Population: Do we face Under-population, just right population or Over-population?

I have heard the claim that climate change is the greatest moral challenge of our time. Well I strongly suggest it is population, not climate change, that is the greatest moral challenge facing humanity.

Firstly, for background, here are the three positions that can be taken on human poluation.

1. Under-population – the world needs more people.

Well, in truth, this argument is presented more often as a 'we need population growth' argument than as a 'the world is under-populated' argument. The main argument is that population growth generates positive economic outcomes. Simplistically, the argument is that more people equals greater wealth and that a growing population generates a higher ratio of young people to help look after old people.

Strangely, everyone I have seen arguing this case seems to declare that even though they are arguing the case for growing the population, that the world population will stop growing and start declining anyway and there is no need to prevent this happening. So the argument ends up retreating into 'lets grow now, but soon we can stop growing and start declining'.

2. The Global Population is just right.

Well in truth, I have not heard this as the initial position of anyone. The actual argument seems to go 'we need population growth as pollution decline is an economic disaster, but do not worry as we will soon have population decline and return to current levels'. The argument is for a rise then fall back to current levels. Which may seem strange as the argument starts with the position that the population decline would be an economic disaster.

3. Over-population.

The global economy does not have anywhere near the capacity to supply the current 7 billion people at the rate of resource consumption per capita by people in Europe or America. More alarmingly, the argument is that we only manage to maintain current global capacity through the non-sustainable consumption of resources some of which are nearing exhaustion. In short, we are eroding the ability to even feed the current global population and are on track for disaster. Against this argument run previous 'doomsday' dates that have passed without the predicted apocalypse.

So which argument is correct? And more significantly, what action should we take about all of this? While I will examine all the arguments further, I will spoil the conclusion by saying that all groups seem to agree that global population decline at some point is inevitable. The reality is that population decline at a global level is an inevitable but huge challenge no matter what perspective you hold.