Sunday, 12 March 2017

Evaluating Existential Threats, Part 2: Non-anthropogenic Threats

Last time, I talked about worry as a driver to action, and how to evaluate problems as to whether they are worth worrying about or not. I think that my approach does work for smaller scale, day-to-day problems, but I was mainly focusing on existential threats—things that promise, at the very least, to wipe out a large chunk of our human population and, at the worst, to bring an end to life on earth. And I promised to go into detail about some such threats.

Today we'll look at a number of "non-anthropogenic" (non-manmade) threats. This list is not meant to be exhaustive, but I think it is a good introduction to the subject.

Non-anthropogenic threats tend to be large scale—forces of nature. In many cases there is little we can do but run away and/or try to be well prepared to cope with their effects. Fortunately, when it comes to coping, similar preparations work for many different types of threats.

For those who like the precise use of terminology I admit to being a little sloppy in my use of the term "existential". As Wikipedia would have it:

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" 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 prevents any chance of civilization recovering.

They actually have a pretty good article on "global catastrophic risks"


A nearby supernova

And for this first one we'll look at all four of the criteria I mentioned in my last post.

From Wikipedia:

A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly less than 10 to 300 parsecs (30 to 1000 light-years) away[2]) to have noticeable effects on its biosphere.

On average, a supernova explosion occurs within 10 parsecs (33 light-years) of the Earth every 240 million years. Gamma rays are responsible for most of the adverse effects a supernova can have on a living terrestrial planet. In Earth's case, gamma rays induce a chemical reaction in the upper atmosphere, converting molecular nitrogen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation (mainly ultra-violet). Phytoplankton and reef communities would be particularly affected, which could severely deplete the base of the marine food chain.


Once in 240 million years? But actually, a closer look shows that the occurrence of supernovas is not a random event that can happen to just any star.

Type II supernovas mark the end of the life of certain massive stars that are bright enough so that they are hard to miss, especially if they are nearby. And it is possible to identify when they are nearing to end of their lives, to within some thousands of years, anyway. The good news is that the nearest of them is over 500 light years away, far enough not to be a concern.

Again from Wikipedia:

Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because Type Ia supernovae arise from dim, common white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably and take place in a star system that is not well studied. The closest known candidate is IK Pegasi. It is currently estimated, however, that by the time it could become a threat, its velocity in relation to the Solar System would have carried IK Pegasi to a safe distance.

Even if a Type Ia candidate is lurking nearby, the odds of it being at the end of its life during my lifetime are small.


Earth's upper atmosphere, in particular the ozone layer, is very effective at blocking x-ray and gamma rays, so radiation from a supernova is not the main concern at ground level. But gamma rays can cause chemical reactions between nitrogen and ozone and deplete the ozone layer. There is the possibility that this effect of radiation from a nearby supernova could result in a mass extinction, and may have done so in the past.

Difficulty of Mounting a response

It is difficult to see how we could do much about the effects of a nearby supernova. As I've said before, it seems likely that our capacity for global scale responses to such challenges is either at of just past its peak. In other words, in my opinion, they are in the realm of science fiction—fun to dream about, but unlikely to happen.


It appears that there the likelihood of a nearby supernova in the near future is quite small.


The rarity of the event and the difficulty of doing anything about it would seem to make this a threat that there is no point in worrying about.

A Nearby Gamma Ray Burst

Gamma-ray bursts (GRBs) are extremely energetic explosions that have been observed in distant galaxies. A nearby one (thousands instead of billions of light years away) would affect our upper atmosphere in the same way as a nearby supernova.

My evaluation is that we need not worry—the risk is small and there is little we could do in any case.

A change in the sun's output

Our Sun is a remarkably constant star, its output varying only by 0.1% over the course of the 11-year solar cycle. NASA has a good article about how this can affect our climate. And while it is true that the changes during the solar cycle do seem to be amplified beyond what one might expect, their impact is far from existential.

A large solar flare

From Wikipedia:

A solar flare is a sudden flash of brightness observed near the Sun's surface. It involves a very broad spectrum of emissions, an energy release of typically 1 × 1020 joules of energy for a well-observed event. A major event can emit up to 1 × 1025 joules (the latter is roughly the equivalent of 1 billion megatons of TNT.... Flares are often, but not always, accompanied by a coronal mass ejection. The flare ejects clouds of electrons, ions, and atoms through the corona of the sun into space. These clouds typically reach Earth a day or two after the event.

The Carrington Event (Solar Storm of 1859), from Wikipedia:

The Solar storm of 1859—known as the Carrington Event—was a powerful geomagnetic solar storm during solar cycle 10 (1855–1867). A solar coronal mass ejection hit Earth's magnetosphere and induced one of the largest geomagnetic storms on record, September 1–2, 1859. The associated "white light flare" in the solar photosphere was observed and recorded by English astronomers Richard C. Carrington (1826–1875) and Richard Hodgson (1804–1872).

