Holocene extinction

Source: Wikipedia, the free encyclopedia.
The dodo became extinct during the mid-to-late 17th century due to habitat destruction, overhunting, and predation by introduced mammals.[1] It is an often-cited example of a modern extinction.[2]

The Holocene extinction or Anthropocene extinction,

fungi, plants,[5][6][7] and animals, including mammals, birds, reptiles, amphibians, fish, invertebrates, and affecting not just terrestrial species but also large sectors of marine life.[8] With widespread degradation of highly biodiverse habitats 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] and increasing.[13]

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

humankind has either entered a period of mass extinction,[14][15] or is on the cusp of doing so.[16][17] As such, the event has also been referred to as the sixth mass extinction or sixth extinction.[18]

The Holocene extinction includes the disappearance of large land animals known as

last glacial period. Megafauna outside of the African mainland, which did not evolve alongside 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.[19][20] Many African species have also gone extinct in the Holocene, along with species in North America, South America, and Australia, but – with some exceptions – the megafauna of the Eurasian mainland was largely unaffected until a few hundred years ago.[21] These extinctions, occurring near the PleistoceneHolocene boundary, are sometimes referred to as the Quaternary extinction event
.

The most popular theory is that human

Hawaii. Aside from humans, climate change may have been a driving factor in the megafaunal extinctions, especially at the end of the Pleistocene
.

In the

, and on smaller islands.

Overall, the Holocene extinction can be linked to the

wetlands,[38] and the decline in amphibian populations[39] are a few broader examples of global biodiversity loss
.

Background

Extinction intensity.svgCambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogene
Marine extinction intensity during the Phanerozoic
%
Millions of years ago
Extinction intensity.svgCambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogene
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

better source needed
]

Extinction rate

The contemporary rate of extinction of species is estimated at 100 to 1,000 times higher than the

Theoretical ecologist Stuart Pimm stated that the extinction rate for plants is 100 times higher than normal.[52]

Some contend that contemporary extinction has yet to reach the level of the previous five mass extinctions,[53] and that this comparison downplays how severe the first five mass extinctions were.[54] 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.[55] 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.[17][56] 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.[17]

In The Future of Life (2002),

Edward Osborne Wilson of Harvard calculated that, if the current rate of human disruption of the biosphere continues, one-half of Earth's higher lifeforms will be extinct by 2100. A 1998 poll conducted by the American Museum of Natural History found that 70% of biologists acknowledge an ongoing anthropogenic extinction event.[57]

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.[58][59] 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.[60][61]

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 roughly one million species of plants and animals face extinction within decades as the result of human actions.[31][62][63][64] 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.[65] 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."[66][67] 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."[68][69] In a 2022 report, IPBES listed unsustainable fishing, hunting and logging as being some of the primary drivers of the global extinction crisis.[70]

Attribution

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

IPBES executive secretary[71]

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.[46] That humans have become the primary driver of modern extinctions is undeniable, rising extinction trends impacting numerous animal groups including mammals, birds, reptiles, and amphibians have prompted scientists to declare a biodiversity crisis.[72]

Scientific debate

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

overconsumption, population growth and intensive farming, which is further evidence that humans have unleashed a sixth mass extinction event; however, this finding has been disputed by one 2020 study, which posits that this major decline was primarily driven by a few extreme outlier populations, and that when these outliers are removed, the trend shifts to that of a decline between the 1980s and 2000s, but a roughly positive trend after 2000.[75][76][77][78] A 2021 report in Frontiers in Conservation Science which cites both of the aforementioned studies, says "population sizes of vertebrate species that have been monitored across years have declined by an average of 68% over the last five decades, with certain population clusters in extreme decline, thus presaging the imminent extinction of their species," and asserts "that we are already on the path of a sixth major extinction is now scientifically undeniable."[79] A 2022 study published in Biological Reviews builds upon previous studies documenting biodiversity decline to assert that a sixth mass extinction event caused by anthropogenic activity is currently underway.[80][81]

