Holocene extinction

The Holocene extinction, or Anthropocene extinction,^[3][4] is the ongoing extinction event caused by humans during the Holocene epoch. These extinctions span numerous families of plants^[5][6][7] and animals, including mammals, birds, reptiles, amphibians, fish, and invertebrates, and affecting not just terrestrial species but also large sectors of marine life.^[8] With widespread degradation of biodiversity hotspots, such as coral reefs and rainforests, as well as other areas, the vast majority of these extinctions are thought to be undocumented, as the species are undiscovered at the time of their extinction, which goes unrecorded. The current rate of extinction of species is estimated at 100 to 1,000 times higher than natural background extinction rates^{[9][10][11][12][13]} and is increasing.^[14]

During the past 100–200 years, biodiversity loss and species extinction have accelerated,

The Holocene extinction follows the extinction of many large (megafaunal) animals during the preceding Late Pleistocene as part of the Quaternary extinction event. It has been suggested that megafauna outside of the African mainland, which did not evolve alongside modern humans, proved highly sensitive to the introduction of human predation, and many died out shortly after early humans began spreading and hunting across the Earth.^[24][25]

The most popular theory is that human

Marine extinction intensity during the Phanerozoic

%

Millions of years ago

(H)

K–Pg

Tr–J

P–Tr

Cap

Late D

O–S

The percentage of marine animal extinction at the

mass extinctions

The Holocene is the current geological epoch.

Overview

There is no general agreement on where the

Some contend that contemporary extinction has yet to reach the level of the previous five mass extinctions,[62] and that this comparison downplays how severe the first five mass extinctions were.^[63] John Briggs argues that there is inadequate data to determine the real rate of extinctions, and shows that estimates of current species extinctions varies enormously, ranging from 1.5 species to 40,000 species going extinct due to human activities each year.^[64] Both papers from Barnosky et al. (2011) and Hull et al. (2015) point out that the real rate of extinction during previous mass extinctions is unknown, both as only some organisms leave fossil remains, and as the temporal resolution of the fossil layer is larger than the time frame of the extinction events.^[18][65] However, all these authors agree that there is a modern biodiversity crisis with population declines affecting numerous species, and that a future anthropogenic mass extinction event is a big risk. The 2011 study by Barnosky et al. confirms that "current extinction rates are higher than would be expected from the fossil record" and adds that anthropogenic ecological stressors, including climate change, habitat fragmentation, pollution, overfishing, overhunting, invasive species, and expanding human biomass, will intensify and accelerate extinction rates in the future without significant mitigation efforts.^[18]

In The Future of Life (2002),

In a pair of studies published in 2015, extrapolation from observed extinction of Hawaiian snails led to the conclusion that 7% of all species on Earth may have been lost already.[67]^[68] A 2021 study published in the journal Frontiers in Forests and Global Change found that only around 3% of the planet's terrestrial surface is ecologically and faunally intact, meaning areas with healthy populations of native animal species and little to no human footprint.^[69][70]

The 2019 Global Assessment Report on Biodiversity and Ecosystem Services, published by the United Nations' Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), posits that out of around eight million species of plants and animals, roughly one million species face extinction within decades as the result of human actions.^{[37][71][72][73]} Organized human existence is jeopardized by increasingly rapid destruction of the systems that support life on Earth, according to the report, the result of one of the most comprehensive studies of the health of the planet ever conducted.^[74] Moreover, the 2021 Economics of Biodiversity review, published by the UK government, asserts that "biodiversity is declining faster than at any time in human history."^[75][76] According to a 2022 study published in Frontiers in Ecology and the Environment, a survey of more than 3,000 experts says that the extent of the mass extinction might be greater than previously thought, and estimates that roughly 30% of species "have been globally threatened or driven extinct since the year 1500."^[77][78] In a 2022 report, IPBES listed unsustainable fishing, hunting, and logging as being some of the primary drivers of the global extinction crisis.^[79] A 2022 study published in Science Advances suggests that if global warming reaches 2.7 °C (4.9 °F) or 4.4 °C (7.9 °F) by 2100, then 13% and 27% of terrestrial vertebrate species will go extinct by then, largely due to climate change (62%), with anthropogenic land conversion and co-extinctions accounting for the rest.^[80][21][81] A 2023 study published in PLOS One shows that around two million species are threatened with extinction, double the estimate put forward in the 2019 IPBES report.^[82]

According to a 2023 study published in

Attribution

We are currently, in a systematic manner, exterminating all non-human living beings.

