Discussions about population and the environment often depend on technical vocabulary. Colcom Foundation, a Pittsburgh nonprofit established in 1996 by the late Cordelia S. May, uses four key terms to explain its mission and the data behind it. Understanding them makes the Foundation’s arguments easier to follow.
Footprint and Deficit
The first term, Ecological Footprint, comes from the Global Footprint Network. It measures how much biologically productive land and water an individual, population, or activity needs to produce what it consumes and absorb the waste it creates, based on current technology and resource management.
An ecological deficit follows when a population’s footprint exceeds the biocapacity of the area available to it. At the national level, the Global Footprint Network explains that a deficit means a country is importing biocapacity through trade, depleting its own ecological assets, or emitting carbon dioxide into the atmosphere.
Overshoot and Fertility
Biocapacity overshoot describes consumption of natural resources at a pace faster than ecosystems can regenerate them. Colcom Foundation reports that the United States was consuming approximately 240 percent of its available biocapacity as of 2020, up from 227 percent in 1970. Per capita use fell more than 20 percent across that span, and the Foundation attributes the net increase in overshoot entirely to population growth.
The fourth term is total fertility rate, or TFR. It refers to the average number of children a woman is expected to have during her lifetime. A TFR of 2.1 is considered replacement level, where a population holds steady without growth or decline from births and deaths alone. U.S. fertility fell below that threshold in 1972 and has remained there since. The Foundation notes that the population nonetheless kept growing, with immigration becoming the primary driver.
These concepts feed into the equation at the core of the Foundation’s work: I = P x A x T. Developed by Paul Ehrlich and John Holdren, it holds that environmental impact equals population times per capita affluence or consumption times technological efficiency.
Colcom Foundation funds public education and research built on these measures, alongside regional conservation and cultural grants in southwestern Pennsylvania. Readers seeking the underlying data can consult the Global Footprint Network directly. See related link for more information.
More about Colcom Foundation on https://waterlandlife.org/land-conservation/colcom-revolving-fund-for-local-land-trusts/