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Artist's impression of a major asteroid impact. An asteroid with an impact strength of a billion atomic bombs may have caused the extinction of the dinosaurs.^[1]

A global catastrophic risk is a hypothetical future event which could damage human well-being on a global scale,^[2] even crippling or destroying modern civilization.^[3] An event that could cause human extinction or permanently and drastically curtail humanity's potential is known as an existential risk.^[4]

Potential global catastrophic risks include anthropogenic risks, caused by humans (technology, governance, climate change), and non-anthropogenic or external risks.^[3] Examples of technology risks are hostile artificial intelligence and destructive biotechnology or nanotechnology. Insufficient or malign global governance creates risks in the social and political domain, such as a global war, including nuclear holocaust, bioterrorism using genetically modified organisms, cyberterrorism destroying critical infrastructure like the electrical grid; or the failure to manage a natural pandemic. Problems and risks in the domain of earth system governance include global warming, environmental degradation, including extinction of species, famine as a result of non-equitable resource distribution, human overpopulation, crop failures and non-sustainable agriculture.

Examples of non-anthropogenic risks are an asteroid impact event, a supervolcanic eruption, a lethal gamma-ray burst, a geomagnetic storm destroying electronic equipment, natural long-term climate change, hostile extraterrestrial life, or the predictable Sun transforming into a red giant star engulfing the Earth.

Classifications

Scope/intensity grid from Bostrom's paper "Existential Risk Prevention as Global Priority"^[5]

Global catastrophic vs. existential

A "global catastrophic risk" is any risk that is at least "global" in scope, and is not subjectively "imperceptible" in intensity. Those that are at least "trans-generational" (affecting all future generations) in scope and "terminal"^{[clarification needed]} in intensity are classified as existential risks. While a global catastrophic risk may kill the vast majority of life on earth, humanity could still potentially recover. An existential risk, on the other hand, is one that either destroys humanity (and, presumably, all but the most rudimentary species of non-human lifeforms and/or plant life) entirely or at least prevents any chance of civilization recovering.^[6]

Similarly, in Catastrophe: Risk and Response, Richard Posner singles out and groups together events that bring about "utter overthrow or ruin" on a global, rather than a "local or regional" scale. Posner singles out such events as worthy of special attention on cost-benefit grounds because they could directly or indirectly jeopardize the survival of the human race as a whole.^[7] Posner's events include meteor impacts, runaway global warming, grey goo, bioterrorism, and particle accelerator accidents.

Researchers experience difficulty in studying near human extinction directly, since humanity has never been destroyed before.^[8] While this does not mean that it will not be in the future, it does make modelling existential risks difficult, due in part to survivorship bias. However, civilizations vanished rather frequently in human history.

Likelihood

Some risks are due to phenomena that have occurred in earth's past and left a geological record. Together with contemporary observations, it is possible to make informed estimates of the likelihood such events will occur in the future. For example, an extinction-level comet or asteroid impact event before the year 2100 has been estimated at one-in-a-million.^{[9][10][further explanation needed]}Supervolcanoes are another example. There are several known supervolcanos, including Mt. Toba, which some say almost wiped out humanity at the time of its last eruption. The geologic record suggests this particular supervolcano re-erupts about every 50,000 years.^{[11][12][further explanation needed]}

Without the benefit of geological records and direct observation, the relative danger posed by other threats is much more difficult to calculate. In addition, it is one thing to estimate the likelihood of an event taking place, something else to assess how likely an event will cause extinction if it does occur, and most difficult of all, the risk posted by synergistic effects of multiple events taking place simultaneously.^{[citation needed]}

Given the limitations of ordinary calculation and modeling, expert elicitation is frequently used instead to obtain probability estimates.^[13] In 2008, an informal survey of experts on different global catastrophic risks at the Global Catastrophic Risk Conference at the University of Oxford suggested a 19% chance of human extinction by the year 2100. The conference report cautions that the results should be taken "with a grain of salt", the results were not meant to capture all large risks and did not include things like climate change, and the results likely reflect many cognitive biases of the conference participants.^[14]

Risk	Estimated probability for human extinction before 2100
Overall probability	19%
Molecular nanotechnology weapons	5%
Superintelligent AI	5%
All wars (including civil wars)	4%
Engineered pandemic	2%
Nuclear war	1%
Nanotechnology accident	0.5%
Natural pandemic	0.05%
Nuclear terrorism	0.03%

Table source: Future of Humanity Institute, 2008.^[15]

The 2016 annual report by the Global Challenges Foundation estimates that an average American is more than five times more likely to die during a human-extinction event than in a car crash.^[16][17]

There are significant methodological challenges in estimating these risks with precision. Most attention has been given to risks to human civilization over the next 100 years, but forecasting for this length of time is difficult. The types of threats posed by nature have been argued to be relatively constant, though this has been disputed,^[18] and new risks could be discovered. Anthropogenic threats, however, are likely to change dramatically with the development of new technology; while volcanoes have been a threat throughout history, nuclear weapons have only been an issue since the 20th century. Historically, the ability of experts to predict the future over these timescales has proved very limited. Man-made threats such as nuclear war or nanotechnology are harder to predict than natural threats, due to the inherent methodological difficulties in the social sciences. In general, it is hard to estimate the magnitude of the risk from this or other dangers, especially as both international relations and technology can change rapidly.

