Oceanic anoxic events or anoxic events (anoxia conditions) describe periods wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic (anoxic and sulphidic) waters.[2] Although anoxic events have not happened for millions of years, the geological record shows that they happened many times in the past. Anoxic events coincided with several mass extinctions and may have contributed to them.[3] These mass extinctions include some that geobiologists use as time markers in biostratigraphic dating.[4] On the other hand, there are widespread, various black-shale beds from the mid-Cretaceous which indicate anoxic events but are not associated with mass extinctions.[5] Many geologists believe oceanic anoxic events are strongly linked to the slowing of ocean circulation, climatic warming, and elevated levels of greenhouse gases. Researchers have proposed enhanced volcanism (the release of CO2) as the "central external trigger for euxinia."[6][7]
British oceanologist and atmospheric scientist, Andrew Watson, explained that, while the Holocene epoch exhibits many processes reminiscent of those that have contributed to past anoxic events, full-scale ocean anoxia would take "thousands of years to develop."[8]
https://en.wikipedia.org/wiki/Anoxic_event
A mass mortality event (MME) is an incident that kills a vast number of individuals of a single species in a short period of time.[1] The event may put a species at risk of extinction or upset an ecosystem.[2] This is distinct from the mass die-off associated with short lived and synchronous emergent insect taxawhich is a regular and non-catastrophic occurrence.[3]
Causes of MME's include disease and human-related activities such as pollution. Climatic extremes and other environmental influences such as oxygen stress in aquatic environments play a role, as does starvation. In many MME's there are multiple stressors.[2] An analysis of such events from 1940 to 2012 found that these events have become more common for birds, fish and marine invertebrates, but have declined for amphibians and reptiles and not changed for mammals.[4]
https://en.wikipedia.org/wiki/Mass_mortality_event
An ecological cascade effect is a series of secondary extinctions that are triggered by the primary extinction of a key species in an ecosystem. Secondary extinctions are likely to occur when the threatened species are: dependent on a few specific food sources, mutualistic (dependent on the key species in some way), or forced to coexist with an invasive species that is introduced to the ecosystem. Species introductions to a foreign ecosystem can often devastate entire communities, and even entire ecosystems. These exotic species monopolize the ecosystem's resources, and since they have no natural predators to decrease their growth, they are able to increase indefinitely. Olsen et al.[1] showed that exotic species have caused lake and estuaryecosystems to go through cascade effects due to loss of algae, crayfish, mollusks, fish, amphibians, and birds. However, the principal cause of cascade effects is the loss of top predators as the key species. As a result of this loss, a dramatic increase (ecological release) of prey species occurs. The prey is then able to overexploit its own food resources, until the population numbers decrease in abundance, which can lead to extinction. When the prey's food resources disappear, they starve and may go extinct as well. If the prey species is herbivorous, then their initial release and exploitation of the plants may result in a loss of plant biodiversity in the area.[2] If other organisms in the ecosystem also depend upon these plants as food resources, then these species may go extinct as well. An example of the cascade effect caused by the loss of a top predator is apparent in tropical forests. When hunters cause local extinctions of top predators, the predators' prey's population numbers increase, causing an overexploitation of a food resource and a cascade effect of species loss.[3] Recent studies have been performed on approaches to mitigate extinction cascades in food-web networks.[4]
https://en.wikipedia.org/wiki/Cascade_effect_(ecology)
A nuclear holocaust, nuclear apocalypse or atomic holocaust is a theoretical scenario where the mass detonation of nuclear weapons causes globally widespread destruction and radioactive fallout. Such a scenario envisages large parts of the Earth becoming uninhabitable due to the effects of nuclear warfare, potentially causing the collapse of civilization, extinction of humanity and, in the worst case, termination of life on earth.
