Physical Menaces to Long Term Sustainability

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Here are some potential physical menaces to the survival of the human species and some comments on their likelihood. Actually most of them are lesser calamities. None seem likely in the immediate future. Ideological menaces are both more likely and have the possibility of doing humanity greater harm. The disaster flic is a current art form, but don't hope to get facts from movies.

My opinion is that science, technology, and the wide dispersal of humanity has turned us into a very tough species. Because of journalism, humanity is readily annoyed, but we are capable of surviving any of the catastrophes to life that have occurred in past, and science is very likely to give us plenty of warning for most of them.

In discussing any menace, journalists, lawyers, and politicians, movie makers, and even scientists who have enrolled themselves in a cause, often take a worst-case approach. They say X could happen if we do Y, and therefore Y should be avoided at all costs. The anti-nukes make up worst cases as do the proponents of extreme laws about potential terrorism. So did the advocates of preventive war against the Soviet Union, and so do some present advocates of preventive war agains Islam. A worst case attitude to the possibility of an asteroid hitting the earth would require devoting most of the GDP of the whole world to defenses against it. A worst case policy to a possible pandemic would require that every country quarantine itself, and indeed every state in the US quarantine itself.

Human society is not yet technologically powerful enough, economically rich enough or politically united enough to afford a worst case attitude. On a personal level, no person can afford a worst case attitude to menaces to his own survival, e.g. to protect himself against a meteorite or an airplane hitting his house.

Most of the menaces that people or organizations see have not done much harm yet. They forsee harm, urge us to act now, are disturbed if the public is unresponsive, and predict doom. However, the public will support action when sufficient harm actually occurs. Thus the American failure to continue building nuclear power plants bothers me, and I think we have suffered from it. However, if this negligence causes a severe shortage of electricity, we will then build new plants. (Actually, building new plants seems to be in the works because of the greatly increased price of natural gas - a warning of more severe shortages to come). Human society has many feedback mechanisms - servomechanisms they are sometimes called.

Here are some menaces.

Very large asteroid collision

To destroy humanity, the collision would have to be much larger than those that have hit the earth since 3.8 billion years ago after life started. Much smaller collisions could kill a lot, perhaps most, of the people. A repetition of the Chicxulub asteroid collision would, according to some theories, temporarily wipe out agriculture, but there is enough stored food for a large number of people to survive and re-establish an economy. One can complicate the asteroid collision with a war, as science fiction writers have done.

Suppose we just now got 500 years warning of a strike by a Chicxulub class asteroid.

Q. What should we do *now* about deflecting it?

A. Nothing.

Our descendants 200 years from now will know enough more about how to deflect it because of the general advance of science and technology. They'll still have 300 years. I'm optimistic about the capabilities of our descendants.

The asteroids whose orbits cross earth's orbit are being observed and their orbits calculated, but the astronomers haven't got all of those that are small but still large enough to do damage. At least twice an asteroid has been observed for which the initial orbit calculations showed it might come dangerously close to the earth in the next hundred years. In each case further observation showed that the asteroid wouldn't come close.

According to an astronomer I asked, about 20 percent of the asteroids that cross the earth's orbit come from so far out that we can't expect to know their orbits in advance. If one of them was going to hit the earth, the amount of warning would depend on how big it was and on luck. This would justify making asteroid deflection experiments in advance. Depending on the orbit and the amount of warning, nuclear explosions might be the only way of deflecting it. The effects of nuclear explosions at different distances on various kinds of asteroid is sufficiently uncertain to justify advance experiments. At present these experiments are prevented by superstitions about nuclear explosions. One or two generations from now, people, including the media and do-good scientists, may be more sensible.

Here's a web page on why experiments with nuclear explosions should not be forbidden. The US hasn't ratified the non-proliferation treaty that forbids them, and I hope it won't, but it is still not planning any explosions. The opponents of the treaty today are mainly concerned with US national defense. My reasons are different.