Existential risks pose unique challenges to prediction, even more than other long-term events, because of observation selection effects. Unlike with most events, the failure of a complete extinction event to occur in the past is not evidence against their likelihood in the future, because every world that has experienced such an extinction event has no observers, so regardless of their frequency, no civilization observes existential risks in its history.^[8] These anthropic issues can be avoided by looking at evidence that does not have such selection effects, such as asteroid impact craters on the Moon, or directly evaluating the likely impact of new technology.^[5]

In addition to known and tangible risks, unforeseeable black swan extinction events may occur, presenting an additional methodological problem.^[19]

Moral importance of existential risk

Some scholars have strongly favored reducing existential risk on the grounds that it greatly benefits future generations. Derek Parfit argues that extinction would be a great loss because our descendants could potentially survive for four billion years before the expansion of the Sun makes the Earth uninhabitable.^[20][21]Nick Bostrom argues that there is even greater potential in colonizing space. If future humans colonize space, they may be able to support a very large number of people on other planets, potentially lasting for trillions of years.^[6] Therefore, reducing existential risk by even a small amount would have a very significant impact on the expected number of people who will exist in the future.

Exponential discounting might make these future benefits much less significant. However, Jason Matheny has argued that such discounting is inappropriate when assessing the value of existential risk reduction.^[9]

Some economists have discussed the importance of global catastrophic risks, though not existential risks. Martin Weitzman argues that most of the expected economic damage from climate change may come from the small chance that warming greatly exceeds the mid-range expectations, resulting in catastrophic damage.^[22]Richard Posner has argued that we are doing far too little, in general, about small, hard-to-estimate risks of large-scale catastrophes.^[23]

Numerous cognitive biases can influence people's judgment of the importance of existential risks, including scope insensitivity, hyperbolic discounting, availability heuristic, the conjunction fallacy, the affect heuristic, and the overconfidence effect.^[24]

Scope insensitivity influences how bad people consider the extinction of the human race to be. For example, when people are motivated to donate money to altruistic causes, the quantity they are willing to give does not increase linearly with the magnitude of the issue: people are roughly as concerned about 200,000 birds getting stuck in oil as they are about 2,000.^[25] Similarly, people are often more concerned about threats to individuals than to larger groups.^[24]

There are economic reasons that can explain why so little effort is going into existential risk reduction. It is a global good, so even if a large nation decreases it, that nation will only enjoy a small fraction of the benefit of doing so. Furthermore, the vast majority of the benefits may be enjoyed by far future generations, and though these quadrillions of future people would in theory perhaps be willing to pay massive sums for existential risk reduction, no mechanism for such a transaction exists.^[5]

Potential sources of risk

Some sources of catastrophic risk are natural, such as meteor impacts or supervolcanoes. Some of these have caused mass extinctions in the past. On the other hand, some risks are man-made, such as global warming,^[26] environmental degradation, engineered pandemics and nuclear war.

Anthropogenic

The Cambridge Project at Cambridge University states that the "greatest threats" to the human species are man-made; they are artificial intelligence, global warming, nuclear war, and rogue biotechnology.^[27] The Future of Humanity Institute also states that human extinction is more likely to result from anthropogenic causes than natural causes.^[5][28]

Artificial intelligence

It has been suggested that learning computers that rapidly become superintelligent may take unforeseen actions, or that robots would out-compete humanity (one technological singularity scenario).^[29] Because of its exceptional scheduling and organizational capability and the range of novel technologies it could develop, it is possible that the first Earth superintelligence to emerge could rapidly become matchless and unrivaled: conceivably it would be able to bring about almost any possible outcome, and be able to foil virtually any attempt that threatened to prevent it achieving its objectives.^[30] It could eliminate, wiping out if it chose, any other challenging rival intellects; alternatively it might manipulate or persuade them to change their behavior towards its own interests, or it may merely obstruct their attempts at interference.^[30] In Bostrom's book, Superintelligence: Paths, Dangers, Strategies, he defines this as the control problem.^[31] Physicist Stephen Hawking, Microsoft founder Bill Gates and SpaceX founder Elon Musk have echoed these concerns, with Hawking theorizing that this A.I. could "spell the end of the human race".^[32]

In 2009, the Association for the Advancement of Artificial Intelligence (AAAI) hosted a conference to discuss whether computers and robots might be able to acquire any sort of autonomy, and how much these abilities might pose a threat or hazard. They noted that some robots have acquired various forms of semi-autonomy, including being able to find power sources on their own and being able to independently choose targets to attack with weapons. They also noted that some computer viruses can evade elimination and have achieved "cockroach intelligence." They noted that self-awareness as depicted in science-fiction is probably unlikely, but that there were other potential hazards and pitfalls.^[33] Various media sources and scientific groups have noted separate trends in differing areas which might together result in greater robotic functionalities and autonomy, and which pose some inherent concerns.^[34][35]

A survey of AI experts estimated that the chance of human-level machine learning having an "extremely bad (e.g., human extinction)" long-term effect on humanity is 5%.^[36] A 2008 survey by the Future of Humanity Institute estimated a 5% probability of extinction by superintelligence by 2100.^[14]Eliezer Yudkowsky believes that risks from artificial intelligence are harder to predict than any other known risks due to bias from anthropomorphism. Since people base their judgments of artificial intelligence on their own experience, he claims that they underestimate the potential power of AI.^[37]

Biotechnology

Biotechnology can pose a global catastrophic risk in the form of bioengineered organisms (viruses, bacteria, fungi, plants or animals). In many cases the organism will be a pathogen of humans, livestock, crops or other organisms we depend upon (e.g. pollinators or gut bacteria). However, any organism able to catastrophically disrupt ecosystem functions, e.g. highly competitive weeds, outcompeting essential crops, poses a biotechnology risk.

