Overpopulation is a condition where an organism's numbers exceed thecarrying capacity of its habitat. In common parlance, the term often refers to the relationship between the human population and its environment, theEarth.
Overpopulation does not depend only on the size or density of the population, but on the ratio of population to available sustainable resources. It also depends on the way resources are used and distributed throughout the population If a given environment has a population of 10 individuals, but there is food or drinking water enough for only 9, then in a closed system where no trade is possible, that environment is overpopulated; if the population is 100 but there is enough food, shelter, and water for 200 for the indefinite future, then it is not overpopulated. Overpopulation can result from an increase in births, a decline in mortality rates due to medical advances, from an increase in immigration, or from an unsustainable biome and depletion of resources. It is possible for very sparsely-populated areas to be overpopulated, as the area in question may have a meager or non-existent capability to sustain human life (e.g. the middle of the Sahara Desert).
The resources to be considered when evaluating whether an ecologicalniche is overpopulated include clean water, clean air, food, shelter, warmth, and other resources necessary to sustain life. If the quality of human life is addressed, there may be additional resources considered, such as medical care, education, proper sewage treatment and waste disposal. Overpopulation places competitive stress on the basic life sustaining resources, leading to a diminished quality of life.The rapid increase in human population over the course of the 20th century has raised concerns about the Earth's ability to sustain a large number of inhabitants. In 2009, the estimated annual growth rate was 1.10%, and the world population stood at roughly 6.7 billion. Current projections show a steady decline in the growth rate, and a population of around 9 billion by the year 2050. The scientific consensus is that the current population expansion and accompanying increase in usage of resources is linked to threats to the ecosystem. The InterAcademy Panel Statement on Population Growth, which was ratified by 58 member academies in 1994, called the expansion in human numbers "unprecedented", and stated that many environmental problems were aggravated by the population expansion. At the time, the world population stood at 5.5 billion, and optimistic scenarios predicted a peak of 7.8 billion by 2050, a number that current estimates show will be reached around 2030.