Human Population: Why set One Billion as the Upper limit?

by Ted Mosquin January, 2006

The Manifesto for Earth ( estimates the maximum sustainable limit for world human population as ‘one billion or less’. This estimate is consistent with the ecological reality of the planet and with the idea that there can be little or no social justice among peoples, particularly on a depleted and degraded Earth, as is already the case. Principles 1 through 6 of the Manifesto provide the ecological and social justice framework for the ‘one billion or less’ estimate. This number was not pulled out of the air; it is based on evidence and on several specific rationales which show that major reductions of human population are desirable, necessary, and credible, as note the following:


1). Population Overshoot. ‘The biological phenomenon of ‘population overshoot’ is used by ecologists to describe a species whose numbers exceed the ecological carrying capacity of the place where it lives. We humans are in a state of overshoot on Earth. It is the discovery and use of vast fossil fuel reserves that has enabled human numbers to reach the level of very severe overshoot. In the past 10,000 years the human population has increased from 5-10 million to about 6.5 billion in 2005. At first, this growth was sustained by displacing other species from land areas, but in the past two hundred years, humanity has expanded enormously based on a much more precarious practice of rapidly drawing down finite natural resources, many of which are becoming scarce or already depleted. The knowledge of the human ecological predicament has been clearly articulated during the past fifty years, but the response has been to deny it and to continue to increase human numbers and consumption with serious effects on the orderly functioning of the Ecosphere.


Overshoot assesses the relationship between humanity and the rest of the Ecosphere, a relationship that has become dangerously out of balance, as witness large-scale contamination of food webs, destruction of valued resources, extinctions of species, global warming, and the like. As humans go deeper into overshoot, the consequences to Earth’s evolved life-support systems are becoming ever more severe. Growing shortages of essential resources are already leading to impoverishment of populations. The harsh effects can be mitigated by a reversal of present day policies of promoting ever more economic growth; good choices can still be made to reverse local, regional and global trends.

2) Social Justice. When scientists warn that humans are demanding more than the Earth can provide sustainably over the long-term, there are those who claim that any reduction of production will fail to meet the needs and wants of a rapidly growing population and therefore will diminish conditions required for social justice. These are two distinct issues. Social justice is internal to the human family and stems from the genetic predisposition of human beings as a social species to share (or hoard) what we can glean from the Ecosphere. Ultimately, higher standards of social justice depend upon radical reductions of human numbers and demands coming safely within the bounds of what Earth’s Ecosphere can provide sustainably over the long-term, emulating the successful ways and methods that Nature has refined over eons

3) Terrestrial and Marine Ecosystems Required to Restore Planetary Sustainability. Today, the world’s fisheries, forests, agricultural lands are being depleted; toxification of soils, waters and organisms is continuing to increase with no sign of ending. Huge regions are experiencing desertification. In view of these negative trends, what percentage of Earth’s ‘geo-ecosystems’ should be protected or restored to return to ecological sustainability? Some holistic ecologists (Eugene Odum, for example) have proposed 50 % of each of Earth's major ecosystems be retained/restored to naturally functioning systems, leaving 50% modified to various degrees by human activities (agriculture, cities, industry ). Others have proposed 1/3 natural, 1/3 with small settlements, organic agriculture and 1/3 for urban areas, agriculture, industry. Realistically, all of these scenarios and others like them do require an enormous reduction in population size.

4) Studies of CO2 Emissions. Yet another ecological rationale for the less than one billion maximum figure comes from studies of per capita CO2 emissions in different countries. This assumes that present levels of CO2 are already far in excess of what should be a global norm and hence need to be drastically reduced to prevent the accelerating large scale destruction of terrestrial and marine ecosystems and their evolved biodiversity. One example of conclusions drawn is for Canada where the level of per capita CO2 emissions suggests that Canada’s population should not exceed 6 million (about 1/6th or 1/7 of present population). This bit of ecological calculation was not considered by the authors of the Manifesto. Yet it is in accord with the conclusion that a sustainable world population would be 1/6 or less of the present day number.


5) Number of Earth’s Required by Humans. Estimates by ecologists that at the present time two to four Earths would be required for a western life style in order to satisfy the consumption desires of the 6.5 billion people now inhabiting the planet. The reality today is that well over two billion of the world’s poor people also cause major ecological impacts, including extensive deforestation, desertification, soil erosion, depletion of fisheries, with attendant misery and poverty. Another reality if that huge populations not yet living at western life styles are aspiring to do so, with China, India and Indonesia being only three examples. At the same time, there is scant evidence that the differential between western life styles and those of up-and-coming nations will narrow. Considering this complex global human predicament, and also considering that there is no chance for additional Earths to be found, it follows that human population should be adjusted to fit on the one Earth that actually exists.

6) The Early mid-19th Century Benchmark for Ecological Sustainability. The authors of the Manifesto asked: when were human numbers still in relative balance with the Ecosphere's ability to sustain them without undermining the Earth’s time-tested capacity for regeneration and renewal? The time was roughly at the beginning of the Industrial Revolution early in the 19th Century, when human population was around 950 million, one seventh of today’s numbers. Other estimates by scientists have been both higher and lower.


7) The issue of Ethical Guidance. It is simply wrong to usurp vast regions of land and sea and allocate them for exclusive human exploitation and utilitarian uses and continue on the path of exterminating thousands of other evolved species and beautiful integral ecosystems. The Manifesto provides the ecological and ethical foundation for a radical new worldview, namely a shift from homocentrism to ecocentrism. This change also requires a major reduction in human numbers.


An important question asked by the authors of the Manifesto: How will a reduction of human numbers down to less than one billion be accomplished? The Manifesto says that it will be accomplished by shifting from today’s homocentric (anthropocentric) worldview to the ecocentric one described in the Manifesto, and of necessity, by intelligent policies – or inevitably by plague, famine, and warfare.



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