Eugenics

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Eugenics

1930s exhibit by the Eugenics Society. Some of the signs read "Healthy and Unhealthy Families", "Heredity as the Basis of Efficiency", and "Marry Wisely".

Eugenics is a set of largely discredited beliefs and practices that aim to improve the genetic quality of a human population. Historically, eugenicists have attempted to alter the frequency of various human phenotypes by inhibiting the fertility of those considered inferior, or promoting that of those considered superior.

The contemporary history of eugenics began in the late 19th century, when a popular eugenics movement emerged in the United Kingdom, and then spread to many countries, including the United States, Canada, Australia, and most European countries (e.g., Sweden and Germany).

Historically, the idea of eugenics has been used to argue for a broad array of practices ranging from prenatal care for mothers deemed genetically desirable to the forced sterilisation and murder of those deemed unfit. To population geneticists, the term has included the avoidance of inbreeding without altering allele frequencies; for example, British-Indian scientist J. B. S. Haldane wrote in 1940 that "the motor bus, by breaking up inbred village communities, was a powerful eugenic agent." Debate as to what qualifies as eugenics continues today.

A progressive social movement promoting eugenics had originated in the 19th century, with diverse support, but by the mid 20th century the term was closely associated with scientific racism and authoritarian coercion. With modern medical genetics, genetic testing and counselling have become common, and new or liberal eugenics rejects coercive programmes in favour of individual parental choice.

Common distinctions

Lester Frank Ward wrote the early paper: "Eugenics, Euthenics and Eudemics", making yet further distinctions.

Eugenic programmes included both positive measures, such as encouraging individuals deemed particularly "fit" to reproduce, and negative measures, such as marriage prohibitions and forced sterilisation of people deemed unfit for reproduction.

Positive eugenics is aimed at encouraging reproduction among the genetically advantaged, for example, the intelligent, the healthy, and the successful. Possible approaches include financial and political stimuli, targeted demographic analyses, in vitro fertilisation, egg transplants, and cloning. Negative eugenics aimed to eliminate, through sterilisation or segregation, those deemed physically, mentally, or morally undesirable. This includes abortions, sterilisation, and other methods of family planning. Both positive and negative eugenics can be coercive; in Nazi Germany, for example, abortion was illegal for women deemed by the state to be superior.

As opposed to "euthenics"

See also: Nature-nurture debate

 

Ellen Swallow Richards (top), the first female student and instructor at MIT, was one of the first to use the term, while Julia Clifford Lathrop (bottom) continued to promote it in the form of an interdisciplinary academic program later to be mostly absorbed into the field of home economics.

Euthenics (/juːˈθɛnɪks/) is the study of the improvement of human functioning and well-being by the improvement of living conditions. "Improvement" is conducted by altering external factors such as education and the controllable environments, including environmentalism, education regarding employment, home economics, sanitation, and housing, as well as the prevention and removal of contagious disease and parasites.

In a New York Times article dated May 23, 1926, Rose Field notes of the description, "the simplest [is] efficient living". It is also described as "a right to environment", commonly as dual to a "right of birth" that correspondingly falls under the purview of eugenics.

Euthenics is normally not interpreted as having anything to do with changing the composition of the human gene pool by definition, although everything that affects society has some effect on who reproduces and who does not.

The influential historian of education Abraham Flexner questions its scientific value in stating:

[T]he “science” is artificially pieced together of bits of mental hygiene, child guidance, nutrition, speech development and correction, family problems, wealth consumption, food preparation, household technology, and horticulture. A nursery school and a school for little children are also included. The institute is actually justified in an official publication by the profound question of a girl student who is reported as asking, “What is the connection of Shakespeare with having a baby?” The Vassar Institute of Euthenics bridges this gap!

Eugenicist Charles Benedict Davenport noted in his article "Euthenics and Eugenics," reprinted in Popular Science Monthly:

Thus the two schools of euthenics and eugenics stand opposed, each viewing the other unkindly. Against eugenics it is urged that it is a fatalistic doctrine and deprives life of the stimulus toward effort. Against euthenics the other side urges that it demands an endless amount of money to patch up conditions in the vain effort to get greater efficiency. Which of the two doctrines is true?

The thoughtful mind must concede that, as is so often the case where doctrines are opposed, each view is partial, incomplete and really false. The truth does not exactly lie between the doctrines; it comprehends them both.

[...] [I]n the generations to come, the teachings and practice of euthenics [...] [may] yield greater result because of the previous practice of the principles of eugenics.

Along similar lines argued psychologist and early intelligence researcher Edward L. Thorndike some two years later for an understanding that better integrates eugenic study:

The more rational the race becomes, the better roads, ships, tools, machines, foods, medicines and the like it will produce to aid itself, though it will need them less. The more sagacious and just and humane the original nature that is bred into man, the better schools, laws, churches, traditions and customs it will fortify itself by. There is no so certain and economical a way to improve man's environment as to improve his nature.

Historical eugenics

Main article: History of eugenics

Ancient and medieval origins

See also: Sparta § Birth and death

Giuseppe Diotti's The selection of the infant Spartans (1840)

In ancient Sparta, according to Plutarch (fl. 50 to 120 CE), the council of elders (the Gerousia) inspected every proper citizen's child and determined whether or not the child was fit to live. A child deemed unfit was allegedly thrown into a chasm. Plutarch's account is the sole historical source for the Spartan practice of infanticide motivated by eugenics. While ancient Greeks practiced infanticide, no contemporary sources support Plutarch's claims of infanticide on eugenic grounds. In 2007, the tradition of dumping infants near Mount Taygete was called into question due to a lack of physical evidence: anthropologist Theodoros Pitsios' research of the site found only bodies ranging in age from 18 to 35 years.

Plato's political philosophy included the belief that the state should cautiously monitor and control human reproduction through selective breeding.

According to Tacitus (c. 56 – c. 120), a Roman of the Imperial Period, the Germanic tribes of his day killed any member of their community they deemed cowardly, un-warlike or "stained with abominable vices", usually by drowning them in swamps. Modern historians regard Tacitus' ethnographic writing as unreliable in such details.

Academic origins

See also: Galton Laboratory and Eugenics Record Office

Francis Galton (1822–1911) was a British polymath who coined the term "eugenics"

The term eugenics and its modern field of study were first formulated by Francis Galton in 1883, directly drawing on the recent work delineating natural selection by his half-cousin Charles Darwin. He published his observations and conclusions chiefly in his influential book Inquiries into Human Faculty and Its Development. Galton himself defined it as "the study of all agencies under human control which can improve or impair the racial quality of future generations". The first to systematically apply Darwinism theory to human relations, Galton believed that various desirable human qualities were also hereditary ones, although Darwin strongly disagreed with this elaboration of his theory.

Eugenics became an academic discipline at many colleges and universities and received funding from various sources. Organisations were formed to win public support for and to sway opinion towards responsible eugenic values in parenthood, including the British Eugenics Education Society of 1907 and the American Eugenics Society of 1921. Both sought support from leading clergymen and modified their message to meet religious ideals. In 1909, the Anglican clergymen William Inge and James Peile both wrote for the Eugenics Education Society. Inge was an invited speaker at the 1921 International Eugenics Conference, which was also endorsed by the Roman Catholic Archbishop of New York Patrick Joseph Hayes.

Three International Eugenics Conferences presented a global venue for eugenicists, with meetings in 1912 in London, and in 1921 and 1932 in New York City. Eugenic policies in the United States were first implemented by state-level legislators in the early 1900s. Eugenic policies also took root in France, Germany, and Great Britain. Later, in the 1920s and 1930s, the eugenic policy of sterilising certain mental patients was implemented in other countries including Belgium, Brazil, Canada, Japan and Sweden.

Frederick Osborn's 1937 journal article "Development of a Eugenic Philosophy" framed eugenics as a social philosophy—a philosophy with implications for social order. That definition is not universally accepted. Osborn advocated for higher rates of sexual reproduction among people with desired traits ("positive eugenics") or reduced rates of sexual reproduction or sterilisation of people with less-desired or undesired traits ("negative eugenics").