Besides the immediate destruction of cities by nuclear blasts, the potential aftermath of a nuclear war could involve firestorms, a nuclear winter, widespread radiation sickness from fallout, and/or the temporary (if not permanent) loss of much modern technology due to electromagnetic pulses. Some scientists, such as Alan Robock, have speculated that a thermonuclear war could result in the end of modern civilization on Earth, in part due to a long-lasting nuclear winter. In one model, the average temperature of Earth following a full thermonuclear war falls for several years by 7 - 8 °C (13 to 15 degrees Fahrenheit) on average.[1]
Early Cold War-era studies suggested that billions of humans would survive the immediate effects of nuclear blasts and radiation following a global thermonuclear war.[2][3][4][5] Some scholars[who?] argue that nuclear war could indirectly contribute to human extinction via secondary effects, including environmental consequences, societal breakdown, and economic collapse. Additionally, it has been argued that even a relatively small-scale nuclear exchange between India and Pakistan involving 100 Hiroshima yield (15 kilotons) weapons, could cause a nuclear winter and kill more than a billion people.[6]
The threat of a nuclear holocaust plays an important role in the popular perception of nuclear weapons. It features in the security concept of mutually assured destruction (MAD)[citation needed] and is a common scenario in survivalism. Nuclear holocaust is a common feature in literature and film, especially in speculative genres such as science fiction, dystopian and post-apocalyptic fiction.
https://en.wikipedia.org/wiki/Nuclear_holocaust
A cobalt bomb is a type of "salted bomb": a nuclear weapon designed to produce enhanced amounts of radioactive fallout, intended to contaminate a large area with radioactive material. The concept of a cobalt bomb was originally described in a radio program by physicist Leó Szilárd on February 26, 1950.[1]His intent was not to propose that such a weapon be built, but to show that nuclear weapon technology would soon reach the point where it could end human life on Earth, a doomsday device.[2][3] Such "salted" weapons were requested by the U.S. Air Force and seriously investigated, but not deployed.[citation needed] In the 1962 edition of the U.S. Department of Defense book The Effects of Nuclear Weapons, a section titled radiological warfareaddressed the issue.[4]
https://en.wikipedia.org/wiki/Cobalt_bomb
The cataclysmic pole shift hypothesis suggests that there have been geologically-rapid shifts in the relative positions of the modern-day geographic locations of the poles and the axis of rotation of Earth, causing calamities such as floods and tectonic events.[1]
There is evidence of precession and changes in axial tilt, but this change is on much longer time-scales and does not involve relative motion of the spin axis with respect to the planet. However, in what is known as true polar wander, the solid Earth can rotate with respect to a fixed spin axis. Research shows that during the last 200 million years a total true polar wander of some 30° has occurred, but that no super-rapid shifts in Earth's pole were found during this period.[2] A characteristic rate of true polar wander is 1° or less per million years.[3] Between approximately 790 and 810 million years ago, when the supercontinent Rodinia existed, two geologically-rapid phases of true polar wander may have occurred. In each of these, the magnetic poles of Earth shifted by approximately 55° – from a large shift in the crust.[4]
https://en.wikipedia.org/wiki/Cataclysmic_pole_shift_hypothesis
Desertification is a type of land degradation in drylands in which biological productivity is lost due to natural processes or induced by human activities whereby fertile areas become increasingly arid.[2] It is the spread of arid areas caused by a variety of factors, such as climate change (particularly the current global warming)[3] and overexploitationof soil as a result of human activity.[4]
Throughout geological history, the development of deserts has occurred naturally. In recent times, the potential influences of human activity, improper land management, deforestation and climate change on desertification is the subject of many scientific investigations.[5][6][7]
https://en.wikipedia.org/wiki/Desertification
A tipping point in the climate system is a threshold that, when exceeded, leads to large and often irreversible changes in the state of the system. Tipping points have been identified in the physical climate system and in ecosystems, which will have severe impacts on humans when crossed.[2]
Tipping points may be crossed even at a moderate increase of global temperature of 1.5–2 °C (2.7–3.6 °F) over pre-industrial times, due to current global warming.[3] Climate scientists have identified over a dozen possible tipping points.[4][5] If the tipping point in one system is crossed, this could lead to a cascade of other tipping points. One of these cascades could take the world into a greenhouse Earthstate 4 or 5 degrees Celsius above pre-industrial levels.[6][7]
