What is the human population growth projected to be in the next century, and how will that affect population size?

You have seen that this question is highly dependent on the factors that ultimately control the number of births and deaths, or population growth, of humans over time. If the population growth rate projections are correct, there will be roughly 11 billion humans in 2100. Is 11 billion above the carrying capacity of humans? Estimates of the carrying capacity published in 1994 varied 10-fold: from less than 3 billion to 44 billion, with the median estimated at 12 billion. As opposed to the carrying capacities of other species, human carrying capacity depends on natural constraints important to all species, but also on individual and collective choices concerning the distribution of material goods, the use of technology, and the right to political, economic, and cultural freedoms. The number of people that can live on Earth will depend in part on how many will own cars, eat meat, or have air conditioning. For example, estimates suggest that if the carrying capacity values for the population in the United States were applied worldwide, Earth’s carrying capacity would be limited to 1.2 billion. Compare this with the estimated values for India, where the worldwide carrying capacity could be extrapolated to 14 billion. Given that the current population size on Earth is 7.4 billion, it is clear that the vast majority of humans do not, and will not, experience the quality of life inherent to many in the United States.

Future directions

Some have argued that the number of people that can ultimately live on Earth will depend on the ability of humans to continue to expand their carrying capacity through technological innovations and greater efficiencies in food production and energy generation. These technological innovations will require that we increase food production and natural resource extraction without a heavy reliance on fossil fuels, which have a limited supply and adverse effects on the climate. Ultimately, to believe that no ceiling to human population size is inevitable defies what we know about natural populations.