The Photosynthetic Ceiling: Don’t Duck Your Head Just Yet

Daniel Tanuro
“Le ‘plafond photosynthétique’ n’est pas prêt de nous tomber sur la tête!” [The ‘photosynthetic ceiling’ isn’t about to fall on our heads] Europe solidaire sans frontiers, August 30, 2007
[See note on translation at end of this review.]

reviewed by Ian Angus

Many writers argue that population growth is the central environmental problem facing humanity today. Best-selling author Jared Diamond, for example:

“Given the rate of increase of human population, and especially of population impact, since 1986, we are projected to be utilizing most of the world’s terrestrial photosynthetic capacity by the middle of this century. That is, most energy fixed from sunlight will be used for human purposes, and little will be left over to support the growth of natural plant communities, such as natural forests.” (Collapse: How Societies Choose to Fail or Survive. Penguin, 2005. p. 491)

Surely if a Pulitzer Prize winner says so, it must be true. He must have done careful research before making such a dire prediction, right?

Well, no.

A recent article by Belgian ecosocialist Daniel Tanuro examines Diamond’s claim carefully, and discovers significant problems. He shows that Diamond’s argument conflates two different points.

• It is obvious that “there is a limit to the number of plants that can grow in a given area over a given time,” so it is equally obvious that “there is an absolute limit to the expansion of life on earth.” The words ‘photosynthetic ceiling’ may be new, but the idea was fully explained by the Russian scientist Vladimir Vernadsky in his pioneering book The Biosphere, in 1926.
• The real question is not whether a “photosynthetic ceiling” exists, but “whether we are approaching it as rapidly as Diamond claims.”

So where does Diamond get the idea that by 1986 humans “used … or diverted, or wasted” about half of the planet’s photosynthetic capacity and that we will use “most” of it by 2050?

Unlike most readers, Tanuro has read the sources that Diamond cites. Only one of them deals with this issue, a 1997 article in the journal Science — “Human Domination of Earth’s Ecosystems,” by Peter Vitousek and others.

But that article is not a reliable source. Tanuro shows that its estimate of biological production “used or dominated” by humans is based on statistics that just don’t hold water — and then it draws wide-ranging conclusions that don’t flow even from those unreliable numbers.

“The calculations of Vitousek and friends are far from robust and of very little use for ecologists, because they give a doubly distorted image of our impact on the biosphere. On one hand, by mixing up ‘use’ and ‘domination’, they tend to exaggerate human appropriation of natural resources. On the other hand, paradoxically, they understate the proportion of ecosystems that are affected in one way or another by our activity.”

All that we can really conclude from the numbers in the Vitousek article, Tanuro says, is that humans occupy 16% to 23% of the earth’s land area, consume 3.2% to 6% of biological production, and have an impact (through CO2 emissions in particular) on 100% of the earth.

Those are important facts, but they aren’t enough for the authors, because they want to prove a predetermined thesis: that humanity takes too much space on the earth and consumes too great a part of its resources. This prejudice takes them from questionable numbers to the even more questionable conclusion that humanity is the only animal species that “controls a disproportionate share of the resources of planet.”

Tanuro responds:

“Why is it disproportionate? Compared to what? No scientific argument is advanced to demonstrate that we are being abusive by consuming between 3.2% and 6% of the biological production of the planet….

“The assertion that total consumption of 3.2% to 6% is ‘disproportionate’ is just an opinion, and a misanthropic one at that. Humanist opinions should also be heard in this discussion. This debate cannot be settled by science alone, especially when the science involves inventing parameters that are specifically designed to camouflage opinions as natural laws.”

So that’s the single “scientific” source behind the “photosynthetic ceiling” argument in Collapse. But Diamond goes further — what Vitousek calls “biological production used or dominated” is transformed in Collapse into production that is “used, wasted or diverted,” a far harsher judgement. That in turn leads to an argument for population control in the south and immigration barriers in the north. In Collapse, Diamond even compares Chinese immigrants to Australia and the U.S. with invasive insects and plants that are damaging American forests.

Tanuro rightly concludes:

“Those who muddle the facts about the ecological crisis by blaming the poor rather than capitalism play a dangerous game, one that promotes racism and the irrational while making barbarism seem acceptable.”

A note on translation: In this review, all of the quoted passages from Tanuro’s article are my own translations. A rather different translation of his entire article appears under the title “The ‘photosynthetic ceiling’ is not about to fall on our head!” in the Spring 2008 issue of the British journal Socialist Outlook.