Earth’s Sixth Mass Extinction Event Already Under Way, Scientists Warn

Researchers talk of “biological annihilation” as study reveals billions of populations of animals have been lost in recent decades.

Photo Credit: Maggy Meyer/Shutterstock

A “biological annihilation” of wildlife in recent decades means a sixth mass extinction in Earth’s history is under way and is more severe than previously feared, according to research.

Scientists analyzed both common and rare species and found billions of regional or local populations have been lost. They blame human overpopulation and overconsumption for the crisis and warn that it threatens the survival of human civilization, with just a short window of time in which to act.

The study, published in the peer-reviewed journal Proceedings of the National Academy of Sciences, eschews the normally sober tone of scientific papers and calls the massive loss of wildlife a “biological annihilation” that represents a “frightening assault on the foundations of human civilization”.

Prof Gerardo Ceballos, at the Universidad Nacional Autónoma de México, who led the work, said: “The situation has become so bad it would not be ethical not to use strong language.”

Previous studies have shown species are becoming extinct at a significantly faster rate than for millions of years before, but even so extinctions remain relatively rare giving the impression of a gradual loss of biodiversity. The new work instead takes a broader view, assessing many common species which are losing populations all over the world as their ranges shrink, but remain present elsewhere.

The scientists found that a third of the thousands of species losing populations are not currently considered endangered and that up to 50 percent of all individual animals have been lost in recent decades. Detailed data is available for land mammals, and almost half of these have lost 80 percent of their range in the last century. The scientists found billions of populations of mammals, birds, reptiles and amphibians have been lost all over the planet, leading them to say a sixth mass extinction has already progressed further than was thought.

Nearly half of the 177 mammal species surveyed lost more than 80% of their distribution between 1900 and 2015

Percent of species which have lost more than 80 percent of their range

Billions of animals have been lost as their habitats have become smaller with each passing year. (Guardian graphic | source: PNAS)

The scientists conclude: “The resulting biological annihilation obviously will have serious ecological, economic and social consequences. Humanity will eventually pay a very high price for the decimation of the only assemblage of life that we know of in the universe.”

They say, while action to halt the decline remains possible, the prospects do not look good: “All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life.”

Wildlife is dying out due to habitat destruction, overhunting, toxic pollution, invasion by alien species and climate change. But the ultimate cause of all of these factors is “human overpopulation and continued population growth, and overconsumption, especially by the rich”, say the scientists, who include Prof Paul Ehrlich, at Stanford University in the U.S., whose 1968 book The Population Bomb is a seminal, if controversial, work.

“The serious warning in our paper needs to be heeded because civilization depends utterly on the plants, animals, and microorganisms of Earth that supply it with essential ecosystem services ranging from crop pollination and protection to supplying food from the sea and maintaining a livable climate,” Ehrlich told the Guardian. Other ecosystem services include clean air and water.

“The time to act is very short,” he said. “It will, sadly, take a long time to humanely begin the population shrinkage required if civilization is to long survive, but much could be done on the consumption front and with ‘band aids’—wildlife reserves, diversity protection laws—in the meantime.” Ceballos said an international institution was needed to fund global wildlife conservation.

The research analyzed data on 27,500 species of land vertebrates from the IUCN and found the ranges of a third have shrunk in recent decades. Many of these are common species and Ceballos gave an example from close to home: “We used to have swallows nesting every year in my home near Mexico city—but for the last 10 years there are none.”

The researchers also point to the “emblematic” case of the lion: “The lion was historically distributed over most of Africa, southern Europe, and the Middle East, all the way to northwestern India. [Now] the vast majority of lion populations are gone.”

Current and historic distribution of lions

Historically lions lived across Africa, southern Europe, the Middle East, all the way up to Northwestern India. Today their habitat has been reduced to a few tiny pockets of the original area. (Guardian graphic | source: PNAS)

Prof. Stuart Pimm, at Duke University in the US and not involved in the new work, said the overall conclusion is correct, but he disagrees that a sixth mass extinction is already under way: “It is something that hasn’t happened yet—we are on the edge of it.”

