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 nature can repair it, potentially leading to an ecological and societal collapse. Overpopulation could apply to the population of a specific region, or to world population as a whole.
Overpopulation can result from an increase in births, a decline in mortality rates, an increase in immigration, or an unsustainable biome and depletion of resources. It is possible for very sparsely populated areas to be overpopulated if the area has a meagre or non-existent capability to sustain life (e.g. a desert).
Advocates of population moderation cite issues like exceeding the Earth's carrying capacity, global warming, potential or imminent ecological collapse, impact on 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.
Scientists suggest that the overall human impact on the environment, due to overpopulation, overconsumption, pollution, and proliferation of technology, has pushed the planet into a new geological epoch known as the Anthropocene.