Large-scale components of the Earth system that may pass a tipping point have been referred to as tipping elements.[8] Tipping elements are found in the Greenland and Antarctic ice sheets, possibly causing tens of meters of sea level rise. These tipping points are not always abrupt. For example, at some level of temperature rise the melt of a large part of the Greenland ice sheet and/or West Antarctic Ice Sheet will become inevitable; but the ice sheet itself may persist for many centuries.[9] Some tipping elements, like the collapse of ecosystems, are irreversible.[2]
https://en.wikipedia.org/wiki/Tipping_points_in_the_climate_system
A runaway greenhouse effect occurs when a planet's atmosphere contains greenhouse gas in an amount sufficient to block thermal radiation from leaving the planet, preventing the planet from cooling and from having liquid water on its surface. A runaway version of the greenhouse effect can be defined by a limit on a planet's outgoing longwave radiation which is asymptotically reached due to higher surface temperatures evaporating a condensable species (often water vapor) into the atmosphere, increasing its optical depth.[1] This positive feedback means the planet cannot cool down through longwave radiation (via the Stefan–Boltzmann law) and continues to heat up until it can radiate outside of the absorption bands[2] of the condensable species.
The runaway greenhouse effect is often formulated with water vapor as the condensable species. In this case the water vapor reaches the stratosphere and escapes into space via hydrodynamic escape, resulting in a desiccated planet.[3] This may have happened in the early history of Venus.
https://en.wikipedia.org/wiki/Runaway_greenhouse_effect
A flood basalt is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot reaching the surface of the earth via a mantle plume.[1] Flood basalt provinces such as the Deccan Traps of India are often called traps, after the Swedish word trappa (meaning "stairs"), due to the characteristic stairstep geomorphology of many associated landscapes. Michael R. Rampino and Richard Stothers (1988) cited eleven distinct flood basalt episodes occurring in the past 250 million years, creating large volcanic provinces, lava plateaus, and mountain ranges.[2] However, more have been recognized such as the large Ontong Java Plateau,[3]and the Chilcotin Group, though the latter may be linked to the Columbia River Basalt Group. Large igneous provinces have been connected to five mass extinction events, and may be associated with bolide impacts.[4]
https://en.wikipedia.org/wiki/Flood_basalt
Global dimming is the reduction in the amount of global direct irradiance at the Earth's surface that has been observed since systematic measurements began in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4–20% reduction. However, after discounting an anomaly caused by the eruption of Mount Pinatubo in 1991, a very slight reversal in the overall trend has been observed.[1]
Global dimming is thought to have been caused by an increase in particulates or aerosols, such as sulfate aerosols in the atmosphere due to human action. It has interfered with the hydrological cycle by reducing evaporation and may have reduced rainfall in some areas. Global dimming has been attributed as the leading factor in the 1984 Ethiopian famine by reducing heating at the tropics which drives the annual monsoon, or wet season.[2]
Causes[edit]
It is thought that global dimming is probably due to the increased presence of aerosol particles in Earth's atmosphere, caused by pollution, dust, or volcanic eruptions.[3] Aerosols and other particulates absorb solar energy and reflect sunlight back into space. The pollutants can also become nuclei for cloud droplets. Water droplets in clouds coalesce around the particles.[4] Increased pollution causes more particulates and thereby creates clouds consisting of a greater number of smaller droplets (that is, the same amount of water is spread over more droplets). The smaller droplets make clouds more reflective, so that more incoming sunlight is reflected back into space and less reaches the Earth's surface. This same effect also reflects radiation from below, trapping it in the lower atmosphere. In models, these smaller droplets also decrease rainfall.[5]
Clouds intercept both heat from the sun and heat radiated from the Earth. Their effects are complex and vary in time, location, and altitude. Usually during the daytime the interception of sunlight predominates, giving a cooling effect; however, at night the re-radiation of heat to the Earth slows the Earth's heat loss.[citation needed]
The incomplete combustion of fossil fuels (such as diesel) and wood releases black carbon into the air. Though black carbon, most of which is soot, is an extremely small component of air pollution at land surface levels, the phenomenon has a significant heating effect on the atmosphere at altitudes above two kilometers (6,562 ft). Also, it dims the surface of the ocean by absorbing solar radiation.[7]
Experiments in the Maldives (comparing the atmosphere over the northern and southern islands) in the 1990s showed that the effect of macroscopic pollutants in the atmosphere at that time (blown south from India) caused about a 10% reduction in sunlight reaching the surface in the area under the Asian brown cloud – a much greater reduction than expected from the presence of the particles themselves.[8] Prior to the research being undertaken, predictions were of a 0.5–1% effect from particulate matter; the variation from prediction may be explained by cloud formation with the particles acting as the focus for droplet creation.