—

IPBES executive secretary^[86]

There is widespread consensus among scientists that human activity is accelerating the extinction of many animal species through the destruction of habitats, the consumption of animals as resources, and the elimination of species that humans view as threats or competitors.[55] Rising extinction trends impacting numerous animal groups including mammals, birds, reptiles, and amphibians have prompted some scientists to declare a biodiversity crisis.^[87]

Scientific debate

Characterization of recent extinction as a mass extinction has been debated among scientists.

land-use changes, could result in the loss of more than a tenth of plant and animal species by the end of the century.^[96][97] A 2023 study published in Biological Reviews found that, of 70,000 monitored species, some 48% are experiencing population declines from anthropogenic pressures, whereas only 3% have increasing populations.^{[98][99][100]}

According to the

UNDP's 2020 Human Development Report

, The Next Frontier: Human Development and the Anthropocene:

The planet's biodiversity is plunging, with a quarter of species facing extinction, many within decades. Numerous experts believe we are living through, or on the cusp of, a mass species extinction event, the sixth in the history of the planet and the first to be caused by a single organism—us.[101]

The 2022 Living Planet Report found that vertebrate wildlife populations have plummeted by an average of almost 70% since 1970, with agriculture and fishing being the primary drivers of this decline.^[102][103]

Some scientists, including Rodolfo Dirzo and Paul R. Ehrlich, contend that the sixth mass extinction is largely unknown to most people globally and is also misunderstood by many in the scientific community. They say it is not the disappearance of species, which gets the most attention, that is at the heart of the crisis, but "the existential threat of myriad population extinctions."^[104]

Anthropocene

Main article: Anthropocene

The abundance of species extinctions considered anthropogenic, or due to human activity, has sometimes (especially when referring to hypothesized future events) been collectively called the "Anthropocene extinction".^{[55][105][106]} Anthropocene is a term introduced in 2000.^[107][108] Some now postulate that a new geological epoch has begun, with the most abrupt and widespread extinction of species since the Cretaceous–Paleogene extinction event 66 million years ago.^[51]

The term "anthropocene" is being used more frequently by scientists, and some commentators may refer to the current and projected future extinctions as part of a longer Holocene extinction.

industrial revolution

and also say that "[f]ormal adoption of this term in the near future will largely depend on its utility, particularly to earth scientists working on late Holocene successions."

It has been suggested that human activity has made the period starting from the mid-20th century different enough from the rest of the Holocene to consider it a new

geological epoch, known as the Anthropocene,^[112][113] a term which was considered for inclusion in the timeline of Earth's history by the International Commission on Stratigraphy in 2016.^[114][115] In order to constitute the Holocene as an extinction event, scientists must determine exactly when anthropogenic greenhouse gas emissions began to measurably alter natural atmospheric levels on a global scale, and when these alterations caused changes to global climate. Using chemical proxies from Antarctic ice cores, researchers have estimated the fluctuations of carbon dioxide (CO₂) and methane (CH₄) gases in the Earth's atmosphere during the Late Pleistocene and Holocene epochs.^[111] Estimates of the fluctuations of these two gases in the atmosphere, using chemical proxies from Antarctic ice cores, generally indicate that the peak of the Anthropocene occurred within the previous two centuries: typically beginning with the Industrial Revolution, when the highest greenhouse gas levels were recorded.^[116][117]

Human ecology

Further information: Human ecology

A 2015 article in

Extinction of animals, plants, and other organisms caused by human actions may go as far back as the late Pleistocene, over 12,000 years ago.^[55] There is a correlation between megafaunal extinction and the arrival of humans.^{[120][121][122]} Megafauna that are still extant also suffered severe declines that were highly correlated with human expansion and activity.^[123] Over the past 125,000 years, the average body size of wildlife has fallen by 14% as actions by prehistoric humans eradicated megafauna on all continents with the exception of Africa.^[124]

