On a scale of 500 years the planet is warming after the Little Ice Age 500 years ago.

On a scale of 5,000 years there have been many periods of warming and cooling.

On a scale of 5,000,000 years there have been numerous periods of intense cold and many short periods of warmth.

The average global temperature over the past 2.67 million years is less than the current global temperature. Why? Because we are living in the Pleistocene glaciation which has not yet run its full course.

This logic is sound.

Plimer’s cogent argument is that on geological timeframes the climate has been both hotter and significantly cooler than at present and that to really understand climate change, it is geological time that provides the best context and insight.

The earth is, after all, very old leaving plenty of time and opportunity for a range of climate conditions everywhere. It is hard to imagine that not so long ago in geological terms the current continents were in a very different configuration, that in an epoch mountains can form and erode away, and all the time sediments form and are consumed into the mantle of the earth at plate margins.

It is the rare the talent of the geologist to think on the time scales that matter to the formation of sediment, rocks and ore bodies.

What is interesting is to map global human population size onto the points in time that Pilmer quotes to illustrate his understanding of climate change.

For this purpose ‘human’ means both the species Homo sapiens that first appeared around 250,000 years ago and the genus Homo that the fossil record suggests has been present as various species since around 2.3 million years ago.

• 500 years ago after the Little Ice Age at 1500 AD there were 500 million humans. This is roughly the present day population of the United States and Indonesia combined, 7% of the current global total.

• 5,000 years ago there were just 5 million humans, or roughly the population of present day Finland and today there are over 100 countries with more people than Finland.  At the advent of agriculture 10,000 years ago there were perhaps 1 million H. sapiens.

• Around 70,000 years ago there is genetic evidence that H. sapiens went through a population bottleneck when for some reason, perhaps the eruption of the supervolcano Toba in Indonesia, numbers went as low as 15,000 individuals.

• 5,000,000 years ago there were no recognizable humans.

Calculations suggest that there may have been 110 billion humans that have ever lived and a full 6% of them are alive today. Human population growth is an explosion in comparison to geological time.

So when discussion stalls on the causes of climate change or even on its existence, it is worth remembering that the real challenge for humans is to handle the resource needs of 7 billion souls alive today, the 6% of those that have ever lived, without destroying the resource use opportunity for the descendents of this 7 billion.

This is, of course, the standard definition of sustainable development.

It would be a shame if we forgot about sustainable development to focus on the latest fad that, if we think about it on the time scale of the geologists, we can do little about.