Coronal mass ejection, solar storm of 1859, and possible damage.

From Wikipedia, the free encyclopedia

 

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This video shows the particle flow around Earth as solar ejecta associated with a coronal mass ejection strike.

A coronal mass ejection (CME) is a significant release of plasma and accompanying magnetic field from the solar corona. They often follow solar flares and are normally present during a solar prominence eruption. The plasma is released into the solar wind, and can be observed in coronagraph imagery.

Coronal mass ejections are often associated with other forms of solar activity, but a broadly accepted theoretical understanding of these relationships has not been established. CMEs most often originate from active regions on the Sun's surface, such as groupings of sunspots associated with frequent flares. Near solar maxima, the Sun produces about three CMEs every day, whereas near solar minima, there is about one CME every five days.

Description

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Follow a CME as it passes Venus then Earth, and explore how the Sun drives Earth's winds and oceans.

 

Arcs rise above an active region on the surface of the Sun.

 

Coronal mass ejections release large quantities of matter and electromagnetic radiation into space above the Sun's surface, either near the corona (sometimes called a solar prominence), or farther into the planetary system, or beyond (interplanetary CME). The ejected material is a magnetized plasma consisting primarily of electrons and protons. While solar flares are very fast (being electromagnetic radiation), CMEs are relatively slow.

Coronal mass ejections are associated with enormous changes and disturbances in the coronal magnetic field. They are usually observed with a white-light coronagraph.

Cause

Scientific research has shown that the phenomenon of magnetic reconnection is closely associated with CMEs and solar flares. In magnetohydrodynamic theory, the sudden rearrangement of magnetic field lines when two oppositely directed magnetic fields are brought together is called "magnetic reconnection". Reconnection releases energy stored in the original stressed magnetic fields. These magnetic field lines can become twisted in a helical structure, with a 'right-hand twist' or a 'left hand twist'. As the Sun's magnetic field lines become more and more twisted, CMEs appear to be a 'valve' to release the magnetic energy being built up, as evidenced by the helical structure of CMEs, that would otherwise renew itself continuously each solar cycle and eventually rip the Sun apart.

On the Sun, magnetic reconnection may happen on solar arcades—a series of closely occurring loops of magnetic lines of force. These lines of force quickly reconnect into a low arcade of loops, leaving a helix of magnetic field unconnected to the rest of the arcade. The sudden release of energy during this process causes the solar flare and ejects the CME. The helical magnetic field and the material that it contains may violently expand outwards forming a CME. This also explains why CMEs and solar flares typically erupt from what are known as the active regions on the Sun where magnetic fields are much stronger on average.

Aurora borealis stretch across Quebec and Ontario early on the morning of 8 October 2012.

Impact on Earth

When the ejection is directed towards Earth and reaches it as an interplanetary CME (ICME), the shock wave of traveling mass causes a geomagnetic storm that may disrupt Earth's magnetosphere, compressing it on the day side and extending the night-side magnetic tail. When the magnetosphere reconnects on the nightside, it releases power on the order of terawatt scale, which is directed back toward Earth's upper atmosphere.

Solar energetic particles can cause particularly strong aurorae in large regions around Earth's magnetic poles. These are also known as the Northern Lights (aurora borealis) in the northern hemisphere, and the Southern Lights (aurora australis) in the southern hemisphere. Coronal mass ejections, along with solar flares of other origin, can disrupt radio transmissions and cause damage to satellites and electrical transmission line facilities, resulting in potentially massive and long-lasting power outages.

Energetic protons released by a CME can cause an increase in the number of free electrons in the ionosphere, especially in the high-latitude polar regions. The increase in free electrons can enhance radio wave absorption, especially within the D-region of the ionosphere, leading to Polar Cap Absorption (PCA) events.

Humans at high altitudes, as in airplanes or space stations, risk exposure to relatively intense solar particle events. The energy absorbed by astronauts is not reduced by a typical spacecraft shield design and, if any protection is provided, it would result from changes in the microscopic inhomogeneity of the energy absorption events.

Physical properties

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A video of the series of CMEs in August 2010.

 

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This video features two model runs. One looks at a moderate coronal mass ejection (CME) from 2006. The second run examines the consequences of a large coronal mass ejection, such as the Carrington-class CME of 1859.

 

A typical coronal mass ejection may have any or all of three distinctive features: a cavity of low electron density, a dense core (the prominence, which appears on coronagraph images as a bright region embedded in this cavity), and a bright leading edge.

Most ejections originate from active regions on the Sun's surface, such as groupings of sunspots associated with frequent flares. These regions have closed magnetic field lines, in which the magnetic field strength is large enough to contain the plasma. These field lines must be broken or weakened for the ejection to escape from the Sun. However, CMEs may also be initiated in quiet surface regions, although in many cases the quiet region was recently active. During solar minimum, CMEs form primarily in the coronal streamer belt near the solar magnetic equator. During solar maximum, they originate from active regions whose latitudinal distribution is more homogeneous.

Coronal mass ejections reach velocities from 20 to 3,200 km/s (12 to 1,988 mi/s) with an average speed of 489 km/s (304 mi/s), based on SOHO/LASCO measurements between 1996 and 2003. These speeds correspond to transit times from the Sun out to the mean radius of Earth's orbit of about 13 hours to 86 days (extremes), with about 3.5 days as the average. The average mass ejected is 1.6×10¹² kg (3.5×10¹² lb). However, the estimated mass values for CMEs are only lower limits, because coronagraph measurements provide only two-dimensional data. The frequency of ejections depends on the phase of the solar cycle: from about one every fifth day near the solar minimum to 3.5 per day near the solar maximum. These values are also lower limits because ejections propagating away from Earth (backside CMEs) usually cannot be detected by coronagraphs.

