Modern ‘Sixth Mass Extinction’ Event Will Be Worse Than First Predicted

The report argues that nearly half of the planet’s animal species are now in decline, but unlike past mass extinctions, this one has been entirely caused by humans

F I G U R E 1 | Percentage of species per taxonomic group which have decreasing, stable, increasing … [+] or unknown/unassessed (NA) population trends. Each group is represented by a silhouette from left to right; mammals (N=5969), birds (N=11,162), amphibians (N=7316), reptiles (N=10,150), fishes (N=24,356) and insects (N=12,161). Data were sourced from the IUCN Red List. (doi:10.1111/brv.12974)

doi:10.1111/brv.12974

Tragically, the global mass extinction event that we find ourselves in the midst of will be even worse than originally predicted, according to a recent study (ref). The international team of scientists came to their conclusion after analyzing population trends data for more than 71,000 animal species — including mammals, birds, reptiles, amphibians, fish and insects — from around the world to see how their numbers have changed since record-keeping first began.

Generally, scientists agree that an extinction event is occurring when species vanish much faster than they are replaced. A mass extinction event is usually defined as losing 75% of the world’s species in a short period of geological time — less than 2.8 million years, according to the Natural History Museum (here).

Previous research has established that the current rates of extinction are between 1000-10,000 times higher than ‘background’ extinction rates, which has led some scientists to argue that life on Earth has entered its sixth mass extinction event. But uniquely, when compared to the planet’s previous five mass extinction events, this is the first mass extinction event that is the result of the actions of just one species — humans.

Globally, many species are declining as the result of a variety of destructive human activities, particularly habitat loss, fragmentation and degradation, the widespread use of pesticides, herbicides and other chemicals, and the effects of invasive species, aggravated by runaway climate change.

Gauging a species’ conservation status has traditionally been based on assessments issued by the International Union for Conservation of Nature (IUCN). Of the population numbers and extinction risks for more than 150,300 species evaluated by the IUCN, 28% are considered to be facing the threat of extinction, and approximately 1% have been declared extinct. However, the study authors noted that extinctions are preceded by progressive population declines through time that leave demographic ‘footprints’ warning of impending extinctions — and this downward population trajectory is what the researchers analyzed.

According to the team’s analysis, 49% of these species populations are stable, but 48% have shrinking populations, whilst only 3% have populations that are increasing (Figure 1). They also found evidence that 33% of species currently classified as ‘least concern’ (not threatened) on the IUCN’s Red List are actually trending toward extinction.

Additionally, the researchers found that some taxonomic classes of animals are experiencing greater threats to their continued existence than others. For example, the team found that amphibians are experiencing the greatest population drops of any animal classes. Geography is also important. Declines are steeper amongst animals living in the tropics compared to temperate region species, probably because tropical species tend to be more sensitive to change.

“Collectively, our findings reinforce the warning that biodiversity is on the brink of an extinction crisis,” the authors point out in their study, noting that this extinction event will be far more serious than prior research has suggested, particularly as entire ecosystems unravel and collapse.

“This crisis will have extensive ecological and ecosystemic consequences, given that ecological functioning is severely impacted by population declines and the resulting changes in community compositions.”

Further, the study authors found that relying solely on the IUCN’s Red List “runs a risk of downplaying the severity of biodiversity loss”, especially after they found that some 33% of the species classified as not threatened actually have declining populations, too. For example, just 13% of bird species are considered “threatened” by the IUCN but the study authors found that 53% have declining populations.

Despite this, the IUCN classifications are still “an excellent resource” for conservation scientists, although this study’s methodology provides additional information regarding impending biodiversity loss. Combining the IUCN data with the findings in this study provides a reasonably precise picture about what is happening and why.

The reason for this impending massive biodiversity loss is obvious. It cannot be denied that human activities are the sole cause of this extinction event, which is driven by our unsustainable use of land, water and energy, along with driving runaway climate change. Currently, 40% of all land on Earth has been altered specifically for food production to support the growing human population. Agriculture alone is responsible for 90% of global deforestation and 70% of the planet’s freshwater consumption, thereby pushing species that inhabit those habitats towards extinction.

“To make matters worse, unsustainable food production and consumption are significant contributors to greenhouse gas emissions that are causing atmospheric temperatures to rise, wreaking havoc across the globe,” the authors write (ref). “The climate crisis is causing everything from severe droughts to more frequent and intense storms. It also exacerbates the challenges associated with food production that stress species, while creating conditions that make their habitats inhospitable. Increased droughts and floods have made it more difficult to maintain crops and produce sufficient food in some regions. The intertwined relationships among the food system, climate change, and biodiversity loss are placing immense pressure on our planet.”

Source:

Catherine Finn, Florencia Grattarola, and Daniel Pincheira-Donoso (2023). Review: More losers than winners: investigating Anthropocene defaunation through the diversity of population trends, Biological Reviews | doi:10.1111/brv.12974

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