I think there is actually no real way to stop world populations reducing to 1 billion or less by 2100 AD

 What do I mean by this?

I think it is only a matter of choice how the world goes down to 1 billion people or less by 2100 AD

This seems very solid to me now.

So, the only real question is how do we get there?

Do we get there by awful wars between Russia and China and Europe and the U.S.?

Or do we get there through global climate changes and no insurance on any buildings worldwide and flooding and droughts and fires?

Or is it a combination of these things?

However, another thing is mass extinctions of Birds and animals causing pandemics too.

Somehow in any timeline we seem to get to less than 1 billion humans still alive on earth in all these different scenarios on the present timeline we are headed on right now.

So, God Help us All!

We only live by the Grace of God anyway!

So, the real choice is that how humane do we want to be as earth born humans getting to below 1 billion people in 2100AD.

The two real choices appear to be Starvation or War or Pandemics or a combination of the three combined with Flooding, droughts and hurricanes and fires and tornadoes worldwide.

So, God Help us anyway it is going to happen!