Humans are transgressing planetary boundaries on several fronts.

In November of 2019, 11,000+ of the world’s foremost climate scientists published a bleak forecast of rising global temperatures that cannot be averted apart from drastic societal alterations the world over. It allows for little time to course-correct, meaning that the required changes will likely be painful. Such reports understandably dominate both science news and public policy debate, but they fail to take the full measure of human-caused environmental injury.

That’s because human activity currently portends irreversible damage to several planetary boundaries necessary to human life. Among the most alarming crises are biodiversity loss, nitrogen cycle change, groundwater depletion, ocean acidification, and peak phosphorous. Alone, each of these crises is enough to precipitate widespread human suffering. Together, along with climate change, they present the gravest threat in the history of humanity to the survival of our species.

Biodiversity Loss

Biodiversity is the variety of life on earth. Human beings rely on a host of organisms for food, medicine, shelter, and clothing; as biodiversity diminishes, so do our basic necessities. Fostering biodiverse biomes is, therefore, a fundamental human concern.

Numerous human activities daily erode biodiversity on earth. Deforestation is a principal contributor to biodiversity loss; human demand for land development, fossil and wood fuels, and building materials result in the loss of 18 million square acres of forest each year. Many animal species rely on old-growth forest habitats for survival and gradually die out in the aftermath of forest consumption by humans.

Experts estimate that the human-caused species extinction rate is up to 10,000 times greater than the natural background extinction rate; ironically, the more forests that humans convert to farmland, the more the pool of available resources shrinks. In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services reported that up to one million plant and animal species are facing extinction due to human activity.

Overexploitation — such as overfishing, overhunting, and over-harvesting — also threatens the earth’s biodiversity. So too do pollution and human introduction of invasive species. Infectious disease, nutritional decline, and medicine shortages are all consequences of biodiversity loss for humans, and that is before we even calculate the impact of those losses on global warming.

Nitrogen Cycle Change

All of earth's organisms — including humans — require nitrogen for survival. Peptides, amino acids, and proteins all incorporate nitrogen in their molecular structure and each of those compounds is essential to life (Cunningham, The Principles of Environmental Science 46). 78% of the earth’s atmosphere is constituted by nitrogen, and the nitrogen cycle transfers nitrogen into numerous vital chemical compounds as it circulates throughout the planet.

Human agricultural and industrial practices have dramatically altered the earth’s natural nitrogen cycle. Synthetic fertilizers, industrial pollution, and vehicle exhaust double the natural conversion of nitrogen to ammonia and nitrates every year. The excess of those nutrients in the environment results in the mass elimination of saltwater fish, thus reducing the food supply and oceanic biodiversity.

Additionally, excess nitrogen depletes soil nutrients necessary for crops, such as calcium and potassium. Again, our ever-growing consumption of produce reared on industrial farms is serving to make food increasingly scarce. Consider, too, that nitrous oxide is a greenhouse gas and the consequences of human-caused changes to the nitrogen cycle appear grim, indeed.

Groundwater Depletion

Groundwater accounts for nearly half of the domestic and agricultural water supply in the United States. Unfortunately, current consumption vastly outstrips the water table refill rate, and demand is only expected to increase in the coming decades. The United States is not alone in this problem; every nation on Earth is scrambling for freshwater reserves.

Alarmingly, groundwater pumping compounds the duration of refill times and sometimes makes replenishment impossible altogether. As wells and aquifers run dry, the absence of water pressure precipitates surface settling and collapse that closes spaces once occupied by groundwater. Thus, the more groundwater we use, the less we are able to store going forward.

In addition to obvious consequences like crop and sanitation failure, groundwater depletion can lead to disastrous social conflicts and even war. Between 2007 and 2010, drought in Syria drove millions of rural people into cities, where tensions quickly mounted and civil war ensued. Rising temperatures associated with climate change exacerbate the problem, which means that competition for freshwater will only intensify going forward.