Human Population Growth
The global human population was likely less than 100 million for most of the past 10,000 years. It grew to 1 billion by approximately 1800, reached 2 billion in approximately 1927, 3 billion in 1960, and has risen to over 7 billion today. Several indicators suggest that we are depleting or damaging the supply of fresh water, fossil fuels, and arable land. On the other hand, technological advances in agriculture, medicine, and energy have supported the continued population growth of the past 200 years.
During the 1900s, the human population has gone through a period of explosive growth. We went have gone from 2 billion in 1924 to over 7 billion today. This growth is exponential and rejects the typical restraints applied to the population models applied to other organisms. There are controls that act on the populations of other organisms the collectively form what is called ‘carrying capacity’ or the ability of a particular environmental frame of reference to sustain the number of individuals in a given population. Resources are finite: space, food, water, and reproduction potential are limited in all environments and for all species except for one: the human species. This is not a natural event, is not an accident, and is not sustainable. By both increasing the birthrate and decreasing the deathrate, humans have orchestrated the largest attempt to break free of the laws of nature.
For all populations, their change in size can be calculated and predicted using the same equation (see Fig. 1). This takes into account the births, deaths, immigrations, and emigrations occurring over a given unit of time. To describe the human population, we will have to consider our environmental frame of reference (or population range) to be the surface of the planet Earth where humans are found. We do not have space colonies yet and as far as I know, there aren’t humans immigrating to Earth from other planets. Therefore, we can drop the second part of the population growth equation and only need to consider the difference between the births and the deaths to figure out what our population is doing.
Humans are able to have a large number of offspring and since we provide intensive parental care (the length of ‘childhood’ development is longer for humans than any other species) we can ensure the successful development of our children to reproductive age when they can start having their own babies. Additionally, we have become the best competitors on the planet. For example: we deal with the competition of predators eating our livestock by killing them off or scaring them away and we deal with the competition of herbivores eating our agriculture the same way. We are able to live a long time because we have either killed off or are very good at fending off attacks from other animals and we have found extremely effective ways of escaping disease through modern medicine. All of these combine for an increased birthrate, a decreased deathrate, and an increase length of life.
Population sizes in nature are limited through their inter/intra-specific competition for a limited number of available resources. This results in the carrying capacity mentioned above. If the planet Earth is the frame of reference then the carrying capacity for humans would be the maximum population size that the planet would be able to support. Once the population surpassed this point, population growth would slam on the breaks because of the lack of available resources such as drinkable water and arable land. Without the resources required to live the deathrate will increase and the birthrate will decrease (as there will be less people around to have babies and people capable of reproducing will be less capable of having and then protecting viable children). Even resources that are typically overlooked (such as the various way that natural ecosystem absorb and process our waste products) are limiting factors on the human population.
Homo sapiens reached their carrying capacity on planet Earth decades ago. The Earth can arguable only support from about one-hundred million to one billion people. Currently, we have over 7 billion people and even if we implement strict population control policies, it is estimated that we will reach 9 to 10 billion people before leveling off to a growth rate of zero (without such policies we will reach over 18 billion people in less than a few hundred years). How is it possible that we have far overshot the carrying capacity and why has there not been a devastating crash in our population size? Human technology, innovation, and progress have allowed us to increase food production. This is mainly through the use of artificial nitrogen rich fertilizers that allow us to grow more food on an industrial scale to feed all of the people. We have also used and continue to use the sun’s energy stored in fossil fuels to increase the production of food and extend the length of our lives. This is problematic because more people means more consumption and that means more waste production and addition stress on resources.
The world’s resources are finite. When we use all of the freshwater available in rivers, streams, and aquifers (for industrial and residential purposes), there will be no more freshwater. Ignoring the issues this causes for the rest of the biosphere, atmosphere, hydrosphere and geosphere, we simply will not have water to drink and will die. So the question becomes: Do we limit and partition the use of the rest of the resources on the planet or continue to create technology to increase the Earth’s carrying capacity for humans? At what point do we begin to sacrifice our standard of living so that more people can live? We already do that of course (food across the globe is lower in nutrients, billions of people are facing severe starvation, drinkable water is running out faster than oil, and our ignorant release of chemicals into the air has caused global warming to begin) but how far will the human species be willing to go?
by Earlee Tee