Human civilization was founded on and grew from agriculture.^[125] The more land used for farming, the greater the population a civilization could sustain,^[111][125] and subsequent popularization of farming led to widespread habitat conversion.^[10]

Habitat destruction by humans, thus replacing the original local ecosystems, is a major driver of extinction.^[126] The sustained conversion of biodiversity rich forests and wetlands into poorer fields and pastures (of lesser carrying capacity for wild species), over the last 10,000 years, has considerably reduced the Earth's carrying capacity for wild birds and mammals, among other organisms, in both population size and species count.^{[127][128][129]}

Other, related human causes of the extinction event include

Recent investigations into the practice of landscape burning during the Neolithic Revolution have a major implication for the current debate about the timing of the Anthropocene and the role that humans may have played in the production of greenhouse gases prior to the Industrial Revolution.^[125] Studies of early hunter-gatherers raise questions about the current use of population size or density as a proxy for the amount of land clearance and anthropogenic burning that took place in pre-industrial times.^[131][132] Scientists have questioned the correlation between population size and early territorial alterations.^[132] Ruddiman and Ellis' research paper in 2009 makes the case that early farmers involved in systems of agriculture used more land per capita than growers later in the Holocene, who intensified their labor to produce more food per unit of area (thus, per laborer); arguing that agricultural involvement in rice production implemented thousands of years ago by relatively small populations created significant environmental impacts through large-scale means of deforestation.^[125]

While a number of human-derived factors are recognized as contributing to rising atmospheric concentrations of CH₄ (methane) and CO₂ (carbon dioxide), deforestation and territorial clearance practices associated with agricultural development may have contributed most to these concentrations globally in earlier millennia.^{[116][125][133]} Scientists that are employing a variance of archaeological and paleoecological data argue that the processes contributing to substantial human modification of the environment spanned many thousands of years on a global scale and thus, not originating as late as the Industrial Revolution. Palaeoclimatologist William Ruddiman has argued that in the early Holocene 11,000 years ago, atmospheric carbon dioxide and methane levels fluctuated in a pattern which was different from the Pleistocene epoch before it.^{[111][131][133]} He argued that the patterns of the significant decline of CO₂ levels during the last ice age of the Pleistocene inversely correlate to the Holocene where there have been dramatic increases of CO₂ around 8000 years ago and CH₄ levels 3000 years after that.^[133] The correlation between the decrease of CO₂ in the Pleistocene and the increase of it during the Holocene implies that the causation of this spark of greenhouse gases into the atmosphere was the growth of human agriculture during the Holocene.^[111][133]

Climate change

A 2020 study published in Science Advances found that human population size and/or specific human activities, not climate change, caused rapidly rising global mammal extinction rates during the past 126,000 years. Around 96% of all mammalian extinctions over this time period are attributable to human impacts. According to Tobias Andermann, lead author of the study, "these extinctions did not happen continuously and at constant pace. Instead, bursts of extinctions are detected across different continents at times when humans first reached them. More recently, the magnitude of human driven extinctions has picked up the pace again, this time on a global scale."^[147][87]

Megafaunal extinction

Megafauna play a significant role in the lateral transport of mineral nutrients in an ecosystem, tending to translocate them from areas of high to those of lower abundance. They do so by their movement between the time they consume the nutrient and the time they release it through elimination (or, to a much lesser extent, through decomposition after death).

Recent studies have indicated that the extinction of megafaunal herbivores may have caused a reduction in atmospheric methane. One study examined the methane emissions from the bison that occupied the Great Plains of North America before contact with European settlers. The study estimated that the removal of the bison caused a decrease of as much as 2.2 million tons per year.^[154] Another study examined the change in the methane concentration in the atmosphere at the end of the Pleistocene epoch after the extinction of megafauna in the Americas. After early humans migrated to the Americas about 13,000 BP, their hunting and other associated ecological impacts led to the extinction of many megafaunal species there. Calculations suggest that this extinction decreased methane production by about 9.6 million tons per year. This suggests that the absence of megafaunal methane emissions may have contributed to the abrupt climatic cooling at the onset of the Younger Dryas.^[155] The decrease in atmospheric methane that occurred at that time, as recorded in ice cores, was 2–4 times more rapid than any other decrease in the last half million years, suggesting that an unusual mechanism was at work.^[155]

Disease

The hyperdisease hypothesis, proposed by Ross MacPhee in 1997, states that the megafaunal die-off was due to an indirect transmission of diseases by newly arriving humans.

