keep trying to turn even more. But the time the initial steering change actually takes place, they have already steered too far.
The population on Earth is like steering an ocean liner. There is a huge delay between changing birth rates and actually feeling the effect.
In fact we have, to use the analogy, altered the steering position to stop the population growth problem, with almost all countries moving to an average of around two children per family. But it takes time to see the effects. Actually the biggest danger is that governments and big corporations addicted to population growth are in denial about the change, and will seek to restore the old course heading of unbounded growth as they feel the effects of the change in course.