The phenomenon underlying global dimming may also have regional effects. While most of the earth has warmed, the regions that are downwind from major sources of air pollution (specifically sulfur dioxide emissions) have generally cooled. This may explain the cooling of the eastern United States relative to the warming western part.[9]
However some research shows that black carbon will increase global warming, being second only to CO2. They believe that soot will absorb solar energy and transport it to other areas such as the Himalayas where glacial melting occurs. It can also darken Arctic ice reducing reflectivity and increasing absorption of solar radiation.[10]
Airborne volcanic ash can reflect the Sun's rays back into space and thereby contribute to cooling the planet. Dips in earth temperatures have been observed after large volcano eruptions such as Mount Agung in Bali that erupted in 1963, El Chichon (Mexico) 1983, Ruiz (Colombia) 1985, and Pinatubo (Philippines) 1991. But even for major eruptions, the ash clouds remain only for relatively short periods.[3] It has also been theorized that today's rapid climate change may increase volcanic activity.[11]
Contrails and clouds[edit]
A study theorized that aircraft contrails (also called vapor trails) are implicated in regional cooling, but the constant flow of air traffic previously meant that this could not be tested. The near-total shutdown of civil air traffic during the three days following the September 11, 2001 attacks afforded a unique opportunity in which to observe the climate of the United States absent from the effect of contrails. During this period, an increase in diurnal temperature variation of 1.1 °C (1.8 °F) was observed in some parts of the U.S., i.e. aircraft contrails may have been raising nighttime temperatures and/or lowering daytime temperatures by much more than previously thought.[6] However, a follow-up study attributed cloud cover to the temperature change. The authors wrote, "The variations in high cloud cover, including contrails and contrail-induced cirrus clouds, contribute weakly to the changes in the diurnal temperature range, which is governed primarily by lower altitude clouds, winds, and humidity."[12]
https://en.wikipedia.org/wiki/Global_dimming
Global terrestrial stilling is the decrease of wind speed observed near the Earth's surface (~10-meter height) over the last three decades (mainly since the 1980s), originally termed "stilling".[1] This slowdown of near-surface terrestrial winds has mainly affected mid-latitude regions of both hemispheres, with a global average reduction of −0.140 m s−1 dec−1 (meters per second per decade) or between 5 and 15% over the past 50 years.[2] With high-latitude (> 75° from the equator) showing increases in both hemispheres. In contrast to the observed weakening of winds over continental surfaces, winds have tended to strengthen over ocean regions.[3][4] In the last few years, a break in this terrestrial decrease of wind speed has been detected suggesting a recovery at global scales since 2013.[5]
The exact cause(s) of the global terrestrial stilling are uncertain and has been mainly attributed to two major drivers: (i) changes in large scale atmospheric circulation, and (ii) an increase of surface roughness due to e.g. forest growth, land use changes, and urbanization.
