Paul Ehrlich a biologist says that the long-term carrying capacity of Earth to be in the range of around two billion people. ("Life on Earth is Killing Us" 9/25/98). Yet Laurie Mazur notes that overpopulation is not just about human numbers, so much as it is about the way in which our activities affect ecology, agriculture and economics (Beyond the Numbers: A Reader on Population and Consumption Issues).
According to the United Nation's Environment Program (UNEP), "The continued poverty of the majority of the planet's inhabitants and the excessive consumption by the minority are the two major causes of environmental degradation," Yet it is no so much unsustainable population growth that forces the rural poor in the Third World into destructive practices which deplete the environment, as it is the drive of their societies to develop and modernize by converting natural resources into products that can be exported to affluent nations (Mark Hertsgaard Earth Odyssey Around the World in Search of our Environmental Future 1998 P207).
The potential risk of abusing technology leading to overdevelopment is that it could lead to us humans "overshooting our Carrying Capacity on a systemic and planetary scale with many unintended consequences such as for example Global Climate Change. Tne risk that we are currently in a phase of overdevelopment and are overshooting our carrying capacity was a central concern that expressed by Ehrlich and also was put forward by the Club of Rome in their promotion of the book Limits to Growth by fellow CoR members Donella and Dennis Meadows as well as Jay Hansen who was one of the people who coined the term "DieOff" to refer to the possibility that humans by overshooting their carrying capacity are on path to a breakdown in human civilization.
Net Primary Productivity is a term that relates to a planetary definition of carrying capacity for humans. Some ecologist say their research indicates that humans now directly use 25 percent or more of the NPP. They question whether this is sustainable and see a link between how we have converted natural areas to human agricultural and forestry monocultures and higher species extinctions rates.
Mathis Wackernagel and Martin Rees came up with the Ecological Footprint as a way to attempt to measure human's impact on the environment.