In 2009 a group of scientists led by Johan Rockström, in Sweden, defined nine limits “within which humanity can continue to develop and thrive for generations to come” as long as we do not exceed them. That is, in essence, the concept of planetary boundaries.
It’s another way of saying that there are limits to growth and that our planet is a living organism which can sustain life only as long as our human activities do not have disastrous and irreparable consequences.
We have far surpassed the planetary boundary related to the production and use of nitrogen and phosphorous. Modern agriculture is a major cause of this, producing large-scale nitrogen- and phosphorus-induced environmental changes causing major damages and jeopardizing life on planet Earth. This is a very good reason to recycle our excrements as fertilizer, or putting our poop back into the loop. To learn more about planetary boundaries visit this site.
The graphic below illustrates the nine planetary boundaries and their actual status. In the Biogeochemical flows boundary, the letters P and N stand for phosphorus and nitrogen.