A key cause of climate change

Just what does human domination of the natural world mean in biological terms? It means that over 90% of the mammals on the planet (by biomass) are humans and their livestock.

I recently came across the following statement from Vaclav Smil:

My calculations based on the best available head counts and on typical average body weights result in less than 180 Mt [“Mt” is a megatonne, or a billion kilograms] of live weight of domesticated zoomass in 1900, and in no less than 620 Mt in 2000, a nearly 3.5-fold increase during the twentieth century (Smil 2002a); in contrast, the zoomass of wild terrestrial mammals is now most likely below 40 Mt, or less than 10 percent of the biomass of domesticated meat and dairy species (Smil 2002a).

— From “Eating Meat” (Population and Development Review 28(4):599–639, December 2002), p. 618. “Smil 2002a” is Smil’s book The Earth’s Biosphere (Cambridge: MIT Press, 2002).

I have quoted this in full so that there will be no mistake here. The total of domesticated and wild mammals is 660 Mt (620 Mt plus 40 Mt); of which humans and their livestock (the domesticated portion) is about 94%. That leaves 6% for all other wild mammals: all the elephants, lions, tigers, deer, antelope, and squirrels in the world. Elephants, he further tells us, are so diminished in numbers that they are less than 1 Mt, “or not even 0.2 percent of the worldwide mass of cows, bulls, calves, steers, and heifers” (which is about 450 Mt).  Smil does not mention pets such as dogs and cats, but these would have to be counted as domestic rather than wild.

Anyone who questions why any wild mammals are going extinct surely does not need to go much further than this.