A biotechnology catastrophe may be caused by accidentally releasing a genetically engineered organism from controlled environments, by the planned release of such an organism which then turns out to have unforeseen and catastrophic interactions with essential natural or agro-ecosystems, or by intentional usage of biological agents in biological warfare, bioterrorism attacks.^[38] Pathogens may be intentionally or unintentionally genetically modified to change virulence and other characteristics.^[38] For example, a group of Australian researchers unintentionally changed characteristics of the mousepox virus while trying to develop a virus to sterilize rodents.^[38] The modified virus became highly lethal even in vaccinated and naturally resistant mice.^[39][40] The technological means to genetically modify virus characteristics are likely to become more widely available in the future if not properly regulated.^[38]

Terrorist applications of biotechnology have historically been infrequent. To what extent this is due to a lack of capabilities or motivation is not resolved.^[38] However, given current development, more risk from novel, engineered pathogens is to be expected in the future.^[38] Exponential growth has been observed in the biotechnology sector, and Noun and Chyba predict that this will lead to major increases in biotechnological capabilities in the coming decades.^[38] They argue that risks from biological warfare and bioterrorism are distinct from nuclear and chemical threats because biological pathogens are easier to mass-produce and their production is hard to control (especially as the technological capabilities are becoming available even to individual users).^[38] In 2008, a survey by the Future of Humanity Institute estimated a 2% probability of extinction from engineered pandemics by 2100.^[14]

Noun and Chyba propose three categories of measures to reduce risks from biotechnology and natural pandemics: Regulation or prevention of potentially dangerous research, improved recognition of outbreaks and developing facilities to mitigate disease outbreaks (e.g. better and/or more widely distributed vaccines).^[38]

Cyberattack

Cyberattacks have the potential to destroy everything from personal data to electric grids. Christine Peterson, co-founder and past president of the Foresight Institute, believes a cyberattack on electric grids has the potential to be a catastrophic risk.^[41]

Environmental disaster

An environmental or ecological disaster, such as world crop failure and collapse of ecosystem services, could be induced by the present trends of overpopulation, economic development,^[42] and non-sustainable agriculture. Most environmental scenarios involve one or more of the following: Holocene extinction event,^[43]scarcity of water that could lead to approximately one half of the Earth's population being without safe drinking water, pollinator decline, overfishing, massive deforestation, desertification, climate change, or massive water pollution episodes. Detected in the early 21st century, a threat in this direction is colony collapse disorder,^[44] a phenomenon that might foreshadow the imminent extinction^[45] of the Western honeybee. As the bee plays a vital role in pollination, its extinction would severely disrupt the food chain.

An October 2017 report published in The Lancet stated that toxic air, water, soils, and workplaces were collectively responsible for 9 million deaths worldwide in 2015, particularly from air pollution which was linked to deaths by increasing susceptibility to non-infectious diseases, such as heart disease, stroke, and lung cancer.^[46] The report warned that the pollution crisis was exceeding "the envelope on the amount of pollution the Earth can carry" and “threatens the continuing survival of human societies”.^[46]

Experimental technology accident

Nick Bostrom suggested that in the pursuit of knowledge, humanity might inadvertently create a device that could destroy Earth and the Solar System.^[47] Investigations in nuclear and high-energy physics could create unusual conditions with catastrophic consequences. For example, scientists worried that the first nuclear test might ignite the atmosphere.^[48][49] Others worried that the RHIC^[50] or the Large Hadron Collider might start a chain-reaction global disaster involving black holes, strangelets, or false vacuum states. These particular concerns have been refuted,^{[51][52][53][54]} but the general concern remains.

Biotechnology could lead to the creation of a pandemic, chemical warfare could be taken to an extreme, nanotechnology could lead to grey goo in which out-of-control self-replicating robots consume all living matter on earth while building more of themselves—in both cases, either deliberately or by accident.^[55]

Global warming

Global warming refers to the warming caused by human technology since the 19th century or earlier. Projections of future climate change suggest further global warming, sea level rise, and an increase in the frequency and severity of some extreme weather events and weather-related disasters. Effects of global warming include loss of biodiversity, stresses to existing food-producing systems, increased spread of known infectious diseases such as malaria, and rapid mutation of microorganisms. In November 2017, a statement by 15,364 scientists from 184 countries indicated that increasing levels of greenhouse gases from use of fossil fuels, human population growth, deforestation, and overuse of land for agricultural production, particularly by farming ruminants for meat consumption, are trending in ways that forecast an increase in human misery over coming decades.^[3]