In addition to being practiced in a number of countries, eugenics was internationally organised through the International Federation of Eugenics Organisations. Its scientific aspects were carried on through research bodies such as the Kaiser Wilhelm Institute of Anthropology, Human Heredity, and Eugenics, the Cold Spring Harbor Carnegie Institution for Experimental Evolution, and the Eugenics Record Office. Politically, the movement advocated measures such as sterilisation laws. In its moral dimension, eugenics rejected the doctrine that all human beings are born equal and redefined moral worth purely in terms of genetic fitness. Its racist elements included pursuit of a pure "Nordic race" or "Aryan" genetic pool and the eventual elimination of "unfit" races.

Many leading British politicians subscribed to the theories of eugenics. Winston Churchill supported the British Eugenics Society and was an honorary vice president for the organisation. Churchill believed that eugenics could solve "race deterioration" and reduce crime and poverty.

As a social movement, eugenics reached its greatest popularity in the early decades of the 20th century, when it was practiced around the world and promoted by governments, institutions, and influential individuals. Many countries enacted various eugenics policies, including: genetic screenings, birth control, promoting differential birth rates, marriage restrictions, segregation (both racial segregation and sequestering the mentally ill), compulsory sterilisation, forced abortions or forced pregnancies, ultimately culminating in genocide. By 2014, gene selection (rather than "people selection") was made possible through advances in genome editing, leading to what is sometimes called new eugenics, also known as "neo-eugenics", "consumer eugenics", or "liberal eugenics"; which focuses on individual freedom and allegedly pulls away from racism, sexism or a focus on intelligence.

Early opposition

Early critics of the philosophy of eugenics included the American sociologist Lester Frank Ward, the English writer G. K. Chesterton, and Scottish tuberculosis pioneer and author Halliday Sutherland. Ward's 1913 article "Eugenics, Euthenics, and Eudemics", Chesterton's 1917 book Eugenics and Other Evils, and Franz Boas' 1916 article "Eugenics" (published in The Scientific Monthly) were all harshly critical of the rapidly growing movement.

Several biologists were also antagonistic to the eugenics movement, including Lancelot Hogben. Other biologists who were themselves eugenicists, such as J. B. S. Haldane and R. A. Fisher, however, also expressed scepticism in the belief that sterilisation of "defectives" (i.e. a purely negative eugenics) would lead to the disappearance of undesirable genetic traits.

Among institutions, the Catholic Church opposes sterilisation for eugenic purposes. Attempts by the Eugenics Education Society to persuade the British government to legalise voluntary sterilisation were opposed by Catholics and by the Labour Party. The American Eugenics Society initially gained some Catholic supporters, but Catholic support declined following the 1930 papal encyclical Casti connubii. In this, Pope Pius XI explicitly condemned sterilisation laws: "Public magistrates have no direct power over the bodies of their subjects; therefore, where no crime has taken place and there is no cause present for grave punishment, they can never directly harm, or tamper with the integrity of the body, either for the reasons of eugenics or for any other reason."

The eugenicists' political successes in Germany and Scandinavia were not at all matched in such countries as Poland and Czechoslovakia, even though measures had been proposed there, largely because of the Catholic church's moderating influence.

Eugenic feminism

Marie Stopes in her laboratory, 1904

Eugenic feminism was a current of the women's suffrage movement which overlapped with eugenics. Originally coined by the Lebanese-British physician and vocal eugenicist Caleb Saleeby, the term has since been applied to summarize views held by prominent feminists of Great Britain and the United States. Some early suffragettes in Canada, especially a group known as The Famous Five, also pushed for various eugenic policies.

Eugenic feminists argued that if women were provided with more rights and equality, the deteriorating characteristics of a given race could be averted.

North American eugenics

American eugenicists generally pursued more public-facing work and accordingly became widely known for their racism in particular. Along these lines, they were often harshly criticised by their British counterparts.

 

While its American practice was ostensibly about improving genetic quality, it has been argued that eugenics was more about preserving the position of the dominant groups in the population. Scholarly research has determined that people who found themselves targets of the eugenics movement were those who were seen as unfit for society—the poor, the disabled, the mentally ill, and specific communities of color—and a disproportionate number of those who fell victim to eugenicists' sterilization initiatives were women who were identified as African American, Asian American, or Native American. As a result, the United States' eugenics movement is now generally associated with racist and nativist elements, as the movement was to some extent a reaction to demographic and population changes, as well as concerns over the economy and social well-being, rather than scientific genetics.

In Mexico

Following the Mexican Revolution, the eugenics movement gained prominence in Mexico. Seeking to change the genetic make-up of the country's population, proponents of eugenics in Mexico focused primarily on rebuilding the population, creating healthy citizens, and ameliorating the effects of perceived social ills such as alcoholism, prostitution, and venereal diseases. Mexican eugenics, at its height in the 1930s, influenced the state's health, education, and welfare policies.

Mexican elites adopted eugenic thinking and raised it under the banner of “the Great Mexican family” (Spanish: la gran familia mexicana).

Unlike in other countries, the eugenics movements in Latin America were largely founded on the idea of neo-Lamarckian eugenics. Neo-Lamarckian eugenics stated that the outside effects experienced by an organism, throughout its lifetime, changed its genetics, permanently, allowing the organism to pass acquired traits onto its offspring. In the Neo-Lamarckian genetic framework, activities, such as prostitution and alcoholism, could result in the degeneration of future generations, amplifying fears about the effects of certain social ills. However, the supposed genetic malleability also offered hope, to certain Latin American eugenicists, as social reform would have the ability to transform the population, more permanently.

Nazism and the decline of eugenics

See also: Nazi eugenics, Racial hygiene, Life unworthy of life, and Scientific racism

Schloss Hartheim, a former centre for Nazi Germany's Aktion T4 campaign

The reputation of eugenics started to decline in the 1930s, a time when Ernst Rüdin used eugenics as a justification for the racial policies of Nazi Germany. Adolf Hitler had praised and incorporated eugenic ideas in Mein Kampf in 1925 and emulated eugenic legislation for the sterilisation of "defectives" that had been pioneered in the United States once he took power. Some common early 20th century eugenics methods involved identifying and classifying individuals and their families. This included racial groups (such as the Roma and Jews in Nazi Germany), the poor, mentally ill, blind, deaf, developmentally disabled, promiscuous women, and homosexuals as "degenerate" or "unfit". This led to segregation, institutionalisation, sterilisation, and mass murder. The Nazi policy of identifying German citizens deemed unfit and then systematically murdering them with poison gas, referred to as the Aktion T4 campaign, paved the way for the Holocaust.

"All practices aimed at eugenics, any use of the human body or any of its parts for financial gain, and human cloning shall be prohibited."

Hungarian Constitution

By the end of World War II, many eugenics laws were abandoned, having become associated with Nazi Germany. H. G. Wells, who had called for "the sterilisation of failures" in 1904, stated in his 1940 book The Rights of Man: Or What Are We Fighting For? that among the human rights, which he believed should be available to all people, was "a prohibition on mutilation, sterilisation, torture, and any bodily punishment". After World War II, the practice of "imposing measures intended to prevent births within [a national, ethnical, racial or religious] group" fell within the definition of the new international crime of genocide, set out in the Convention on the Prevention and Punishment of the Crime of Genocide. The Charter of Fundamental Rights of the European Union also proclaims "the prohibition of eugenic practices, in particular those aiming at selection of persons".

In Singapore

Main article: Population control in Singapore § Demographic transition and the Graduate Mothers Scheme

Lee Kuan Yew, the founding father of Singapore, actively promoted eugenics as late as 1983. In 1984, Singapore began providing financial incentives to highly educated women to encourage them to have more children. For this purpose was introduced the "Graduate Mother Scheme" that incentivised graduate women to get married as much as the rest of their populace. The incentives were extremely unpopular and regarded as eugenic, and were seen as discriminatory towards Singapore's non-Chinese ethnic population. In 1985, the incentives were partly abandoned as ineffective, while the government matchmaking agency, the Social Development Network, remains active.

