Issues Magazine

What’s Carrying Capacity Got to Do with It?

By Jane O’Sullivan

On a finite planet, no rational person can entertain the idea of infinite population. But when is enough enough, or is that the wrong question?

As 16-year-old Jessica Watson set out on her journey sailing solo around the world, our planet must have seemed like an awfully big place. Yet, as she sailed back into the familiar embrace of Sydney harbour only months later, perhaps she reflected that it was finite after all. Her journey had an end.

A big planet for a little boat to be blown around by the wind may not be such a big planet for 6.8 billion people to find their sustenance and deal with their waste. In the time it took Jessica to circle the globe, Americans will have discarded enough water bottles to circle the globe 150 times, according to Annie Leonard’s Story of Bottled Water. Even our smallest actions have big impacts if enough of us do them together.

The concept of carrying capacity is well-known to farmers with livestock. Land is often valued for sale on the basis of how many sheep per hectare it can carry. But the figure is more complex than it appears. It depends, in the first instance, on what the farmer is trying to optimise. Is it the weight of wool he harvests per year, or the number of lambs, or the size and quality of the stock?

It depends further on many management choices he could make, such as sowing better pasture species, applying fertilisers, dividing the farm into paddocks to give pasture a rest from grazing, making hay or silage to even out the feed over the year or buying in supplementary food and so on.

It depends a lot on how variable conditions are from year to year: how often and how severe droughts may be, and what strategies are available for him to cope with them. It depends on how much of the land he leaves for trees and bush: how many trees does he need before the loss of pasture outweighs the benefits of shelter from winter frosts and summer sun? How much vegetation is needed to support the birds that keep insect pests at bay? Perhaps he chooses to leave bush through a sense of custodianship of the land, or for the joy of sharing his world with wildlife, even if the kangaroos are eating his lucerne.

It also depends, frustratingly, on how his neighbours manage their land, whether salt or silt or chemicals flow onto his farm, or groundwater is depleted or raised, bringing salt to the surface, and whether wildlife has corridors to support resilient populations.

Then it depends on what evidence he has to indicate whether the stocking level is sustainable or whether it is slowly running his farm down. Is it getting harder to “finish” the lambs before the summer drought? Is the nutritious clover dying out and being replaced by weedy species? Do his soil tests show carbon levels rising or falling? Is the run of dry years a temporary event or part of a long-term trend?

Carrying capacity for humans on Earth is a much more complex question than the carrying capacity of a farm. What quality of life should be provided for each person? What technologies and behaviours and institutions will apply that will determine the utility we get from our limited resources? How do we deal with variability and risk? And how do we accommodate other species?

The question of how many people the Earth can support has entertained thinkers for centuries. In 1995, Joel Cohen published a thorough review of past studies in the book How Many People can the Earth Support? He emphasised the “undefinability” of global carrying capacity, and even less definable regional or national carrying capacity.

Nevertheless, he appreciated the importance of having some idea of where the limit lies in relation to our current population and where our demographic momentum will take it. Putting aside judgements of the validity of different estimates, he offered the median value of the lower and upper estimates from 67 studies as our collective “best guess”. The range was from 7.7 billion to 12 billion. His conclusion? We are now “entering the zone”. That means our past success in increasing capacity to meet growing demand can’t be expected to continue much longer.

It bears reflecting that most of those estimates are based on optimising the output of all the Earth’s resources for the sustenance of humans, leaving to other species only those resources we can’t make use of. To give an idea of how close to the limit we are of appropriating the world’s resources, the palaeoanthropologist Donald Johanson cited this startling calculation: picture, if you dare, all mammalian flesh on the planet collected into one pile. Ten thousand years ago, the proportion of the pile composed of humans and their livestock represented about 0.1%. Now the proportion is 98%!

Also, few studies took account of the depletion of soils or the exhaustion of fertiliser reserves. Few consider that it may be our pollution that first limits us before we exhaust the capacity for food supply. Most take no account of variability, assuming all years are average years and that average current conditions will continue into the future. The maximum load a rope can lift without breaking is much greater when the load is kept still than if it is bouncing up and down. We might prudently consider the possibility that we are already well into “the zone”, or substantially in overshoot.