Given climate change, changes in wind speed are currently a potential concern for society, due to their impacts on a wide array of spheres, such as wind power generation, ecohydrological implications for agriculture and hydrology, wind-related hazards and catastrophes, or air quality and human health, among many others.
https://en.wikipedia.org/wiki/Global_terrestrial_stilling
An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and greenhouse periods, during which there are no glaciers on the planet. Earth is currently in the Quaternary glaciation.[1] Individual pulses of cold climate within an ice age are termed glacial periods (or, alternatively, glacials, glaciations, glacial stages, stadials, stades, or colloquially, ice ages), and intermittent warm periods within an ice age are called interglacials or interstadials.[2]
In glaciology, ice age implies the presence of extensive ice sheets in both northern and southern hemispheres.[3] By this definition, Earth is currently in an interglacial period—the Holocene. The amount of anthropogenic greenhouse gases emitted into Earth's oceans and atmosphere is predicted to prevent the next glacial period for the next 500,000 years, which otherwise would begin in around 50,000 years, and likely more glacial cycles after.[4][5][6]
https://en.wikipedia.org/wiki/Ice_age
Ocean acidification is the ongoing decrease in the pH value of the Earth's oceans, caused by the uptake of carbon dioxide (CO
2) from the atmosphere.[2] The main cause of ocean acidification is the burning of fossil fuels. Ocean acidification is one of several effects of climate change on oceans. Seawater is slightly basic (meaning pH > 7), and ocean acidification involves a shift towards pH-neutral conditions rather than a transition to acidic conditions (pH < 7).[3] The concern with ocean acidification is that it can lead to the decreased production of the shells of shellfish and other aquatic life with calcium carbonate shells, as well as some other physiological challenges for marine organisms. The calcium carbonate shelled organisms can not reproduce under high saturated acidotic waters. An estimated 30–40% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes.[4][5] Some of it reacts with the water to form carbonic acid. Some of the resulting carbonic acid molecules dissociate into a bicarbonate ion and a hydrogen ion, thus increasing ocean acidity (H+ ion concentration).
Between 1751 and 1996, the pH value of the ocean surface is estimated to have decreased from approximately 8.25 to 8.14,[6] representing an increase of almost 30% in H+ ion concentration in the world's oceans (note the pH scale is logarithmic so a change of one in pH unit is equivalent to a ten fold change in H+ ion concentration).[7][8] Increasing acidity is thought to have a range of potentially harmful consequences for marine organisms such as depressing metabolic rates and immune responses in some organisms and causing coral bleaching.[9] By increasing the presence of free hydrogen ions, the additional carbonic acid that forms in the oceans ultimately results in the conversion of carbonate ions into bicarbonate ions. Ocean alkalinity (roughly equal to [HCO3−] + 2[CO32−]) is not changed by the process, or may increase over long time periods due to carbonate dissolution.[10] This net decrease in the amount of carbonate ions available may make it more difficult for marine calcifying organisms, such as coral and some plankton, to form biogenic calcium carbonate, and such structures become vulnerable to dissolution.[11]Ongoing acidification of the oceans may threaten future food chains linked with the oceans.[12][13]
Ocean acidification has been compared to anthropogenic climate change and called the "evil twin of global warming"[14][15][16][17][18] and "the other CO
2 problem".[15][17][19] Freshwater bodies also appear to be acidifying, although this is a more complex and less obvious phenomenon.[20][21] To ensure that ocean acidification is minimized, the United Nation's Sustainable Development Goal 14 ("Life below Water") aims to ensure that oceans are conserved and sustainably used.[22] As members of the InterAcademy Panel, 105 science academies have issued a statement on ocean acidification recommending that by 2050, global CO
2emissions be reduced by at least 50% compared to the 1990 level.[23]
Ocean acidification has occurred previously in Earth's history,[24] and the resulting ecological collapse in the oceans had long-lasting effects for global carbon cycling and climate.[25][26] The most notable example is the Paleocene-Eocene Thermal Maximum (PETM),[27] which occurred approximately 56 million years ago when massive amounts of carbon entered the ocean and atmosphere, and led to the dissolution of carbonate sediments in all ocean basins.
https://en.wikipedia.org/wiki/Ocean_acidification
Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions.[1] The latter phenomenon is referred to as the ozone hole. There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events.