Modern eugenics

See also: New eugenics

Liberal eugenics, also called new eugenics, aims to make genetic interventions morally acceptable by rejecting coercive state programmes and relying on parental choice. Bioethicist Nicholas Agar, who coined the term, argues that the state should intervene only to forbid interventions that excessively limit a child’s ability to shape their own future. Unlike "authoritarian" or "old" eugenics, liberal eugenics draws on modern scientific knowledge of genomics to enable informed choices aimed at improving well-being. Julien Savulescu further argues that some eugenic practices, like prenatal screening for Down syndrome, are already widely practiced, without being labelled "eugenics", as they are seen as enhancing freedom rather than restricting it.

UC Berkeley sociologist Troy Duster argued that modern genetics is a "back door to eugenics". This view was shared by then-White House Assistant Director for Forensic Sciences, Tania Simoncelli, who stated in a 2003 publication by the Population and Development Programme at Hampshire College that advances in pre-implantation genetic diagnosis (PGD) are moving society to a "new era of eugenics", and that, unlike the Nazi eugenics, modern eugenics is consumer driven and market based, "where children are increasingly regarded as made-to-order consumer products". The United Nations' International Bioethics Committee also noted that while human genetic engineering should not be confused with the 20th century eugenics movements, it nonetheless challenges the idea of human equality and opens up new forms of discrimination and stigmatisation for those who do not want or cannot afford the technology.

In 2025, geneticist Peter Visscher published a paper in Nature, arguing genome editing of human embryos and germ cells may become feasible in the 21st century, and raising ethical considerations in the context of previous eugenics movements. A response argued that human embryo genetic editing is "unsafe and unproven". Nature also published an editorial, stating: "The fear that polygenic gene editing could be used for eugenics looms large among them, and is, in part, why no country currently allows genome editing in a human embryo, even for single variants".

Contested scientific status

In the decades after World War II, the term "eugenics" had taken on a negative connotation and as a result, the use of it became increasingly unpopular within the scientific community. Many organizations and journals that had their origins in the eugenics movement began to distance themselves from the philosophy which spawned them, as when Eugenics Quarterly was renamed Social Biology in 1969.

One general concern is that the reduced genetic diversity that may be a feature of long-term, species-wide eugenics plans could eventually result in inbreeding depression, increased spread of infectious disease, and decreased resilience to changes in the environment.

Arguments for scientific validity

See also: Selective breeding, De novo domestication, List of domesticated animals, List of domesticated plants, and Self-domestication

In his original lecture "Darwinism, Medical Progress and Eugenics", Karl Pearson claimed that everything concerning eugenics fell into the field of medicine. Anthropologist Aleš Hrdlička said in 1918 that "[t]he growing science of eugenics will essentially become applied anthropology." The economist John Maynard Keynes was a lifelong proponent of eugenics and described it as a branch of sociology.

In a 2006 newspaper article, Richard Dawkins said that discussion regarding eugenics was inhibited by the shadow of Nazi misuse, to the extent that some scientists would not admit that breeding humans for certain abilities is at all possible. He believes that it is not physically different from breeding domestic animals for traits such as speed or herding skill. Dawkins felt that enough time had elapsed to at least ask just what the ethical differences were between breeding for ability versus training athletes or forcing children to take music lessons, though he could think of persuasive reasons to draw the distinction.

Objections to scientific validity

Amanda Caleb, Professor of Medical Humanities at Geisinger Commonwealth School of Medicine, says "Eugenic laws and policies are now understood as part of a specious devotion to a pseudoscience that actively dehumanises to support political agendas and not true science or medicine."

The first major challenge to conventional eugenics based on genetic inheritance was made in 1915 by Thomas Hunt Morgan. He demonstrated the event of genetic mutation occurring outside of inheritance involving the discovery of the hatching of a fruit fly (Drosophila melanogaster) with white eyes from a family with red eyes, demonstrating that major genetic changes occurred outside of inheritance.^{[clarification needed]} Morgan criticised the view that traits such as intelligence or criminality were hereditary, because these traits were subjective.

Pleiotropy occurs when one gene influences multiple, seemingly unrelated phenotypic traits, an example being phenylketonuria, which is a human disease that affects multiple systems but is caused by one gene defect. Andrzej Pękalski, from the University of Wroclaw, argues that eugenics can cause harmful loss of genetic diversity if a eugenics programme selects a pleiotropic gene that could possibly be associated with a positive trait. Pękalski uses the example of a coercive government eugenics programme that prohibits people with myopia from breeding but has the unintended consequence of also selecting against high intelligence since the two were associated.

While the science of genetics has increasingly provided means by which certain characteristics and conditions can be identified and understood, given the complexity of human genetics, culture, and psychology, at this point there is no agreed objective means of determining which traits might be ultimately desirable or undesirable. Some conditions such as sickle-cell disease and cystic fibrosis respectively confer immunity to malaria and resistance to cholera when a single copy of the recessive allele is contained within the genotype of the individual, so eliminating these genes is undesirable in places where such diseases are common.

Edwin Black, journalist, historian, and author of War Against the Weak, argues that eugenics is often deemed a pseudoscience because what is defined as a genetic improvement of a desired trait is a cultural choice rather than a matter that can be determined through objective scientific inquiry. This aspect of eugenics is often considered to be tainted with scientific racism and pseudoscience.

Logo from the Second International Eugenics Conference, 1921. The bottom text reads: "Like A Tree, Eugenics Draws Its Materials From Many Sources And Organises Them Into An Harmonious Entity" (such sources, i.e. roots, purportedly including e.g. genetics, physiology, mental testing, anthropology, statistics, medicine, politics and sociology).

Contested ethical status

Contemporary ethical opposition

See also: Larry Arnhart, Leon Kass, and Preimplantation genetic diagnosis § Religious objections

In a book directly addressed at socialist eugenicist J.B.S. Haldane and his once-influential Daedalus, Bertrand Russell had one serious objection of his own: eugenic policies might simply end up being used to reproduce existing power relations "rather than to make men happy."

Environmental ethicist Bill McKibben argued against germinal choice technology and other advanced biotechnological strategies for human enhancement. He writes that it would be morally wrong for humans to tamper with fundamental aspects of themselves (or their children) in an attempt to overcome universal human limitations, such as vulnerability to aging, maximum life span and biological constraints on physical and cognitive ability. Attempts to "improve" themselves through such manipulation would remove limitations that provide a necessary context for the experience of meaningful human choice. He claims that human lives would no longer seem meaningful in a world where such limitations could be overcome with technology. Even the goal of using germinal choice technology for clearly therapeutic purposes should be relinquished, he argues, since it would inevitably produce temptations to tamper with such things as cognitive capacities. He argues that it is possible for societies to benefit from renouncing particular technologies, using Ming China, Tokugawa Japan and the contemporary Amish as examples.

Contemporary ethical advocacy

See also: Peter Sloterdijk § Reprogenetics dispute

Bioethicist Stephen Wilkinson has said that some aspects of modern genetics can be classified as eugenics, but that this classification does not inherently make modern genetics immoral.

Historian Nathaniel C. Comfort has claimed that the change from state-led reproductive-genetic decision-making to individual choice has moderated the worst abuses of eugenics by transferring the decision-making process from the state to patients and their families.

In their book published in 2000, From Chance to Choice: Genetics and Justice, bioethicists Allen Buchanan, Dan Brock, Norman Daniels and Daniel Wikler argued that liberal societies have an obligation to encourage as wide an adoption of eugenic enhancement technologies as possible (so long as such policies do not infringe on individuals' reproductive rights or exert undue pressures on prospective parents to use these technologies) in order to maximise public health and minimise the inequalities that may result from both natural genetic endowments and unequal access to genetic enhancements.

In popular culture

See also: Speculative evolution, Evolution in fiction, and Genetics in fiction

In the movie, Gattaca also refers to the futuristic building complex that hosts the astronauts for an ongoing space colonisation programme.

The novel Brave New World by the English author Aldous Huxley (1931), is a dystopian social science fiction novel which is set in a futuristic World State, whose citizens are environmentally engineered into an intelligence-based social hierarchy.

