Review: Harvesting the Biosphere

Posted: April 5, 2015 in Environment, Nomenclature, Politics, Science
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The comic below alerted me some time ago to the existence of Vaclav Smil, whose professional activity includes nothing less than inventorying the planet’s flora and fauna.

Although the comic (more infographic, really, since it’s not especially humorous) references Smil’s book The Earth’s Biosphere: Evolution, Dynamics, and Change (2003), I picked up instead Harvesting the Biosphere: What We Have Taken from Nature (2013), which has a somewhat more provocative title. Smil observes early in the book that mankind has had a profound, some would even say geological, impact on the planet:

Human harvesting of the biosphere has transformed landscapes on vast scales, altered the radiative properties of the planet, impoverished as well as improved soils, reduced biodiversity as it exterminated many species and drove others to a marginal existence, affected water supply and nutrient cycling, released trace gases and particulates into the atmosphere, and played an important role in climate change. These harvests started with our hominin ancestors hundreds of thousands of years ago, intensified during the era of Pleistocene hunters, assumed entirely new forms with the adoption of sedentary life ways, and during the past two centuries transformed into global endeavors of unprecedented scale and intensity. [p. 3]

Smil’s work is essentially a gargantuan accounting task: measuring the largest possible amounts of biological material (biomass) in both their current state and then across millennia of history in order to observe and plot trends. In doing so, Smil admits that accounts are based on far-from-perfect estimates and contain wide margins of error. Some of the difficulty owes to lack of methodological consensus among scientists involved in these endeavors as to what counts, how certain entries should be categorized, and what units of measure are best. For instance, since biomass contains considerable amounts of water (percentages vary by type of organism), inventories are often expressed in terms of fresh or live weight (phytomass and zoomass, respectively) but then converted to dry weight and converted again to biomass carbon.

Because inventorying global biomass is still a relatively young specialty within the whole of science, wide margins of error and acknowledgement of highly speculative assessments seems to me a necessary step in the maturation of the field, much as Freud’s initial psychological theories were a significant starting point for later refinement (still underway). Further, concluding a static number (or range) for this or that category is like taking a snapshot of a moving target, essentially fixing it in time. Whereas photography can do that handily, biomass measurements are like counting global human population, which is constantly in flux due to births and deaths but for now still growing.

If there is an overall criticism to be made, it is a familiar one that has characterized science for centuries, namely, that if a field of inquiry can be broken into pieces, measured, and analyzed sufficiently, it can be understood, and presumably, acted upon with confidence and clarity. Some fields have yielded impressive results from application of the scientific method and perspective, but others have remained notoriously opaque and/or simply too complex for us to grasp. Human cognition/consciousness is one such mystery despite considerable effort having been directed to discovering its workings. Although Smil doesn’t come straight out and say that application of his work would enable humanity to better manage the Earth’s resources (a task assigned by whom?), that would be the obvious conclusion based on our aggregate activity over the ages. What Smil does rather lamely conclude at various points is that measurement allows us to see the impacts of our behaviors in better light, even if we don’t fully understand them yet. In contrast, Smil sometimes concludes that we just don’t yet know the full measure of our impact, which is frequently confounding. For example, Smil’s discussion of increased carbon in the atmosphere, which scientifically illiterate political hacks suggest is merely “tree food,” falls notoriously short of stating the obvious: even minute changes in atmospheric chemistry destabilize the relative ecological steady state under which trees have evolved. It doesn’t take a Ph.D. in biology to see that this is unlikely to end well.

Let me pluck a few additional observations from the book that I find of particular interest. Here, I will admit that I am indeed part of the lay public the book addresses (i.e., not a scientist or specialist in the field) but also that I approached my reading with more than a little confirmation bias. The subtitle says it all: “what we have taken from nature,” as distinguished from what we left undisturbed. Smil evades political and sociological conclusions that might follow from clear recognition that humans have gobbled laid claim to everything. He even argues against the loaded terms anthrome and anthropocene, which define place and time specifically in terms of human interference activity. Whereas I understand and even agree — to a point — with his perspective and arguments, it is undeniable that human impacts are now felt globally, which Bill McKibben expressed decades ago in his book The End of Nature. I will demur at this stage any discussion of what constitutes natural, artificial, man-made, synthetic, etc., having already traversed some of that ground.

One of the most interesting things was that, in contrast to Smil’s constant reminders of lack of recordkeeping and thus reconstructed historical estimates, a rather complete record was available of hardwood used for shipbuilding during the Middle Ages. For instance, building

… a ship containing 4,000 t of wood (requiring 6,000 t of delivered wood) … claimed anywhere between 30 and 50 ha [hectares of forest] … We also have a comprehensive estimate of the Royal Navy’s wood requirements during the last decades of the wooden ship era. In 1810, the fleet’s tonnage was some 800,000 tons, and with roughly 1.5 tons of timber needed per ton, it took approximately 1.2 million loads, or 1.1 Mt if all of it were oak and less than 1 Mt if it were a mixture of hard- and softwood species dominated by oak. The average lifetime of naval ships was about 30 years, but substantial repairs were needed after 15 years. When these realities are taken into account, the annual rate of timber for consumption for new construction and repairs prorated to about 110,000 loads, or at least 90,000 t of timber a year. [pp. 147–148]

Thus, this single use of timber (i.e., not counting fuelwood for heating and cooking and timber for building housing and furniture) contributing to deforestation gives the reader an idea of just how rapacious our needs were even hundreds of years ago.

