Population Structure, not Growth

I stumbled upon an interesting body of literature that discusses the role of population structure and dynamics in affecting climate change. Rather than simply looking at the size and growth of populations, Jiang and Hardee (2011) (along with various others) study how population composition affects carbon emissions and climate systems. The idea is whether different energy consumption levels exist among population groups with different characteristics and whether (and how) these groups' behaviour will change in the future. They find that population size; ageing; urbanisation and household size are all important factors.

Urbanisation

If we look at the case of urbanisation, on the one hand cities provide economies of scale, technical innovation, efficient land use and lower fertility rates. On the other, as people go from living in rural areas to urban ones, their behaviour changes: their consumption patterns, and their lifestyle. Conclusions are mixed and it depends on the regions studied and whether it's the long-run or the short-run impacts being considered.

Ageing

For ageing, there is also a shift in consumption behaviour and income structure. Like urbanisation it is difficult to determine whether there is a rise in energy use or a decline. An ageing population may reduce public transport demand but use cars more and increase energy demand for heating/cooling; it may also reduce overall labour productivity and so energy consumption. However, as York (2007) points out, the elderly tend to have smaller household sizes which means energy consumption per capita increases. (Imagine heating a house that 3 people live in vs 1 person living in it.)

York makes an historical analysis of demographic trends and energy consumption in 14 EU countries. He runs a regression and finds a positive relationship between an 'elderly' population and energy use. The interaction between population growth, size and ageing is complex. Low fertility leads to a decrease in population growth and eventually size which decreases energy consumption but then this leads to an ageing of said population which increases energy consumption! 

This certainly challenges the idea of less population growth being a good thing for the environment. However, the solution definitely isn't to keep growing and growing for fear of having too large a portion of the population over the age of 65. Surely that would eventually be even worse for the environment? It sort of goes back to the social and economic problems that arise when a population stops growing and starts ageing. The solution can't be to just tell everyone to have more children, because all that will do is delay the issue for a couple of generations until those children are pensioners and living on their own in heated houses. 

It seems to me like there might be some sort of 'Environmental Kuznets Curve' for ageing, whereby there will be environmental pressure for years to come as the population ages, but once it stabilises again (i.e. once the bulge of pensioners are 'no longer there' – sorry!) environmental pressures will subside and so will those on social services. Once again though, a substantial portion of the world's populations have yet to begin this ageing process and are only in the stage where death rates are falling but birth rates remain the same, so it will be a long time before that happens. The only thing I will say is that better education and family planning will perhaps mean people in countries where death rates are falling will be able to choose the number of children they'd like to have, which may result in less of a bulge in population growth.

In any case I've rambled on. The topic is such a complex one it's hard not to explore all the different avenues. The main point from this post is that the relationship between population growth and environmental degradation is not as simple as it seems. The type of population is important: whether it is urban, for example. It is not simply that smaller populations are better for the environment as this can be coupled by ageing which may (there is debate in the literature) lead to increased energy use.