A fairly common belief among western environmental activists is that “overpopulation is causing our ecological overshoot”. It’s a simple idea to present, as it just requires people to accept that more people cause more environmental damage.

Unfortunately this simple idea has a number of problems.  The main one is the old conundrum of who bears the responsibility for bringing the situation back into balance.  Should rich countries whose population growth is already slowing cut their consumption, or should poor countries that are not overconsuming cut their populations?

I used to believe that population was “the” ecological problem of the world.  I’ve recently changed my mind, as the result of a variety of investigations into the Ecological Footprint.

I’m currently using the EF as my standard for measuring relative amounts of ecological damage both nationally and globally.  According to The Footprint Network the world has about 1.8 Global hectares (Gha) of biocapacity per person, and we use, on average, over 2.6 Gha of biocapacity per person.  The difference is called the ecological debt.  It measures overshoot – the rate at which we are drawing down the earth’s natural resources to support our population in the lifestyle to which we have become accustomed.

I’m not totally satisfied with this method of calculating overshoot. I think it misses some important ecological factors such as ocean acidification and the loss of biodiversity through species extinctions.  It's also a steady state model, and can’t take into account the effects of hitting tipping points in areas like ice loss or methane production from melting hydrates and permafrost.  Such effects would have to be incorporated into the model by estimating their impact on biocapacity, which is an error-prone exercise.  Still, it’s the best we have right now, and given the amount of work being done with Ecological Footprints it makes sense to examine our situation using this tool.

The first thing I discovered was that a country's Ecological Footprint correlates much better to its GDP than it does to its population density:

This implies that countries with high population densities can still have relatively small ecological footprints, whereas those with high consumption are much more likely to have large footprints.  By extension, a world with a high population can still have a relatively low EF, while a world with high overall consumption rates is less likely to achieve that result.

The Ecological Impact of Food Production

The one aspect of ecological damage that I believe is most directly tied to population levels is the damage attributable to food production.  This is because people need an irreducible minimum number of calories to live, and unless food production practices change over time, a rising population will cause more ecological damage because more food must be produced.  I wanted to see if Ecological Footprint data supported this theory.

The Footprint Network provides a data table (XLS) in which the national ecological footprints are broken out for every nation for the year 2006.  For each country the table lists the footprint requirements in a number of areas, including Carbon, Cropland, Grazing land, Forest land, Fishing ground and Built-up land.

To roughly determine the ecological footprint associated with food production I summed the entries for Cropland, Grazing land and Fishing ground.  The table has also conveniently aggregated the numbers into three categories by income (low, medium and high).  I was able to quickly determine how much of our Ecological Footprint comes from food production, and how much from non-food consumption.  Here is what I found:

World food production requires an average of EF of 0.9 Gha, with a range of +60% to -44%.  The range of EF needed for food production between the high income group and the low income group was about 3:1.

Non-food production requires an average of 1.7 Gha, with a range of  +175% to -70%.  The range of EF needed for non-food production between the high income group and the low income group was about 9:1

The difference in the two ranges for food production (3:1) and non-food production (9:1) is striking.  This implies to me that food production has a more direct relationship with population than other forms of consumption.  If it were a fully direct relationship the range would be 1:1 (i.e. food production would have the same EF in poor countries as in rich ones).  The fact that it isn’t points to higher-impact farming practices in rich countries, differences in diet (less meat consumption in poor countries) and possibly to lower caloric intake in low-income countries.

The real message, though, is in that 9:1 range for non-food production.  It says that if we want to reduce our impact on the planet, we MUST reduce our consumption.

Sustainable Standards of Living

Following on from this, I thought it would be interesting to see how many people our battered little planet could sustainably support at various levels of consumption.

To start with I accepted that an EF of 1.8 Gha represents sustainability.  I did this with grave misgivings for the reasons I gave above, but for illustrative purposes it will do.  Then I used the global average figure of 0.9 Gha for food production, and kept that constant (that means each person always requires 0.9 Gha for their food supply).

Since the population in 2006 when the figures were calculated was about 6.5 billion, the Earth has about 11.7 billion Gha of total biocapacity.  This needs to be split between food needs (0.9 Gha per person) and non-food needs (all the rest up to 11.7 billion Gha). The non-food uses give us what we think of as our “standard of living”.

I calculated the following results:

If the Ecological Footprint concept is correct, our population cannot continue to grow much more without resulting in significant global impoverishment, along with the social instability that implies.

Conclusion

This assessment says nothing about how we might get to a sustainable situation with a reasonable standard of living.  Most people are not in favour of limits to either their child-bearing or their consumption, at least if the limits are imposed by policy and legislation.  Given that, we are reduced to nibbling around the edges of the problem.

It seems to me as though this nibbling must consist of improving our food production practices, decarbonizing our economies, improving the energy intensity of our economies, promoting lower fertility rates whenever and however we can, but above all promoting drastically lower-consumption lifestyles in the rich nations.

The numbers are clear – the limits to growth in both consumption and population seem to be here.