Even though humanity represents just a small fraction of the world's total living organisms, we're responsible for the loss of most biodiversity on the planet, a new study found.
The study, called “The biomass distribution on Earth” and written by Yinon M. Bar-On, Rob Phillips, and Ron Milo, takes into account an estimate of the total biomass composition of the atmosphere, and it's the first of its kind to measure the weight of each living creature constituting the ≈550 gigatons of carbon (Gt C) distributed among all kingdoms of life.
Out of the ≈550 Gt C, plants constitute about ≈450 Gt C (80 percent), followed by bacteria ≈70 Gt C , archaea ≈7 Gt C and animals ≈2 Gt C, including us.
Humans represent only ≈0.06 Gt C. That is, 0.01 percent of the total biomass in the atmosphere. In comparison, the Antartic krill species Euphausia superba contributes ≈0.05 Gt C to global biomass.
And yet, human activity and life style have contributed to the loss of 83 percent of wild animals and plants, affecting biodiversity in a more dramatic way that we could imagine.
“Over the relatively short span of human history, major innovations, such as the domestication of livestock, adoption of an agricultural lifestyle, and the Industrial Revolution, have increased the human population dramatically and have had radical ecological effects,” says the report.
According to the study, the biomass of humans and that of livestock (≈0.1 Gt C, dominated by cattle and pigs) far surpasses that of wild mammals (≈0.007 Gt C). And when it comes to birds, domesticated poultry (mostly chickens) constitute ≈0.005 Gt C, way more than that of wild birds (≈0.002 Gt C).
That means that domesticated poultry makes up 70 percent of all birds, and that 60 percent of all mammals are livestock, 36 percent are human and 4 percent are wild animals.
In order to calculate the effect of human life on the composition of known biomass, researchers used an estimate by Anthony D. Barnosky, who calculated the biomass of wild land mammals before the quaternary Megafauna Extinction (between ≈50,000 and ≈3,000 years ago) at ≈0.02 Gt C.
Now, the biomass of wild land mammals is approximately at ≈0.003 Gt C, seven times lower, to which first hunting and then livestock have contributed a great part. Also, exploitation of marine mammals, especially whaling, has drastically reduced their biomass from ≈0.02 Gt C to ≈0.004 Gt C.
“Our dietary choices have a vast effect on the habitats of animals, plants and other organisms,” said Ron Milo, one of the researches involved in the project, ”I have not become vegetarian, but I do take the environmental impact into my decision making, so it helps me think, do I want to choose beef or poultry or use tofu instead?”
But that doesn't mean that the total biomass of mammals has decreased. In fact, the rising human population and its livestock, used for human consumption, have increased the total biomass of mammals four times, from ≈0.04 Gt C to ≈0.17 Gt C.
And it's not only mammals that have been affected by our lifestyle, but plants as well have suffered as our activity has “profoundly reshaped the total quantity of carbon sequestered by plants.”
The study shows that the total plant biomass has decreased twofold since the start of human civilization. Therefore, that means that the total biomass on Earth has also decreased.