The best way to reconcile the maximizing of ideality alone with the maximizing of both ideality and population is to increase the capacity – the amount of renewable resources. With more capacity, more people can be supported at a high standard of living.
My best estimate of currently available capacity is 5.9 billion hectares, or 12 percent of our planet’s total surface area (about 40 percent of the land area). If neither the capacity nor our behavior changes, the population will settle at a sustainable level of about 580 million people with an ideality of 78 (the average of life expectancy in years and happiness in percent). The final sustainable population size will vary roughly in proportion to capacity if we don’t change our behavior: That is, if we double capacity, then the size of the sustainable population will double. If we could increase our capacity to include the Earth’s surface area (doubling the rate of growth to maximize population), we would still suffer 5.2 billion casualties. Ideality would reach the same value as business as usual, but the final population would be nearly nine times larger (5.0 billion, versus 580 million).
For higher multiples of capacity, the proportionality rule breaks down. My theoretical model of population and consumption indicates that capacity would have to be at least 830 billion hectares (more than 16 times Earth’s surface area of 51 billion hectares), reached at a growth rate of two percent per year (four times the current rate), to continue our current consumption trend and avoid population loss. Ideality in this case would level out at 96 (versus 78 for business as usual with a loss of 7.5 billion people from a peak of 8.1 billion).
If we can’t change capacity, but do change our behavior (by stopping population growth and reducing per capita consumption) we could achieve an ideality of 54 with a loss of 29 million people from a peak of 6.6 billion.
It appears that we cannot practically avoid population loss. The main question our species faces then is simply how many casualties we are willing to incur based on how well we want our descendants to live.