Current knowledge of coronal mass ejection kinematics indicates that the ejection starts with an initial pre-acceleration phase characterized by a slow rising motion, followed by a period of rapid acceleration away from the Sun until a near-constant velocity is reached. Some balloon CMEs, usually the slowest ones, lack this three-stage evolution, instead accelerating slowly and continuously throughout their flight. Even for CMEs with a well-defined acceleration stage, the pre-acceleration stage is often absent, or perhaps unobservable.

Association with other solar phenomena

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Video of a solar filament being launched

Coronal mass ejections are often associated with other forms of solar activity, most notably:

• Solar flares
• Eruptive prominence and X-ray sigmoids^[13]
• Coronal dimming (long-term brightness decrease on the solar surface)
• Moreton waves
• Coronal waves (bright fronts propagating from the location of the eruption)
• Post-eruptive arcades

The association of a CME with some of those phenomena is common but not fully understood. For example, CMEs and flares are normally closely related, but there was confusion about this point caused by the events originating beyond the limb. For such events no flare could be detected. Most weak flares do not have associated CMEs; most powerful ones do. Some CMEs occur without any flare-like manifestation, but these are the weaker and slower ones. It is now thought that CMEs and associated flares are caused by a common event (the CME peak acceleration and the flare impulsive phase generally coincide). In general, all of these events (including the CME) are thought to be the result of a large-scale restructuring of the magnetic field; the presence or absence of a CME during one of these restructures would reflect the coronal environment of the process (i.e., can the eruption be confined by overlying magnetic structure, or will it simply break through and enter the solar wind).

Theoretical models

It was first postulated that CMEs might be driven by the heat of an explosive flare. However, it soon became apparent that many CMEs were not associated with flares, and that even those that were often started before the flare. Because CMEs are initiated in the solar corona (which is dominated by magnetic energy), their energy source must be magnetic.

Because the energy of CMEs is so high, it is unlikely that their energy could be directly driven by emerging magnetic fields in the photosphere (although this is still a possibility). Therefore, most models of CMEs assume that the energy is stored up in the coronal magnetic field over a long period of time and then suddenly released by some instability or a loss of equilibrium in the field. There is still no consensus on which of these release mechanisms is correct, and observations are not currently able to constrain these models very well. These same considerations apply equally well to solar flares, but the observable signatures of these phenomena differ.

Interplanetary coronal mass ejections

Illustration of a coronal mass ejection moving beyond the planets toward the heliopause

CMEs typically reach Earth one to five days after leaving the Sun. During their propagation, CMEs interact with the solar wind and the interplanetary magnetic field (IMF). As a consequence, slow CMEs are accelerated toward the speed of the solar wind and fast CMEs are decelerated toward the speed of the solar wind. The strongest deceleration or acceleration occurs close to the Sun, but it can continue even beyond Earth orbit (1 AU), which was observed using measurements at Mars and by the Ulysses spacecraft. CMEs faster than about 500 km/s (310 mi/s) eventually drive a shock wave. This happens when the speed of the CME in the frame of reference moving with the solar wind is faster than the local fast magnetosonic speed. Such shocks have been observed directly by coronagraphs in the corona, and are related to type II radio bursts. They are thought to form sometimes as low as 2 R_s (solar radii). They are also closely linked with the acceleration of solar energetic particles.

Related solar observation missions

NASA mission Wind

On 1 November 1994, NASA launched the Wind spacecraft as a solar wind monitor to orbit Earth's L₁ Lagrange point as the interplanetary component of the Global Geospace Science (GGS) Program within the International Solar Terrestrial Physics (ISTP) program. The spacecraft is a spin axis-stabilized satellite that carries eight instruments measuring solar wind particles from thermal to >MeV energies, electromagnetic radiation from DC to 13 MHz radio waves, and gamma-rays. Though the Wind spacecraft is over two decades old, it still provides the highest time, angular, and energy resolution of any of the solar wind monitors. It continues to produce relevant research as its data has contributed to over 150 publications since 2008 alone.

NASA mission STEREO

On 25 October 2006, NASA launched STEREO, two near-identical spacecraft which, from widely separated points in their orbits, are able to produce the first stereoscopic images of CMEs and other solar activity measurements. The spacecraft orbit the Sun at distances similar to that of Earth, with one slightly ahead of Earth and the other trailing. Their separation gradually increased so that after four years they were almost diametrically opposite each other in orbit.

NASA mission Parker Solar Probe

The Parker Solar Probe was launched on 12 August 2018 to measure the mechanisms which accelerate and transport energetic particles i.e. the origins of the solar wind.

History

First traces

The largest recorded geomagnetic perturbation, resulting presumably from a CME, coincided with the first-observed solar flare on 1 September 1859. The resulting solar storm of 1859 is now referred to as the Carrington Event, The flare and the associated sunspots were visible to the naked eye (both as the flare itself appearing on a projection of the Sun on a screen and as an aggregate brightening of the solar disc), and the flare was independently observed by English astronomers R. C. Carrington and R. Hodgson. The geomagnetic storm was observed with the recording magnetograph at Kew Gardens. The same instrument recorded a crochet, an instantaneous perturbation of Earth's ionosphere by ionizing soft X-rays. This could not easily be understood at the time because it predated the discovery of X-rays by Röntgen and the recognition of the ionosphere by Kennelly and Heaviside. The storm took down parts of the recently created US telegraph network, starting fires and shocking some telegraph operators.

