LECTURE 9: EXTINCTION SCENARIOS
Ice age: In the history of the Earth, many ice ages have occurred. More ice ages will almost certainly come at an interval of 40,000–100,000 years. This would have a serious impact on civilization, because vast areas of land (mainly in North-America, Europe, and Asia) could become uninhabitable. It would still be possible to live in the tropical regions, but with possible loss of humidity/water. Currently, the world is technically existing in a warm period between such ice ages (the last ending c. 10000 years ago), and all civilizations (save a few hunter-gatherer populations) have come into existence within that time.
Global pandemic: A less predictable scenario is a global pandemic. For example, if HIV mutates and becomes as transmissible as the common cold, the consequences would be disastrous, but probably not fatal to the human species,[16] as some people are immune to HIV.[17] This particular scenario would also contradict the observable tendency for pathogens to become less fatal over time as a function of natural selection. A pathogen that quickly kills its hosts will not likely have enough time to spread to new ones, while one that kills its hosts more slowly or not at all will allow carriers more time to spread the infection, and thus likely outcompete a more lethal species or strain. A real-life example of this process can be found in the historical evolution of syphilis towards a less virulent form. Also as a virus mutates in a direction of being easily transmittable it will likely give up much of its virulence in the process. Though this is not to say that a highly destructive and highly transmissible disease is not possible. Of course, a pandemic resulting in human extinction need not arise naturally; the possibility of one caused by a deliberately-engineered pathogen cannot be ruled out.
Megatsunami: Another possibility is the megatsunami. A megatsunami could, for example, destroy the entire east coast of the United States of America (see La Palma). The coastal areas of the entire world could be flooded in case of the collapse of the West Antarctic Ice Sheet.[18] While none of these scenarios could possibly destroy humanity completely, they could regionally threaten civilization.
Ecological disaster: An ecological disaster, such as world crop failure and collapse of ecosystem services, could be induced by the present trends of overpopulation, economic development, and non-sustainable agriculture. Most of these scenarios involve one or more of the following: Holocene extinction event, 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. A very recent threat in this direction is colony collapse disorder, a phenomenon that might foreshadow the imminent extinction of the Western honeybee. As the bee plays a vital role in pollination, its extinction would severely disrupt the food chain.
World population and agricultural crisis: The 20th century saw a rapid increase in human population due to medical advances and massive increase in agricultural productivity[19] made by the Green Revolution.[20] 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. The energy for the Green Revolution was provided by fossil fuels in the form of fertilizers (natural gas), pesticides (oil), and hydrocarbon fueled irrigation.[21] 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 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.[22]
The authors of this study believe that the mentioned agricultural crisis will only begin to impact us after 2020, and will not become critical until 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.[23][24]
Pole shift theory: An abrupt reorientation of Earth's axis of rotation could cause a new extinction event.[25]
Supervolcano: When the supervolcano at Yellowstone last erupted, 600,000 years ago, the magma and ash covered roughly all of the area of North America west of the Mississippi river. Another such eruption could threaten civilization. Such an eruption could also release large amounts of gases that could alter the balance of the planet's carbon dioxide and cause a runaway greenhouse effect, or enough pyroclastic debris and other material may be thrown into the atmosphere to partially block out the sun and cause a natural nuclear winter, similar to 1816, the Year Without A Summer. Such an eruption may cause the death of millions several hundred miles from the epicenter and overall hundreds of millions of deaths worldwide due to the failure of the monsoon, causing starvation on an unthinkable scale.
In the end, Earth will be rendered lifeless by no later than about 7.6 billion years[26]; before this the oceans will evaporate, and even if Earth is lucky not destroyed by tidal forces or dragged into the Sun by friction with the solar atmosphere, Earth will be too frigid to sustain life when the Sun shrinks to a white dwarf star. However, newer research shows there is the tidal interaction is more possible, the Earth can possibly be engulfed anyway.[2]
