We know that people have trouble evaluating risks. (To be more precise, people have trouble with conditional probability) One way this manifests itself is in society’s preoccupation with dramatic but minor threats (like terrorism) while less dramatic (or more abstract), but much more serious threats are ignored. Here are eight bona fide existential threats to humanity, that is, things that could make humans extinct, or at least eradicate any semblance of modern society.

8. Rapid Extinction of Critical Species

Our food supply is composed of various interconnected plant and animal species. We sometimes forget just how interconnected they are. For instance, the entire oceanic ecosystem depends on phytoplankton (little floating plants). If phytoplankton were to rapidly die off, due to changing water temperature, acidity or perhaps a virulent disease, the entire oceanic ecosystem would collapse. Bye bye fish, sharks, whales, krill, crabs, lobster… everything. Our agriculture is also fundamentally dependent on a small number of key species: worms (which aerate the soil) and bees (which pollinate practically everything). If worms or bees were to suddenly die off, horrendous famine and mass extinction would follow.

7. Environmental Collapse

The theory of environmental collapse is based on the idea that most organisms are tightly interconnected. Thus ecosystems are web-like structures where each species depends, directly or indirectly, on many other species. Many scientists believe that there is a kind of diversity threshold such that, if we lose enough species, entire ecosystems will collapse. Given the alarming rate at which species are becoming extinct (somewhere in the order of 100 to 1000 times faster than normal), if such a threshold exists, we may be getting close.

This, of course, would not only cause horrifying environmental destruction for which our grandchildren would never forgive us, and eradicate all sorts of potential medicines, but also produce global famine.

6. Human Disease

The Black Plague killed half the population of Europe in the 14th century, when slow methods of travel (horses and tall ships) impeded its spread. A similar disease today could rapidly spread across six continents. It is possible that the right (wrong?) disease could kill practically everyone on the planet. This could be a natural occurrence or a biological weapon.

As a society, however, we like to flip out about every new strain of the flu and take dramatic, but entirely ineffective, steps to assuage public fear. We close schools and hassle airline passengers. What we don’t do is create a culture where it is unacceptable to go to work, go shopping, take public transit, or generally wander around coughing on people when you have a contagious infection. Meanwhile, we let sick people sit around cross-infecting each other in waiting rooms for hours because we don’t have enough doctors on staff. And more fundamentally, we don’t address the continual degradation of human immune systems due to nutritionally devoid diets and epidemics of obesity, diabetes and respiratory disease.

5. Climate Change

If you still think climate change is a hoax, get help. No scientific conjecture has received more thorough testing and analysis in history than man-made climate change. If the temperature continues to rise, three important things will happen:

sea level will rise

deserts will grow

storms will become more extreme

All of these have severe effects on the food supply. As sea levels rise, farmland close to sea level will be flooded. As deserts grow, they consume previously arable land. As storms grow more extreme, more food and farmland will be destroyed each year. You might think that as the temperature warms, we’ll be able to farm further north, and that will make up for the farmland lost to sea level rise and desertification. You would be wrong. The arctic is already a cold desert. Climate change will likely just make it a less-cold desert.

4. Nuclear War

Any open conflict between two nuclear powers, be they the US and Russia, India and Pakistan or China and North Korea, has the potential to end life as we know it. Even if initial blast only kill millions, the radioactive fallout from a large-scale nuclear conflict could poison not only billions of people but also our food and water supplies.

3. Supervulcanism

Sorry Trekkies, Supervulcanism is not about controlling emotions and mind melds. It refers to a sudden rise in global volcanic activity. Volcanos are like the Earth’s smokestacks. If they all start spewing out ash at once, the atmosphere would become opaque, blocking out the suns rays. Imagine a thousands years of twilight. Now imagine 99% of the worlds plants dying, shortly followed by 100% of the world’s animals, including us.

Supervulcanism contributed to at least three Mass Extinctions.

2. Supernova or Gamma Ray Burst

When two stars collide or a large star goes supernova (collapses into a black hole), it can create an extremely energetic explosion. This energy travels outward in the form of Gamma Rays, which are sort of like X-rays on steroids. If such an energetic explosion occurred somewhere ‘nearby’ earth, say anywhere in our galaxy, the resulting gamma ray burst could destroy the ozone layer and irradiate the earth’s surface. It would be sort of like Marvin the Martian finally getting his giant ray gun to work and frying Earth with it.

Everything dies but the cockroaches.

1. Astronomical Impact

There are a lot of big rocks floating around in space. Every once in a while, two of them come together. Whether it’s an asteroid or a commet or even something from outside our solar system, if any big chunk of space debris come crashing into Earth, we’re dead.

Strong evidence supports an impact causing the Cretaceous–Tertiary extinction event (the one that killed the dinosaurs). How did it happen? Well, when a 10km-wide rock slam into the ground, several things happen. First, there’s the initial explosion – several orders of magnitude more powerful than the nukes dropped on Hiroshima and Nagasaki. Depending where the impact occurs, that could kill millions, or just a whole lot of fish. Then there’s the earthquake. We’re talking a 16 on the Richter Scale – 100 000 time more powerful than any earthquake in human history. The ground would move in waves, tossing people and building about like boats on a seething ocean. It would decimate buildings and infrastructure all over the world. Imagine the aftermath of the worst earthquake ever, and all the hospitals have been destroyed.

Assuming you survive all of that, you’ll have the pleasure to freeze and/or starve to death when all the dust thrown into the atmosphere blocks out the sun, just as in supervulcanism.

Only the cockroaches survive.

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