Historical records were collected and new observations recorded in annual summaries by the Astronomical Society of the Pacific between 1953 and 1960.

First clear detections

The first detection of a CME as such was made on 14 December 1971, by R. Tousey (1973) of the Naval Research Laboratory using the seventh Orbiting Solar Observatory (OSO-7).^[24] The discovery image (256 × 256 pixels) was collected on a Secondary Electron Conduction (SEC) vidicon tube, transferred to the instrument computer after being digitized to 7 bits. Then it was compressed using a simple run-length encoding scheme and sent down to the ground at 200 bit/s. A full, uncompressed image would take 44 minutes to send down to the ground. The telemetry was sent to ground support equipment (GSE) which built up the image onto Polaroid print. David Roberts, an electronics technician working for NRL who had been responsible for the testing of the SEC-vidicon camera, was in charge of day-to-day operations. He thought that his camera had failed because certain areas of the image were much brighter than normal. But on the next image the bright area had moved away from the Sun and he immediately recognized this as being unusual and took it to his supervisor, Dr. Guenter Brueckner, and then to the solar physics branch head, Dr. Tousey. Earlier observations of coronal transients or even phenomena observed visually during solar eclipses are now understood as essentially the same thing.

1989-present

On 9 March 1989 a coronal mass ejection occurred. On 13 March 1989 a severe geomagnetic storm struck the Earth. It caused power failures in Quebec, Canada and short-wave radio interference.

On 1 August 2010, during solar cycle 24, scientists at the Harvard–Smithsonian Center for Astrophysics (CfA) observed a series of four large CMEs emanating from the Earth-facing hemisphere of the Sun. The initial CME was generated by an eruption on 1 August that was associated with NOAA Active Region 1092, which was large enough to be seen without the aid of a solar telescope. The event produced significant aurorae on Earth three days later.

On 23 July 2012, a massive, and potentially damaging, solar superstorm (solar flare, CME, solar EMP) barely missed Earth, according to NASA.

On 31 August 2012 a CME connected with Earth's magnetic environment, or magnetosphere, with a glancing blow causing aurora to appear on the night of 3 September.^[28][29] Geomagnetic storming reached the G2 (Kp=6) level on NOAA's Space Weather Prediction Center scale of geomagnetic disturbances.

14 October 2014 ICME was photographed by the Sun-watching spacecraft PROBA2 (ESA), Solar and Heliospheric Observatory (ESA/NASA), and Solar Dynamics Observatory (NASA) as it left the Sun, and STEREO-A observed its effects directly at 1 AU. ESA's Venus Express gathered data. The CME reached Mars on 17 October and was observed by the Mars Express, MAVEN, Mars Odyssey, and Mars Science Laboratory missions. On 22 October, at 3.1 AU, it reached comet 67P/Churyumov–Gerasimenko, perfectly aligned with the Sun and Mars, and was observed by Rosetta. On 12 November, at 9.9 AU, it was observed by Cassini at Saturn. The New Horizons spacecraft was at 31.6 AU approaching Pluto when the CME passed three months after the initial eruption, and it may be detectable in the data. Voyager 2 has data that can be interpreted as the passing of the CME, 17 months after. The Curiosity rover's RAD instrument, Mars Odyssey, Rosetta and Cassini showed a sudden decrease in galactic cosmic rays (Forbush decrease) as the CME's protective bubble passed by.

Future risk

According to a report published in 2012 by physicist Pete Riley of Predictive Science Inc., the chance of Earth being hit by a Carrington-class storm between 2012 and 2022 is 12%.

Stellar coronal mass ejections

There have been a small number of CMEs observed on other stars, all of which as of 2016 have been found on M dwarfs. These have been detected by spectroscopy, most often by studying Balmer lines: the material ejected toward the observer causes asymmetry in the blue wing of the line profiles due to Doppler shift. This enhancement can be seen in absorption when it occurs on the stellar disc (the material is cooler than its surrounding), and in emission when it is outside the disc. The observed projected velocities of CMEs range from ≈84 to 5,800 km/s (52 to 3,600 mi/s). Compared to activity on the Sun, CME activity on other stars seems to be far less common.

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Solar storm of 1859

From Wikipedia, the free encyclopedia

 

Sunspots of September 1, 1859, as sketched by Richard Carrington. A and B mark the initial positions of an intensely bright event, which moved over the course of five minutes to C and D before disappearing.

The solar storm of 1859 (also known as the Carrington Event) was a powerful geomagnetic solar storm during solar cycle 10 (1855–1867). A solar coronal mass ejection (CME) hit Earth's magnetosphere and induced one of the largest geomagnetic storms on record, September 1–2, 1859. The associated "white light flare" in the solar photosphere was observed and recorded by British astronomers Richard C. Carrington (1826–1875) and Richard Hodgson (1804–1872). The now-standard unique IAU identifier for this flare is SOL1859-09-01.

A solar storm of this magnitude occurring today would cause widespread disruptions and damage due to extended outages of the electrical grid. The solar storm of 2012 was of similar magnitude, but it passed Earth's orbit without striking the planet.

Carrington flare

From August 28 to September 2, 1859, many sunspots appeared on the Sun. On August 29, southern auroras were observed as far north as Queensland, Australia. Just before noon on September 1, the English amateur astronomers Richard Carrington and Richard Hodgson independently made the first observations of a solar flare.^[6] Carrington and Hodgson compiled independent reports which were published side-by-side in the Monthly Notices of the Royal Astronomical Society, and exhibited their drawings of the event at the November 1859 meeting of the Royal Astronomical Society.

