How humans cause mass extinctions

There is no doubt that Earth is undergoing the sixth mass extinction in its history — the first since the cataclysm that wiped out the dinosaurs some 65 million years ago. According to one recent study, species are going extinct between ten and several thousand times faster than they did during stable periods in the planet’s history, and populations within species are vanishing hundreds or thousands of times faster than that. By one estimate, Earth has lost half of its wildlife during the past 40 years. There is also no doubt about the cause: We are it.

We are in the process of killing off our only known companions in the universe, many of them beautiful and all of them intricate and interesting. This is a tragedy, even for those who may not care about the loss of wildlife. The species that are so rapidly disappearing provide human beings with indispensable ecosystem services: regulating the climate, maintaining soil fertility, pollinating crops and defending them from pests, filtering freshwater, and supplying food.

The cause of this great acceleration in the loss of the planet’s biodiversity is clear: rapidly expanding human activity, driven by worsening overpopulation and increasing per capita consumption. We are destroying habitats to make way for farms, pastures, roads and cities. Our pollution is disrupting the climate and poisoning the land, water and air. We are transporting invasive organisms around the globe and overharvesting commercially or nutritionally valuable plants and animals.

The more people there are, the more of Earth’s productive resources must be mobilised to support them. More people means more wild land must be put under the plough or converted to urban infrastructure to support sprawling cities like Manila, Chengdu, New Delhi and San Jose. More people means greater demand for fossil fuels, which means more greenhouse gases flowing into the atmosphere, perhaps the single greatest extinction threat of all. Meanwhile, more of Canada needs to be destroyed to extract low-grade petroleum from oil sands and more of the United States needs to be fracked.

More people also means the production of more computers and more mobile phones, along with more mining operations for the rare earths needed to make them. It means more pesticides, detergents, antibiotics, glues, lubricants, preservatives and plastics, many of which contain compounds that mimic mammalian hormones. Indeed, it means more microscopic plastic particles in the biosphere — particles that may be toxic or accumulate toxins on their surfaces. As a result, all living things — us included — have been plunged into a sickening poisonous stew, with organisms that are unable to adapt pushed further towards extinction.

With each new person, the problem gets worse. Since human beings are intelligent, they tend to use the most accessible resources first. They settle the richest, most productive land, drink the nearest, cleanest water and tap the easiest-to-reach energy sources.

And so as new people arrive, food is produced on less fertile, more fragile land. Water is transported further or purified. Energy is produced from more marginal sources. In short, each new person joining the global population disproportionately adds more stress to the planet and its systems, causing more environmental damage and driving more species to extinction than members of earlier generations.

To see this phenomenon at work, consider the oil industry. When the first well was drilled in Pennsylvania in 1859, it penetrated less than 21 metres into the soil before hitting oil. By comparison, the well drilled by Deepwater Horizon, which famously blew up in the Gulf of Mexico in 2010, began 1.6-kilometre beneath the water’s surface and drilled a few kilometres into the rock before finding oil. This required a huge amount of energy, and when the well blew, it was far harder to contain, causing large-scale, ongoing damage to the biodiversity of the Gulf and the adjacent shorelines, as well as to numerous local economies.

The situation can be summarised simply. The world’s expanding human population is in competition with the populations of most other animals (exceptions include rats, cattle, cats, dogs and cockroaches). Through the expansion of agriculture, we are now appropriating roughly half of the energy from the sun used to produce food for all animals — and our needs are only growing. With the world’s most dominant animal — us — taking half the cake, it is little wonder that the millions of species left fighting over the other half have begun to disappear rapidly. This is not just a moral tragedy; it is an existential threat. Mass extinctions will deprive us of many of the ecosystem services on which our civilisation depends. Our population bomb has already claimed its first casualties. They will not be the last.

Paul R. Ehrlich is professor of population studies, Department of Biological Sciences, Stanford University. Anne H. Ehrlich is the associate director and policy coordinator of the Centre for Conservation Biology, Stanford University. ©Project Syndicate, 2015. www.project-syndicate.org