The Next Ice Age

Ice ages have come at intervals of 15,000 years or so and have had profound effects on life on the planet, presumably including human life. The cause is apparently changes in the inclination and eccentricity of the earth's orbit in turn caused by the gravitational effects of other planets, mainly Jupiter. How soon we are due for another ice age, if events are allowed to take their course is uncertain. There are feedback effects in the climate system as well as the primary astronomical effects. The next hundred years seems to be regarded as extremely unlikely, the next thousand years quite possible, and the next ten thousand years rather certain.

Some years ago there was a scientific conference entitled "When will the present inter-glacial age come to an end". The conference received world-wide press coverage. None of the papers mentioned by the press discussed preventing the next ice age or mitigating its effects. This inhibition about discussing prevention among many scientists is an ideological phenomenon.

My opinion is that humanity will prevent the next ice age. There are a number of possibilities including changing the earth's albedo in many ways. The apparent fact that small quantities of certain substances in the earth's upper atmosphere can affect the heat balance provides helpful tools. Studying these possibilities is of scientific and technological interest, but it seems that humanity will have plenty of time to get ready. Therefore, I advocate complacency for now about the ice age danger. Gregory Benford in his Climate controls discusses many ways of preventing the next ice age.

Nuclear wars
The classical nuclear war scenario was an all out conflict between the U.S. and the Soviet Union. There would be enormous destruction (according to some opinions total) in both countries and possibly in many others, e.g. Europe. The world would have had a hard time recovering.

It might have been much worse than depicted in those scenarios. Even after the enormous destruction, the combatants might have continued to fight until one was conquered by a surviving underground fragment of the other.

The most likely nuclear wars in the present political configuration of the world are minor in comparison.

However, human society has not advanced to the point where major wars are impossible in the long term. I don't see any of the present conflicts in the world as likely to lead to major war, but I have no confidence in my or anyone else's ability to predict even the next 100 years. In the long run the likelihood of war (or any other catastrophe) wiping out the human race will be reduced by the dispersal of humanity throughout the galaxy.

Wars have been very bad, even of demographic significance. The 30 years catholic-protestant war of the 17th century killed 1/3 of the population of Germany. The holocaust killed 2/3 of the Jews of Europe (1/3 of the Jews of the world.) Whole generations of young men have been mostly wiped out by wars.

Technological terrorism
There has always been some terrorism, and it has always been a topic of fiction. Technological terrorism is popular in fiction. Terrorism has never been of demographic significance, i.e. significantly reduced the population of a country. The explosion of a few stolen nuclear bombs would kill many more than terrorists have managed so far but still wouldn't be of demographic significance. The Asahara gang in Japan tried to kill as many subway passengers as they could but only succeeded in killing 12. Some say that they didn't get the nerve gas making process quite right and might have killed many more. Still it wouldn't have killed a significant fraction of the inhabitants of Tokyo. Biological warfare has possibilities for terrorism, but it requires extensive research to get effective agents. This research may have been done during the cold war by various countries. Saddam Hussein is said to have avoided using chemical and biological weapons for fear the American or Israeli retaliation would be nuclear.

[2002 March 23: The above was written before the 2001 September 11 terrorist attack. Neither the WTC attack, nor the anthrax attack, nor the subsequent incrased speculation about terrorist attacks require altering the previous paragraph.] An interesting comparison is with the 1998 ice storm in eastern Canada and New England. Three million power poles were downed and required hundreds of utility crews from as far away has Hawaii to repair the damage. There is no way terrorists, who have blown up a few power poles occasionally, could do as much damage as that ice storm did.

Consider the terrorism againt Israel. It kills far fewer Israelis than automobile accidents but gets much more attention. Here are two reasons. (1) An appropriate response is to catch and disable the terrorists, and that arouses combative instincts in people and is much more interesting than (say) installing more traffic lights. (2) Those injured by human crime always get more attention and sympathy than those suffering equally from accident or disease. Perhaps this remark is a distraction from the main thread about menaces of various magnitudes.