Mineral resource exhaustion

Romanian American economist Nicholas Georgescu-Roegen, a progenitor in economics and the paradigm founder of ecological economics, has argued that the carrying capacity of Earth — that is, Earth's capacity to sustain human populations and consumption levels — is bound to decrease sometime in the future as Earth's finite stock of mineral resources is presently being extracted and put to use; and consequently, that the world economy as a whole is heading towards an inevitable future collapse, leading to the demise of human civilization itself.^[56]:303f Ecological economist and steady-state theorist Herman Daly, a student of Georgescu-Roegen, has propounded the same argument by asserting that "... all we can do is to avoid wasting the limited capacity of creation to support present and future life [on Earth]." ^[57]:370

Ever since Georgescu-Roegen and Daly published these views, various scholars in the field have been discussing the existential impossibility of allocating earth's finite stock of mineral resources evenly among an unknown number of present and future generations. This number of generations is likely to remain unknown to us, as there is no way — or only little way — of knowing in advance if or when mankind will ultimately face extinction. In effect, any conceivable intertemporal allocation of the stock will inevitably end up with universal economic decline at some future point.^{[58]:253–256[59]:165[60]:168–171[61]:150–153[62]:106–109[63]:546–549[64]:142–145[65]}

Nanotechnology

Many nanoscale technologies are in development or currently in use.^[66] The only one that appears to pose a significant global catastrophic risk is molecular manufacturing, a technique that would make it possible to build complex structures at atomic precision.^[67] Molecular manufacturing requires significant advances in nanotechnology, but once achieved could produce highly advanced products at low costs and in large quantities in nanofactories of desktop proportions.^[66][67] When nanofactories gain the ability to produce other nanofactories, production may only be limited by relatively abundant factors such as input materials, energy and software.^[66]

Molecular manufacturing could be used to cheaply produce, among many other products, highly advanced, durable weapons.^[66] Being equipped with compact computers and motors these could be increasingly autonomous and have a large range of capabilities.^[66]

Chris Phoenix and Treder classify catastrophic risks posed by nanotechnology into three categories:

1. From augmenting the development of other technologies such as AI and biotechnology.


2. By enabling mass-production of potentially dangerous products that cause risk dynamics (such as arms races) depending on how they are used.


3. From uncontrolled self-perpetuating processes with destructive effects.

Several researchers state that the bulk of risk from nanotechnology comes from the potential to lead to war, arms races and destructive global government.^[39][66][68] Several reasons have been suggested why the availability of nanotech weaponry may with significant likelihood lead to unstable arms races (compared to e.g. nuclear arms races):

1. A large number of players may be tempted to enter the race since the threshold for doing so is low;^[66]
   


2. The ability to make weapons with molecular manufacturing will be cheap and easy to hide;^[66]
   


3. Therefore, lack of insight into the other parties' capabilities can tempt players to arm out of caution or to launch preemptive strikes;^[66][69]
   


4. Molecular manufacturing may reduce dependency on international trade,^[66] a potential peace-promoting factor;


5. 
   Wars of aggression may pose a smaller economic threat to the aggressor since manufacturing is cheap and humans may not be needed on the battlefield.^[66]
   

Since self-regulation by all state and non-state actors seems hard to achieve,^[70] measures to mitigate war-related risks have mainly been proposed in the area of international cooperation.^[66][71] International infrastructure may be expanded giving more sovereignty to the international level. This could help coordinate efforts for arms control. International institutions dedicated specifically to nanotechnology (perhaps analogously to the International Atomic Energy Agency IAEA) or general arms control may also be designed.^[71] One may also jointly make differential technological progress on defensive technologies, a policy that players should usually favour.^[66] The Center for Responsible Nanotechnology also suggests some technical restrictions.^[72] Improved transparency regarding technological capabilities may be another important facilitator for arms-control.

Grey goo is another catastrophic scenario, which was proposed by Eric Drexler in his 1986 book Engines of Creation^[73] and has been a theme in mainstream media and fiction.^[74][75] This scenario involves tiny self-replicating robots that consume the entire biosphere using it as a source of energy and building blocks. Nowadays, however, nanotech experts—including Drexler—discredit the scenario. According to Phoenix, a "so-called grey goo could only be the product of a deliberate and difficult engineering process, not an accident".^[76]

Warfare and mass destruction

Joseph Pennell's 1918 Liberty bond poster calls up the pictorial image of an invaded, burning New York City.

The scenarios that have been explored most frequently are nuclear warfare and doomsday devices. Although the probability of a nuclear war per year is slim, Professor Martin Hellman has described it as inevitable in the long run; unless the probability approaches zero, inevitably there will come a day when civilization's luck runs out.^[77] During the Cuban missile crisis, U.S. president John F. Kennedy estimated the odds of nuclear war at "somewhere between one out of three and even".^[78] The United States and Russia have a combined arsenal of 14,700 nuclear weapons,^[79] and there is an estimated total of 15,700 nuclear weapons in existence worldwide.^[79] Beyond nuclear, other military threats to humanity include biological warfare (BW). By contrast, chemical warfare, while able to create multiple local catastrophes, is unlikely to create a global one.