The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants, and foam- blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons), referred to as ozone-depleting substances (ODS). These compounds are transported into the stratosphere by turbulent mixing after being emitted from the surface, mixing much faster than the molecules can settle.[2] Once in the stratosphere, they release atoms from the halogen group through photodissociation, which catalyze the breakdown of ozone (O3) into oxygen (O2).[3] Both types of ozone depletion were observed to increase as emissions of halocarbons increased.
Ozone depletion and the ozone hole have generated worldwide concern over increased cancer risks and other negative effects. The ozone layer prevents most harmful wavelengths of ultraviolet (UV) light from passing through the Earth's atmosphere. These wavelengths cause skin cancer, sunburn, permanent blindness, and cataracts, which were projected to increase dramatically as a result of thinning ozone, as well as harming plants and animals. These concerns led to the adoption of the Montreal Protocol in 1987, which bans the production of CFCs, halons, and other ozone-depleting chemicals.
The ban came into effect in 1989. Ozone levels stabilized by the mid-1990s and began to recover in the 2000s, as the shifting of the jet stream in the southern hemisphere towards the south pole has stopped and might even be reversing.[4] Recovery is projected to continue over the next century, and the ozone hole is expected to reach pre-1980 levels by around 2075.[5] In 2019, NASA reported that the ozone hole was the smallest ever since it was first discovered in 1982.[6][7]
The Montreal Protocol is considered the most successful international environmental agreement to date.[8][9]
https://en.wikipedia.org/wiki/Ozone_depletion
Water scarcity (closely related to water stress or water crisis) is the lack of fresh water resources to meet the standard water demand. Two types of water scarcity have been defined: physical or economic water scarcity. Physical water scarcity is where there is not enough water to meet all demands, including that needed for ecosystems to function effectively. Arid areas (for example Central and West Asia, and North Africa) often suffer from physical water scarcity.[1] On the other hand, economic water scarcity is caused by a lack of investment in infrastructure or technology to draw water from rivers, aquifers, or other water sources, or insufficient human capacity to satisfy the demand for water. Much of Sub-Saharan Africa is characterized by economic water scarcity.[2]: 11
The essence of global water scarcity is the geographic and temporal mismatch between fresh water demand and availability.[3][4] At the global level and on an annual basis, enough freshwater is available to meet such demand, but spatial and temporal variations of water demand and availability are large, leading to physical water scarcity in several parts of the world during specific times of the year.[5] The main driving forces for the rising global demand for water are the increasing world population, improving living standards, changing consumption patterns(for example a dietary shift toward more animal products),[6] and expansion of irrigated agriculture.[7][8] Climate change, such as altered weather-patterns (including droughts[9] or floods), deforestation, increased water pollution and wasteful use of water can also cause insufficient water supply.[10] Scarcity varies over time as a result of natural hydrological variability, but varies even more so as a function of prevailing economic policy, planning and management approaches. Scarcity can be expected to intensify with most forms of economic development, but, if correctly identified, many of its causes can be predicted, avoided or mitigated.[11]
Water scarcity assessments need to incorporate information on green water (soil moisture), water quality, environmental flow requirements, globalization, and virtual water trade.[6] There is a need for collaboration between hydrological, water quality, aquatic ecosystem science and social science communities in water scarcity assessment.[6] "Water stress" has been used as parameter to measure water scarcity, for example in the context of Sustainable Development Goal 6.[12] Two-thirds of the global population (4 billion people) live under conditions of severe water scarcity at least one month of the year.[5][13] Half a billion people in the world face severe water scarcity all year round.[5][6] Half of the world's largest cities experience water scarcity.[13]
Options for reducing water scarcity include: supply and demand side management, cooperation between countries, water conservation (including prevention of water pollution), expanding sources of usable water (through wastewater reuse or desalination) and virtual water trade.
https://en.wikipedia.org/wiki/Water_scarcity
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource. The term applies to natural resources such as: wild medicinal plants, grazing pastures, game animals, fish stocks, forests, and water aquifers.
