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.