Hi Bernie Masters,

What do you understand to be the sustainable human population limit for the planet?

Hi Mr Opinion. In theory, there is no sustainable human population limit provided we are prepared to accept more impacts on the environment and a reduction in our standard of living. If everyone was happy to live with the same wealth and standard of living as the poorest African, for example, the world would easily sustain 20 billion people or more.

In practice, however, people aspire to a much higher standard of living, similar to what most western Europeans currently enjoy. On this basis, the world probably could not sustain more than 10 billion people, possibly more with greater environmental damage or possibly less if we were serious about looking after the world we live on.

The book Empty Planet suggests global population will peak at about 9 billion and then decrease significantly over the following decades. Birth rates are dropping right around the world and this trend is unstoppable.

I agree with Moore on both counts; mandated and subsidised renewable energy isn't that great at reducing emissions and that the growing world population will lead to a crisis. In Australia's case we've had a renewable energy target for nearly 20 years yet emissions in key sectors are essentially unchanged. We need a different approach I suggest nuclear power.

The corollary of this is that green high priests will lose their cred so they should tread carefully. A worst of both worlds scenario is persistent emissions and extreme weather coupled with a lacklustre economy. That seems to be the track we are on.

Bernie Masters,

I'm sorry to be the one to bring you the sad news but the sustainable human population limit is 5.6 billion and that was reached in 1986.

Mr Opinion. Where do you get the 5.6 billion number from please?

Bernie Masters,

I'm citing Jared Diamond from his book 'Collapse'.