According to the

, 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.[82]

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.[83][84]

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."[85]

Anthropocene

A diagram showing the ecological processes of coral reefs before and during the 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".[46][86][87] Anthropocene is a term introduced in 2000.[88][89] 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.[42]

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,[93][94] a term which was considered for inclusion in the timeline of Earth's history by the International Commission on Stratigraphy in 2016.[95][96] 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.[92] 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.[97][98]

Human ecology

A 2015 article in

PNAS found that since the dawn of human civilization, the biomass of wild mammals has decreased by 83%. The biomass decrease is 80% for marine mammals, 50% for plants and 15% for fish. Currently, livestock make up 60% of the biomass of all mammals on earth, followed by humans (36%) and wild mammals (4%). As for birds, 70% are domesticated, such as poultry, whereas only 30% are wild.[99][100]

Historic extinction

Human activity

Activities contributing to extinctions

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.[46] There is a correlation between megafaunal extinction and the arrival of humans.[101][102][103] Over the past 125,000 years, the average body size of wildlife has fallen by 14% as human actions eradicated megafauna on all continents with the exception of Africa.[104]

Human civilization was founded on and grew from agriculture.[105] The more land used for farming, the greater the population a civilization could sustain,[92][105] and subsequent popularization of farming led to habitat conversion.[10]

Habitat destruction by humans, thus replacing the original local ecosystems, is a major driver of extinction.[106] 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, among other organisms, in both population size and species count.[107][108][109]

Other, related human causes of the extinction event include

infectious diseases spread through livestock and crops.[50]

Agriculture and climate change

Recent investigations into the practice of landscape burning during the Neolithic Revolution has 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.[105] 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.[111][112] Scientists have questioned the correlation between population size and early territorial alterations.[112] 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 have created significant environmental impacts through large-scale means of deforestation.[105]

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 be contributing most to these concentrations globally.[97][105][113] 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. Gaining popularity on his uncommon hypothesis, palaeoclimatologist William Ruddiman in 2003, 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.[92][111][113] He argued that the patterns of the significant decline of CO2 levels during the last ice age of the Pleistocene inversely correlates to the Holocene where there have been dramatic increases of CO2 around 8000 years ago and CH4 levels 3000 years after that.[113] 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 such as the anthropogenic expansion of (human) land use and irrigation.[92][113]

Climate change

Atlantic Period, warm and wet
Bottom: Potential vegetation in climate now if not for human effects like agriculture.[114]

One of the main theories for the extinction's cause is

interglacial period for the last 10,000 years is no higher than that of previous interglacial periods, yet some of the same megafauna survived similar temperature increases.[118][119][120][121][122][123][excessive citations] In the Americas, a controversial explanation for the shift in climate is presented under the Younger Dryas impact hypothesis, which states that the impact of comets cooled global temperatures.[124][125]

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."[126][72]

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).

modern humans; some recent studies favor this theory.[46][130]

Large populations of megaherbivores have the potential to contribute greatly to the atmospheric concentration of

sauropods could have emitted 520 million tons of methane to the atmosphere annually,[131] contributing to the warmer climate of the time (up to 10 °C warmer than at present).[131][132] This large emission follows from the enormous estimated biomass of sauropods, and because methane production of individual herbivores is believed to be almost proportional to their mass.[131]

Recent studies have indicated that the extinction of megafaunal herbivores may have caused a reduction in

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.[133] 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.[133]

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.

gestation period and a higher population size. Humans are thought to be the sole cause as other earlier migrations of animals into North America from Eurasia did not cause extinctions.[135]

There are many problems with this theory, as this disease would have to meet several criteria: it has to be able to sustain itself in an environment with no hosts; it has to have a high infection rate; and be extremely lethal, with a mortality rate of 50–75%. Disease has to be very virulent to kill off all the individuals in a species, and even such a virulent disease as West Nile fever is unlikely to have caused extinction.[137]

However, diseases have been the cause for some extinctions. The introduction of

endemic birds of Hawaii.[138]

