Human extinction

In futures studies, human extinction is the hypothetical end of the human species. This may be caused by natural causes or it may be anthropogenic, i.e. the result of human action.

The likelihood of human extinction in the near future by wholly natural scenarios, such as a meteorite impact or large-scale volcanism, is generally considered to be extremely low.^[1]

For anthropogenic extinction, many possible scenarios have been proposed: Human global nuclear annihilation, biological warfare or the release of a pandemic-causing agent, dysgenics, overpopulation,^[2] ecological collapse, and global warming; in addition, emerging technologies could bring about new extinction scenarios, such as advanced artificial intelligence, biotechnology or self-replicating nanobots. The probability of anthropogenic human extinction within the next hundred years is the topic of an active debate.

Human extinction needs to be differentiated from the extinction of all life on Earth (see also future of Earth) and from the extinction of major components of human culture (e.g., through a global catastrophe leaving only small, scattered human populations, which might evolve in isolation).

Moral importance of existential risk

"Existential risks" are risks that threaten the entire future of humanity, whether by causing human extinction or by otherwise permanently crippling human progress.^[1] Many scholars make an argument based on the size of the "cosmic endowment" and state that because of the inconceivably large number of potential future lives that are at stake, even small reductions of existential risk have great value. Some of the arguments run as follows:

• Carl Sagan wrote in 1983: "If we are required to calibrate extinction in numerical terms, I would be sure to include the number of people in future generations who would not be born.... (By one calculation), the stakes are one million times greater for extinction than for the more modest nuclear wars that kill "only" hundreds of millions of people. There are many other possible measures of the potential loss—including culture and science, the evolutionary history of the planet, and the significance of the lives of all of our ancestors who contributed to the future of their descendants. Extinction is the undoing of the human enterprise."^[3]
• Philosopher Derek Parfit in 1984 makes an anthropocentric utilitarian argument that, because all human lives have roughly equal intrinsic value no matter where in time or space they are born, the large number of lives potentially saved in the future should be multiplied by the percentage chance that an action will save them, yielding a large net benefit for even tiny reductions in existential risk.^[4]
• Philosopher Robert Adams rejects in 1989 Parfit's "impersonal" views, but speaks instead of a moral imperative for loyalty and commitment to "the future of humanity as a vast project... The aspiration for a better society- more just, more rewarding, and more peaceful... our interest in the lives of our children and grandchildren, and the hopes that they will be able, in turn, to have the lives of their children and grandchildren as projects."^[5]
• Philosopher Nick Bostrom argues in 2013 that preference-satisfactionist, democratic, custodial, and intuitionist arguments all converge on the common-sense view that preventing existential risk is a high moral priority, even if the exact "degree of badness" of human extinction varies between these philosophies.^[1]:23–4

Parfit argues that the size of the "cosmic endowment" can be calculated from the following argument: If Earth remains habitable for a billion more years and can sustainably support a population of more than a billion humans, then there is a potential for 10¹⁶ (or 10,000,000,000,000,000) human lives of normal duration.^[4]:453–4 Bostrom goes further, stating that if the universe is empty, then the accessible universe can support at least 10³⁴ biological human life-years; and, if some humans were uploaded onto computers, could even support the equivalent of 10⁵⁴ cybernetic human life-years.^[1]

Possible scenarios

Severe forms of known or recorded disasters

• Nuclear or biological warfare; for example, a future arms race may result in larger arsenals than those of the Cold War^[6] and a hypothetical World War III could cause the total annihilation of humankind.
• A pandemic^[6] involving one or more viruses, prions, or antibiotic-resistant bacteria. Past examples include the Spanish flu outbreak in 1918 and the various European viruses that decimated indigenous American populations. A deadly pandemic restricted to humans alone would be self-limiting as its mortality would reduce the density of its target population. A pathogen with a broad host range in multiple species, however, could eventually reach even isolated human populations, e.g. when using animals as "carriers".^[7] U.S. officials assess that an engineered pathogen capable of "wiping out all of humanity", if left unchecked, is technically feasible and that the technical obstacles are "trivial". However, they are confident that in practice, countries would be able to "recognize and intervene effectively" to halt the spread of such a microbe and prevent human extinction.^[8]
• Population decline through a preference for fewer children. If developing world demographics are assumed to become developed world demographics, and if the latter are extrapolated, data suggest an extinction before 3000 AD. John A. Leslie estimates that if the reproduction rate drops to the German level the extinction date will be 2400. However, evolutionary biology suggests the demographic transition may reverse itself.
• A geological or cosmological disaster such as an impact event of a near-Earth object,^[9] a lethal gamma-ray burst in our part of the Milky Way,^[10][11] a supervolcanic eruption, or natural long-term climate change. Near-Earth objects (NEOs), serve as an absolute threat to the survival of living species, and even small-scale events can result in a substantial amount of local and regional damages.^[12] A single, extraterrestrial event^[13] can lead to the accumulation of more deaths and destruction than any man-made war or epidemic could ever produce. This scenario is special among the non-anthropogenic extinction scenarios insofar, as it is conceivable to develop countermeasures for a large proportion of such impact events.