The flare was associated with a major coronal mass ejection (CME) that travelled directly toward Earth, taking 17.6 hours to make the 150 million kilometre (93 million mile) journey. It is believed that the relatively high speed of this CME (typical CMEs take several days to arrive at Earth) was made possible by a prior CME, perhaps the cause of the large aurora event on August 29 that "cleared the way" of ambient solar wind plasma for the Carrington event.

Because of a geomagnetic solar flare effect ("magnetic crochet") observed in the Kew Observatory magnetometer record by Scottish physicist Balfour Stewart and a geomagnetic storm observed the following day, Carrington suspected a solar-terrestrial connection. Worldwide reports on the effects of the geomagnetic storm of 1859 were compiled and published by American mathematician Elias Loomis, which support the observations of Carrington and Stewart.

On September 1–2, 1859, one of the largest recorded geomagnetic storms (as recorded by ground-based magnetometers) occurred. Auroras were seen around the world, those in the northern hemisphere as far south as the Caribbean; those over the Rocky Mountains in the U.S. were so bright that the glow woke gold miners, who began preparing breakfast because they thought it was morning. People in the northeastern United States could read a newspaper by the aurora's light. The aurora was visible as far from the poles as south-central Mexico, Queensland, Cuba, Hawaii, southern Japan and China, and even at lower latitudes very close to the equator, such as in Colombia. Estimates of the storm strength range from −800 nT to −1750 nT.

Telegraph systems all over Europe and North America failed, in some cases giving telegraph operators electric shocks. Telegraph pylons threw sparks. Some telegraph operators could continue to send and receive messages despite having disconnected their power supplies.

On Saturday, September 3, 1859, the Baltimore American and Commercial Advertiser reported:

Those who happened to be out late on Thursday night had an opportunity of witnessing another magnificent display of the auroral lights. The phenomenon was very similar to the display on Sunday night, though at times the light was, if possible, more brilliant, and the prismatic hues more varied and gorgeous. The light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the moon at its full, but had an indescribable softness and delicacy that seemed to envelop everything upon which it rested. Between 12 and 1 o'clock, when the display was at its full brilliancy, the quiet streets of the city resting under this strange light, presented a beautiful as well as singular appearance.

In 1909, an Australian gold miner C.F. Herbert retold his observations in a letter to The Daily News in Perth:

I was gold-digging at Rokewood, about four miles from Rokewood township (Victoria). Myself and two mates looking out of the tent saw a great reflection in the southern heavens at about 7 o'clock p.m., and in about half an hour, a scene of almost unspeakable beauty presented itself, lights of every imaginable color were issuing from the southern heavens, one color fading away only to give place to another if possible more beautiful than the last, the streams mounting to the zenith, but always becoming a rich purple when reaching there, and always curling round, leaving a clear strip of sky, which may be described as four fingers held at arm's length. The northern side from the zenith was also illuminated with beautiful colors, always curling round at the zenith, but were considered to be merely a reproduction of the southern display, as all colors south and north always corresponded. It was a sight never to be forgotten, and was considered at the time to be the greatest aurora recorded... The rationalist and pantheist saw nature in her most exquisite robes, recognising, the divine immanence, immutable law, cause, and effect. The superstitious and the fanatical had dire forebodings, and thought it a foreshadowing of Armageddon and final dissolution.

In June 2013, a joint venture from researchers at Lloyd's of London and Atmospheric and Environmental Research (AER) in the United States used data from the Carrington Event to estimate the current cost of a similar event to the U.S. alone at $0.6–2.6 trillion.

Other evidence and similar events

Ice cores containing thin nitrate-rich layers have been analysed to reconstruct a history of past solar storms predating reliable observations. Researchers state that data from Greenland ice cores show evidence of individual solar-proton events, including the Carrington event. More recent work by the ice core community shows that nitrate spikes are not a result of solar energetic particle events, and, indeed, no consistency is found in cores from Greenland and Antarctica, and nitrate events can be due to terrestrial events, such as burnings, so use of this technique is in doubt.

Less severe storms have occurred in 1921 and 1960, when widespread radio disruption was reported. The March 1989 geomagnetic storm knocked out power across large sections of Quebec. On July 23, 2012 a "Carrington-class" solar superstorm (solar flare, coronal mass ejection, solar EMP) was observed; its trajectory missed Earth in orbit. Information about these observations was first shared publicly by NASA on April 28, 2014.

Carrying capacity

From Wikipedia, the free encyclopedia

The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment. In population biology, carrying capacity is defined as the environment's maximal load, which is different from the concept of population equilibrium. Its effect on population dynamics may be approximated in a logistic model, although this simplification ignores the possibility of overshoot which real systems may exhibit.

Carrying capacity was originally used to determine the number of animals that could graze on a segment of land without destroying it. Later, the idea was expanded to more complex populations, like humans. For the human population, more complex variables such as sanitation and medical care are sometimes considered as part of the necessary establishment. As population density increases, birth rate often increases and death rate typically decreases. The difference between the birth rate and the death rate is the "natural increase". The carrying capacity could support a positive natural increase or could require a negative natural increase. Thus, the carrying capacity is the number of individuals an environment can support without significant negative impacts to the given organism and its environment. Below carrying capacity, populations typically increase, while above, they typically decrease. A factor that keeps population size at equilibrium is known as a regulating factor.

