We are already overwhelming the earth by just about every measure. We're already using more than one planet's worth of resources, sustainability overshoot comes ever earlier each year. As seen by the sheer number of disparate stories about earth and species' inability to cope.

"Population growth has been slowing"

Which of course means it is still growing. How many decades ago should it have started to fall in order to avoid catastrophic climate change or the incessant stream of environmental bad news and loss of species?

No one should feel obligated to sacrifice themselves. They should feel obligated to replicate less if they want their own children to inhabit somewhere worth living.

Vast majority population of the world hasn't even really contributed to climate change until the last couple decades. It's not the number of people that are doing it, it's the american lifestyle.

It's both. Numbers and our model of what "developed" is.

If only 10,000 people were living an American lifestyle the planet would cope just fine. When it's 1bn it seems like it's clearly becoming problematic. What of when it's 3bn?

If, as seems to be the case, there are 7bn who want, or are advertised at to want, a throwaway Western lifestyle, we're screwed. All 7bn. We can't pretend the numbers are not there or that most are going to happily remain with subsistence lives for all future generations.

It's probably more feasible to make larger families unfashionable or nudge them via the tax system than simply "fixing" climate change globally, habit and species loss.

What's less? What is your approved number of children for each couple? If someone remarries, does that x number of children carry over from their previous?

"Population growth has been slowing since the late 60's, it peaked in 1968."

Misleading phrasing...

"World population projected to reach 9.7 billion by 2050. The current world population of 7.3 billion is expected to reach 8.5 billion by 2030, 9.7 billion in 2050 and 11.2 billion in 2100, according to a new UN DESA report, “World Population Prospects: The 2015 Revision”, launched today."

http://www.un.org/en/development/desa/news/population/2015-r...

Yeah, comp sci 101 alone is sufficient to know that logarithmic growth's second derivative is negative for all x > 0, and ln(x) is still unbounded. "Growth is slowing" can be a very effective sleight of hand.

Slowing does not equal stopped.

It also does not mean it's going to stay under a limit making it a poor yardstick. As throwaway5752 said, the limit of log(x) -> infinity is still infinity even if it starts growing really slowly.

Really though we don't need to kill / sterilize all humans, getting off the planet could work just fine.

Sorry, when did anyone talk about a limit? If the slowing growth continues, then eventually it will cross zero into the negative. Look at the relative growth, by 2100 it's predicted to get close.

> If the slowing growth continues, then eventually it will cross zero into the negative.

Err, no. The growth of log(x) is always decreasing and yet it always stays positive. This is true for a huge range of functions and one of the reasons limits are important.

Now, you can argue that the way human growth is slowing suggests it might possibly go negative at some point. But, that's less obvious.

You're trying to impress us with the maths. I already took all of the statistics, and differential equation classes twenty years ago. I get it. However, there are already countries experiencing negative population growth, and the trend is continuing in other Western countries.

I am not trying to impress with high school math, I defending someone that got down voted for an accurate statement.

At best we are predicting a peak human population 30+ years from now and those kind of predictions are never very accurate. Further, even if that's one peak it says very little about human population 100's or 1,000's of years from now.

THE GREATER GOOD