Guessing how many species there are — or were before the human steamroller got cranked up — on this unique planet has become something of a parlor game for biodiversity scientists. The truth is that we don’t have a very good idea, which is not surprising give that so many of our fellow life forms are bacteria, soil mites, roundworms, parasites, and otherwise obscure microscopic bugs. Some experts guesstimate that there are a few million, others say maybe 20 or 30 million.
But there is something that we do know now, with considerably more precision: of those — let’s say three million — species, a single one now sucks up roughly a quarter of all of earth’s biological production. Can you guess which species that is? Well, duh.
One in every four sunbeams that falls on an upturned plant and miraculously transforms dirt into life, or that could have done so, ultimately ends up in our hamburgers or paper-mill forests or cornfields destined for biodiesel, or has been blocked from the miraculous transformation by the asphalt under our cars or the baking roofs of our buildings on which our AC units are merrily buzzing.
Remember the backpacking T-shirts from the old days (maybe they still make them) emblazoned: “Take only memories, leave only footprints”? That’s one helluva footprint.
A new, comprehensive analysis concludes that humans now appropriate 23.8% of the planet’s total net primary productivity, of which 53% was contributed by harvest, 40% by land-use-induced productivity changes (for example, paving paradise to put up a parking lot), and 7% by human-induced fires.
That is a global average. Looking closer, we should not be surprised to find that the figures are much higher for heavily populated areas. Map b shows the “Human Appropriation of Net Primary Production” (HANPP) as a fraction of the potential net primary productivity — in other words, the fraction used by humans of the plant biomass that could be produced in an area, given local environmental conditions. Notice that the global average of one quarter is actually a gross underestimate for heavily populated areas. Throughout north central North America, much of Europe, all of the Indian subcontinent, China, and southern Australia, the situation is code red, so to speak — we are using between 60 and 100% of potential primary production. One might say that, in those places, we are very close to the edge. And that doesn’t leave much left over for the other 2,999,999 (or so) species.
So how will we solve the central problem of our time, making the transition away from fossil fuel to alternatives, while feeding a doubling population? Through massive land clearance for cultivation of biofuel crops?
The original citation is:
Haberl, H., K.H. Erb, F. Krausmann, V. Gaube, A. Bondeau, C. Plutzar, S. Gingrich, W. Lucht, and M. Fischer-Kowalski. 2007. Quantifying and mapping the human appropriation of net primary production in earth’s terrestrial ecosystems. Proceedings of the National Academy of Sciences 31:12942-12947 (6 July 2007).