Of the estimated 11.5 billion hectares of bio-productive area in the world, a minimum of 2.1 billion hectares is necessary to preserve biodiversity. Humanity has overshot what’s available, using 15.9 of the maximum 9.5 billion hectares that we should be using (in an ideal world); this leaves at least 6.4 billion hectares that must either be reclaimed or replaced without using more.
With a population of 6.6 billion people, each of us should be using no more than an average of 1.4 hectares (3.5 acres); instead we’re using 2.4 hectares (5.9 acres). If current trends continue, the population will peak in 2020 with the average person using 3.3 hectares (8.3 acres) instead of practically the same amount we should be using today. The last time the world per capita footprint was 1.4 hectares, John F. Kennedy was president of the United States and the world was using half of its biocapacity.
We can’t go back to the early 1960s, nor would we want to. Carbon dioxide emissions from our depleting fossil fuel supply use up half of our global footprint, and these will need to be cut drastically to mitigate global warming. Alternatives to the cheap energy supply that was taken for granted in Kennedy’s era will be much different, if successfully exploited. With the need to make more land wild and common resources such as air and water cleaner, energy and the civilization it enables will be much more a part of Nature than a total break from it.
One thing that might be similar to Kennedy’s time involves sending a breeding population to Mars. At a cost of 110 million hectares each year over the decade or so we may have left before our population peaks, Earth’s life would have an insurance policy in place should we fail and civilization crashes.