History

The loss of animal species from ecological communities, defaunation, is primarily driven by human activity.^[50] This has resulted in empty forests, ecological communities depleted of large vertebrates.^[55][172] This is not to be confused with extinction, as it includes both the disappearance of species and declines in abundance.^[173] Defaunation effects were first implied at the Symposium of Plant-Animal Interactions at the University of Campinas, Brazil in 1988 in the context of Neotropical forests.^[174] Since then, the term has gained broader usage in conservation biology as a global phenomenon.^[50][174]

We have driven the rate of biological extinction, the permanent loss of species, up several hundred times beyond its historical levels, and are threatened with the loss of a majority of all species by the end of the 21st century.

— Peter Raven, former president of the American Association for the Advancement of Science (AAAS), in the foreword to their publication AAAS Atlas of Population and Environment^[186]

For the first time since the demise of the dinosaurs 65 million years ago, we face a global mass extinction of wildlife. We ignore the decline of other species at our peril – for they are the barometer that reveals our impact on the world that sustains us.

— Mike Barrett, director of science and policy at WWF's UK branch[206]

A 2023 study published in Current Biology concluded that current biodiversity loss rates could reach a tipping point and inevitably trigger a total ecosystem collapse.^[207]

Recent extinction

Recent extinctions are more directly attributable to human influences, whereas prehistoric extinctions can be attributed to other factors, such as global climate change.^[50][14] The International Union for Conservation of Nature (IUCN) characterizes 'recent' extinction as those that have occurred past the cut-off point of 1500,^[208] and at least 875 plant and animal species have gone extinct since that time and 2009.^[209] Some species, such as the Père David's deer^[210] and the Hawaiian crow,^[211] are extinct in the wild, and survive solely in captive populations. Other populations are only locally extinct (extirpated), still existent elsewhere, but reduced in distribution,^{[212]: 75–77} as with the extinction of gray whales in the Atlantic,^[213] and of the leatherback sea turtle in Malaysia.^[214]

Since the Late Pleistocene, humans (together with other factors) have been rapidly driving the largest vertebrate animals towards extinction, and in the process interrupting a 66-million-year-old feature of ecosystems, the relationship between diet and body mass, which researchers suggest could have unpredictable consequences.^[215][216] A 2019 study published in Nature Communications found that rapid biodiversity loss is impacting larger mammals and birds to a much greater extent than smaller ones, with the body mass of such animals expected to shrink by 25% over the next century. Another 2019 study published in Biology Letters found that extinction rates are perhaps much higher than previously estimated, in particular for bird species.^[217]

The 2019 Global Assessment Report on Biodiversity and Ecosystem Services lists the primary causes of contemporary extinctions in descending order: (1) changes in land and sea use (primarily agriculture and overfishing respectively); (2) direct exploitation of organisms such as hunting; (3) anthropogenic climate change; (4) pollution and (5) invasive alien species spread by human trade.^[37] This report, along with the 2020 Living Planet Report by the WWF, both project that climate change will be the leading cause in the next several decades.^[37][92]

A June 2020 study published in

Humans both create and destroy

In March 2019, Nature Climate Change published a study by ecologists from Yale University, who found that over the next half century, human land use will reduce the habitats of 1,700 species by up to 50%, pushing them closer to extinction.^[220][221] That same month PLOS Biology published a similar study drawing on work at the University of Queensland, which found that "more than 1,200 species globally face threats to their survival in more than 90% of their habitat and will almost certainly face extinction without conservation intervention".^[222][223]

Since 1970, the populations of migratory freshwater fish have declined by 76%, according to research published by the Zoological Society of London in July 2020. Overall, around one in three freshwater fish species are threatened with extinction due to human-driven habitat degradation and overfishing.^[224]