Plate tectonics
Many people worry about earthquakes, but the largest earthquakes in history have not been of demographic significance - except maybe the Thera earthquake of 1600 B.C. that may have damaged Minoan civilization. [2003 November: The Thera event may have been a volcano.] However, the Permian extinction off 225 million years ago may have been caused by very large eruptions of lava covering hundreds of thousands of square miles. This extinction was bigger than the Cretaceous-Triassic extinction of 65 million years ago believed to be caused by the Chicxulub asteroid. Humanity would probably survive that one also. Not a lot more can be said in the present state of knowledge.

Global warming
This is the current most popular menace. Politicians in many countries, e.g. Gore in the U.S., say bad things about any scientist who dissents. Most scientists go along with the report of the Intergovernmental Panel on Climate Change, but there are important and respectable scientific dissenters. Nor is the report as unequivocal as most environmentalists claim. The extreme scenarios, that earth would become like Venus have been dropped. The effect of warming might be mainly positive, but there is a significant chance that it would be very negative, i.e. making some deserts out of some agricultural land, raising sea level, and possibly making Western Europe much colder by interfering with the currents (called the Atlantic conveyor) that carry warmth from the tropics.

Until 1999 I was rather neutral about the danger of global warming. Recently I have moved towards the skeptical side, seeing as so many scientists have been refusing to be stampeded by the politicians. Fred Singer has been a long time skeptic, and here is his tally of some fellow skeptics. He's not alone.

As I have read more about climate change, I have become convinced that I cannot learn enough about the subject to be entitled to an opinion on my own.

If necessary, global warning can be avoided.

Statistics on species longevity
Some have estimated the length of life of the human species from the paleontological record of the average longevity of mammalian species. This is just silly. The human species, by its use of intelligence, culture, science, and technology occupies an entirely different position from that of any past species. Science permits the recognition of dangers long in advance, and technology permits mitigating them. Human scientific and technological capability continues to advance, so the species gets safer and safer from non-human menaces.

Nature doesn't love us.
Recent studies of climate over the last 10,000 years suggests that there have been numerous fluctuations large enough damage humanity. For example, there is evidence of times when both the American Middle West and California have been deserts dominated by sand dunes. The moral I draw is that the best way to avoid disasters is to make humanity more technologically capable. As for prolonged, e.g. 100 year, droughts, desalinating seawater using nuclear energy could supply California's use of 43 million acre-feet per year. At worst it would be a ten percent hit on the state's GDP. Here are more facts about water supply. We don't know enough about 200 year droughts or major climate changes to understand how to avert them, but if they seem imminent, scientists and engineers will work a lot harder. Some global engineering may be needed.

2003 March note: Science for 2003 March 28 has a review article entitled "Abrupt Climate Change" by R. B. Alley, et. al. The article points out that abrupt climate change has occurred many times in the past and is doubtful that present science can readily anticipate such events. The article says, "In the light of these uncertainties, policy-makers should consider expanding research into abrupt climate change, improving monitoring systems, and taking actions designed to enhance the adaptablilty and resilience of ecosystems and economies." This article represents a considerable advance in the thinking of climatologists away from single menace theories associated with human sins.

I only just noticed that this excellent article lacks any discussion of how humanity might prevent undesired climate changes by global engineering.

A super infectious disease
We can imagine a disease with the delayed onset and mortality of AIDS, and the infectiousness of the common cold. History tells us that this has low probability, but it doesn't seem to be impossible. Very likely this risk will be greatly reduced when medicine advances to the point of being able to check people for viral material that doesn't belong.

Should a super-infectious mortal disease develop without the delayed onset of AIDS, we could use, at immense cost, a technology of isolation and quarantine - an extension of the P4 technology on a global scale. It would involve greatly restricting travel and transportation of goods.

