Numbers carry much of the argument on a resource page published by Colcom Foundation, the Pittsburgh nonprofit that Cordelia S. May created in 1996. The page, last updated in May 2026, gathers statistics spanning roughly fifty years to support the Foundation’s view that population size is a central environmental variable.
Emissions and Resource Use
Start with carbon. From 1970 to 2021, per capita CO2 emissions in the United States fell from 21.33 to 14.04 metric tons. The population expanded from 205 million to 332 million. Total emissions rose 15 percent.
Taken together, these first two data sets show the pattern the Colcom Foundation emphasizes most. Individual Americans became more efficient on several measures over fifty years, yet national totals still moved in the wrong direction because the number of people grew faster than per capita impacts declined.
Biocapacity tells a similar story in the Foundation’s telling. The country consumed 227 percent of its available biocapacity in 1970 and about 240 percent in 2020, even though per capita use declined by more than 20 percent.
Land, Wildlife, and People
Converted land rose from roughly 133,000 square miles in 1990 to more than 187,000 by 2020. North American birds declined from approximately 10 billion to 7.1 billion between 1970 and 2020. Globally, the WWF Living Planet Report 2022 recorded a 69 percent drop in vertebrate populations since 1970.
On the demographic side, the U.S. total fertility rate has stayed below the 2.1 replacement level since 1972. Pew Research Center projects that immigration and the U.S.-born children of immigrants will account for 82 percent of population growth from 2005 to 2050.
Colcom Foundation interprets these figures through the I = P x A x T equation from Paul Ehrlich and John Holdren. Its position is that per capita progress keeps getting offset by a larger total population. The Foundation backs public education on this research while keeping its grants away from lobbying and partisan politics. Read this article for related information.
More about Colcom Foundation on https://www.colcomfdn.org/