Pimm also said there were important caveats that result from the broad-brush approach used. “Should we be concerned about the loss of species across large areas—absolutely—but this is a fairly crude way of showing that,” he said. “There are parts of the world where there are massive losses, but equally there are parts of the world where there is remarkable progress. It is pretty harsh on countries like South Africa which is doing a good job of protecting lions.”

Robin Freeman, at the Zoological Society of London, U.K., said: “While looking at things on aggregate is interesting, the real interesting nitty gritty comes in the details. What are the drivers that cause the declines in particular areas?”

Freeman was part of the team that produced a 2014 analysis of 3000 species that indicated that 50 percent of individual animals have been lost since 1970, which tallies with the new work but was based on different IUCN data. He agreed strong language is needed: “We need people to be aware of the catastrophic declines we are seeing. I do think there is a place for that within the [new] paper, although it’s a fine line to draw.”

Citing human overpopulation as the root cause of environmental problems has long been controversial, and Ehrlich’s 1968 statement that hundreds of millions of people would die of starvation in the 1970s did not come to pass, partly due to new high-yielding crops that Ehrlich himself had noted as possible.

Ehrlich has acknowledged “flaws” in The Population Bomb but said it had been successful in its central aim—alerting people to global environmental issues and the the role of human population in them. His message remains blunt today: “Show me a scientist who claims there is no population problem and I’ll show you an idiot.”

Earth’s five previous mass extinctions

End-Ordovician, 443 million years ago

A severe ice age led to sea level falling by 100m, wiping out 60-70 percent of all species which were prominently ocean dwellers at the time. Then soon after the ice melted leaving the oceans starved of oxygen.

Late Devonian, c 360 million years ago

A messy prolonged climate change event, again hitting life in shallow seas very hard, killing 70 percent of species including almost all corals.

Permian-Triassic, c 250 million years ago

The big one—more than 95 percent of species perished, including trilobites and giant insects—strongly linked to massive volcanic eruptions in Siberia that caused a savage episode of global warming.

Triassic-Jurassic, c 200 million years ago

Three-quarters of species were lost, again most likely due to another huge outburst of volcanism. It left the Earth clear for dinosaurs to flourish.

Cretaceous-Tertiary, 65 million years ago

An giant asteroid impact on Mexico, just after large volcanic eruptions in what is now India, saw the end of the dinosaurs and ammonites. Mammals, and eventually humans, took advantage.

Scientists warn of “biological annihilation” as Earth’s mass extinction accelerates

By Josh Varlin
12 July 2017

study published Monday in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) indicates that human activity is precipitating “biological annihilation” and a mass extinction event.

The peer-reviewed paper, “Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines,” argues that the severity of the ongoing biodiversity crisis is often underestimated by looking primarily at extinctions (the loss of all individuals in a species). The study looks more broadly at species’ population decline and argues that “Earth’s sixth mass extinction episode has proceeded further than most assume.”

The study was coauthored by Gerardo Ceballos of the Instituto de Ecología at the Universidad Nacional Autónoma de México in Mexico City and by Paul R. Ehrlich and Rodolfo Dirzo of Stanford University’s Department of Biology.

The authors argue that while the extinction rate is already alarmingly high—including at least two vertebrate species per year for the past century—this does not tell the full story. Even if species have not yet gone extinct, their numbers and geographic distribution are decreasing dramatically, signaling an accelerating trend toward eventual extinction.

Detailed historical data from 1900 to 2015 is available for about 200 mammals, which are often major components of their ecosystems. Most of these key species are in crisis, even though they are not extinct: “In the 177 mammals for which we have detailed data, all have lost 30 percent or more of their geographic ranges and more than 40 percent of the species have experienced severe population declines (>80 percent range shrinkage).”