Studies have shown that a solar storm of this magnitude occurring today would likely cause more widespread problems for a modern and technology-dependent society. The solar storm of 2012 was of similar magnitude, but it passed Earth's orbit without striking the planet....

The probability of a solar storm striking Earth in the next decade with enough force to do serious damage to electricity networks could be as high as 12 percent.

Again from Wikipedia:

In June 2013, a joint venture from researchers at Lloyd's of London and Atmospheric and Environmental Research (AER) in the United States used data from the Carrington Event to estimate the current cost of a similar event to the U.S. alone at $0.6–2.6 trillion.

This cost would result from damage to electrical and electronic equipment that isn't sufficiently hardened against electromagnetic pulses (EMPs). In and of itself, this would cause relatively few human deaths. But it would cause widespread and serious damage to our power grid, and our transportation, communication and computing infrastructure, which could leave many of us without the necessities of life while the damage was being repaired. And it would take many months to replace damaged power transformers which are a critical part of the power grid.

Both the risk and the level of severity seem quite high, and measures to mitigate the effects of such an event are definitely within our grasp, albeit at some considerable cost. I would say that this is definitely something to worry about. For the individual two actions come to mind immediately:

  1. Prepare for extended outages of the power grid, the phone systems, the internet and GPS and expect that many of your electronic devices will not survive the EMP associated with the flare.
  2. When your local grid authority announces that power prices will be going up due to measures being taken to harden the grid against large solar flares, rather than complaining, support them. The same goes for other infrastructure that may be affected.

A collision with an asteroid

From Wikipedia:

Small objects frequently collide with Earth. There is an inverse relationship between the size of the object and the frequency of such events. The lunar cratering record shows that the frequency of impacts decreases as approximately the cube of the resulting crater's diameter, which is on average proportional to the diameter of the impactor. Asteroids with a 1 km (0.62 mi) diameter strike Earth every 500,000 years on average. Large collisions – with 5 km (3 mi) objects – happen approximately once every twenty million years. The last known impact of an object of 10 km (6 mi) or more in diameter was at the Cretaceous–Paleogene extinction event 66 million years ago.

Based on the odds quoted above, large collisions are rare enough to disregard but asteroids large enough to survive their trip through the atmosphere (larger than 35 m in diameter) and less than 1 km. in diameter are more common and can still do enough damage on a local or regional scale that it may be worth doing something about them.

As is often the case, though, this threat is not completely random. Astronomers have already identified a large number of asteroids whose orbits bring them close to Earth and efforts are underway to identify the rest of them, map their orbits and determine if/when they are likely to constitute a threat. Because an asteroid's orbit is changed by the Earth's gravity when it passes nearby, this is an ongoing task. And occasionally large asteroids, that have been missed previously, do show up on surveys.

Several methods have been proposed to divert an asteroid and prevent it from hitting Earth. Some of these are within our current technological and economic grasp, at least for now. If we were to make preparations ahead of time and have the appropriate hardware standing by in orbit, we could even divert asteroids on fairly short notice.


This is one to worry about. There is appropriate action which an individual can support when voting, if nothing else. A comprehensive and on-going asteroid survey would be relatively inexpensive and would allow us to evacuate the population from the area where a small to medium size asteroid is about to strike. And if it turns up a larger asteroid that is headed our way, it would give us the option of trying to do something about it.

A reversal of the earth's magnetic field

The Earth's magnetic field does reverse on a regular though seemingly random basis. Since the magnetic field goes to zero during the reversal and that field plays a role in diverting cosmic radiation and solar flares, there is some chance that more radiation would reach the Earth's surface during that period. Currently, expert opinion says this is unlikely to be an existential or even catastrophic threat.

There is some (less creditable) chance that seismic activity might increase during a magnetic reversal, causing earthquakes and tsunamis. My guess is that if you live in an earthquake or tsunami zone, the preparations you should already be making would suffice.

An eruption of the Yellowstone super-volcano

If the supervolcano underneath Yellowstone National Park ever had another massive eruption, it could spew ash for thousands of miles across the United States, damaging buildings, smothering crops, and shutting down power plants. It would be a huge disaster.

From Wikipedia:

The U.S. Geological Survey, University of Utah and National Park Service scientists with the Yellowstone Volcano Observatory maintain that they "see no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future. Recurrence intervals of these events are neither regular nor predictable." This conclusion was reiterated in December 2013 in the aftermath of the publication of a study by University of Utah scientists finding that the "size of the magma body beneath Yellowstone is significantly larger than had been thought." The Yellowstone Volcano Observatory issued a statement on its website stating, "Although fascinating, the new findings do not imply increased geologic hazards at Yellowstone, and certainly do not increase the chances of a 'supereruption' in the near future. Contrary to some media reports, Yellowstone is not 'overdue' for a supereruption."

