It is quite a fun fact that these two days actually exist and how they are related to each other. It is a debate about humanity’s expanding needs and what the planet can actually provide.
As our population grows, we also tend to overconsume and overdevelop to support the human’s demands. Perhaps some understanding of the World Population Day and the Earth Overshoot Day will help to picture the situation in a clearer way.
World Population Day
World Population Day, which seeks to focus attention on the urgency and importance of population issues, was established by the then-Governing Council of the United Nations Development Programme in 1989, an outgrowth of the interest generated by the Day of Five Billion, which was observed on 11 July 1987.
The Day was first marked on 11 July 1990 in more than 90 countries. In the same year, the United Nations General Assembly decided to continue observing World Population Day to enhance awareness of population issues, including their relations to the environment and development.
Why do we need to look into the World Population Day? Well, a tremendous change occurred with the industrial revolution: whereas it had taken all of human history until around 1800 for world population to reach one billion, the second billion was achieved in only 130 years (1930), the third billion in 30 years (1960), the fourth billion in 15 years (1974), and the fifth billion in only 13 years (1987).
According to the worldometers.info, we will have roughly about 7.8 billion populations by 2020, and the latest world population projections indicate that the world population will reach 10 billion persons in year 2057. This is where problems happen.
Human overpopulation (or population overshoot) is when there are too many people for the environment to sustain (with food, drinkable water, breathable air, etc.). In more scientific terms, there is overshoot when the ecological footprint of a human population in a geographical area exceeds that place's carrying capacity, damaging the environment faster than it can be repaired by nature, potentially leading to ecological and societal collapse.
Concern about overpopulation is an ancient topic. Tertullian was a resident of the city of Carthage in the second century CE, when the population of the world was about 190 million (only 3–4% of what it is today). He notably said:
"What most frequently meets our view (and occasions complaint) is our teeming population. Our numbers are burdensome to the world, which can hardly support us... In very deed, pestilence, and famine, and wars, and earthquakes have to be regarded as a remedy for nations, as the means of pruning the luxuriance of the human race."
Before that, Plato, Aristotle and others broached the topic as well.
Overpopulation could apply to the population of a specific region, or to world population as a whole, which can result from an increase in births, a decline in mortality rates, an increase in immigration, or an unsustainable biome and depletion of resources.
Advocates of population moderation cite issues like exceeding the Earth's carrying capacity, global warming, potential or imminent ecological collapse, impact on the quality of life, and risk of mass starvation or even extinction as a basis to argue for population decline.
A more controversial definition of overpopulation, as advocated by Paul Ehrlich, is a situation where a population is in the process of depleting non-renewable resources. Under this definition, changes in lifestyle could cause an overpopulated area to no longer be overpopulated without any reduction in population, or vice versa.
About one-fifth of those on Earth still don't have access to reliable electricity. So as we debate population, things we take for granted—reliable lighting and cooking facilities, for example—remain beyond the reach of about 1.3 billion or more people. Lifting people from the darkness of energy poverty could help improve lives.
What if we are already overconsuming despite this population issue?
Earth Overshoot Day
Earth Overshoot Day (EOD), which previously known as Ecological Debt Day, is the calculated illustrative calendar date on which humanity's resource consumption for the year exceeds Earth’s capacity to regenerate those resources that year. The term "overshoot" represents the level by which human population overshoots the sustainable amount of resources on Earth.
In a famous 1798 essay, the Reverend Thomas Malthus proposed that human population would grow more rapidly than our ability to grow food, and that eventually we would starve. He asserted that the population would grow geometrically—1, 2, 4, 8, 16, 32—and that food production would increase only arithmetically—1, 2, 3, 4, 5, 6. So food production would not keep up with our expanding appetites.
Even though more than 800 million people worldwide don’t have enough to eat now, the mass starvation Mathus envisioned hasn't happened. This is primarily because advances in agriculture—including improved plant breeding and the use of chemical fertilizers—have kept global harvests increasing fast enough to mostly keep up with demand.
But how long will this last?
A general scenario of human overconsumed is when food waste becomes the greatest amount of waste that we send to landfill in our country, especially during festive seasons. Besides, the growth of fast fashion and plastic packaging pollution are also evident to the fact that humanity’s annual demand on the natural world has exceeded what the Earth can renew.
Since 1970s, this “ecological overshoot” has continued to grow over the years, reaching a 50 per cent deficit in 2008. This means that it takes 1.5 years for the Earth to regenerate the renewable resources that people use, and absorb the CO2 waste they produce, in that same year.
The consequences of excess greenhouse gases in the atmosphere are also already being seen, like climate change and ocean acidification. These place additional stresses on biodiversity and ecosystems. As climate change damages crop yields and extreme weather disrupts harvests, growing enough food for our expanding population has become what The 2014 World Food Prize Symposium calls "the greatest challenge in human history."
At present, people are often able to shift their sourcing when this happens; however, at current consumption rates, these sources will eventually run out of resources too – and some ecosystems will collapse even before the resource is completely gone. As a conclusion, maximising our resources is very important if our population are going to continue growing. Well, before everything is too late, recycling and reusing the existing resources will help to slow down the depletion while changing of consuming pattern and lifestyle will be able to turn this whole thing around.