Nuclear war could yield unprecedented human death tolls and habitat destruction. Detonating large numbers of nuclear weapons would have an immediate, short term and long-term effects on the climate, causing cold weather and reduced sunlight and photosynthesis^[80] that may generate significant upheaval in advanced civilizations.^[81] However, while popular perception sometimes takes nuclear war as "the end of the world", experts assign low probability to human extinction from nuclear war.^[82][83] In 1982, Brian Martin estimated that a US–Soviet nuclear exchange might kill 400–450 million directly, mostly in the United States, Europe and Russia, and maybe several hundred million more through follow-up consequences in those same areas.^[82] In 2008, a survey by the Future of Humanity Institute estimated a 4% probability of extinction from warfare by 2100, with a 1% chance of extinction from nuclear warfare.^[14]

World population and agricultural crisis

The 20th century saw a rapid increase in human population due to medical developments and massive increases in agricultural productivity^[84] such as the Green Revolution.^[85] Between 1950 and 1984, as the Green Revolution transformed agriculture around the globe, world grain production increased by 250%. The Green Revolution in agriculture helped food production to keep pace with worldwide population growth or actually enabled population growth. The energy for the Green Revolution was provided by fossil fuels in the form of fertilizers (natural gas), pesticides (oil), and hydrocarbon-fueled irrigation.^[86] David Pimentel, professor of ecology and agriculture at Cornell University, and Mario Giampietro, senior researcher at the National Research Institute on Food and Nutrition (INRAN), place in their 1994 study Food, Land, Population and the U.S. Economy the maximum U.S. population for a sustainable economy at 200 million. To achieve a sustainable economy and avert disaster, the United States must reduce its population by at least one-third, and world population will have to be reduced by two-thirds, says the study.^[87]

The authors of this study believe that the mentioned agricultural crisis will begin to have an effect on the world after 2020, and will become critical after 2050. Geologist Dale Allen Pfeiffer claims that coming decades could see spiraling food prices without relief and massive starvation on a global level such as never experienced before.^[88][89]

Wheat is humanity's third-most-produced cereal. Extant fungal infections such as Ug99^[90] (a kind of stem rust) can cause 100% crop losses in most modern varieties. Little or no treatment is possible and infection spreads on the wind. Should the world's large grain-producing areas become infected, the ensuing crisis in wheat availability would lead to price spikes and shortages in other food products.^[91]

Non-anthropogenic

Asteroid impact

Several asteroids have collided with earth in recent geological history. The Chicxulub asteroid, for example, is theorized to have caused the extinction of the non-avian dinosaurs 66 million years ago at the end of the Cretaceous. No sufficiently large asteroid currently exists in an Earth-crossing orbit; however, a comet of sufficient size to cause human extinction could impact the Earth, though the annual probability may be less than 10⁻⁸.^[92] Geoscientist Brian Toon estimates that a 60-mile meteorite would be large enough to "incinerate everybody".^[93] Asteroids with around a 1 km diameter have impacted the Earth on average once every 500,000 years; these are probably too small to pose an extinction risk, but might kill billions of people.^[92][94] Larger asteroids are less common. Small near-Earth asteroids are regularly observed and can impact anywhere on the Earth injuring local populations.^[95] As of 2013, Spaceguard estimates it has identified 95% of all NEOs over 1 km in size.^[96]

In April 2018, the B612 Foundation reported "It's a 100 per cent certain we'll be hit [by a devastating asteroid], but we're not 100 per cent sure when."^[97][98] Also in 2018, physicist Stephen Hawking, in his final book Brief Answers to the Big Questions, considered an asteroid collision to be the biggest threat to the planet.^{[99][100][101]} In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, and has developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare.^{[102][103][104][105][106]} According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched.^[107]

Cosmic threats

A number of astronomical threats have been identified. Massive objects, e.g. a star, large planet or black hole, could be catastrophic if a close encounter occurred in the Solar System. In April 2008, it was announced that two simulations of long-term planetary movement, one at the Paris Observatory and the other at the University of California, Santa Cruz, indicate a 1% chance that Mercury's orbit could be made unstable by Jupiter's gravitational pull sometime during the lifespan of the Sun. Were this to happen, the simulations suggest a collision with Earth could be one of four possible outcomes (the others being Mercury colliding with the Sun, colliding with Venus, or being ejected from the Solar System altogether). If Mercury were to collide with Earth, all life on Earth could be obliterated entirely: an asteroid 15 km wide is believed to have caused the extinction of the non-avian dinosaurs, whereas Mercury is 4,879 km in diameter.^[108]

Another cosmic threat is a gamma-ray burst, typically produced by a supernova when a star collapses inward on itself and then "bounces" outward in a massive explosion. Under certain circumstances, these events are thought to produce massive bursts of gamma radiation emanating outward from the axis of rotation of the star. If such an event were to occur oriented towards the Earth, the massive amounts of gamma radiation could significantly affect the Earth's atmosphere and pose an existential threat to all life. Such a gamma-ray burst may have been the cause of the Ordovician–Silurian extinction events. Neither this scenario nor the destabilization of Mercury's orbit are likely in the foreseeable future.^[109]

A powerful solar flare or solar superstorm, which is a drastic and unusual decrease or increase in the Sun's power output, could have severe consequences for life on Earth.^[110][111]

If our universe lies within a false vacuum, a bubble of lower-energy vacuum could come to exist by chance or otherwise in our universe, and catalyze the conversion of our universe to a lower energy state in a volume expanding at nearly the speed of light, destroying all that we know without forewarning. Such an occurrence is called vacuum decay.^[112][113]

The most predictable outcome for the future of the Earth is the Sun's expansion into a red giant star. The Sun will be about 12 billion years old and expand to swallow both Mercury and Venus, reaching a maximum radius of 1.2 AU (180,000,000 km). The Earth will interact tidally with the Sun's outer atmosphere, which would serve to decrease Earth's orbital radius. Drag from the chromosphere of the Sun would also reduce the Earth's orbit. These effects will act to counterbalance the effect of mass loss by the Sun, and the Earth will probably be engulfed by the Sun.^[114]

Extraterrestrial invasion

Intelligent extraterrestrial life, if existent, could invade Earth^[115] either to exterminate and supplant human life, enslave it under a colonial system, steal the planet's resources, or destroy the planet altogether.