That's good enough for me, so I won't be worrying about this one.

A Pandemic arising from nature

From Wikipedia:

The death toll for a pandemic is equal to the virulence (deadliness) of the pathogen or pathogens, multiplied by the number of people eventually infected. It has been hypothesised that there is an upper limit to the virulence of naturally evolved pathogens. This is because a pathogen that quickly kills its hosts might not 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 out-compete a more lethal species or strain. This simple model predicts that if virulence and transmission are not linked in any way, pathogens will evolve towards low virulence and rapid transmission. However, this assumption is not always valid and in more complex models, where the level of virulence and the rate of transmission are related, high levels of virulence can evolve. The level of virulence that is possible is instead limited by the existence of complex populations of hosts, with different susceptibilities to infection, or by some hosts being geographically isolated. The size of the host population and competition between different strains of pathogens can also alter virulence. However, a pathogen that only infects humans as a secondary host and usually infects another species (a zoonosis) may have little constraint on its virulence in people, since infection here is an accidental event and its evolution is driven by events in another species. There are numerous historical examples of pandemics that have had a devastating effect on a large number of people, which makes the possibility of global pandemic a realistic threat to human civilization.

The Wikipedia article on Global Catastrophic risk estimates the chance of a naturally occurring disease causing the extinction of the human race before 2100 is .05%, or 1 chance in 2,000. So it seems that this threat is worthy of some degree of worry. But existing public health organizations are on watch for diseases spreading from animals to humans, and quarantines can be put into effect to control the spread of such a disease until vaccines can be developed. In case one finds oneself under quarantine, a well stocked pantry would be handy to have, and that is also a basic preparation for many other sorts of disaster.

Small scale threats

While volcanoes, earthquakes, tsunamis, hurricanes, tornadoes, floods, droughts and so forth may not be existential threats for the human race as a whole, they can be quite serious to the individuals who find themselves at ground zero. And in many areas the degree of risk is fairly high. Being prepared for emergencies is always a good idea, in my opinion.

Early in the history of this blog I wrote a couple of posts on emergency preparation, and I think they have stood the test of time.

The only thing I might add is that in some locations, taking the progress of climate change and/or growing political unrest into account may lead you to think about moving to a less hazardous location. This is best done sooner, rather than later, while the infrastructure to support your move is still intact and you can still get a least some of the value out of your home.

Looking back over this list of non-anthropogenic threats, it's interesting to note that the majority of them are not something to worry about. Of those that are worthy of our concern, a few observations can be made in the light of the collapse that I expect is coming during the next few decades:

  • A large solar flare in only dangerous because of the unprotected high-tech infrastructure that we have become dependent on.
  • Asteroid collisions, on the other hand, will continue to be a threat regardless of the level of technology we are using. An effective response to the approach of a large asteroid requires the capability to conduct operations in space, and an economy that is doing well enough to finance such expensive endeavours. Evacuating people from the areas where smaller asteroids will touch down would require some intermediate level of technology and financial support.
  • Pandemics are another thing again. Crowding millions of people together in large cities and making it easy to travel between those cities certainly makes it easier for a pandemic to spread. A smaller and less connected "post-collapse" population would be less vulnerable, but without the full force of modern medicine and public health infrastructure, they would be less resistant to infectious diseases in general.

In my next post I'll look at anthropogenic (manmade) threats and explain why I think some of them are more serious than the threats we've looked at this time.

Note on Wikipedia as a source:
some will no doubt have noted with distain that I have used Wikipedia as a reference throughout this blog post. But I was not trying to write an academic article, and I can assure you I do approach the information I find in Wikipedia with a skeptical eye. I've noticed that the biggest critics of Wikipedia are those who are disappointed that they can't find support therein for their favourite brand of pseudoscience. To me, that is a pretty good recommendation, and it supports what I have found, i.e. that Wikipedia does a pretty good job of excluding pseudoscience, and of presenting the current scientific consensus on most subjects.


Brian Dalton said...

Fascinating information, made readable, thanks.

Irv Mills said...

Thanks for the kind words, Brian. I'm particularly glad you found it readable, since it is fairly technical stuff. None of this is stuff to loose sleep over--worry yes, in the sense that there are things that can and probably should be done and we should let our politicians know that they should be taking threats like asteroids, solar flares and pandemics seriously and spending some money on responding to them.
Next time, I'll be looking at some man-made threats that I think are more serious and require more immediate action.