BACKGROUND: My population-consumption model shows that the world's human population has, on average, been consuming resources as though they were non-renewable for more than 2,000 years. To survive indefinitely (barring any major changes in conditions, including moving to other planets), we would need to meet existing consumption using resources that could be replenished at the rate we are consuming them. I have recommended building capacity – the mass of renewable and reusable resources – as fast as possible to equal the amount of mass we consume annually. The effect of this solution is to eliminate our consumption of non-renewable resources, which is currently reducing our population growth and may lead to a sudden drop in population when growth stops (consumption and population will reach a peak).
I have assumed that we will somehow be able to exactly match our consumption with capacity that the biosphere can't provide, likely with efficiency technology. For example, we could create structures that can last as long as we need, which are effectively one-time uses of our remaining non-renewable resources. What if this assumption is wrong?
The model shows that if, beginning at the end of 2012, we held consumption constant, relied on available biocapacity, and reused an amount of resources equal to 90% of the remaining consumption, we would need to reach the maximum capacity within two years, and our non-renewable resources would last until 2377. Raising reuse from 90% to 99% would give us 65 years to reach maximum capacity and extend resources to 2864. At the low end, if capacity was limited to available biocapacity and no reuse, and reached in no more than three years, resources would last until only 2050, which is 29 years longer than if we had no capacity at all.
A sustainable alternative is to provide all of the 2012 consumption with biocapacity, which would need to be increased by at least 81%. In a crude sense, this may correspond to additional habitat, perhaps as land area that is available for other species to use. If we occupy that land for purely human use, we might have to abandon it. Because we would replacing non-renewable resources with renewable resources, what we consume it for would change. Because we could no longer extract and use the metal, oil, coal, minerals, and other resources that comprise our artificial existence, nearly every aspect of what we think of as “modern civilization” would be replaced by natural and very likely labor-intensive alternatives.
If we can't increase biocapacity or find an alternative to it (which seems unlikely given the time we have left), and don't want to lose population, we should reexamine the idea of reducing consumption. Cultural measures, such as government controls, might conceivably be used to keep people from killing each other while a rapid conversion is made to all-natural economy that uses no more than the biocapacity we have (and preferably less). If one hectare of global ecological footprint corresponds to 1,000 pounds of mass consumed, then a minimum of 1.5 hectares per person needed to maintain a society would, beginning with a 47% drop in consumption in 2012, allow us until 2133 to fully convert our economy.
In what appears to be a recurring theme in these discussions, humanity is faced with a tradeoff between lifestyle and species longevity. If no “magic bullet” technology can be found to meet our desires with replenishing resources, we must use only what a healthy biosphere can spare, and change our desires accordingly.