Sixth mass extinction looms as humanity fails to act, scientists say

“We will destroy these ecosystems, and the species composing them, at the peril of our own existence – and unfortunately we are destroying them with ingenuity and ceaseless energy.”

E. O. Wilson (2007)

Life on Earth is disappearing so rapidly that some scientists believe a mass extinction event is now underway for the first time since the dinosaurs were wiped out 66 million years ago. 

The implications of such profound biodiversity loss impact humanity not only in the long term, but have immediate spillover effects on food systems, human rights and global health, including the rise of pandemics.

However, there are two sides to every story, and this one is no exception. In a sometimes opposing camp are researchers who hold very different views on evolution and its many intersections with extinction. 

Some say estimates of present extinction rates are exaggerated, claiming the true rate is not much higher than the natural background rate – the standard rate of extinction in pre-human times. Others postulate that extinctions are compensated for by the evolution of new species, and that human-caused extinctions are part of the natural trajectory of life on the planet since Homo sapiens belong to nature.

Where there is little dispute is that the current rate of extinction, which is now often deemed a ‘biodiversity crisis,’ is unique: It has been caused entirely by humans through their impact on the natural world, especially since the Industrial Revolution. 

This, then, raises the question: In light of evolution and the ways that life forms stay alive or die off, do we have a moral obligation to stop killing off other species?

Abnormal rates

Extinctions are a normal part of evolutionary life. It is estimated that more than 99 percent of all species that have ever lived on Earth are now gone. 

Many of these animals, plants and micro-organisms died out during five mass extinctions over the past 500 million years. These were periods when species vanished at abnormally high rates due to dramatic climate change, volcanic activity or an asteroid collision.

Mass extinction is generally defined as loss of at least 75 percent of all species over a short geological period – less than 2.8 million years. And scientists are increasingly pointing to indicators that we are in the beginning phase of such a die-off.

In 2015, journalist and author Elizabeth Kolbert published a Pulitzer Prize–winning nonfiction novel called The Sixth Extinction: An Unnatural History, which made a meticulously researched case for why the next mass extinction is upon us and thrust the issue into the spotlight in a way it hadn’t been put forth before. “In pushing other species to extinction, humanity is busy sawing the limb on which it perches,” she wrote. Since then, evidence has only grown.

One of the most recent studies estimates that around 7.5 percent to 13 percent of the 2 million known species on Earth have become extinct since 1500, the baseline year used in the IUCN Red List of Threatened Species to assess biodiversity loss. 

“Clearly, 75 percent of species have not gone extinct during the so-called Anthropocene, which arguably began when people started migrating out of Africa tens of thousands of years ago,” says Robert H. Cowie, a professor in the Pacific Biosciences Research Center at the University of Hawaii and the study’s lead author. “But the rate of extinction is probably around 100 times the background extinction rate, and if it continues to increase, we are headed for the next mass extinction.” 

The IUCN Red List calculates an extinction figure of 0.04 percent of those 2 million species. However, the study’s authors say this underestimates the extent of species loss due to a heavy bias toward birds and mammals, while most invertebrates have not been evaluated by IUCN. To extrapolate figures for all species, including those not evaluated for the Red List, the study used mollusks – the second-largest animal group – to estimate the real extent of extinction.

Inherent uncertainties

It is no easy task to declare the start of a mass extinction event that will eventually claim three-quarters of life on Earth. The number of species that have died out without ever being discovered and characterized is a major known unknown. Scientists have estimated that there might be up to five times more species living on Earth than those that have been discovered – and these unidentified life forms could be as threatened as the charismatic megafauna that dominate the public psyche, such as tigers, polar bears, whales and condors. And some scientists have predicted that recovery from a mass extinction could take 10 million years.

“Only a tiny fraction of known invertebrates – such as insects, snails and worms – have been evaluated, so very few of those that are probably extinct have been listed as such,” says Cowie. “And most invertebrates leave no trace behind when they go extinct.”

There is also the risk that a life form assumed to be extinct may later be rediscovered – dubbed the ‘Romeo Error’ after the Shakespearean character who wrongly thinks his lover is dead. This helps explain the general tendency toward conservative estimates of extinction.

“Given our fragmentary state of knowledge about biodiversity, we can only say that current extinction is in the ballpark of an official mass extinction,” says Shahid Naeem, a professor of ecology at Columbia University in New York. “The starting point, if we are in a mass extinction, is even less clear. I would choose agriculture as the start date – about 10,000 years ago – because it’s what led to the great land transformations of three-quarters of Earth’s surface and the devastation of marine fauna as fishing expanded.”

To be sure, new species continue to evolve against the backdrop of the biodiversity crisis. While mass extinctions kill off a lot of biodiversity, they also promote the growth of some minor branches in the tree of life. As plants and animals in certain habitats go extinct, surviving species gain new ground and their descendants acquire special functions through natural selection to adapt to their new environment.