Although evidence of alien life has never been documented, scientists such as Carl Sagan have postulated that the existence of extraterrestrial life is very likely. In 1969, the "Extra-Terrestrial Exposure Law" was added to the United States Code of Federal Regulations (Title 14, Section 1211) in response to the possibility of biological contamination resulting from the U.S. Apollo Space Program. It was removed in 1991.^[116] Scientists consider such a scenario technically possible, but unlikely.^[117]

An article in The New York Times discussed the possible threats for humanity of intentionally sending messages aimed at extraterrestrial life into the cosmos in the context of the SETI efforts. Several renowned public figures such as Stephen Hawking and Elon Musk have argued against sending such messages on the grounds that extraterrestrial civilizations with technology are probably far more advanced than humanity and could pose an existential threat to humanity.^[118]

Global pandemic

Numerous historical examples of pandemics^[119] had a devastating effect on a large number of people. The present, unprecedented scale and speed of human movement make it more difficult than ever to contain an epidemic through local quarantines, and other sources of uncertainty and the evolving nature of the risk means natural pandemics may pose a realistic threat to human civilization.^[18]

There are several classes of argument about the likelihood of pandemics. One class of argument about likelihood stems from the history of pandemics, where the limited size of historical pandemics is evidence that larger pandemics are unlikely. This argument has been disputed on several grounds, including the changing risk due to changing population and behavioral patterns among humans, the limited historical record, and the existence of an anthropic bias.^[18]

Another argument about the likelihood of pandemics is based on an evolutionary model that predicts that naturally evolving pathogens will ultimately develop an upper limit to their virulence.^[120] This is because pathogens with high enough virulence quickly kill their hosts and reduce their chances of spread the infection to new hosts or carriers.^[121] This model has limits, however, because the fitness advantage of limited virulence is primarily a function of a limited number of hosts. Any pathogen with a high virulence, high transmission rate and long incubation time may have already caused a catastrophic pandemic before ultimately virulence is limited through natural selection. Additionally, a pathogen that infects humans as a secondary host and primarily infects another species (a zoonosis) has no constraints on its virulence in people, since the accidental secondary infections do not affect its evolution.^[122] Lastly, in models where virulence level and rate of transmission are related, high levels of virulence can evolve.^[123] Virulence is instead limited by the existence of complex populations of hosts with different susceptibilities to infection, or by some hosts being geographically isolated.^[120] The size of the host population and competition between different strains of pathogens can also alter virulence.^[124]

Neither of these arguments is applicable to bioengineered pathogens, and this poses entirely different risks of pandemics. Experts have concluded that "Developments in science and technology could significantly ease the development and use of high consequence biological weapons," and these "highly virulent and highly transmissible [bio-engineered pathogens] represent new potential pandemic threats."^[125]

Natural climate change

Climate change refers to a lasting change in the Earth's climate. The climate has ranged from ice ages to warmer periods when palm trees grew in Antarctica. It has been hypothesized that there was also a period called "snowball Earth" when all the oceans were covered in a layer of ice. These global climatic changes occurred slowly, prior to the rise of human civilization about 10 thousand years ago near the end of the last Major Ice Age when the climate became more stable. However, abrupt climate change on the decade time scale has occurred regionally. Since civilization originated during a period of stable climate, a natural variation into a new climate regime (colder or hotter) could pose a threat to civilization.^[126][127]

In the history of the Earth, many ice ages are known to have occurred. An ice age would have a serious impact on civilization because vast areas of land (mainly in North America, Europe, and Asia) could become uninhabitable. Currently, the world is in an interglacial period within a much older glacial event. The last glacial expansion ended about 10,000 years ago, and all civilizations evolved later than this. Scientists do not predict that a natural ice age will occur anytime soon.^{[citation needed]} The amount of heat trapping gases emitted into Earth's Oceans and atmosphere will prevent the next ice age, which otherwise would begin in around 50,000 years, and likely more glacial cycles.^[128][129]

Volcanism

A geological event such as massive flood basalt, volcanism, or the eruption of a supervolcano^[130] could lead to a so-called volcanic winter, similar to a nuclear winter. One such event, the Toba eruption,^[131] occurred in Indonesia about 71,500 years ago. According to the Toba catastrophe theory,^[132] the event may have reduced human populations to only a few tens of thousands of individuals. Yellowstone Caldera is another such supervolcano, having undergone 142 or more caldera-forming eruptions in the past 17 million years.^[133]
A massive volcano eruption would eject extraordinary volumes of volcanic dust, toxic and greenhouse gases into the atmosphere with serious effects on global climate (towards extreme global cooling: volcanic winter if short-term, and ice age if long-term) or global warming (if greenhouse gases were to prevail).