Gerardo Ceballos et al., 2017, “Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines,” Proceedings of the National Academy of Sciences Online,

Because population declines presage extinction, the study concludes that the planet has already begun its sixth mass extinction—the first since humans evolved.

The last mass extinction was at the end of the Cretaceous Period, about 66 million years ago, which saw the end of the dinosaurs, paving the way for mammals to dominate on land. The end-Cretaceous extinction was caused by an asteroid colliding with Earth, creating nuclear winter-like atmospheric effects.

The most catastrophic known mass extinction occurred at the end of the Permian Period (252 million years ago), and is known as “The Great Dying.” Approximately 70 percent of terrestrial species died during this cataclysmic event, which is thought to have occurred due to massive volcanic eruptions.

The fact that PNAS, one of the top science journals worldwide, published an article raising the possibility of events along the lines of “The Great Dying” is a sign that the ecological crisis is far advanced.

The paper, which is only about five pages long, not counting graphs or references, uses the word “annihilation” six times, “catastrophic” twice and a variety of “decimation” three times. Ceballos told the Atlantic that such frank language is warranted. “It would be alarmist if we didn’t have the data,” he said. “Now it would be irresponsible on our part to not use strong language. I wish we could say we are wrong but unfortunately, this is what is happening.”

The breakthrough made by Ceballos, Ehrlich and Dirzo is their thorough examination of populations, rather than staying at the level of species. A population is a group of individuals separated from other populations, usually by geography. Each species is made up of one or more populations.

If a species is losing several key populations but its overall numbers have not collapsed, it often will not be recognized as being in crisis. However, if a species is atomized into disparate, isolated populations, with its overall habitat shrinking, that makes its eventual extinction more likely.

In other words, the loss of each population of a species is one major step toward its overall extinction, unless measures are taken to restore the population and reverse the crisis.

Because most studies focus on extinction and not the loss of populations, they understate the scale of the crisis. Not only is the decline in populations a prelude to a significant number of extinctions, but the pace of population loss is accelerating.

Moreover, many species with decreasing populations are not yet recognized as being endangered. Of all land vertebrates with decreasing populations, about 70 percent have been recognized as endangered by the International Union for Conservation of Nature (IUCN). However, less than half of decreasing bird species are recognized as endangered by the IUCN.

Because of the complexity of the environment, removing even a seemingly minor population or species can severely impact other species—if enough species go extinct, it can damage whole ecosystems. Human life as we know it relies on an increasingly strained ecological balance, and may be impossible if biodiversity is reduced too much. The loss of this dynamic balance, once it reaches a certain point, can cascade into a catastrophic, possibly irreversible collapse.

The study identifies “the proximate causes of population extinctions” as “habitat conversion, climate disruption, overexploitation, toxification, species invasions, disease and (potentially) large-scale nuclear war—all tied to one another in complex patterns and usually reinforcing each other’s impacts.”

These factors are all caused or greatly exacerbated by humans’ unplanned and irrational interaction with the environment, rooted in the subordination of all social and economic life to private profit. It is worth noting in this context the mention of the potential environmental consequences of a nuclear war, which could be set off by any number of conflicts around the world caused by the division of the world into competing capitalist nation-states.

The authors identify “the ultimate drivers of those immediate causes of biotic destruction” as “human overpopulation and continued population growth, and overconsumption, especially by the rich.” One need not agree that population growth itself is the problem to recognize that human activity, without scientific planning, places immense strains on the environment.

Ceballos, Ehrlich and Dirzo conclude their paper by noting that “the window for effective action is very short, probably two or three decades at most.” Their article should serve as a notice that the clock is ticking for humanity to establish socialism—a social system in which life is scientifically organized around human need, including the need to be in harmony with the natural environment. Only through the conscious effort to place humanity on such a rational basis can ecological collapse be prevented.