Various works by the author Robert A. Heinlein mention the Howard Foundation, a group which attempts to improve human longevity through selective breeding.

Among Frank Herbert's works, the Dune series, starting with the eponymous 1965 novel, describes selective breeding by a powerful sisterhood, the Bene Gesserit, to produce a supernormal male being, the Kwisatz Haderach.

The Star Trek franchise features a race of genetically engineered humans which is known as "Augments", the most notable of them being Khan Noonien Singh. These "supermen" were the cause of the Eugenics Wars, a dark period in Earth's fictional history, before they were deposed and exiled. Spin-offs like Star Trek: Deep Space Nine and Star Trek: Strange New Worlds present the Eugenics Wars as the main reason why genetic enhancement is illegal in the United Federation of Planets.

Naoki Urasawa's manga Monster and its anime adaptation of the same name mention "The Eugenics Experiment" conducted in the premises of 511 Kinderheim, a clandestine East German orphanage where the main antagonist Johan Liebert grew up into a psychopathic serial killer.

The film Gattaca (1997) provides a fictional example of a dystopian society that uses eugenics to decide what people are capable of and their place in the world. The title alludes to the letters G, A, T and C, the four nucleobases of DNA, and depicts the possible consequences of genetic discrimination in the present societal framework. Relegated to the role of a cleaner owing to his genetically projected death at age 32 due to a heart condition (being told: "The only way you'll see the inside of a spaceship is if you were cleaning it"), the protagonist observes enhanced astronauts as they are demonstrating their superhuman athleticism. Although it was not a box office success, it was critically acclaimed and influenced the debate over human genetic engineering in the public consciousness. As to its accuracy, its production company, Sony Pictures, consulted with a gene therapy researcher and prominent critic of eugenics known to have stated that "[w]e should not step over the line that delineates treatment from enhancement", W. French Anderson, to ensure that the portrayal of science was realistic. Disputing their success in this mission, Philim Yam of Scientific American called the film "science bashing" and Nature's Kevin Davies called it a "surprisingly pedestrian affair", while molecular biologist Lee Silver described its extreme determinism as "a straw man".

In his 2018 book Blueprint, the behavioural geneticist Robert Plomin writes that while Gattaca warned of the dangers of genetic information being used by a totalitarian state, genetic testing could also favour better meritocracy in democratic societies which already administer a variety of standardised tests to select people for education and employment. He suggests that polygenic scores might supplement testing in a manner that is essentially free of biases.

Carbon sequestration

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Carbon_sequestration

Geologic and biologic carbon sequestration of excess carbon dioxide in the atmosphere emitted by human activities

Carbon sequestration is a natural process of storing carbon in a carbon pool. It plays a crucial role in effectively managing the global carbon cycle and limiting climate change by reducing the amount of carbon dioxide in the atmosphere. There are two main types of carbon sequestration: biologic (also called biosequestration) and geologic.

Biologic carbon sequestration is a naturally occurring process as part of the carbon cycle. Humans can enhance it through deliberate actions and use of technology. Carbon dioxide (CO
₂) is naturally captured from the atmosphere through biological, chemical, and physical processes. These processes can be accelerated for example through changes in land use and agricultural practices, called carbon farming. Artificial processes have also been devised to produce similar effects. This approach is called carbon capture and storage. It involves using technology to capture and sequester (store) CO
₂ that is produced from human activities underground or under the sea bed.

Plants absorb carbon dioxide from the air as they grow, and bind it into biomass. However, biological stores (such as forests and kelp beds) may be temporary carbon sinks, as long-term sequestration cannot be guaranteed. Wildfires, disease, economic pressures, and changing political priorities may release the sequestered carbon back into the atmosphere.

Carbon dioxide that has been removed from the atmosphere can also be stored in the Earth's crust by injecting it underground, or in the form of insoluble carbonate salts. The latter process is called mineral sequestration. These methods are considered non-volatile because they not only remove carbon dioxide from the atmosphere but also sequester it indefinitely. This means the carbon is "locked away" for thousands to millions of years.

To enhance carbon sequestration processes in oceans the following chemical or physical technologies have been proposed: ocean fertilization, artificial upwelling, basalt storage, mineralization, deep-sea sediments, and adding bases to neutralize acids. However, none have achieved large scale application so far. Large-scale seaweed farming on the other hand is a biological process and could sequester significant amounts of carbon. The potential growth of seaweed for carbon farming would see the harvested seaweed transported to the deep ocean for long-term burial. The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" on seaweed farming as a mitigation tactic.

Terminology

The term carbon sequestration has diverse meanings in the literature and media. The IPCC Sixth Assessment Report defines carbon sequestration as "The process of storing carbon in a carbon pool". Subsequently, a pool is defined as "a reservoir in the Earth system where elements, such as carbon and nitrogen, reside in various chemical forms for a period of time".

The United States Geological Survey (USGS) defines carbon sequestration as follows: "Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide." Because the wording in this definition makes it very similar to the definition of carbon capture and storage (CCS), carbon sequestration is sometimes confounded with CCS (the IPCC defines CCS as "a process in which a relatively pure stream of carbon dioxide (CO₂) from industrial sources is separated, treated and transported to a long-term storage location").

Roles

In nature

Carbon sequestration is part of the natural carbon cycle by which carbon is exchanged among the biosphere, pedosphere (soil), geosphere, hydrosphere, and atmosphere of Earth. Carbon dioxide is naturally captured from the atmosphere through biological, chemical, or physical processes, and stored in long-term reservoirs.

Plants absorb carbon dioxide from the air as they grow, and bind it into biomass. However, biological stores (such as forests and kelp beds) are considered volatile carbon sinks as long-term sequestration cannot be guaranteed. Events such as wildfires or disease, economic pressures, and changing political priorities can result in the sequestered carbon being released back into the atmosphere.

In climate change mitigation and policies

Further information: Climate change mitigation and Politics of climate change

Carbon sequestration, which acts as a carbon sink, helps to mitigate climate change and thus reduce harmful effects of climate change. It helps to slow the atmospheric and marine accumulation of greenhouse gases, which is mainly carbon dioxide released by burning fossil fuels.

Carbon sequestration for climate change mitigation can involve either enhancing natural carbon sinks or employing technological methods to capture and store carbon.

Within the carbon capture and storage approaches, carbon sequestration refers to the storage component. Artificial carbon storage technologies can be applied, such as gaseous storage in deep geological formations (including saline formations and exhausted gas fields), and solid storage by reaction of CO₂ with metal oxides to produce stable carbonates.

For carbon to be sequestered artificially—that is, outside the natural processes of the carbon cycle—it must first be captured, or its release into the atmosphere must be significantly delayed or prevented. This can be achieved by incorporating carbon-rich materials into long-lasting applications, such as construction, thereby avoiding release through processes like combustion or decay. Thereafter it can be passively stored or remain productively utilized over time in a variety of ways. For instance, upon harvesting, wood (as a carbon-rich material) can be incorporated into construction or a range of other durable products, thus sequestering its carbon over years or even centuries. In industrial production, engineers typically capture carbon dioxide from emissions from power plants or factories.

For example, in the United States, the Executive Order 13990 (officially titled "Protecting Public Health and the Environment and Restoring Science to Tackle the Climate Crisis") passed in 2021 and revoked January 2025, included several mentions of carbon sequestration via conservation and restoration of carbon sink ecosystems, such as wetlands and forests. The document emphasized the importance of farmers, landowners, and coastal communities in carbon sequestration. It directed the Treasury Department to promote conservation of carbon sinks through market based mechanisms.

Noting that the planet's carbon sequestration capacity is not unlimited, a 2025 study concluded that fully using Earth's geologic storage capacity would help limit global warming by only 0.7 °C (1.3 °F).

Biological carbon sequestration on land

Biological carbon sequestration (also called biosequestration) is the capture and storage of the atmospheric greenhouse gas carbon dioxide by continual and enhanced biological processes. This form of carbon sequestration occurs through increased rates of photosynthesis via land-use practices such as reforestation and sustainable forest management. Land-use changes that enhance natural carbon capture have the potential to capture and store large amounts of carbon dioxide each year. These include the conservation, management, and restoration of ecosystems such as forests, peatlands, wetlands, and grasslands, in addition to carbon sequestration methods in agriculture. Methods and practices exist to enhance soil carbon sequestration in both agriculture and forestry.