We know from all the data we have for threatened species, that the biggest threats are agriculture expansion and the global demand for meat. Pasture land, and the clearing of rainforests for production of soy, for me, are the largest drivers – and the direct consumption of animals.[232]

Urbanization has also been cited as a significant driver of biodiversity loss, particularly of plant life. A 1999 study of local plant extirpations in Great Britain found that urbanization contributed at least as much to local plant extinction as did agriculture.^[234]

Climate change

Overhunting can reduce the local population of

Fishing has had a devastating effect on marine organism populations for several centuries even before the explosion of destructive and highly effective fishing practices like trawling.^[252] Humans are unique among predators in that they regularly prey on other adult apex predators, particularly in marine environments;^[30] bluefin tuna, blue whales, North Atlantic right whales,^[253] and over fifty species of sharks and rays are vulnerable to predation pressure from human fishing, in particular commercial fishing.^[254] A 2016 study published in Science concludes that humans tend to hunt larger species, and this could disrupt ocean ecosystems for millions of years.^[255] A 2020 study published in Science Advances found that around 18% of marine megafauna, including iconic species such as the Great white shark, are at risk of extinction from human pressures over the next century. In a worst-case scenario, 40% could go extinct over the same time period.^[256] According to a 2021 study published in Nature, 71% of oceanic shark and ray populations have been destroyed by overfishing (the primary driver of ocean defaunation) from 1970 to 2018, and are nearing the "point of no return" as 24 of the 31 species are now threatened with extinction, with several being classified as critically endangered.^{[257][258][259]} Almost two thirds of sharks and rays around coral reefs are threatened with extinction from overfishing, with 14 of 134 species being critically endangered.^[260]

If this pattern goes unchecked, the future oceans would lack many of the largest species in today's oceans. Many large species play critical roles in ecosystems and so their extinctions could lead to ecological cascades that would influence the structure and function of future ecosystems beyond the simple fact of losing those species.

— Jonathan Payne, associate professor and chair of geological sciences at Stanford University^[261]

Disease

The decline of amphibian populations has also been identified as an indicator of environmental degradation. As well as habitat loss, introduced predators and pollution,

Millions of bats in the US have been dying off since 2012 due to a fungal infection known as white-nose syndrome that spread from European bats, who appear to be immune. Population drops have been as great as 90% within five years, and extinction of at least one bat species is predicted. There is currently no form of treatment, and such declines have been described as "unprecedented" in bat evolutionary history by Alan Hicks of the New York State Department of Environmental Conservation.^[266]

Between 2007 and 2013, over ten million beehives were abandoned due to colony collapse disorder, which causes worker bees to abandon the queen.^[267] Though no single cause has gained widespread acceptance by the scientific community, proposals include infections with Varroa and Acarapis mites; malnutrition; various pathogens; genetic factors; immunodeficiencies; loss of habitat; changing beekeeping practices; or a combination of factors.^[268][269]

By region

Megafauna were once found on every continent of the world, but are now almost exclusively found on the continent of Africa. In some regions, megafauna experienced population crashes and trophic cascades shortly after the earliest human settlers.^[56][57] Worldwide, 178 species of the world's largest mammals died out between 52,000 and 9,000 BC; it has been suggested that a higher proportion of African megafauna survived because they evolved alongside humans.^[270][51] The timing of South American megafaunal extinction appears to precede human arrival, although the possibility that human activity at the time impacted the global climate enough to cause such an extinction has been suggested.^[51]

Africa

Africa experienced the smallest decline in megafauna compared to the other continents. This is presumably due to the idea that Afroeurasian megafauna evolved alongside humans, and thus developed a healthy fear of them, unlike the comparatively tame animals of other continents.^[270][271]

Eurasia

Unlike other continents, the megafauna of Eurasia went extinct over a relatively long period of time, possibly due to climate fluctuations fragmenting and decreasing populations, leaving them vulnerable to over-exploitation, as with the

In the western Mediterranean region, anthropogenic forest degradation began around 4,000 BP, during the Chalcolithic, and became especially pronounced during the Roman era. The reasons for the decline of forest ecosystems stem from agriculture, grazing, and mining.^[274] During the twilight years of the Western Roman Empire, forests in northwestern Europe rebounded from losses incurred throughout the Roman period, though deforestation on a large scale resumed once again around 800 BP, during the High Middle Ages.^[275]

