Overpopulation is a major environmental issue that exceeds the sustainable size within a particular physical habitat. 

George Morris defined the term overpopulation as the state of the population where he stated that "When there are more people than can live on the earth in comfort, happiness and health and still leave the world a fit future for future generations."  By definition he tries to explain that there are similarities between people regarding comfort, health and happiness and that future generations may find more or less depending on the influence of the level of technology.  Overpopulation refers to an unwanted condition that affects the existing human population by exceeding the actual carrying capacity of the earth's surface.

While on the other the main concern of the effect of overpopulation is caused by several factors: Natural Resources Depletion, Environmental Degradation, Pandemics and Epidemics, Increase of the Unemployment Problem, Low Life Expectancy, and Extinction of Plants and Animals. These factors may lead to serious problems that give rise to overpopulation.

Cutting down trees that may lead to deforestation, hunting wildlife in a reckless manner, shortage of food and water, and causing pollution are some of the causes of overpopulation by depletion of natural resources. Overuse of coal and iron-ore mining by human activities, lead to the rise of Carbon dioxide level and cause global warming in a global environment, melting poor icecaps and climate change are the serious problem of environmental degradation by overpopulation. Overcrowded and unhygienic living conditions of the people, non-existent health care should raise the problem of Pandemics and Epidemics in an environment. Due to the increase of unemployment, it may cause crime, violence, and theft where the people want to feed their own families to provide them with the amenities of life. Due to the large proportion of population growth occurring in developing and underdeveloped countries, it may cause low life expectancy for the people. Due to this reason, people of these countries may suffer from a shortage of economic resources like jobs, medical care food and shelter.  Destruction of trees and shrubs, and extinction of plants and animals of an ecosystem may cause the destruction of natural habitats and wildlife, natural vegetation is another main cause of overpopulation.

"Overpopulation is the root problem of all the environmental issues if you can control the population, you can control almost everything"

-Rinkesh Kukreja (456)

Finally, the effects of overpopulation may cause due to depletion of precious resources, due to the fastest changes of climate change and global warming may lead to cause serious problems of and environmental issues and an overcrowded population should create a deep impact on the environment and cause population explosion, extinction of biodiversity of an ecosystem such as plants and animals ecosystem is another important major concern of causing overpopulation.