Forestry

Proportion of carbon stock in forest carbon pools, 2020

Total forest carbon stock, by carbon pool, 2025.

Forests are an important part of the global carbon cycle because trees and plants absorb carbon dioxide through photosynthesis. Therefore, they play an important role in climate change mitigation. By removing the greenhouse gas CO₂ from the air, forests function as terrestrial carbon sinks, meaning they store large amounts of carbon in the form of biomass, encompassing roots, stems, branches, and leaves. By doing so, forests sequester approximately 25% of human carbon emissions annually, playing a critical role in Earth's climate. Throughout their lifespan, trees continue to sequester carbon, storing atmospheric CO₂ long-term. Sustainable forest management, afforestation, reforestation are therefore important contributions to climate change mitigation.

An important consideration in such efforts is that forests can turn from sinks to carbon sources. In 2019 forests took up a third less carbon than they did in the 1990s, due to higher temperatures, droughts and deforestation. National-scale forest inventory data also shows trends from 1999 to 2020 that some forests were already approaching climate thresholds shifting them from carbon sinks to carbon sources. The typical tropical forest may become a carbon source by the 2060s.

Researchers have found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the latter leads to irreversible effects in terms of biodiversity loss and soil degradation. Furthermore, the probability that legacy carbon will be released from soil is higher in a younger boreal forest. In particular, boreal forests have been noted to support the growth of Armillaria (honey fungus), which is a root pathogen that breaks down compounds necessary for wood integrity, increasing the likelihood of carbon release. Global greenhouse gas emissions caused by damage to tropical rainforests may have been substantially underestimated until around 2019. Additionally, the effects of afforestation and reforestation will be farther in the future than keeping existing forests intact. It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation. Therefore, scientists consider "the protection and recovery of carbon-rich and long-lived ecosystems, especially natural forests" to be "the major climate solution".

The planting of trees on marginal crop and pasture lands helps to incorporate carbon from atmospheric CO
₂ into biomass. For this carbon sequestration process to succeed the carbon must not return to the atmosphere from biomass burning or rotting when the trees die. Several species of Ficus such as Ficus wakefieldii have been observed to sequester atmospheric CO₂ as calcium oxalate in the presence of oxalotrophic bacteria and fungi, which catabolize the oxalate, which produces calcium carbonate. The calcium carbonate is precipitated throughout the tree, which also alkalinizes the surrounding soil. These species are current candidates for carbon sequestration in agroforestry. This Calcium-oxalate fixation process was first observed in the Iroko tree, which can sequester up to a ton of calcium carbonate in the soil over its lifespan. Also Cacti, such as the Saguaro, transfer carbon from the biological cycle to the geological cycle by forming the mineral calcium carbonate.

Earth offers enough room to plant an additional 0.9 billion ha of tree canopy cover, although this estimate has been criticized, and the true area that has a net cooling effect on the climate when accounting for biophysical feedbacks like albedo is 20-80% lower. Planting and protecting these trees would sequester 205 billion tons of carbon if the trees survive future climate stress to reach maturity. To put this number into perspective, this is about 20 years of current global carbon emissions (as of 2019). This level of sequestration would represent about 25% of the atmosphere's carbon pool in 2019.

Life expectancy of forests varies throughout the world, influenced by tree species, site conditions, and natural disturbance patterns. In some forests, carbon may be stored for centuries, while in other forests, carbon is released with frequent stand replacing fires. Forests that are harvested prior to stand replacing events allow for the retention of carbon in manufactured forest products such as lumber. However, only a portion of the carbon removed from logged forests ends up as durable goods and buildings. The remainder ends up as sawmill by-products such as pulp, paper, and pallets. If all new construction globally utilized 90% wood products, largely via adoption of mass timber in low rise construction, this could sequester 700 million net tons of carbon per year. This is in addition to the elimination of carbon emissions from the displaced construction material such as steel or concrete, which are carbon-intense to produce.

A meta-analysis found that mixed species plantations would increase carbon storage alongside other benefits of diversifying planted forests.

Although a bamboo forest stores less total carbon than a mature forest of trees, a bamboo plantation sequesters carbon at a much faster rate than a mature forest or a tree plantation. Therefore, the farming of bamboo timber may have significant carbon sequestration potential.

The Food and Agriculture Organization (FAO) reported that: "The total carbon stock in forests decreased from 668 gigatonnes in 1990 to 662 gigatonnes in 2020". In Canada's boreal forests as much as 80% of the total carbon is stored in the soils as dead organic matter.

The IPCC Sixth Assessment Report says: "Secondary forest regrowth and restoration of degraded forests and non-forest ecosystems can play a large role in carbon sequestration (high confidence) with high resilience to disturbances and additional benefits such as enhanced biodiversity."

Impacts on temperature are affected by the location of the forest. For example, reforestation in boreal or subarctic regions has less impact on climate. This is because it substitutes a high-albedo, snow-dominated region with a lower-albedo forest canopy. By contrast, tropical reforestation projects lead to a positive change such as the formation of clouds. These clouds then reflect the sunlight, lowering temperatures.

Planting trees in tropical climates with wet seasons has another advantage. In such a setting, trees grow more quickly (fixing more carbon) because they can grow year-round. Trees in tropical climates have, on average, larger, brighter, and more abundant leaves than non-tropical climates. A study of the girth of 70,000 trees across Africa has shown that tropical forests fix more carbon dioxide pollution than previously realized. The research suggested almost one-fifth of fossil fuel emissions are absorbed by forests across Africa, Amazonia and Asia. Simon Lewis stated, "Tropical forest trees are absorbing about 18% of the carbon dioxide added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of change."

Wetlands

See also: Blue carbon and Wetland § Climate change mitigation

A healthy wetland ecosystem

Global distribution of blue carbon (rooted vegetation in the coastal zone): tidal marshes, mangroves and seagrasses.

Wetland restoration involves restoring a wetland's natural biological, geological, and chemical functions through re-establishment or rehabilitation. It is a good way to reduce climate change. Wetland soil, particularly in coastal wetlands such as mangroves, sea grasses, and salt marshes, is an important carbon reservoir; 20–30% of the world's soil carbon is found in wetlands, while only 5–8% of the world's land is composed of wetlands. Studies have shown that restored wetlands can become productive CO₂ sinks and many are being restored. Aside from climate benefits, wetland restoration and conservation can help preserve biodiversity, improve water quality, and aid with flood control.

The plants that make up wetlands absorb carbon dioxide (CO₂) from the atmosphere and convert it into organic matter. The waterlogged nature of the soil slows down the decomposition of organic material, resulting in the accumulation of carbon-rich sediments, that act as a long-term carbon sink. Additionally, anaerobic conditions in waterlogged soils hinder the complete breakdown of organic matter, promoting the conversion of carbon into more stable forms.

As with forests, for the sequestration process to succeed, the wetland must remain undisturbed. If it is disturbed the carbon stored in the plants and sediments will be released back into the atmosphere, and the ecosystem will no longer function as a carbon sink. Additionally, some wetlands can release non-CO₂ greenhouse gases, such as methane and nitrous oxide which could offset potential climate benefits. The amounts of carbon sequestered via blue carbon by wetlands can also be difficult to measure.

Wetland soil is an important carbon sink; 14.5% of the world's soil carbon is found in wetlands, while only 5.5% of the world's land is composed of wetlands. Not only are wetlands a great carbon sink, they have many other benefits like collecting floodwater, filtering out air and water pollutants, and creating a home for numerous birds, fish, insects, and plants.

Climate change could alter wetland soil carbon storage, changing it from a sink to a source. With rising temperatures comes an increase in greenhouse gasses from wetlands especially locations with permafrost. When this permafrost melts it increases the available oxygen and water in the soil. Because of this, bacteria in the soil would create large amounts of carbon dioxide and methane to be released into the atmosphere.