When the supervolcano at Yellowstone last erupted 640,000 years ago, the thinnest layers of the ash ejected from the caldera spread over most of the United States west of the Mississippi River and part of northeastern Mexico. The magma covered much of what is now Yellowstone National Park and extended beyond, covering much of the ground from Yellowstone River in the east to the Idaho falls in the west, with some of the flows extending north beyond Mammoth Springs.^[134]

According to a recent study, if the Yellowstone caldera erupted again as a supervolcano, an ash layer one to three millimeters thick could be deposited as far away as New York, enough to "reduce traction on roads and runways, short out electrical transformers and cause respiratory problems". There would be centimeters of thickness over much of the U.S. Midwest, enough to disrupt crops and livestock, especially if it happened at a critical time in the growing season. The worst-affected city would likely be Billings, Montana, population 109,000, which the model predicted would be covered with ash estimated as 1.03 to 1.8 meters thick.^[135]

The main long-term effect is through global climate change, which reduces the temperature globally by about 5–15 degrees C for a decade, together with the direct effects of the deposits of ash on their crops. A large supervolcano like Toba would deposit one or two meters thickness of ash over an area of several million square kilometers.(1000 cubic kilometers is equivalent to a one-meter thickness of ash spread over a million square kilometers). If that happened in some densely populated agricultural area, such as India, it could destroy one or two seasons of crops for two billion people.^[136]

However, Yellowstone shows no signs of a supereruption at present, and it is not certain that a future supereruption will occur there.^[137][138]

Research published in 2011 finds evidence that massive volcanic eruptions caused massive coal combustion, supporting models for significant generation of greenhouse gases. Researchers have suggested that massive volcanic eruptions through coal beds in Siberia would generate significant greenhouse gases and cause a runaway greenhouse effect.^[139] Massive eruptions can also throw enough pyroclastic debris and other material into the atmosphere to partially block out the sun and cause a volcanic winter, as happened on a smaller scale in 1816 following the eruption of Mount Tambora, the so-called Year Without a Summer. Such an eruption might cause the immediate deaths of millions of people several hundred miles from the eruption, and perhaps billions of death worldwide, due to the failure of the monsoons^[140], resulting in major crop failures causing starvation on a profound scale.^[140]

A much more speculative concept is the verneshot: a hypothetical volcanic eruption caused by the buildup of gas deep underneath a craton. Such an event may be forceful enough to launch an extreme amount of material from the crust and mantle into a sub-orbital trajectory.

Proposed mitigation

Planetary management and respecting planetary boundaries have been proposed as approaches to preventing ecological catastrophes. Within the scope of these approaches, the field of geoengineering encompasses the deliberate large-scale engineering and manipulation of the planetary environment to combat or counteract anthropogenic changes in atmospheric chemistry. Space colonization is a proposed alternative to improve the odds of surviving an extinction scenario.^[141] Solutions of this scope may require megascale engineering.
Food storage has been proposed globally, but the monetary cost would be high. Furthermore, it would likely contribute to the current millions of deaths per year due to malnutrition.^[142]

Some survivalists stock survival retreats with multiple-year food supplies.

The Svalbard Global Seed Vault is buried 400 feet (120 m) inside a mountain on an island in the Arctic. It is designed to hold 2.5 billion seeds from more than 100 countries as a precaution to preserve the world's crops. The surrounding rock is −6 °C (21 °F) (as of 2015) but the vault is kept at −18 °C (0 °F) by refrigerators powered by locally sourced coal.^[143][144]

More speculatively, if society continues to function and if the biosphere remains habitable, calorie needs for the present human population might in theory be met during an extended absence of sunlight, given sufficient advance planning. Conjectured solutions include growing mushrooms on the dead plant biomass left in the wake of the catastrophe, converting cellulose to sugar, or feeding natural gas to methane-digesting bacteria.^[145][146]

Global catastrophic risks and global governance

Insufficient global governance creates risks in the social and political domain, but the governance mechanisms develop more slowly than technological and social change. There are concerns from governments, the private sector, as well as the general public about the lack of governance mechanisms to efficiently deal with risks, negotiate and adjudicate between diverse and conflicting interests. This is further underlined by an understanding of the interconnectedness of global systemic risks.^[147]

Climate emergency plans

In 2018, the Club of Rome submitted a plan to the European Parliament, urging to address the existential threat from climate change more forcefully, calling for a collaborative climate action afford.^[148]

Organizations

The Bulletin of the Atomic Scientists (est. 1945) is one of the oldest global risk organizations, founded after the public became alarmed by the potential of atomic warfare in the aftermath of WWII. It studies risks associated with nuclear war and energy and famously maintains the Doomsday Clock established in 1947. The Foresight Institute (est. 1986) examines the risks of nanotechnology and its benefits. It was one of the earliest organizations to study the unintended consequences of otherwise harmless technology gone haywire at a global scale. It was founded by K. Eric Drexler who postulated "grey goo".^[149][150]

Beginning after 2000, a growing number of scientists, philosophers and tech billionaires created organizations devoted to studying global risks both inside and outside of academia.^[151]