Population size decreases above carrying capacity due to a range of factors depending on the species concerned, but can include insufficient space, food supply, or sunlight. The carrying capacity of an environment may vary for different species and may change over time due to a variety of factors including: food availability, water supply, environmental conditions and living space. The origins of the term "carrying capacity" are uncertain, with researchers variously stating that it was used "in the context of international shipping" or that it was first used during 19th-century laboratory experiments with micro-organisms. A recent review finds the first use of the term in an 1845 report by the US Secretary of State to the US Senate.

Humans

Several estimates of the carrying capacity have been made with a wide range of population numbers. A 2001 UN report said that two-thirds of the estimates fall in the range of 4 billion to 16 billion with unspecified standard errors, with a median of about 10 billion. More recent estimates are much lower, particularly if non-renewable resource depletion and increased consumption are considered. Changes in habitat quality or human behavior at any time might increase or reduce carrying capacity. In the view of Paul and Anne Ehrlich, "for earth as a whole (including those parts of it we call Australia and the United States), human beings are far above carrying capacity today."  (DJS:  For what it's worth, I disagree; and Ehrlich has been disastrously wrong in the past about this.)

The application of the concept of carrying capacity for the human population has been criticized for not successfully capturing the multi-layered processes between humans and the environment, which have a nature of fluidity and non-equilibrium, and for sometimes being employed in a blame-the-victim framework.

Supporters of the concept argue that the idea of a limited carrying capacity is just as valid applied to humans as when applied to any other species. Animal population size, living standards, and resource depletion vary, but the concept of carrying capacity still applies. The number of people is not the only factor in the carrying capacity of Earth. Waste and over-consumption, especially by wealthy and near-wealthy people and nations, are also putting significant strain on the environment together with human overpopulation. Population and consumption together appear to be at the core of many human problems. Some of these issues have been studied by computer simulation models such as World3. When scientists talk of global change today, they are usually referring to human-caused changes in the environment of sufficient magnitude eventually to reduce the carrying capacity of much of Earth (as opposed to local or regional areas) to support organisms, especially Homo sapiens.

Factors that govern carrying capacity

Some aspects of a system's carrying capacity may involve matters such as available supplies of food, water, raw materials, and/or other similar resources. In addition, there are other factors that govern carrying capacity which may be less instinctive or less intuitive in nature, such as ever-increasing and/or ever-accumulating levels of wastes, damage, and/or eradication of essential components of any complex functioning system. Eradication of, for example, large or critical portions of any complex system (envision a space vehicle, for instance, or an airplane, or an automobile, or computer code, or the body components of a living vertebrate) can interrupt essential processes and dynamics in ways that induce systems failures or unexpected collapse. (As an example of these latter factors, the "carrying capacity" of a complex system such an airplane is more than a matter of available food, or water, or available seating, but also reflects total weight carried and presumes that its passengers do not damage, destroy, or eradicate parts, doors, windows, wings, engine parts, fuel, and oil, and so forth.) Thus, on a global scale, food and similar resources may affect planetary carrying capacity to some extent so long as Earth's human passengers do not dismantle, eradicate, or otherwise destroy critical biospheric life-support capacities for essential processes of self-maintenance, self-perpetuation, and self-repair.

Thus, carrying capacity interpretations that focus solely on resource limitations alone (such as food) may neglect wider functional factors. If the humans neither gain nor lose weight in the long-term, the calculation is fairly accurate. If the quantity of food is invariably equal to the "Y" amount, carrying capacity has been reached. Humans, with the need to enhance their reproductive success (see Richard Dawkins' The Selfish Gene), understand that food supply can vary and also that other factors in the environment can alter humans' need for food. A house, for example, might mean that one does not need to eat as much to stay warm as one otherwise would. Over time, monetary transactions have replaced barter and local production, and consequently modified local human carrying capacity. However, purchases also impact regions thousands of miles away. For example, carbon dioxide from an automobile travels to the upper atmosphere. This led Paul R. Ehrlich to develop the I = PAT equation.

I = P ∙ A ∙ T

where:

I is the impact on the environment resulting from consumption

P is the population number

A is the consumption per capita (affluence)

T is the technology factor

This is a graph of the population due to the logistic curve model. When the population is above the carrying capacity it decreases, and when it is below the carrying capacity it increases.

An important model related to carrying capacity (K), is the logistic, growth curve. The logistic growth curve depicts a more realistic version of how population growth rate, available resources, and the carrying capacity are inter-connected. As illustrated in the logistic growth curve model, when the population size is small and there are many resources available, population over-time increases and so does the growth rate. However, as population size nears the carrying capacity and resources become limited, the growth rate decreases and population starts to level out at K. This model is based on the assumption that carrying capacity does not change. One thing to keep in mind, however, is that carrying capacity of a population can increase or decrease and there are various factors that affect it. For instance, an increase in the population growth can lead to over-exploitation of necessary natural resources and therefore decrease the overall carrying capacity of that environment.

Technology can play a role in the dynamics of carrying capacity and while this can sometimes be positive, in other cases its influence can be problematic. For example, it has been suggested that in the past that the Neolithic revolution increased the carrying capacity of the world relative to humans through the invention of agriculture. In a similar way, viewed from the perspective of foods, the use of fossil fuels has been alleged to artificially increase the carrying capacity of the world by the use of stored sunlight, even though that food production does not guarantee the capacity of the Earth's climatic and biospheric life-support systems to withstand the damage and wastes arising from such fossil fuels. However, such interpretations presume the continued and uninterrupted functioning of all other critical components of the global system. It has also been suggested that other technological advances that have increased the carrying capacity of the world relative to humans are: polders, fertilizer, composting, greenhouses, land reclamation, and fish farming. In an adverse way, however, many technologies enable economic entities and individual humans to inflict far more damage and eradication, far more quickly and efficiently on a wider-scale than ever. Examples include machine guns, chainsaws, earth-movers, and the capacity of industrialized fishing fleets to capture and harvest targeted fish species faster than the fish themselves can reproduce are examples of such problematic outcomes of technology.