The link between climate change and wetlands is still not fully known.  It is also not clear how restored wetlands manage carbon while still being a contributing source of methane. However, preserving these areas would help prevent further release of carbon into the atmosphere.

Peatlands, mires and peat bogs

Despite occupying only 3% of the global land area, peatlands hold approximately 30% of the carbon in our ecosystem - twice the amount stored in the world's forests. Most peatlands are situated in high latitude areas of the northern hemisphere, with most of their growth occurring since the last ice age, but they are also found in tropical regions, such as the Amazon and Congo Basin.

Peatlands grow steadily over thousands of years, accumulating dead plant material – and the carbon contained within it – due to waterlogged conditions which greatly slow rates of decay. If peatlands are drained, for farmland or development, the plant material stored within them decomposes rapidly, releasing stored carbon. These degraded peatlands account for 5-10% of global carbon emissions from human activities. The loss of one peatland could potentially produce more carbon than 175–500 years of methane emissions.

Peatland protection and restoration are therefore important measures to mitigate carbon emissions, and also provide benefits for biodiversity, freshwater provision, and flood risk reduction.

Agriculture

See also: Carbon sink § Soils, and Greenhouse gas emissions from agriculture

Panicum virgatum switchgrass, valuable in biofuel production, soil conservation, and carbon sequestration in soils

Compared to natural vegetation, cropland soils are depleted in soil organic carbon (SOC). When soil is converted from natural land or semi-natural land, such as forests, woodlands, grasslands, steppes, and savannas, the SOC content in the soil reduces by about 30–40%. This loss is due to harvesting, as plants contain carbon. When land use changes, the carbon in the soil will either increase or decrease, and this change will continue until the soil reaches a new equilibrium. Deviations from this equilibrium can also be affected by variated climate.

The decreasing of SOC content can be counteracted by increasing the carbon input. This can be done with several strategies, e.g. leave harvest residues on the field, use manure as fertilizer, or include perennial crops in the rotation. Perennial crops have a larger below-ground biomass fraction, which increases the SOC content.

Perennial crops reduce the need for tillage and thus help mitigate soil erosion, and may help increase soil organic matter. Globally, soils are estimated to contain >8,580 gigatons of organic carbon, about ten times the amount in the atmosphere and much more than in vegetation.

Researchers have found that rising temperatures can lead to population booms in soil microbes, converting stored carbon into carbon dioxide. In laboratory experiments heating soil, fungi-rich soils released less carbon dioxide than other soils.

Following carbon dioxide (CO2) absorption from the atmosphere, plants deposit organic matter into the soil. This organic matter, derived from decaying plant material and root systems, is rich in carbon compounds. Microorganisms in the soil break down this organic matter, and in the process, some of the carbon becomes further stabilized in the soil as humus - a process known as humification.

On a global basis, it is estimated that soil contains about 2,500 gigatons of carbon. This is greater than 3-fold the carbon found in the atmosphere and 4-fold of that found in living plants and animals. About 70% of the global soil organic carbon in non-permafrost areas is found in the deeper soil within the upper metre and is stabilized by mineral-organic associations.

Carbon farming

Carbon farming is a set of agricultural methods that aim to store carbon in the soil and biomass. The technical term for this is carbon sequestration. The overall goal of carbon farming is to create a net loss of carbon from the atmosphere. This is done by increasing the rate at which carbon is sequestered into soil and plant material. The increase of biomass from roots and the soil's microbiome leads to an increase in the organic matter content of the soil. Increasing organic matter content in soils aids plant growth, improves soil water retention capacity and reduces fertilizer use. Sustainable forest management is another tool that is used in carbon farming. Carbon farming is one component of climate-smart agriculture. It is also one way to remove carbon dioxide from the atmosphere.

Agricultural methods for carbon farming include adjusting how tillage and livestock grazing is done, using organic mulch or compost, working with biochar and terra preta, and changing the crop types. Methods used in forestry include reforestation and bamboo farming. As of 2016, variants of carbon farming reached hundreds of millions of hectares globally, of the nearly 5 billion hectares (1.2×10¹⁰ acres) of world farmland.

Carbon farming tends to be more expensive than conventional agricultural practices. Depending on the region, carbon farmings costs US$3-130 per tonne of carbon dioxide sequestered. Some countries provide subsidies to farmers to use carbon farming methods. While the implementation of carbon farming methods can reduce/sequester emissions, it is important to also consider the effects of land use changes with respect to the conversion of forests to agricultural production.

Prairies

Prairie restoration is a conservation effort to restore prairie lands that were destroyed due to industrial, agricultural, commercial, or residential development. The primary aim is to return areas and ecosystems to their previous state before their depletion. The mass of SOC able to be stored in these restored plots is typically greater than the previous crop, acting as a more effective carbon sink.

Biochar

Main article: Biochar

Biochar is charcoal created by pyrolysis of biomass waste. The resulting material is added to a landfill or used as a soil improver to create terra preta. Adding biochar may increase the soil-C stock for the long term and so mitigate global warming by offsetting the atmospheric C (up to 9.5 Gigatons C annually). In the soil, the biochar carbon is unavailable for oxidation to CO
₂ and consequential atmospheric release. However concerns have been raised about biochar potentially accelerating release of the carbon already present in the soil.

Terra preta, an anthropogenic, high-carbon soil, is also being investigated as a sequestration mechanism. By pyrolysing biomass, about half of its carbon can be reduced to charcoal, which can persist in the soil for centuries, and makes a useful soil amendment, especially in tropical soils (biochar or agrichar).^[106]

Burial of biomass

Biochar can be landfilled, used as a soil improver or burned using carbon capture and storage.

Burying biomass (such as trees) directly mimics the natural processes that created fossil fuels.^[108] The global potential for carbon sequestration using wood burial is estimated to be 10 ± 5 GtC/yr and largest rates in tropical forests (4.2 GtC/yr), followed by temperate (3.7 GtC/yr) and boreal forests (2.1 GtC/yr). In 2008, Ning Zeng of the University of Maryland estimated 65 GtC lying on the floor of the world's forests as coarse woody material which could be buried and costs for wood burial carbon sequestration run at US$50/tC which is much lower than carbon capture from e.g. power plant emissions. CO₂ fixation into woody biomass is a natural process carried out through photosynthesis. This is a nature-based solution and methods being trialled include the use of "wood vaults" to store the wood-containing carbon under oxygen-free conditions.

In 2022, a certification organization published methodologies for biomass burial. Other biomass storage proposals have included the burial of biomass deep underwater, including at the bottom of the Black Sea.

Geological carbon sequestration

Underground storage in suitable geologic formations

Main articles: Carbon capture and storage and Direct air capture

Wellhead near Estevan, SK, where CO₂ is injected into a 3.4km deep saline aquifer

Geological sequestration refers to the storage of CO₂ underground in depleted oil and gas reservoirs, saline formations, or deep, coal beds unsuitable for mining.

Once CO₂ is captured from a point source, such as a cement factory, it can be compressed to ≈100 bar into a supercritical fluid. In this form, the CO₂ could be transported via pipeline to the place of storage. The CO₂ could then be injected deep underground, typically around 1 km (0.6 mi), where it would be stable for hundreds to millions of years. Under these storage conditions, the density of supercritical CO₂ is 600 to 800 kg/m³.

The important parameters in determining a good site for carbon storage are: rock porosity, rock permeability, absence of faults, and geometry of rock layers. The medium in which the CO₂ is to be stored ideally has a high porosity and permeability, such as sandstone or limestone. Sandstone can have a permeability ranging from 1 to 10⁻⁵ Darcy, with a porosity as high as ≈30%. The porous rock must be capped by a layer of low permeability, which function as a seal, or caprock, for the CO₂. Shale is an example of a very good caprock, with a permeability of 10⁻⁵ to 10⁻⁹ Darcy. Once injected, the CO₂ plume will rise via buoyant forces, since it is less dense than its surroundings. Once it encounters a caprock, it will spread laterally until it encounters a gap. If there are fault planes near the injection zone, there is a possibility the CO₂ could migrate along the fault to the surface, leaking into the atmosphere, which would be potentially dangerous to life in the surrounding area. Another risk related to carbon sequestration is induced seismicity. If the injection of CO₂ creates pressures underground that are too high, the formation will fracture, potentially causing an earthquake.