Cohen put ideas for dealing with future human demands into three categories: “bigger pie”, “fewer forks” and “better manners”. It is a useful separation, and helps put in perspective the disparate views held by different people about population issues. “Bigger pie” refers to improvements in technology to increase the carrying capacity. “Fewer forks” includes both efforts to slow and stop population growth, and efforts to reduce material inputs and outputs (ecological footprint) per person. “Better manners” concerns issues of equity and distribution, cooperation and compassion, mutual assistance, conflict resolution and risk management. All interact and impact on the future condition of humanity and the planet, and none are unimportant.

But all still boil down to efforts to increase carrying capacity, and efforts to limit population. A bigger pie, better manners or smaller footprint all enable greater well-being, but as we reach the planet’s physical limits we are seeing diminishing returns on efforts to expand the pie, and many past advances appear increasingly precarious. Efforts to reduce fertility, on the other hand, have been startlingly successful at stimulating development and prosperity whenever they have been embraced by government and conducted in sympathy with community needs.

Cohen concludes: “If most people would prefer a decline in birth rates to a rise in death rates, then they should take actions to support a decline in fertility while time remains to realize that choice.”

Where does this leave us in relation to Australia’s population policy options? Many people are calling for a population policy inquiry focusing on our carrying capacity rather than any economic considerations. In a recent forum discussing the need for population policy reform, I suggested that carrying capacity is a distraction. I was admonished by several people for this heresy. Yet I firmly believe that focusing the terms of reference for such an inquiry on the carrying capacity of Australia would guarantee an inconclusive outcome, as did the inquiry of 1994.

Even if it were possible to resolve all the uncertainties about future technologies and behaviours, what would putting a number on Australia’s carrying capacity tell us about our current policy options? If the number was greater than we currently have, would it imply that we should increase our population? If we found it to be smaller than the current population, how helpful would that be given that we don’t have any mechanism for rapid reduction.

We have only two possible policy directions: to continue deliberate growth of the population, or to take measures to decelerate our growth towards a sooner and lower peak. Whether we then choose to stabilise at that level, or let population decline gradually to a lower level, is not a choice we have to make now. It doesn’t change the immediate path of deceleration.

To choose to grow, we must be convinced that a bigger population is demonstrably better than our current level. There is no evidence at all to support such a stance. The arguments for growth are generally founded in the benefits of growth rate itself. If we accept that growth can’t be maintained forever, then such a position (even if its benefits were real) would breach intergenerational equity, putting the burden of stabilisation on a future population with far fewer per capita resources than we currently enjoy.

Any one of a number of findings could provide justification for decelerating our growth. One would be that we are over our carrying capacity. This would imply that our current burden on the natural environment is unsustainable, placing future people at unacceptable and escalating risk.

We can say with confidence that Australia is currently overpopulated. Our current carrying capacity is determined by what we actually do now, not by any possible future behaviours, technologies or institutions. If any single environmental indicator is going backwards due to human pressure, we are by definition overpopulated.

A decade of State of the Environment reports show that almost all indicators are going backwards. Surely to justify deliberate population growth we need to show that we can increase our carrying capacity (reversing environmental health indicators) faster than we increase population.

But even if agreement could not be reached on carrying capacity, we might establish that we have exceeded our “ideal” population, which is very different from carrying capacity. At carrying capacity, we have very little resilience to cope with negative events, such as climate change and sea level rise, because our resources are already stretched to the limit.

The smaller our population, the more resources we have per capita and the less we need to focus on productivity. We can have greater choice, greater variety and greater adaptability.

The “ideal” population would arguably be the lowest population that would satisfy our desires for social interactions. It would not require anyone to eke out a living in a hostile environment.