Contemporary extinction

History

mountain gorillas remaining. 60% of primate species face an anthropogenically driven extinction crisis and 75% have declining populations.[139]

Contemporary

consumption growth, prominently in the past two centuries, are regarded as the underlying causes of extinction.[10][13][29][31][79]

The loss of animal species from ecological communities, defaunation, is primarily driven by human activity.[41] This has resulted in empty forests, ecological communities depleted of large vertebrates.[46][141] This is not to be confused with extinction, as it includes both the disappearance of species and declines in abundance.[142] 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.[143] Since then, the term has gained broader usage in conservation biology as a global phenomenon.[41][143]

Some scholars assert that the emergence of

CUNY professor David Harvey, for example, posits that the neoliberal era "happens to be the era of the fastest mass extinction of species in the Earth's recent history".[147] Major lobbying organizations representing corporations in the agriculture, fisheries, forestry and paper, mining, and oil and gas industries, including the United States Chamber of Commerce, have been pushing back against legislation that could address the extinction crisis. A 2022 report by the climate think tank InfluenceMap stated that "although industry associations, especially in the US, appear reluctant to discuss the biodiversity crisis, they are clearly engaged on a wide range of policies with significant impacts on biodiversity loss."[148]

tigers are down to 3,000 in the wild, from 50,000.[149] A December 2016 study by the Zoological Society of London, Panthera Corporation and Wildlife Conservation Society showed that cheetahs are far closer to extinction than previously thought, with only 7,100 remaining in the wild, existing within only 9% of their historic range.[150] Human pressures are to blame for the cheetah population crash, including prey loss due to overhunting by people, retaliatory killing from farmers, habitat loss and the illegal wildlife trade.[151]

We are seeing the effects of 7 billion people on the planet. At present rates, we will lose the big cats in 10 to 15 years.

The term

Sussex University stated that their study suggested that humans are making large parts of the planet uninhabitable for wildlife. Goulson characterized the situation as an approaching "ecological Armageddon", adding that "if we lose the insects then everything is going to collapse."[154] A 2019 study found that over 40% of insect species are threatened with extinction.[155] The most significant drivers in the decline of insect populations are associated with intensive farming practices, along with pesticide use and climate change.[156] The world's insect population decreases by around 1 to 2 per cent per year.[157]

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[158]
Angalifu, a male northern white rhinoceros at the San Diego Zoo Safari Park (died December 2014).[159] Sudan, the last male of the subspecies died on March 19, 2018.[160]

Various species are predicted to

Biodiversity Action Plan, a first step at identifying specific endangered species and habitats, country by country[needs update].[177]

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.

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.[41][13] The International Union for Conservation of Nature (IUCN) characterises 'recent' extinction as those that have occurred past the cut-off point of 1500,[179] and at least 875 plant and animal species have gone extinct since that time and 2009.[180] Some species, such as the Père David's deer[181] and the Hawaiian crow,[182] 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,[183]: 75–77  as with the extinction of gray whales in the Atlantic,[184] and of the leatherback sea turtle in Malaysia.[185]

Humans are 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.[186][187] 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.[188]

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.[31] 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.[31][77]

A June 2020 study published in

PNAS posits that the contemporary extinction crisis "may be the most serious environmental threat to the persistence of civilization, because it is irreversible" and that its acceleration "is certain because of the still fast growth in human numbers and consumption rates." The study found that more than 500 vertebrate species are poised to be lost in the next two decades.[74]

Habitat destruction

Biomass of mammals on Earth as of 2018[99][100]

  Livestock, mostly cattle and pigs (60%)
  Humans (36%)
  Wild mammals (4%)

Humans both create and destroy

silphium and the passenger pigeon.[189] It was estimated in 2012 that 13 percent of Earth's ice-free land surface is used as row-crop agricultural sites, 26 percent used as pastures, and 4 percent urban-industrial areas.[190]

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.[191][192] 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".[193][194]

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.[195]

oil palm plantations.[196]