Independent non-governmental organizations (NGOs) include the Machine Intelligence Research Institute (est. 2000), which aims to reduce the risk of a catastrophe caused by artificial intelligence,^[152] with donors including Peter Thiel and Jed McCaleb.^[153] The Nuclear Threat Initiative (est. 2001) seeks to reduce global threats from nuclear, biological and chemical threats, and containment of damage after an event.^[154] It maintains a nuclear material security index.^[155] The Lifeboat Foundation (est. 2009) funds research into preventing a technological catastrophe.^[156] Most of the research money funds projects at universities.^[157] The Global Catastrophic Risk Institute (est. 2011) is a think tank for catastrophic risk. It is funded by the NGO Social and Environmental Entrepreneurs. The Global Challenges Foundation (est. 2012), based in Stockholm and founded by Laszlo Szombatfalvy, releases a yearly report on the state of global risks.^[16][17] The Future of Life Institute (est. 2014) aims to support research and initiatives for safeguarding life considering new technologies and challenges facing humanity.^[158]Elon Musk is one of its biggest donors.^[159]

University-based organizations include the Future of Humanity Institute (est. 2005) which researches the questions of humanity's long-term future, particularly existential risk. It was founded by Nick Bostrom and is based at Oxford University. The Centre for the Study of Existential Risk (est. 2012) is a Cambridge-based organization which studies four major technological risks: artificial intelligence, biotechnology, global warming and warfare. All are man-made risks, as Huw Price explained to the AFP news agency, "It seems a reasonable prediction that some time in this or the next century intelligence will escape from the constraints of biology". He added that when this happens "we're no longer the smartest things around," and will risk being at the mercy of "machines that are not malicious, but machines whose interests don't include us."^[160]Stephen Hawking was an acting adviser. The Millennium Alliance for Humanity and the Biosphere is a Stanford University-based organization focusing on many issues related to global catastrophe by bringing together members of academic in the humanities.^[161][162] It was founded by Paul Ehrlich among others.^[163] Stanford University also has the Center for International Security and Cooperation focusing on political cooperation to reduce global catastrophic risk.^[164] The Center for Security and Emerging Technology was established in January 2019 at Georgetown's Walsh School of Foreign Service and will focus on policy research of emerging technologies with an initial emphasis on artificial intelligence.^[165] They received a grant of 55M USD from Good Ventures as suggested by the Open Philanthropy Project.^[165]

Other risk assessment groups are based in or are part of governmental organizations. The World Health Organization (WHO) includes a division called the Global Alert and Response (GAR) which monitors and responds to global epidemic crisis.^[166] GAR helps member states with training and coordination of response to epidemics.^[167] The United States Agency for International Development (USAID) has its Emerging Pandemic Threats Program which aims to prevent and contain naturally generated pandemics at their source.^[168] The Lawrence Livermore National Laboratory has a division called the Global Security Principal Directorate which researches on behalf of the government issues such as bio-security and counter-terrorism.^[169]

See also

Notes

Further reading

• 
  Classifying global catastrophic risks Avin et al. (2018)


• 
  Corey S. Powell (2000). "Twenty ways the world could end suddenly", Discover Magazine
  


• 
  Martin Rees (2004). OUR FINAL HOUR: A Scientist's warning: How Terror, Error, and Environmental Disaster Threaten Humankind's Future in This Century—On Earth and Beyond.
  ISBN 0-465-06863-4
  


• 
  Jean-Francois Rischard (2003). High Noon 20 Global Problems, 20 Years to Solve Them.
  ISBN 0-465-07010-8
  


• 
  Edward O. Wilson (2003). The Future of Life.
  ISBN 0-679-76811-4
  


• Roger-Maurice Bonnet and Lodewijk Woltjer, Surviving 1,000 Centuries Can We Do It? (2008), Springer-Praxis Books.


• 
  Derrick Jensen (2006) Endgame (
  ISBN 1-58322-730-X).


• 
  Jared Diamond, Collapse: How Societies Choose to Fail or Succeed, Penguin Books, 2005 and 2011 (
  ISBN 9780241958681).


• Huesemann, Michael H., and Joyce A. Huesemann (2011). Technofix: Why Technology Won't Save Us or the Environment, Chapter 6, “Sustainability or Collapse”, New Society Publishers, Gabriola Island, British Columbia, Canada, 464 pages (
  ISBN 0865717044).


• 
  Joel Garreau, Radical Evolution, 2005 (
  ISBN 978-0385509657).


• 
  John A. Leslie (1996). The End of the World (
  ISBN 0-415-14043-9).


• 
  Donella Meadows (1972). The Limits to Growth (
  ISBN 0-87663-165-0).


• 
  Joseph Tainter, (1990). The Collapse of Complex Societies, Cambridge University Press, Cambridge, UK (
  ISBN 9780521386739).

External links

• 
  Annual Reports on Global Risk by the Global Challenges Foundation
  


• 
  "What a way to go" from The Guardian. Ten scientists name the biggest dangers to Earth and assess the chances they will happen. April 14, 2005.


• 
  Stephen Petranek: 10 ways the world could end, a TED talk
  


• 
  "Top 10 Ways to Destroy Earth". livescience.com. LiveScience. Archived from the original on 2011-01-01.
  


• 
  "Are we on the road to civilisation collapse?". BBC. 19 February 2019.