Agricultural capability on Earth expanded in the last quarter of the 20th century. But now there are many projections of a continuation of the decline in world agricultural capability (and hence carrying capacity) which began in the 1990s. Most conspicuously, China's food production is forecast to decline by 37% by the last half of the 21st century, placing a strain on the entire carrying capacity of the world, as China's population could expand to about 1.5 billion people by the year 2050. This reduction in China's agricultural capability (as in other world regions) is largely due to the world water crisis and especially due to mining groundwater beyond sustainable yield, which has been happening in China since the mid-20th century.

Lester Brown of the Earth Policy Institute, has said: "It would take 1.5 Earths to sustain our present level of consumption. Environmentally, the world is in an overshoot mode."  ^{(DJS:  Again, disagree.)}

Ecological footprint

One way to estimate human demand compared to ecosystem's carrying capacity is "ecological footprint" accounting. Rather than speculating about future possibilities and limitations imposed by carrying capacity constraints, Ecological Footprint accounting provides empirical, non-speculative assessments of the past. It compares historic regeneration rates, biocapacity, against historical human demand, ecological footprint, in the same year. One result shows that humanity's demand footprint in 1999 exceeded the planet's bio-capacity by >20%. However, this measurement does not take into account the depletion of the actual fossil fuels, "which would result in a carbon Footprint many hundreds of times higher than the current calculation."

There is also concern of the ability of countries around to globe to decrease and maintain their ecological footprints. Holden and Linnerud, scholars working to provide a better framework that adequately judge sustainability development and maintenance in policy making, have generated a diagram that measures the global position of different countries around the world, which shows a linear relation between GDP PPP and ecological foot print in 2007. Possible answers to the question of where we are as individual countries attempting to reach sustainability and development methods to reduce ecological foot print. According to the Figure 1 diagram, the United States had the largest ecological foot print per capita along with Norway, Sweden, and Austria, in comparison to Cuba, Bangladesh, and Korea.

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Overexploitation

From Wikipedia, the free encyclopedia

 

Atlantic cod stocks were severely overexploited in the 1970s and 1980s, leading to their abrupt collapse in 1992.

 

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. Ecologists use the term to describe populations that are harvested at a rate that is unsustainable, 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. 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.

History

When the giant flightless birds called moa were overexploited to the point of extinction, the giant Haast's eagle that preyed on them also became extinct.

Concern about overexploitation is relatively recent, though overexploitation itself is not a new phenomenon. It has been observed for millennia. For example, ceremonial cloaks worn by the Hawaiian kings were made from the mamo bird; a single cloak used the feathers of 70,000 birds of this now-extinct species. The dodo, a flightless bird from Mauritius, is another well-known example of overexploitation. As with many island species, it was naive about certain predators, allowing humans to approach and kill it with ease.

From the earliest of times, hunting has been an important human activity as a means of survival. There is a whole history of overexploitation in the form of overhunting. The overkill hypothesis (Quaternary extinction events) explains why the megafaunal extinctions occurred within a relatively short period of time. This can be traced with human migration. The most convincing evidence of this theory is that 80% of the North American large mammal species disappeared within 1000 years of the arrival of humans on the western hemisphere continents. The fastest ever recorded extinction of megafauna occurred in New Zealand, where by 1500 AD, just 200 years after settling the islands, ten species of the giant moa birds were hunted to extinction by the Māori. A second wave of extinctions occurred later with European settlement.

In more recent times, overexploitation has resulted in the gradual emergence of the concepts of sustainability and sustainable development, which has built on other concepts, such as sustainable yield, eco-development and deep ecology.

Overview

Overexploitation doesn't necessarily lead to the destruction of the resource, nor is it necessarily unsustainable. However, depleting the numbers or amount of the resource can change its quality. For example, footstool palm is a wild palm tree found in Southeast Asia. Its leaves are used for thatching and food wrapping, and overharvesting has resulted in its leaf size becoming smaller.

Tragedy of the commons

Cows on Selsley Common. The tragedy of the commons is a useful parable for understanding how overexploitation can occur.

The tragedy of the commons refers to a dilemma described in an article by that name written by Garrett Hardin and first published in the journal Science in 1968.

Central to Hardin's essay is an example which is a useful parable for understanding how overexploitation can occur. This example was first sketched in an 1833 pamphlet by William Forster Lloyd, as a hypothetical and simplified situation based on medieval land tenure in Europe, of herders sharing a common on which they are each entitled to let their cows graze. In Hardin's example, it is in each herder's interest to put each succeeding cow he acquires onto the land, even if the carrying capacity of the common is exceeded and it is temporarily or permanently damaged for all as a result. The herder receives all of the benefits from an additional cow, while the damage to the common is shared by the entire group. If all herders make this individually rational economic decision, the common will be overexploited or even destroyed to the detriment of all. However, since all herders reach the same rational conclusion, overexploitation in the form of overgrazing occurs, with immediate losses, and the pasture may be degraded to the point where it gives very little return.

