Negative Growth
Study on population and ecological footprint leads to the conclusion, realistically, that the population needs to decline if we are to experience a reduction in footprint. This isn't clear at first glance, but becomes evident once one starts to understand the math behind it.
Generally, ecological footprint is displayed as global hectares per person. Total footprint equals global hectares per person times population. As the earths footprint is limited and as we are in a current state of overshoot, we have only two options to reduce footprint; reduce the footprint per person or reduce population. Both are difficult. However, if footprint is reduced, but population is increased, the state of overshoot will remain. The best case scenario, one that would result in the largest reduction in footprint, would be to see negative growth in both population and footprint. The result of this can be seen after working through these two equations.
Population growth can be calculated using the equation:
P(t) = Poert,
where Po = initial population, r = rate of growth and t = time.
Similarly, changes in ecological footprint can be calculated using the same equation, substituting ecological footprint for population.
A 1% growth per year in population results in a doubling of population in 70 years, also for ecological footprint. Thus an initial population of 1,000,000 with an average global footprint of 7.0 hectares per person will have a total footprint of 7,000,000 hectares at time zero, a population of approximately 2,000,000 people in seventy years and a footprint of about 14,000,000 hectares at that time. However, if footprint also grew exponentially, we would see a footprint of 7,000,000 hectares at time zero and a total footprint of just over 28,000,000 hectares in 70 years. This is clearly unsustainable.
However, if we saw a negative growth in population of negative one per cent with no change in footprint, we would have a footprint of about 3.5 million hectares in seventy years. This is starting to ease things off a bit. Additionally, and this is where we start to see real savings, if we had a reduction in footprint of 1% a year as well, in seventy years the population would be just under half a million and the footprint would be only about 1.7 million hectares. This is starting to look better!
Looking at the world situation, in 2006, the average biologically productive area was approximately 1.8 global hectares per person1. With a current population of just over 6.8 billion and a state of overshoot of 1.52, that means we are using:
6.8 billion x 1.8 x 1.5 = 18.36 billion hectares
when we have available 12.24 billion hectares (assuming no net change in global hectares per person between 2006 and 2010).
Working backwards at a 1% reduction in population per year assuming no change in footprint, it would take, approximately 40 years to get back to a state of equilibrium, assuming limited non renewable resources remain available.
Again, looking at a reduction in footprint as well as population growth, both at negative 1% per year, it would take only 20 years to get back to a level of sustainability. This would be at a population of 5.57 billion and an average global footprint of 2.21 hectares per person.
If we wanted to factor in a margin of safety, and operate at only 80% of capacity, then we would need to aim for a total ef of about 9.6 billion hectares. This would take about 65 years with only a population reduction, but only about 32 years with both a reduction in footprint and population.
Thus exponential growth can be turned on its head and made to work in our favour if reductions are sought.
1. http://en.wikipedia.org/wiki/Ecological_footprint (Retrieved Dec 20, 2010).
2. Global Footprint Network, 2010 Edition. www.footprintnetwork.org.