While technology can increase our carrying capacity, technology can also lower our ideal population by improving communication across distances. But that’s just my opinion, and it matters little how far below the current population size our ideal might be, since reduction is not an option for now. Others (evidently suffering from nature deficit disorder and a faith in technology quite divorced from reality) profess that they would enjoy an endless tapestry of high-rise urban hubbub.

In the end, an ideal population is as open to opinion as carrying capacity, and both fail to address the arguments for growth. The issue appears to be whether the economic benefits of population growth outweigh the negative social and environmental impacts.

It seems that neither the intrinsic value of other species nor the case for intergenerational equity hold sway against immediate economic gain. So the real challenge for a population policy inquiry is to put the economic claims under the spotlight, objectively and without influence from the vested interests in property development and big business.

Divorced of these vested interests, the case for growth rapidly falls apart.

  • A consensus of international studies finds that ageing is not a crisis after all, and raising immigration has little influence on it anyway. Recently announced increases in pension age and superannuation will negate any impacts on the public purse, and impacts in the private sector are mostly positive.
  • It is hard to sustain a case for immigration to address skills shortages when training places for Australians have stagnated for a decade, youth unemployment expanded by 100,000 last year, and immigration increases the demand for skilled people more than it increases the supply.
  • The argument that escalating property values enrich us as a nation is the most bizarre of all. It massively increases the cost of living with no increase in utility at all. Perhaps equally damaging is its effect in tying up national savings in unproductive assets, forcing us to seek overseas investment to fund enterprise and infrastructure.
  • Finally, there is the circular argument that additional people add to our tax revenue, and that this revenue is imperative to pay for the infrastructure needed to accommodate them. In fact, the extra costs of an additional person (whether by birth or migration) far outweigh the extra revenue.

The last point is interesting, because it is completely missed in the macroeconomic analyses of Treasury. No attempt has been made to collate the costs of capacity expansion, which (unlike the aged pension) are disbursed across all portfolios and levels of government, as well as burdening ordinary people. This omission is largely down to the power of one word, “investment”. That word magically transforms a burden into a virtue, and simultaneously moves it from the current account ledger to the discretionary spending over which politicians can puff their chests.

Every major item with a long life span is regarded as an investment. The theory is that it would be unfair to count the cost entirely in the current year because the value is retained in the asset itself and benefits flow in future years. But if capacity expansion is only keeping pace with population, there is no benefit to existing residents. If we didn’t add the people, we wouldn’t need to spend that money, and we could then spend it on real investments that improve quality of life and help us move to a low-carbon society.

Yet it is precisely these long-lived assets whose costs are increased disproportionately by population growth. The longer their life, the smaller fraction we need to replace in any year. If we have to expand our total stock (of power stations, for instance) at the same rate as population growth, this can be a considerable increase on the replacement burden. How is the extra revenue from 2% more taxpayers expected to cover 100% more infrastructure construction, 50% more university places, 30% more buses and more besides? The fact that it doesn’t is why the Queensland government, at the height of a mining boom, feels compelled to sell public assets to balance its books.

There remains only the issue of compassion, and whether we are meeting our moral obligations by limiting migration. A few numbers help put this in perspective. Australia’s net immigration was almost 300,000 last year, four times higher than in the mid-1990s and twice the per capita level of any other developed country. Of that number, refugees were less than 5%, and boat arrivals only around 1%. Over 80,000 people left Australia long term last year, so we could receive far more refugees than we currently do even with zero net immigration.

The annual increase in global population is around 80 million, so we alleviated this burden by less than 0.4%. In doing so, we discouraged countries with high emigration rates from reducing their fertility, possibly adding more people into poverty than we received here. Given that accommodating migrants is a significant cost to us, for the same cost we could alleviate poverty to a far greater extent by assisting people in their own country, and most importantly by helping them to reduce fertility rates.

We could, and would, argue about Australia’s carrying capacity until the cows came home. But regardless of the conclusion, there is no plausible argument for increasing our population, and many good reasons for limiting it. What’s carrying capacity got to do with it? Everything – and not much.