"Therein is the tragedy. Each man is locked into a system that compels him to increase his herd without limit—in a world that is limited. Ruin is the destination toward which all men rush, each pursuing his own interest in a society that believes in the freedom of the commons." (Hardin, 1968)

In the course of his essay, Hardin develops the theme, drawing in many examples of latter day commons, such as national parks, the atmosphere, oceans, rivers and fish stocks. The example of fish stocks had led some to call this the "tragedy of the fishers". A major theme running through the essay is the growth of human populations, with the Earth's finite resources being the general common.
The tragedy of the commons has intellectual roots tracing back to Aristotle, who noted that "what is common to the greatest number has the least care bestowed upon it", as well as to Hobbes and his Leviathan. The opposite situation to a tragedy of the commons is sometimes referred to as a tragedy of the anticommons: a situation in which rational individuals, acting separately, collectively waste a given resource by underutilizing it.

The tragedy of the commons can be avoided if it is appropriately regulated. Hardin's use of "commons" has frequently been misunderstood, leading Hardin to later remark that he should have titled his work "The tragedy of the unregulated commons".

Fisheries

The Atlantic bluefin tuna is currently seriously overexploited. Scientists say 7,500 tons annually is the sustainable limit, yet the fishing industry continue to harvest 60,000 tons.

In wild fisheries, overexploitation or overfishing occurs when a fish stock has been fished down "below the size that, on average, would support the long-term maximum sustainable yield of the fishery". However, overexploitation can be sustainable.

When a fishery starts harvesting fish from a previously unexploited stock, the biomass of the fish stock will decrease, since harvesting means fish are being removed. For sustainability, the rate at which the fish replenish biomass through reproduction must balance the rate at which the fish are being harvested. If the harvest rate is increased, then the stock biomass will further decrease. At a certain point, the maximum harvest yield that can be sustained will be reached, and further attempts to increase the harvest rate will result in the collapse of the fishery. This point is called the maximum sustainable yield, and in practice, usually occurs when the fishery has been fished down to about 30% of the biomass it had before harvesting started.

It is possible to fish the stock down further to, say, 15% of the pre-harvest biomass, and then adjust the harvest rate so the biomass remains at that level. In this case, the fishery is sustainable, but is now overexploited, because the stock has been run down to the point where the sustainable yield is less than it could be.

Fish stocks are said to "collapse" if their biomass declines by more than 95 percent of their maximum historical biomass. Atlantic cod stocks were severely overexploited in the 1970s and 1980s, leading to their abrupt collapse in 1992. Even though fishing has ceased, the cod stocks have failed to recover. The absence of cod as the apex predator in many areas has led to trophic cascades.

About 25% of world fisheries are now overexploited to the point where their current biomass is less than the level that maximizes their sustainable yield. These depleted fisheries can often recover if fishing pressure is reduced until the stock biomass returns to the optimal biomass. At this point, harvesting can be resumed near the maximum sustainable yield.

The tragedy of the commons can be avoided within the context of fisheries if fishing effort and practices are regulated appropriately by fisheries management. One effective approach may be assigning some measure of ownership in the form of individual transferable quotas (ITQs) to fishermen. In 2008, a large scale study of fisheries that used ITQs, and ones that didn't, provided strong evidence that ITQs help prevent collapses and restore fisheries that appear to be in decline.

Water resources

Overexploitation of groundwater from an aquifer can result in a peak water curve.

 

Water resources, such as lakes and aquifers, are usually renewable resources which naturally recharge (the term fossil water is sometimes used to describe aquifers which don't recharge). Overexploitation occurs if a water resource, such as the Ogallala Aquifer, is mined or extracted at a rate that exceeds the recharge rate, that is, at a rate that exceeds the practical sustained yield. Recharge usually comes from area streams, rivers and lakes. An aquifer which has been overexploited is said to be overdrafted or depleted. Forests enhance the recharge of aquifers in some locales, although generally forests are a major source of aquifer depletion. Depleted aquifers can become polluted with contaminants such as nitrates, or permanently damaged through subsidence or through saline intrusion from the ocean.

This turns much of the world's underground water and lakes into finite resources with peak usage debates similar to oil. These debates usually centre around agriculture and suburban water usage but generation of electricity from nuclear energy or coal and tar sands mining is also water resource intensive. A modified Hubbert curve applies to any resource that can be harvested faster than it can be replaced. Though Hubbert's original analysis did not apply to renewable resources, their overexploitation can result in a Hubbert-like peak. This has led to the concept of peak water.

Forest resources

Clear cutting of old growth forests in Canada.

Forests are overexploited when they are logged at a rate faster than reforestation takes place. Reforestation competes with other land uses such as food production, livestock grazing, and living space for further economic growth. Historically utilization of forest products, including timber and fuel wood, have played a key role in human societies, comparable to the roles of water and cultivable land. Today, developed countries continue to utilize timber for building houses, and wood pulp for paper. In developing countries almost three billion people rely on wood for heating and cooking. Short-term economic gains made by conversion of forest to agriculture, or overexploitation of wood products, typically leads to loss of long-term income and long term biological productivity. West Africa, Madagascar, Southeast Asia and many other regions have experienced lower revenue because of overexploitation and the consequent declining timber harvests.

Biodiversity

The rich diversity of marine life inhabiting coral reefs attracts bioprospectors. Many coral reefs are overexploited; threats include coral mining, cyanide and blast fishing, and overfishing in general.

Overexploitation is one of the main threats to global biodiversity. Other threats include pollution, introduced and invasive species, habitat fragmentation, habitat destruction, uncontrolled hybridization, global warming, ocean acidification and the driver behind many of these, human overpopulation.