In southern China, human land use is believed to have permanently altered the trend of vegetation dynamics in the region, which was previously governed by temperature. This is evidenced by high fluxes of charcoal from that time interval.^[276]

Americas

The ecosystems encountered by the first Americans had not been exposed to human interaction, and may have been far less resilient to human made changes than the ecosystems encountered by industrial era humans. Therefore, the actions of the Clovis people, despite seeming insignificant by today's standards could indeed have had a profound effect on the ecosystems and wild life which was entirely unused to human influence.[51]

In the Yukon, the mammoth steppe ecosystem collapsed between 13,500 and 10,000 BP, though wild horses and woolly mammoths somehow persisted in the region for millennia after this collapse.^[280] In what is now Texas, a drop in local plant and animal biodiversity occurred during the Younger Dryas cooling, though while plant diversity recovered after the Younger Dryas, animal diversity did not.^[281] In the Channel Islands, multiple terrestrial species went extinct around the same time as human arrival, but direct evidence for an anthropogenic cause of their extinction remains lacking.^[282] In the montane forests of the Colombian Andes, spores of coprophilous fungi indicate megafaunal extinction occurred in two waves, the first occurring around 22,900 BP and the second around 10,990 BP.^[283] A 2023 study of megafaunal extinctions in the Junín Plateau of Peru found that the timing of the disappearance of megafauna was concurrent with a large uptick in fire activity attributed to human actions, implicating humans as the cause of their local extinction on the plateau.^[284]

Australia

A 2021 study found that the rate of extinction of Australia's megafauna is rather unusual, with some generalistic species having gone extinct earlier while highly specialized ones having become extinct later or even still surviving today. A mosaic cause of extinction with different anthropogenic and environmental pressures has been proposed.[290]

Caribbean

Human arrival in the Caribbean around 6,000 years ago is correlated with the extinction of many species.^[291] These include many different genera of ground and arboreal sloths across all islands. These sloths were generally smaller than those found on the South American continent. Megalocnus were the largest genus at up to 90 kilograms (200 lb), Acratocnus were medium-sized relatives of modern two-toed sloths endemic to Cuba, Imagocnus also of Cuba, Neocnus and many others.^[292]

Macaronesia

The arrival of the first human settlers in the Azores saw the introduction of invasive plants and livestock to the archipelago, resulting in the extinction of at least two plant species on Pico Island.^[293] On Faial Island, the decline of Prunus lusitanica has been hypothesized by some scholars to have been related to the tree species being endozoochoric, with the extirpation or extinction of various bird species drastically limiting its seed dispersal.^[294] Lacustrine ecosystems were ravaged by human colonization, as evidenced by hydrogen isotopes from C₃₀ fatty acids recording hypoxic bottom waters caused by eutrophication in Lake Funda on Flores Island beginning between 1500 and 1600 AD.^[295]

The arrival of humans on the archipelago of Madeira caused the extinction of approximately two-thirds of its endemic bird species, with two non-endemic birds also being locally extirpated from the archipelago.^[296] Of thirty-four land snail species collected in a subfossil sample from eastern Madeira Island, nine became extinct following the arrival of humans.^[297] On the Desertas Islands, of forty-five land snail species known to exist before human colonization, eighteen are extinct and five are no longer present on the islands.^[298] Eurya stigmosa, whose extinction is typically attributed to climate change following the end of the Pleistocene rather than humans, may have survived until the colonization of the archipelago by the Portuguese and gone extinct as a result of human activity.^[299] Introduced mice have been implicated as a leading driver of extinction on Madeira following its discovery by humans.^[296]

In the Canary Islands, native thermophilous woodlands were decimated and two tree taxa were driven extinct following the arrival of its first humans, primarily as a result of increased fire clearance and soil erosion and the introduction of invasive pigs, goats, and rats. Invasive species introductions accelerated during the Age of Discovery when Europeans first settled the Macaronesian archipelago. The archipelago's laurel forests, though still negatively impacted, fared better due to being less suitable for human economic use.^[300]

Within centuries of the arrival of

Extinction symbol