Habitat threats

• Human-induced changes to the atmosphere's composition may render Earth uninhabitable for humans. Carbon dioxide is toxic at high concentrations, causing death by respiratory acidosis (acidification of the blood), and lifelong exposure to even the moderately elevated concentrations projected to occur during the 21st century could cause chronic physical and mental health conditions in all humans. The upper limit, above which human survival and reproduction would be impossible, is still unknown.^[14]
• There is no other population of a large vertebrate animal like humans in the history of the planet has grown so much, so fast, or with such devastating consequences to fellow earthlings. The growth of population rapidly from 1 billion in 1800 to 2 billion in 1930, and has reached over 7 billion today. With the population going up, people will annually absorb more primary productivity of the Earth’s terrestrial net, and increasing the use of land.^[15] Mentioned by Center for Biological Diversity, the species will eventually lead to a crash when its population grows beyond the capacity of its environmental sustainment and reduces its capacity below the original level.^[16] Evidence suggests birth rates may be rising in the 21st century in the developed world.^[17] The work of Hans Rosling, a Swedish medical doctor, academic, statistician and public speaker predicts Global populations peaking at less than 12 billion.^[18]
• In around 1 billion years from now, the Sun's brightness may increase as a result of a shortage of hydrogen and the heating of its outer layers may cause the Earth's oceans to evaporate, leaving only minor forms of life.^[19] Well before this time, the level of carbon dioxide in the atmosphere will be too low to support plant life, destroying the foundation of the food chains.^[20] See Future of the Earth.
• About 7–8 billion years from now, if and after the Sun has become a red giant, the Earth will probably be engulfed by an expanding Sun and destroyed.^[21][22]

Scientific accidents

Without regulation, scientific advancement has a potential to risk human extinction as a result of the effects or use of totally new technologies. Some scenarios include:

• The creators of a "superintelligent" entity could inadvertently give it goals that lead it to "annihilate" the human race.^[6][23]
• Uncontrolled nanotechnology (grey goo) incidents resulting in the destruction of the Earth's ecosystem (ecophagy).^[24][25]
• Creation of a "micro black hole" on Earth during the course of a scientific experiment, or other unlikely scientific accidents in high-energy physics research, such as vacuum phase transition or strangelet incidents. There were worries concerning the Large Hadron Collider at CERN as it is feared that collision of protons at a speed near the speed of light will result in the creation of a black hole, but it has been pointed out that much more energetic collisions take place currently in Earth's atmosphere.^[24][26][27]

Further scenarios of extraterrestrial origin

(Major impact events.^[9] and Gamma-ray burst in our part of the Milky Way^[10][11] were already mentioned above.)

• Invasion by militarily superior extraterrestrials (see alien invasion) — often considered to be a scenario purely from the realms of science fiction, professional SETI researchers have given serious consideration to this possibility, but conclude that it is unlikely.

Evolution of a posthuman species

Normal biological evolution of humanity will continue and change humans over geological time scales. Although this could, in a non-phylogenetic taxonomy, be considered to give rise of a new species, such an ongoing evolution would biologically not be considered a species extinction. Given the likelihood that significant genetic exchange between human populations will continue, it is highly unlikely that humans will split into multiple species through natural evolution.

Some scenarios envision that humans could use genetic engineering or technological modifications to split into normal humans and a new species – posthumans.^{[28][29][30][31][32][33][34]} Such a species could be fundamentally different from any previous life form on earth, e.g. by merging humans with technological systems.^[35][36] Such scenarios do harbor a risk of the extinction of the "old" human species by means of the new, posthuman entity.

Perception of and reactions to human extinction risk

Probability estimates

Because human extinction is unprecedented, speculation about the probability of different scenarios is highly subjective. Nick Bostrom argues that it would be "misguided" to assume that the probability of near-term extinction is less than 25% and that it will be "a tall order" for the human race to "get our precautions sufficiently right the first time", given that an existential risk provides no opportunity to learn from failure.^[1][37] A little more optimistically, philosopher John Leslie assigns a 70% chance of humanity surviving the next five centuries, based partly on the controversial philosophical doomsday argument that Leslie champions. The 2006 Stern Review for the UK Treasury assumes the 100-year probability of human extinction is 10% in its economic calculations.^[37]

Some scholars believe that certain scenarios such as global thermonuclear war would have difficulty eradicating every last settlement on Earth. Physicist Willard Wells points out that any credible extinction scenario would have to reach into a diverse set of areas, including the underground subways of major cities, the mountains of Tibet, the remotest islands of the South Pacific, and even to McMurdo Station in Antarctica, which has contingency plans and supplies for a long isolation.^[38] In addition, elaborate bunkers exist for government leaders to occupy during a nuclear war.^[37] Any number of events could lead to a massive loss of human life; but if the last few, most resilient, humans are unlikely to also die off, then that particular human extinction scenario is not credible.^[39]

Psychology

Eliezer Yudkowsky theorizes that scope neglect plays a role in public perception of existential risks:^[1][40]

Substantially larger numbers, such as 500 million deaths, and especially qualitatively different scenarios such as the extinction of the entire human species, seem to trigger a different mode of thinking... People who would never dream of hurting a child hear of an existential risk, and say, "Well, maybe the human species doesn't really deserve to survive".