Structural trapping is considered the principal storage mechanism, impermeable or low permeability rocks such as mudstone, anhydrite, halite, or impermeable carbonates act as a barrier to the upward buoyant migration of CO₂, resulting in the retention of CO₂ within a storage formation. While trapped in a rock formation, CO₂ can be in the supercritical fluid phase or dissolve in groundwater/brine. It can also react with minerals in the geologic formation to become carbonates.

In 2025, research indicated that, of nearly 12,000 GtCO2 of theoretical carbon storage capacity, just 1,460 GtCO2 is risk-free, significantly less than most estimates suggested.

Mineral sequestration

Mineral sequestration aims to trap carbon in the form of solid carbonate salts. This process occurs slowly in nature and is responsible for the deposition and accumulation of limestone over geologic time. Carbonic acid in groundwater slowly reacts with complex silicates to dissolve calcium, magnesium, alkalis and silica and leave a residue of clay minerals. The dissolved calcium and magnesium react with bicarbonate to precipitate calcium and magnesium carbonates, a process that organisms use to make shells. When the organisms die, their shells are deposited as sediment and eventually turn into limestone. Limestones have accumulated over billions of years of geologic time and contain much of Earth's carbon. Ongoing research aims to speed up similar reactions involving alkali carbonates.^[121]

Zeolitic imidazolate frameworks (ZIFs) are metal–organic frameworks similar to zeolites. Because of their porosity, chemical stability and thermal resistance, ZIFs are being examined for their capacity to capture carbon dioxide.

Mineral carbonation

CO₂ exothermically reacts with metal oxides, producing stable carbonates (e.g. calcite, magnesite). This process (CO₂-to-stone) occurs naturally over periods of years and is responsible for much surface limestone. Olivine is one such metal oxide. Rocks rich in metal oxides that react with CO₂, such as MgO and CaO as contained in basalts, have been proven as a viable means to achieve carbon-dioxide mineral storage. The reaction rate can in principle be accelerated with a catalyst or by increasing pressures, or by mineral pre-treatment, although this method can require additional energy.

Ultramafic mine tailings are a readily available source of fine-grained metal oxides that could serve this purpose. Accelerating passive CO₂ sequestration via mineral carbonation may be achieved through microbial processes that enhance mineral dissolution and carbonate precipitation.

Carbon, in the form of CO
₂ can be removed from the atmosphere by chemical processes, and stored in stable carbonate mineral forms. This process (CO
₂-to-stone) is known as "carbon sequestration by mineral carbonation" or mineral sequestration. The process involves reacting carbon dioxide with abundantly available metal oxides – either magnesium oxide (MgO) or calcium oxide (CaO) – to form stable carbonates. These reactions are exothermic and occur naturally (e.g., the weathering of rock over geologic time periods).

CaO + CO
₂ → CaCO
₃

MgO + CO
₂ → MgCO
₃

Calcium and magnesium are found in nature typically as calcium and magnesium silicates (such as forsterite and serpentinite) and not as binary oxides. For forsterite and serpentine the reactions are:

Mg
₂SiO
₄ + 2 CO
₂ → 2 MgCO
₃ + SiO
₂

Mg
₃Si
₂O
₅(OH)
₄+ 3 CO
₂ → 3 MgCO
₃ + 2 SiO
₂ + 2 H
₂O

These reactions are slightly more favorable at low temperatures. This process occurs naturally over geologic time frames and is responsible for much of the Earth's surface limestone. The reaction rate can be made faster however, by reacting at higher temperatures and/or pressures, although this method requires some additional energy. Alternatively, the mineral could be milled to increase its surface area, and exposed to water and constant abrasion to remove the inert silica as could be achieved naturally by dumping olivine in the high energy surf of beaches.

When CO
₂ is dissolved in water and injected into hot basaltic rocks underground it has been shown that the CO
₂ reacts with the basalt to form solid carbonate minerals. A test plant in Iceland started up in October 2017, extracting up to 50 tons of CO₂ a year from the atmosphere and storing it underground in basaltic rock.

Sequestration in oceans

Several start-ups are trying to do this at scale.

Marine carbon pumps

Further information: Solubility pump and Biological pump

The pelagic food web, showing the central involvement of marine microorganisms in how the ocean imports carbon and then exports it back to the atmosphere and ocean floor

The ocean sequesters carbon through diverse processes. The solubility pump moves carbon dioxide from the atmosphere into the surface ocean where it reacts with water molecules to form carbonic acid. The solubility of carbon dioxide increases with decreasing water temperatures. Thermohaline circulation moves dissolved carbon dioxide to cooler waters where it is more soluble, increasing carbon concentrations in the ocean interior. The biological pump moves dissolved carbon dioxide from the surface ocean to the ocean's interior through the conversion of inorganic carbon to organic carbon by photosynthesis. Organic matter that survives respiration and remineralization can be transported through sinking particles and organism migration to the deep ocean.

The low temperatures, high pressure, and reduced oxygen levels in the deep sea slow down decomposition processes, preventing the rapid release of carbon back into the atmosphere and acting as a long-term storage reservoir.

Vegetated coastal ecosystems

Blue carbon is a concept within climate change mitigation that refers to "biologically driven carbon fluxes and storage in marine systems that are amenable to management". Most commonly, it refers to the role that tidal marshes, mangroves and seagrass meadows can play in carbon sequestration.^{[139]: 2220} These ecosystems can play an important role for climate change mitigation and ecosystem-based adaptation. However, when blue carbon ecosystems are degraded or lost, they release carbon back to the atmosphere, thereby adding to greenhouse gas emissions.

Seaweed farming and algae

Further information: Seaweed farming § Climate change mitigation

Kelp forest

Seagrass meadow

Seaweed grows in shallow and coastal areas, and captures significant amounts of carbon that can be transported to the deep ocean by oceanic mechanisms; seaweed reaching the deep ocean sequester carbon and prevent it from exchanging with the atmosphere over millennia. Growing seaweed offshore with the purpose of sinking the seaweed in the depths of the sea to sequester carbon has been suggested. In addition, seaweed grows very fast and can theoretically be harvested and processed to generate biomethane, via anaerobic digestion to generate electricity, via cogeneration/CHP or as a replacement for natural gas. One study suggested that if seaweed farms covered 9% of the ocean they could produce enough biomethane to supply Earth's equivalent demand for fossil fuel energy, remove 53 gigatonnes of CO₂ per year from the atmosphere and sustainably produce 200 kg per year of fish, per person, for 10 billion people. Ideal species for such farming and conversion include Laminaria digitata, Fucus serratus and Saccharina latissima.

Both macroalgae and microalgae are being investigated as possible means of carbon sequestration. Marine phytoplankton perform half of the global photosynthetic CO₂ fixation (net global primary production of ~50 Pg C per year) and half of the oxygen production despite amounting to only ~1% of global plant biomass.

Because algae lack the complex lignin associated with terrestrial plants, the carbon in algae is released into the atmosphere more rapidly than carbon captured on land. Algae have been proposed as a short-term storage pool of carbon that can be used as a feedstock for the production of various biogenic fuels.

Women working with seaweed

Large-scale seaweed farming could sequester significant amounts of carbon. Wild seaweed will sequester large amount of carbon through dissolved particles of organic matter being transported to deep ocean seafloors where it will become buried and remain for long periods of time. With respect to carbon farming, the potential growth of seaweed for carbon farming would see the harvested seaweed transported to the deep ocean for long-term burial. Seaweed farming occurs mostly in the Asian Pacific coastal areas where it has been a rapidly increasing market. The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" on seaweed farming as a mitigation tactic.

Ocean fertilization

An oceanic phytoplankton bloom in the South Atlantic Ocean, off the coast of Argentina. Encouraging such blooms with iron fertilization could lock up carbon on the seabed. However, this approach is currently (2022) no longer being actively pursued.