Naeem says evolution is sometimes seen as a battle between extinction and origination. But species loss, in many cases, simply means the evolution of older forms, such as dinosaurs living on as birds, he says. Old species upgrade into newer versions of themselves, or diversify, yielding multiple different species with a single common ancestor. “Life is doing what it always did,” says Naeem. 

Crisis unfolding

In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) – an independent body of 137 member states – warned that around 1 million species face extinction, many within decades, unless action is taken to reduce the intensity of drivers of biodiversity loss. It also estimated the global rate of species extinction to be at least tens, if not hundreds, of times higher than it has averaged over the past 10 million years.

“We have the ability, unlike any other species, to manipulate nature at a huge scale,” says Margaret Kinnaird, the global wildlife practice leader at the World Wide Fund for Nature (WWF International). “Our impacts on the natural world are abnormally high, and there is no way that evolution or speciation is going to keep up with that.”

Kinnaird highlights the importance of conserving certain keystone species, which can have positive knock-on effects for other living creatures in ecosystems. For example, the survival of forest elephants in the Congo Basin benefits a number of other species, from bees to humans, because of how the elephants aerate and fertilize soils, she says.

“We’ve got to be much wiser about land use and apply sustainable and regenerative agriculture,” says Kinnaird, who is based in Nairobi. “If landscapes are highly fragmented, wildlife won’t be able to disperse, and that impedes critical ecological processes, like stream flows, pollination and all the essential things for agricultural production.”

Missed targets

International efforts to address biodiversity loss have largely failed so far. In 2020, the Convention on Biological Diversity (CBD) – a U.N. body involving 196 parties – reported that none of its targets set in Aichi, Japan, a decade earlier had been fully reached, including the goal of preventing the extinction of known threatened species (Target 12).

An updated CBD framework strategy is scheduled for final negotiation at the 15th meeting of the Conference of the Parties (COP15) from 25 April to 8 May in Kunming, China. Leaders aim to reverse biodiversity loss by 2030 on a path to living in harmony with nature by 2050.

“At COP15 in Kunming, and over the course of the remainder of this decade, the global community will determine whether we take the road to continuing decline, or if we chart a new path toward living in harmony with nature,” says David Cooper, the CBD deputy executive secretary, based in Montreal.

The first part of COP15 took place in October 2021, when ministers issued a declaration acknowledging “with grave concern that the unprecedented and interrelated crises of biodiversity loss, climate change, land degradation and desertification, ocean degradation, pollution, and increasing risks to human health and food security, pose an existential threat to our society, our culture, our prosperity and our planet.”

The post-2020 global biodiversity framework has the potential to avert another mass extinction, but only if it embodies urgent and effective action to address all the drivers of biodiversity loss, such as land-use change, overexploitation, climate change, pollution and invasive alien species, according to Cooper.

“While change is inevitable, failure to address the biodiversity crisis would impoverish humanity though the loss of nature and its contributions to people, jeopardizing achievement of the sustainable development goals,” he says. “The current pandemic – and the increased risk of further pandemics – is a signal that humanity’s relationship with the rest of nature is out of balance and must change.”

Denial and responsibility

So, do we have a moral obligation to prevent biodiversity loss? From a human rights perspective, yes: failing to protect biodiversity can constitute a violation of the right to a healthy environment, legally recognized by 155 member states to the U.N. and including the right to life, health, food and safe water.

“Denying the crisis, accepting it and doing nothing about it, or embracing it and manipulating it for the fickle benefit of people, defined no doubt by politicians and business interests, is an abrogation of moral responsibility,” Cowie and his co-authors wrote.

Given the lack of consensus between those opposed to anthropogenic devastation of Earth’s systems and those who believe in a sort of unwritten law of human primacy – no matter the cost – Naeem calls for a conservative approach to avoid irreversible change to biodiversity.

“If the poor and vulnerable are the ones suffering the adverse effects of global change, then, from a human perspective, we are morally and ethically obligated to put a stop to it all. The only way to do this is to restore and preserve biodiversity,” he says.

Billions of people are potentially impacted through lack of food, lost livelihoods and denied land rights, compounded by social exclusion. Biodiversity loss can disproportionately harm the human rights of Indigenous Peoples, local communities, women and girls, children and youth, the poor, and those in vulnerable situations, according to the United Nations Environment Programme.

Naeem adds that if we include humanity as part of the biota, then it becomes even more morally and ethically critical for us to do all we can to sustain a vibrant and resilient world in partnership with millions and millions of other species. 

WWF’s Kinnaird agrees that humankind must end the biodiversity crisis to avoid the catastrophic impacts not just on wildlife, but also on ourselves.

“I don’t think it’s too late – biodiversity can still be conserved and, in many cases, restored,” she says. “There is no excuse to abuse the Earth for short-term gain. We have a moral obligation to use science for a better world, not a lesser world.”