This extinction event spans numerous families of plants[5][6][7] and animals, including mammals, birds, reptiles, amphibians, fish, and invertebrates, impacting both terrestrial and marine species.

[74][21][75] The 2019 Global Assessment Report on Biodiversity and Ecosystem Services, published by the United Nations IPBES, estimated that about one million species are currently at risk of extinction within decades due to human activities.

[76][77][78] Organized human existence is jeopardised 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.

[20][98] A December 2022 study published in Science Advances states that "the planet has entered the sixth mass extinction" and warns that current anthropogenic trends, particularly regarding climate and land-use changes, could result in the loss of more than a tenth of plant and animal species by the end of the century.

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.

[115] 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.

[121][122] A 2015 article in Science suggested that humans are unique in ecology as an unprecedented "global superpredator", regularly preying on large numbers of fully grown terrestrial and marine apex predators, and with a great deal of influence over food webs and climatic systems worldwide.

[133][134][135] Other, related human causes of the extinction event include deforestation, hunting, pollution,[136] the introduction in various regions of non-native species, and the widespread transmission of infectious diseases spread through livestock and crops.

[131] 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.

[138] 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.

[121][131][139] 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.

[113][141] Some scientists favor abrupt climate change as the catalyst for the extinction of the megafauna at the end of the Pleistocene, most who believe increased hunting from early modern humans also played a part, with others even suggesting that the two interacted.

[10][14][40][39][97][149] Inger Andersen, the executive director of the United Nations Environment Programme, stated that "we need to understand that the more people there are, the more we put the Earth under heavy pressure.

[156] 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.

[187][188] Contemporary assessments have discovered that roughly 41% of amphibians, 25% of mammals, 21% of reptiles and 14% of birds are threatened with extinction, which could disrupt ecosystems on a global scale and eliminate billions of years of phylogenetic diversity.

[201] 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.

[202][203] 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.

[39][95] 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."

[206] 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.

[54][215][46][216][217] A 2017 study by the World Wildlife Fund (WWF) found that 60% of biodiversity loss can be attributed to the vast scale of feed crop cultivation required to rear tens of billions of farm animals.

[218] More recently, in 2019, the IPBES Global Assessment Report on Biodiversity and Ecosystem Services attributed much of this ecological destruction to agriculture and fishing, with the meat and dairy industries having a very significant impact.

[79] A 2020 study published in Nature Communications warned that human impacts from housing, industrial agriculture and in particular meat consumption are wiping out a combined 50 billion years of Earth's evolutionary history (defined as phylogenetic diversity[a]) and driving to extinction some of the "most unique animals on the planet," among them the Aye-aye lemur, the Chinese crocodile lizard and the pangolin.

[231][232] Several conservationist organizations, among them IFAW and HSUS, assert that trophy hunters, particularly from the United States, are playing a significant role in the decline of giraffes, which they refer to as a "silent extinction".

[242] 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.

[271] Humans in New Guinea used volcanically fertilised soil following major eruptions and interfered with vegetation succession patterns since the Late Pleistocene, with this process intensifying in the Holocene.

[285] 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.

[287] 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.

[303] In American Samoa, deposits dating back to the period of initial human colonisation contain elevated quantities of bird, turtle, and fish remains caused by increased predation pressure.

[304] On Mangaia in the Cook Islands, human colonisation was associated with a major extinction of endemic avifauna,[305] along with deforestation, erosion of volcanic hillsides, and increased charcoal influx, causing additional environmental damage.

[97][334] Reducing human population growth has been suggested as a means of mitigating climate change and the biodiversity crisis,[335][336][337] although many scholars believe it has been largely ignored in mainstream policy discourse.