Environment & Energy

Two new studies quantify key features of human and animal presence on Earth. The first study finds that the movement of human biomass today is 40 times greater than that of all wild land mammals, birds, and arthropods combined. Another study reveals that the combined biomass of wild land and marine mammals has plummeted by about 70 percent since 1850, whereas the biomass of humans has soared by roughly 700 percent and that of domesticated animals by 400 percent; those two categories have a combined biomass approaching about 1.1 billion tons.

The studies are collaborations between the Caltech laboratory of Rob Phillips, the Fred and Nancy Morris Professor of Biophysics, Biology, and Physics, and Ron Milo, professor of systems biology at the Weizmann Institute of Science in Israel.

"Centuries of work by naturalists have made it abundantly clear that living organisms are connected in giant webs of interactions," says Phillips. "But this is not just a vague idea; it is instead an idea that can be rendered quantitatively. These two papers make huge steps toward turning those intuitive ideas into concrete and quantitative time series."

Humanity has become a dominant force in shaping the face of Earth1,2,3,4,5,6,7,8,9. An emerging question is how the overall material output of human activities compares to the overall natural biomass. Here we quantify the human-made mass, referred to as ‘anthropogenic mass’, and compare it to the overall living biomass on Earth, which currently equals approximately 1.1 teratonnes10,11. We find that Earth is exactly at the crossover point; in the year 2020 (± 6), the anthropogenic mass, which has recently doubled roughly every 20 years, will surpass all global living biomass. On average, for each person on the globe, anthropogenic mass equal to more than his or her bodyweight is produced every week. This quantification of the human enterprise gives a mass-based quantitative and symbolic characterization of the human-induced epoch of the Anthropocene.