At a lower level come the epidemics in human history. The black plague is said to have killed 1/3 of the population of Europe in the 14th century. The worst recent epidemic was the influenza epidemic of 1918-20, which killed 20 million worldwide, including 600 thousand Americans. European diseases are said to have killed a large fraction of the original inhabitants of the Americas after first contact. Probably either renewed plague or a repeat of the 1918 influenza would have a much lower death rate, just because of improvements in nursing.

At present the U.S. Government Centers for Disease Control with headquarters in Atlanta is pursuing some rather small scale threats from newly recognized infectious diseases. For example, there is a hantavirus spread by rodents. There have been 160 cases of which half died of pneumonia. The death rate among recent cases is about 20 percent. The major outbreaks were in the Four Corners region of New Mexico and in the Sierras in California. Another small outbreak is occurring in 1998, because the increased rains caused by El Nino increased the population of the mice that carry the disease. The point is that CDC is reduced to pursuing small threats. It's good that pursuing the small threats will keep them in practice for when bigger threats arise.

Dangerous artificial life
We can imagine creating self-reproducing, intelligent micro-machines and these getting out of human control and wiping us out. Indeed we can imagine some Unabomber type (with a somewhat different grudge against society) doing it intentionally. All I can say is that we have to be careful. I don't think we are very close at present to a technology that could do it. Antti Karttunen reminded me to mention this.

Great depression
A depression would have to be much greater than that of the 1930s to menace human survival. However, one can imagine a depression giving rise to political forces that would menace survival. There has been no major depression since the 1930s, and the economists have some self-confidence about tinkering with the money supply and interest rate. However, there is no convincing theory, so we must still consider it a menace.

Alien invasion
This could happen, but given that it hasn't happened in 4 billion years, it seems unlikely to happen soon. The scarier scenarios of science fiction depend on present physics not being correct, e.g. bombs that can be carried in a space ship and can blow up a planet or sun and faster than light travel. Some imagine aliens to whom humans taste good.

Cascading collapse of systems
It has often been claimed that civilization depends on many interdependent systems in such a way that a failure in one part of the system, e.g. in electricity supply somewhere, could bring down the whole of technology. So far failures have been localized, and the 1965 failure of a major part of the Northeastern electricity grid led to measures for limiting failure. I regard a cascading failure as implausible; remember the dire predictions that the Y2K bug would cause a collapse; remember the advice for people to store food. This was particularly foolish advice, since failure of computers would not destroy food. It's just that the agencies that offer advice, offer the same advice for all emergencies; 9/11 elicited much the same advice as did Y2K.
See Population for a general discussion.


Present civilization is much more capable of surviving catastrophes than any past civilization, because every part of the system has so much reserve capacity. Here are some of the reserves.

  1. The major part of society works 40 hour weeks. 80 hour weeks are possible to deal with an emergency.
  2. The US has perhaps a year supply of food for us gluttons in various kinds of storage. In an emergency we would ration food and avoid waste. Past famines have been more associated with inability to transport food to where it was needed than with an absolute lack of food. Today, because of modern shipping, the whole world can share food, so a food emergency would have to be prolonged and worldwide to kill a substantial fraction of the population. Nuclear war or an asteroid strike might do that.
  3. A very large part of the population is engaged in activities that can be postponed making available additional labor. These include universities, entertainment, the armed forces, and producers and sellers of luxury goods.
  4. Automobiles are available for evacuations.
  5. Trucks operated 8 hours per day can be operated 24 hours per day.
  6. If housing is destroyed, people can crowd into the housing that is intact. Compared to past eras the amount of housing per capita is enormous.
  7. World War II forced many countries to mobilize most of their resources to fight it. The US was less affected than European countries, and was quite prosperous in 1945 even though 55 percent of the GDP that year was involved in pursuing the war, including supplying our allies and liberated populations.
  8. The population may decline from lack of births.

It's not possible to be more detailed except in connection with a specific menace.

More menaces to come - but smaller. The dangers of running out food, etc. are discussed in the main page.

There are also social menaces that have been most imaginatively portrayed in science fiction.

There are also imaginary menaces.

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