Climate change and overpopulation are the two problems that threaten the future of life on Earth. The two problems intersect and are interactive, but they are separate and distinct, and either is sufficient to cause the Holocene (6th) Mass Extinction.
Planet Earth is becoming warmer. This may be due solely to natural phenomena or there may be an anthropogenic contribution to the process, but it is certain the planet is undergoing a cyclical change in surface temperature and in climate. The regional distribution of hotter/cooler, wetter/drier areas is changing as part of the overall change in the climate. If the change is largely attributable to natural processes, it may be beyond the power of humans to do anything about it, except, perhaps, to stop pouring accelerant on the fire.
Overpopulation is not a “natural” process: it is an artefact, the outcome of human behaviour. We caused the problem, we can solve it. Unfortunately, it is inherent in the collective mindset of our species that most people avoid even thinking about the problem, let alone acting to try to solve it.
What is the justification for saying there are too many human beings on Earth? It comes down to simple arithmetic. The capacity of the Earth to provide the resources we need to sustain us - that is, the arable land, grazing land, forests, fisheries, potable water, fossil fuels - and the means to dispose of the waste we generate is limited.
How many people the Planet can support depends primarily on how much “bioresource” each of us consumes. The Planet is not a Magic Pudding that is continually replenished as it’s eaten; it is more like a can of ice-cream - if everyone has a one-scoop cone it can supply, say, 100 people, but if every customer demands a two-scoop cone it can only supply 50 people. And this is the trade-off: the more people, the less bioresource available for each person, and conversely, the fewer people the higher each person’s sustainable level of consumption.
The total capacity of Planet Earth to sustain life, which is referred to as its “biocapacity” in the Living Planet Report (LPR) 2008, is expressed as billions of “global hectares” (Ggha). The LPRs are published biennially by The Global Footprint Network (GFN). The most recent of these, LPR 2008, is based on 2005 data. The methodology by which LPRs are prepared is scientifically sound, and they provide the data used by a number of sovereign states in formulating their environmental policies.
In 2005 the biocapacity of the Earth was 13.6 Ggha, and the population was 6.5 billions; therefore, the sustainable per capita global footprint was 2.1 gha. But aggregate demand was for 17.5 Ggha, which represents a per capita demand of 2.7 gha.
In other words, in 2005 we were overdrawing the bioresource account by about 29 per cent per annum.
Since 2005, the world population has increased to over 6.8 billion and the demand for resources from developing economies, such as China, India, Brazil, and Indonesia has increased substantially. On the supply side of the ledger, the biocapacity of the Planet has, if anything, been reduced as the result of ongoing land degradation, forest destruction, and fish stock depletion. Consequently, at a conservative estimate, demand now exceeds supply by something like 35-40 per cent per annum.
According to the UN’s most-likely, medium growth scenario (PDF 1.77MB), by 2050 the population of the world is projected to have increased to at least 9.1 billion, although it is understood this figure is likely to be revised upwards. Some would suggest the 2050 population will be nearer 9.5-10 billion.
Under appropriate assumptions relating to population increase and increased consumption by poor and middle-income countries, total world demand in 2050 will be for about 34.8 Ggha, which represents the biocapacity of more than 2.6 Planet Earths. This is obviously not a feasible scenario, even in the very-short term. In fact, even if nothing changed, the present overconsumption (1.3 x the biocapacity of the Planet) cannot continue. Business as usual is not an option.
And bear in mind, these data make no allowance for wildlife species that have the misfortune to need to share the arable land, forest, and fishing grounds we use.