All past predictions of human extinction have proven to be false. To some, this makes future warnings seem less credible. Nick Bostrom argues that the lack of human extinction in the past is weak evidence that there will be no human extinction in the future, due to survivor bias and other anthropic effects.^[41]

Some behavioural finance scholars claim that recent evidence is given undue significance in risk analysis. Roughly speaking, "100 year storms" tend to occur every twenty years in the stock market as traders become convinced that the current good times will last forever. Doomsayers who hypothesize rare crisis-scenarios are dismissed even when they have statistical evidence behind them. An extreme form of this bias can diminish the subjective probability of the unprecedented.

Research and initiatives

Even though the importance and potential impact of research on existential risks is often highlighted relatively few research efforts are being made in this field. In 2001 Bostrom stated:^[42]

Although existential risks are less manageable by individuals than, e.g., health risks, according to Ken Olum, Joshua Knobe, and Alexander Vilenkin the possibility of human extinction does have practical implications. For instance, if the "universal" Doomsday argument is accepted it changes the most likely source of disasters, and hence the most efficient means of preventing them. They write: "... you should be more concerned that a large number of asteroids have not yet been detected than about the particular orbit of each one. You should not worry especially about the chance that some specific nearby star will become a supernova, but more about the chance that supernovas are more deadly to nearby life then we believe."^[43]

Multiple organizations with the goal of helping prevent human extinction exist. Examples are the Future of Humanity Institute, the Centre for the Study of Existential Risk, the Future of Life Institute, the Machine Intelligence Research Institute, and the Global Catastrophic Risk Institute (est. 2011).

Observations about human extinction

Milankovitch cycles describe the way that the earth moves and how the climatic changes vary depending on where the earth is in space. The orbital shape of the earth causes changes every 100,000 years. The axial tilt of the earth "wobbles" and alters the climate every 41 thousand years. The axial precession is the process in which the climate will change in terms of how the earth rotates about its own axis. David M. Raup did find that every 26 million years, there will be a mass extinction.^[44]

Roland Jansson and Mats Dynesius in their article The Fate of Clades in a World of Recurrent Climatic Change: Milankovitch Oscillations and Evolution,^[45] discuss how these cycles will cause orbitally forced range dynamics (ORD) in which the climate changes induced by the Milankovitch cycles cause changes in the geographic distribution of clades. Clades are a group of organisms that are theorized to have evolved from a common ancestor.

Milankovitch cycles, also known as Quaternary Climatic Oscillations as described by P.A. Barker,^[46] effect the climate in various ways in either extreme cold or extreme heat.

Omnicide

Omnicide is human extinction as a result of human action. Most commonly it refers to extinction through nuclear warfare or biological warfare,^[47][48][49] but it can also apply to extinction through means such as a global anthropogenic ecological catastrophe.^[50]

Omnicide can be considered a subcategory of genocide.^[51] Using the concept in this way, one can argue, for example, that:

Proposed countermeasures

Scientists such as Stephen Hawking have proposed that an initiative to colonize other planets within the solar system could improve the chance of human survival from planet-wide events such as global thermonuclear war.^[53][54]

More economically, some scholars propose the establishment on Earth of one or more self-sufficient, remote, permanently occupied settlements specifically created for the purpose of surviving global disaster.^[37][38] Economist Robin Hanson argues that a refuge permanently housing as few as 100 people would significantly improve the chances of human survival during a range of global catastrophes.^[37][55]

In popular culture

Some 21st century pop-science works, including The World Without Us by Alan Weisman, pose an artistic thought experiment: what would happen to the rest of the planet if humans suddenly disappeared?^[56][57] A threat of human extinction drives the plot of innumerable science fiction stories; an influential early example is the 1951 film adaption of When Worlds Collide.^[58] Usually the extinction threat is narrowly avoided, but some exceptions exist, such as R.U.R. and Steven Spielberg's A.I.^[59]

See also

• Doomsday argument
• Ecocide
• End time
• Extinction event
• Global catastrophic risks
• Great Filter
• Holocene extinction
• Mutual assured destruction
• Space and survival
• Toba catastrophe theory
• Voluntary Human Extinction Movement

Notes

References

Further reading

• Leslie, John. (1996). The End of the World: The Science and Ethics of Human Extinction. Routledge. ISBN 0-415-18447-9
• Rees, Martin. (2003). Our Final Hour: A Scientist's Warning: How terror, error, and environmental disaster threaten humankind's future in the century--on Earth and beyond. Basic Books. ISBN 0-46506862-6.
• Michael Moyer (September 2010). "Eternal Fascinations with the End: Why We're Suckers for Stories of Our Own Demise: Our pattern-seeking brains and desire to be special help explain our fears of the apocalypse". Scientific American. 
• Michel Weber, McPherson, "Near Term Extinction", Cosmos and History: The Journal of Natural and Social Philosophy, vol. 10, no. 2, 2014, pp. 319–326.