One of the key health issues associated with biodiversity is drug discovery and the availability of medicinal resources. A significant proportion of drugs are natural products derived, directly or indirectly, from biological sources. Marine ecosystems are of particular interest in this regard. However unregulated and inappropriate bioprospecting could potentially lead to overexploitation, ecosystem degradation and loss of biodiversity.

Endangered species

It is not just humans that overexploit resources. Overgrazing can be caused by native fauna, as shown in the upper right. However, past human overexploitation (leading to elimination of some predators) may be behind the situation.

Overexploitation threatens one-third of endangered vertebrates, as well as other groups. Excluding edible fish, the illegal trade in wildlife is valued at $10 billion per year. Industries responsible for this include the trade in bushmeat, the trade in Chinese medicine, and the fur trade. The Convention for International Trade in Endangered Species of Wild Fauna and Flora, or CITES was set up in order to control and regulate the trade in endangered animals. It currently protects, to a varying degree, some 33,000 species of animals and plants. It is estimated that a quarter of the endangered vertebrates in the United States of America and half of the endangered mammals is attributed to overexploitation.

All living organisms require resources to survive. Overexploitation of these resources for protracted periods can deplete natural stocks to the point where they are unable to recover within a short time frame. Humans have always harvested food and other resources they have needed to survive. Human populations, historically, were small, and methods of collection limited to small quantities. With an exponential increase in human population, expanding markets and increasing demand, combined with improved access and techniques for capture, are causing the exploitation of many species beyond sustainable levels. In practical terms, if continued, it reduces valuable resources to such low levels that their exploitation is no longer sustainable and can lead to the extinction of a species, in addition to having dramatic, unforeseen effects, on the ecosystem. Overexploitation often occurs rapidly as markets open, utilising previously untapped resources, or locally used species.

The Carolina parakeet was hunted to extinction.

Today, overexploitation and misuse of natural resources is an ever-present threat for species richness. This is more prevalent when looking at island ecology and the species that inhabit them, as islands can be viewed as the world in miniature. Island endemic populations are more prone to extinction from overexploitation, as they often exist at low densities with reduced reproductive rates. A good example of this are island snails, such as the Hawaiian Achatinella and the French Polynesian Partula. Achatinelline snails have 15 species listed as extinct and 24 critically endangered while 60 species of partulidae are considered extinct with 14 listed as critically endangered. The WCMC have attributed over-collecting and very low lifetime fecundity for the extreme vulnerability exhibited among these species.

As another example, when the humble hedgehog was introduced to the Scottish island of Uist, the population greatly expanded and took to consuming and overexploiting shorebird eggs, with drastic consequences for their breeding success. Twelve species of avifauna are affected, with some species numbers being reduced by 39%.

Where there is substantial human migration, civil unrest, or war, controls may no longer exist. With civil unrest, for example in the Congo and Rwanda, firearms have become common and the breakdown of food distribution networks in such countries leaves the resources of the natural environment vulnerable. Animals are even killed as target practice, or simply to spite the government. Populations of large primates, such as gorillas and chimpanzees, ungulates and other mammals, may be reduced by 80% or more by hunting, and certain species may be eliminated altogether. This decline has been called the bushmeat crisis.

Overall, 50 bird species that have become extinct since 1500 (approximately 40% of the total) have been subject to overexploitation, including:

• Great Auk – the penguin-like bird of the north, was hunted for its feathers, meat, fat and oil.
• Carolina parakeet – The only parrot species native to the eastern United States, was hunted for crop protection and its feathers.

Other species affected by overexploitation include:

• The international trade in fur: chinchilla, vicuña, giant otter and numerous cat species
• Insect collectors: butterflies
• Horticulturists: New Zealand mistletoe (Trilepidia adamsii), orchids, cacti and many other plant species
• Shell collectors: Marine molluscs
• Aquarium hobbyists: tropical fish
• Chinese medicine: bears, tigers, rhinos, seahorses, Asian black bear and saiga antelope
• Novelty pets: snakes, parrots, primates and big cats

Cascade effects

Overexploiting sea otters resulted in cascade effects which destroyed kelp forest ecosystems.

Overexploitation of species can result in knock-on or cascade effects. This can particularly apply if, through overexploitation, a habitat loses its apex predator. Because of the loss of the top predator, a dramatic increase in their prey species can occur. In turn, the unchecked prey can then overexploit their own food resources until population numbers dwindle, possibly to the point of extinction.
A classic example of cascade effects occurred with sea otters. Starting before the 17th century and not phased out until 1911, sea otters were hunted aggressively for their exceptionally warm and valuable pelts, which could fetch up to $2500 US. This caused cascade effects through the kelp forest ecosystems along the Pacific Coast of North America.

One of the sea otters’ primary food sources is the sea urchin. When hunters caused sea otter populations to decline, an ecological release of sea urchin populations occurred. The sea urchins then overexploited their main food source, kelp, creating urchin barrens, areas of seabed denuded of kelp, but carpeted with urchins. No longer having food to eat, the sea urchin became locally extinct as well. Also, since kelp forest ecosystems are homes to many other species, the loss of the kelp caused other cascade effects of secondary extinctions.

In 1911, when only one small group of 32 sea otters survived in a remote cove, an international treaty was signed to prevent further exploitation of the sea otters. Under heavy protection, the otters multiplied and repopulated the depleted areas, which slowly recovered. More recently, with declining numbers of fish stocks, again due to overexploitation, killer whales have experienced a food shortage and have been observed feeding on sea otters, again reducing their numbers.