Ocean fertilization or ocean nourishment refers to both natural and intentional processes that replenish iron and other nutrients in the upper ocean, which in turn stimulate the growth of phytoplankton and in some circumstances draw down large amounts of carbon dioxide (CO₂) through photosynthesis. Intentional ocean fertilization is biomimicry of natural processes that have removed atmospheric CO₂ before ice ages as well as after volcanic eruptions, whale defecation, and near hydrothermal vents. The introduction of nutrients to the upper ocean increases marine food production as well as removing carbon dioxide from the atmosphere.

Ocean nutrient fertilization, for example iron fertilization, (OIF) can stimulate photosynthesis in phytoplankton. The phytoplankton converts the ocean's dissolved carbon dioxide into carbohydrate, some of which has been shown to sink into the deeper ocean. More than a dozen open-sea experiments confirmed that adding iron to the ocean increases photosynthesis in phytoplankton by up to 30 times.

Ocean iron fertilization is one of the more well-researched carbon dioxide removal (CDR) approaches, and supported by climate restoration proponents. However, there is uncertainty about this approach regarding the duration of the effective oceanic carbon sequestration. A National Academies of Science, Engineering and Medicine (NASEM) 2021 study on marine CDR (mCDR) concludes that OIF has among the highest potential of mCDR approaches.

Artificial upwelling

Artificial upwelling or downwelling is an approach that would change the mixing layers of the ocean. Encouraging various ocean layers to mix can move nutrients and dissolved gases around. Mixing may be achieved by placing large vertical pipes in the oceans to pump nutrient-rich water to the surface, triggering blooms of algae, which store carbon when they grow and export carbon when they die. This produces results somewhat similar to iron fertilization. One side-effect is a short-term rise in CO
₂, which limits its attractiveness.

Mixing layers involve transporting the denser and colder deep ocean water to the surface mixed layer. As the ocean temperature decreases with depth, more carbon dioxide and other compounds are able to dissolve in the deeper layers. This can be induced by reversing the oceanic carbon cycle through the use of large vertical pipes serving as ocean pumps, or a mixer array. When the nutrient rich deep ocean water is moved to the surface, algae bloom occurs, resulting in a decrease in carbon dioxide due to carbon intake from phytoplankton and other photosynthetic eukaryotic organisms. The transfer of heat between the layers will also cause seawater from the mixed layer to sink and absorb more carbon dioxide. This method has not gained much traction as algae bloom harms marine ecosystems by blocking sunlight and releasing harmful toxins into the ocean. The sudden increase in carbon dioxide on the surface level will also temporarily decrease the pH of the seawater, impairing the growth of coral reefs. The production of carbonic acid through the dissolution of carbon dioxide in seawater hinders marine biogenic calcification and causes major disruptions to the oceanic food chain.

Basalt storage

Carbon dioxide sequestration in basalt involves the injecting of CO
₂ into deep-sea formations. The CO
₂ first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of Ca²⁺ and Mg²⁺ ions forming stable carbonate minerals.

Underwater basalt offers a good alternative to other forms of oceanic carbon storage because it has a number of trapping measures to ensure added protection against leakage. These measures include "geochemical, sediment, gravitational and hydrate formation." Because CO
₂ hydrate is denser than CO
₂ in seawater, the risk of leakage is minimal. Injecting the CO
₂ at depths greater than 2,700 meters (8,900 ft) ensures that the CO
₂ has a greater density than seawater, causing it to sink.

One possible injection site is Juan de Fuca Plate. Researchers at the Lamont–Doherty Earth Observatory found that this plate at the western coast of the United States has a possible storage capacity of 208 gigatons. This could cover the entire current U.S. carbon emissions for over 100 years (as of 2009).

This process is undergoing tests as part of the CarbFix project, resulting in 95% of the injected 250 tonnes of CO₂ to solidify into calcite in two years, using 25 tonnes of water per tonne of CO₂.

Mineralization and deep sea sediments

See also: Pelagic sediment

Similar to mineralization processes that take place within rocks, mineralization can also occur under the sea. The rate of dissolution of carbon dioxide from atmosphere to oceanic regions is determined by the circulation period of the ocean and buffering ability of subducting surface water. Researchers have demonstrated that the carbon dioxide marine storage at several kilometers depth could be viable for up to 500 years, but is dependent on injection site and conditions. Several studies have shown that although it may fix carbon dioxide effectively, carbon dioxide may be released back to the atmosphere over time. However, this is unlikely for at least a few more centuries. The neutralization of CaCO₃, or balancing the concentration of CaCO₃ on the seafloor, land and in the ocean, can be measured on a timescale of thousands of years. More specifically, the predicted time is 1700 years for ocean and approximately 5000 to 6000 years for land. Further, the dissolution time for CaCO₃ can be improved by injecting near or downstream of the storage site.

In addition to carbon mineralization, another proposal is deep sea sediment injection. It injects liquid carbon dioxide at least 3,000 m (9,800 ft) below the surface directly into ocean sediments to generate carbon dioxide hydrate. Two regions are defined for exploration: 1) the negative buoyancy zone (NBZ), which is the region between liquid carbon dioxide denser than surrounding water and where liquid carbon dioxide has neutral buoyancy, and 2) the hydrate formation zone (HFZ), which typically has low temperatures and high pressures. Several research models have shown that the optimal depth of injection requires consideration of intrinsic permeability and any changes in liquid carbon dioxide permeability for optimal storage. The formation of hydrates decreases liquid carbon dioxide permeability, and injection below HFZ is more energetically favored than within the HFZ. If the NBZ is a greater column of water than the HFZ, the injection should happen below the HFZ and directly to the NBZ. In this case, liquid carbon dioxide will sink to the NBZ and be stored below the buoyancy and hydrate cap. Carbon dioxide leakage can occur if there is dissolution into pore fluid or via molecular diffusion. However, this occurs over thousands of years.

Adding bases to neutralize acids

Further information: Ocean acidification § Carbon removal technologies which add alkalinity

Carbon dioxide forms carbonic acid when dissolved in water, making ocean acidification a significant consequence of elevated CO
₂ levels. The acidification also limits the rate at which CO
₂ can be absorbed by the ocean (through the solubility pump). Various bases have been suggested that could neutralize the ocean acidity and thereby enhance CO
₂ absorption. For example, adding crushed limestone to oceans enhances the absorption of carbon dioxide. Another approach involves adding sodium hydroxide, produced through electrolysis of saltwater or brine. The resulting hydrochloric acid byproduct can be neutralized by reacting it with volcanic silicate rocks, such as enstatite—effectively accelerating the natural weathering process to help restore ocean pH.

Single-step carbon sequestration and storage

Single-step carbon sequestration and storage is a saline water-based mineralization technology extracting carbon dioxide from seawater and storing it in the form of solid minerals.

Abandoned ideas

Direct deep-sea carbon dioxide injection

Main article: Direct deep-sea carbon dioxide injection

It was once suggested that CO₂ could be stored in the oceans by direct injection into the deep ocean and storing it there for some centuries. At the time, this proposal was called "ocean storage" but more precisely it was known as "direct deep-sea carbon dioxide injection". However, the interest in this avenue of carbon storage has much reduced since about 2001 because of concerns about the unknown impacts on marine life, high costs and concerns about its stability or permanence. The "IPCC Special Report on Carbon Dioxide Capture and Storage" in 2005 did include this technology as an option. However, the IPCC Fifth Assessment Report in 2014 no longer mentioned the term "ocean storage" in its report on climate change mitigation methods. The 2022 IPCC Sixth Assessment Report does not mention "ocean storage" in its "Carbon Dioxide Removal taxonomy".

Costs

Cost of carbon sequestration (not including capture and transport) varies but is below US$10 per tonne in some cases where onshore storage is available. For example Carbfix cost is around US$25 per tonne of CO₂. A 2020 report estimated sequestration in forests (so including capture) at US$35 for small quantities to US$280 per tonne for 10% of the total required to keep to 1.5 C warming. But there is risk of forest fires releasing the carbon.