Most of the book is about harvesting of terrestrial biomass. However, Smil is wise not to overlook marine ecosystems completely in his inventories. Problems arise almost immediately because of even greater conjecture involved in assessing remote and largely unexplored oceans that cover roughly 2/3 of the Earth’s surface. What numbers are available come mostly from fishing harvests and point to widespread collapses in fisheries and their productivity (euphemism alert). Smil also observes that the “only notable retreat from mass killing of mammals has been the worldwide moratorium on commercial whale hunting imposed in 1986 by the International Whaling Commission” (p. 57). Irrational concern with a few “romance species,” as I’ve heard them called (see mention of elephants below), masks the fact that phytoplankton is at the base of the food chain (or now, dead(!) center of the food web) and are affected by minute changes in pH balances in ocean- and seawater.

Satellite-derived observations of phytoplankton concentrations have been available only since 1979, but numerous standardized ocean transparency measurements … have been available since 1899, and they can be used to calculate surface chlorophyll concentration and augmented by direct in situ optical measurements … this information [was used] to estimate a century of phytoplankton changes on regional and global scales and found significant interannual and decadal phytoplankton fluctuations superimposed on long-term declines in eight out of ten ocean regions, a worrisome trend whose continuation would have significant effects on future catches. [p. 212]

Smil begins to summarize and offer long-term trends and possible worlds with the following disillusioning assessment:

The most obvious, and conceptually the simplest, indicator of the human impact on the biosphere’s productivity and phytomass storage is the total area of the natural ecosystems that have been transformed by human action. To put these changes into an evolutionary context, I will begin with a brief review of phytomass storage during the past 20 millennia, since the last glacial maximum (LGM), when North America north of 50°N and much of Europe beginning at only a slightly higher latitude were covered by massive continental glaciers. Primary productivity and carbon strongly rebounded during the next 15 millennia, reaching maxima by the mid-Holocene, some 5,000–6,000 years ago at the time of the first complex civilizations. This was followed by millennia of locally severe and regionally substantial transformations whose global impact remained still relatively minor.

The most common kind of conversion was to create new fields by converting forests, grasslands, and wetlands (and in some regions also deserts) to new croplands and pastures. Next in overall importance have been the claims made on forest phytomass to remove timber and firewood and, starting in the nineteenth century, wood for making paper. These human transformations of ecosystems began to accelerate during the early modern era (after 1600) and reached an unprecedented pace and extent thanks to the post-1850 combination of rapid population increases and economic growth, marked by extensive urbanization, industrialization, and the construction of transportation networks. [p. 157]

After 150 pages of figures, definitions, and jargon (not intended pejoratively in this case), all of which contain substantial detail and measurements prefixed by mega- (106), giga- (109), tera- (1012), and peta- (1015) that tend to wash out after a while, like economics discussions of so many millions, billions, and trillions (or merely “illions”) of dollars, the appearance of a wide-angle summary is a bit of a relief despite its depressing content.

Smil’s discussion of net primary production (NPP) and human appropriation of NPP (HANPP) bears out the thesis of the book, namely, that as a species, humans have brought under their own control a substantial share, ranging from 20% to about 34%, of NPP. While 20–34% may not seem especially concerning, Smil’s approximate numbers for per capital energy use (measured in gigajoules) was less than 3 GJ for 5,000 BCE when human population was around 20 million and global phytomass stock (measured in gigatonnes carbon) was greater than 1,000, whereas the estimates for 2010 were 75 GJ per capita energy use, 6.9 billion in population, and less than 600 Gt C of global phytomass stock. We are literally consuming the surface of the world. Put a different way that calls back to the infographic above, estimates for global anthropomass in 1900 are 13 megatonnes carbon (Mt C), wild mammalian zoomass was 10, elephants 3, domesticated animals 35, and cattle 23. In 2000, the numbers had changed to anthropomass 55, wild mammalian zoomass 5, elephants 0.3, domesticated animals 120, and cattle 80. So in just 100 years, wild mammals have decreased by 50%, humans have increased more than four-fold (and domesticated animals and cattle each more than three-fold). The primary driver of these changes? Human appetites.

  1. […] Source: Review: Harvesting the Biosphere […]

  2. Juanita says:

    I conjured up a screenplay – a re-do of Stephen King’s “Cujo”, based on another biomass chart I saw similar to this – to complement the abundance of dystopian zombie crap on TV/movies. I concluded that there are a lot of cats and dogs. When the food runs out all those dogs will be hungry. They will be abandoned and pack up (I’ve witnessed this working on a ranch where people would dump their unwanted pets) and hunt deer and calves…where I live the most common “pet” is a pitbull…

  3. […] This came as no surprise to anyone who’s been paying attention. I blogged on this very topic in my review of Vaclav Smil’s book Harvesting the Biosphere, which observed at the end a 50% decrease in wild mammal populations in the last hundred years. The […]

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