Guest  essay by Roger Graves

Predictions of atmospheric CO2 levels at some future time are commonly made, usually with the object of assuring us that beyond a certain point our planet will be fried to a crisp. Most of these predictions are in the form ‘if CO2 levels reach x, the effect will be such-and-such’, without actually indicating why CO2 levels should reach such a value. However, it is possible to make an accurate prediction of future CO2 levels using readily available information.

The graph shown below plots CO2 levels as a function of world population, encompassing the period 1960 to 2015. Note that although each data point represents an individual year in sequential order, time is not explicitly represented on this graph, which merely shows how CO2 levels are related to overall world population.

It is reasonably obvious to the naked eye that CO2 and population seem to…