In ecology, overexploitation describes one of the five main activities threatening global biodiversity.[2]Ecologists use the term to describe populations that are harvested at an unsustainable rate, given their natural rates of mortality and capacities for reproduction. This can result in extinction at the population level and even extinction of whole species. In conservation biology, the term is usually used in the context of human economic activity that involves the taking of biological resources, or organisms, in larger numbers than their populations can withstand.[3] The term is also used and defined somewhat differently in fisheries, hydrology and natural resource management.
Overexploitation can lead to resource destruction, including extinctions. However, it is also possible for overexploitation to be sustainable, as discussed below in the section on fisheries. In the context of fishing, the term overfishing can be used instead of overexploitation, as can overgrazing in stock management, overlogging in forest management, overdrafting in aquifer management, and endangered species in species monitoring. Overexploitation is not an activity limited to humans. Introduced predators and herbivores, for example, can overexploit native flora and fauna.
https://en.wikipedia.org/wiki/Overexploitation
Overpopulation or overabundance occurs when a species' population becomes so large that it is deemed exceeding the carrying capacity and must be actively intervened. It can result from an increase in births (fertility rate), a decline in the mortality rate, an increase in immigration, or a depletion of resources. When overpopulation occurs the available resources become too limited for the entire population to survive comfortably or at all in the long term.
https://en.wikipedia.org/wiki/Overpopulation
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the rate of speciation. The number of major mass extinctions in the last 440 million years are estimated from as few as five to more than twenty. These differences stem from disagreement as to what constitutes an extinction event as "major", and the data chosen to measure past diversity.
Because most diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphererather than the total diversity and abundance of life.[1] Extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomicfamilies of marine animals every million years. Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land animals.
The Great Oxidation Event, which occurred around 2.45 billion years ago, was probably the first major extinction event.[2] Since the Cambrian explosion, five further major mass extinctions have significantly exceeded the background extinction rate. The most recent and arguably best-known, the Cretaceous–Paleogene extinction event, which occurred approximately 66 Ma (million years ago), was a large-scale mass extinction of animal and plant species in a geologically short period of time.[3] In addition to the five major mass extinctions, there are numerous minor ones as well, and the ongoing mass extinction caused by human activity is sometimes called the sixth extinction.[4] Mass extinctions seem to be a mainly Phanerozoic phenomenon, with extinction rates low before large complex organisms arose.[5]
https://en.wikipedia.org/wiki/Extinction_event
Genetic erosion (also known as genetic depletion) is a process where the limited gene pool of an endangered species diminishes even more when reproductive individuals die off before reproducing with others in their endangered low population. The term is sometimes used in a narrow sense, such as when describing the loss of particular alleles or genes, as well as being used more broadly, as when referring to the loss of a phenotype or whole species.
Genetic erosion occurs because each individual organism has many unique genes which get lost when it dies without getting a chance to breed. Low genetic diversity in a population of wild animals and plants leads to a further diminishing gene pool – inbreeding and a weakening immune system can then "fast-track" that species towards eventual extinction.
By definition, endangered species suffer varying degrees of genetic erosion. Many species benefit from a human-assisted breeding program to keep their population viable,[citation needed] thereby avoiding extinction over long time-frames. Small populations are more susceptible to genetic erosion than larger populations.
Genetic erosion gets compounded and accelerated by habitat loss and habitat fragmentation – many endangered species are threatened by habitat loss and (fragmentation) habitat. Fragmented habitat create barriers in gene flow between populations.
The gene pool of a species or a population is the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection. Meanwhile, low genetic diversity (see inbreeding and population bottlenecks) can cause reduced biological fitness and increase the chance of extinction of that species or population.
https://en.wikipedia.org/wiki/Genetic_erosion
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