A new study of population growth published in the Proceedings of the National Academy of Sciences has confirmed UN projection of population growth to the year 2100. Explosive human population growth in Africa will endanger populations of large charismatic African mammals and the ecosystems they inhabit.
Biologists, experienced in modeling wildlife populations, found that human population growth will expand to 10 billion people even if large mortality events, similar to the 1918 influenza outbreak, kill half a billion people. Human population growth has so much momentum that it's almost impossible to stop in this century. The only ways found to keep the human population below 10 billion are to eliminate unwanted pregnancies (which are presently 16% of all pregnancies) and establish a global one child policy. There is no practical way to make and enforce a global one child policy, so empowering women to control their fertility is the only possible way to keep the human population below 10 billion to avert severe loss of biodiversity, and severe ecosystem decline, in Africa and Asia.
If women don't strictly limit their fertility, mass mortality events of half a billion to two billion people will not stop the human population from expanding to levels likely to cause severe ecosystem decline.
The inexorable demographic momentum of the global human population is rapidly eroding Earth’s life-support system. There are consequently more frequent calls to address environmental problems by advocating further reductions in human fertility. To examine how quickly this could lead to a smaller human population, we used scenario-based matrix modeling to project the global population to the year 2100. Assuming a continuation of current trends in mortality reduction, even a rapid transition to a worldwide one-child policy leads to a population similar to today’s by 2100. Even a catastrophic mass mortality event of 2 billion deaths over a hypothetical 5-y window in the mid-21st century would still yield around 8.5 billion people by 2100. In the absence of catastrophe or large fertility reductions (to fewer than two children per female worldwide), the greatest threats to ecosystems—as measured by regional projections within the 35 global Biodiversity Hotspots—indicate that Africa and South Asia will experience the greatest human pressures on future ecosystems.
Conservative economists have asserted that cutting population growth will cause economic decline, but this study found that assertion is false because the benefits of fewer children offset the burdens of caring for the increased percentage of the elderly.
Shrinking populations can support elderly adults.
Some economists argue that shrinking populations create an unsupportable burden of elderly dependents that leads to economic collapse. But the team’s model showed otherwise. When the population is growing, more of the dependents are children, and when the population is shrinking, more are older adults, the model indicates. A dependent is always supported by 1.5 to two workers. The idea that shrinking populations cannot support older adults is a “fallacy,” Bradshaw says.
Two factors did have an impact on human population growth: eliminating unwanted pregnancies, which make up about 16% of all live births, and adopting a global one-child policy. Eliminating those births year after year resulted in population sizes in 2050 and 2100 that are comparable to those produced with a global one-child policy—about 8 billion and 7 billion, respectively.
Because human population growth will be so hard to slow down the best way to avert systemic ecological collapse will be to rapidly transition to sustainable technologies and lifestyles. The highly unsustainable fossil fuel based consumptive lifestyle advocated by today's Republicans will inevitably lead to an catastrophes of unimaginable proportions.
Fertility and natural resource consumption must be rapidly reduced to avert ecological collapse.
Brook, now at the University of Tasmania, said policymakers needed to discuss population growth more, but warned that the inexorable momentum of the global human population ruled out any demographic quick fixes to our sustainability problems.
“Our work reveals that effective family planning and reproduction education worldwide have great potential to constrain the size of the human population and alleviate pressure on resource availability over the longer term,” he said. “Our great-great-great-great grandchildren might ultimately benefit from such planning, but people alive today will not.”
Bradshaw added: “The corollary of these findings is that society’s efforts towards sustainability would be directed more productively towards reducing our impact as much as possible through technological and social innovation.”