Some 13.8 billion years ago, the universe we currently inhabit popped out of the Big Bang. Fast forward several billion years and the Earth gently orbits the sun in a harmonious cosmic tango; a few billion years further, life stumbles onto this planet. Then, through the process of evolution – or creationism, if you prefer to keep things religious– humanity came to be and spread out across the face of the planet. With vastly superior intellectual capabilities, our species quickly rose to the top of the food chain and rightfully earned the title of Ruler of Earth. And while humans today still face suffering and hardships, they are mostly self-inflicted and otherwise have it fairly easy compared to our ancestors.
But enough of all the self-flattering storytelling, this week is all about “The End” and they say that the bigger they are, the harder they fall. Therefore, I think it’s time to hypothetically shake things up for humanity. Since I don’t possess a magical crystal ball, I’ll review a number of theories that people of all walks of life have come up with over the years. I’ll briefly describe the different scenarios then rate how likely they are to occur and just how destructive they would be for life on Earth. In Part 1 we’ll cover some of the most feasible scenarios whereas in Part 2, we’ll explore some more sci-fi-esque ways our world could come to an end.
1) Global warming
When addressing global warming, we should really talk about climate change – it’s an ongoing process and we are already experiencing its consequences. Scientific evidence supporting this phenomenon points to a 2.0 °C temperature rise as the “point of no return” for many species on Earth. This increase in temperature would gradually usher in major disastrous events, the most alarming being the rising sea levels which threaten to submerge a plethora of coastal cities. Additionally, this rise of global temperature fuels natural disasters such as hurricanes, typhoons, floods, tornadoes, wildfires, and droughts. Though this might not spell the impending doom for all of humanity, it would lead to an unprecedented number of climate refugees fleeing from affected urban centers. Simultaneously, climate change could have an important impact on agriculture and food supply through increasingly common droughts, heat waves, and floods. It is difficult to predict just how dire that situation would be – it also depends on how quickly 2.0 °C mark is reached, and whether we prepare for its consequences and cooperate preemptively – but some estimates predict up to a billion people would be threatened by rising sea levels alone. I can only imagine what sort of conflicts or wars would result from the massive ensuing refugee crisis or food shortage, but for good measure, stock up on ramen for your grandchildren!
The ecological impact of climate change is equally severe. This abrupt shift in temperature does not allow enough time for ecosystems and their endemic fauna to adapt, potentially leading to extinction. One of the most tragic example of this is the Great Barrier Reef, a complex environment millions of years old that covers 300,000 square km. As a result of this temperature shift and of ocean acidification, over 90% of it is suffering from a phenomenon known as bleaching – the death of symbiotic algae living on its surface, leading to the whitening of the corals – essentially one step away from death. The real issue here is that ecosystems are incredibly interdependent; the extinction of any one species could lead to myriad problems to all its connected species, be it predators or prey. Scientists estimate that the current extinction rate is 1,000 to 10,000 times the background or natural rate  and that 30-50% of species will be facing extinction in this century alone .
The most troubling aspect of this scenario is that we are to blame. We emit ever greater amount of greenhouse gas since the Industrial Revolution, oblivious to the threat of climate change and reluctant to change our ways. While international agreements such as the Paris Agreement have been signed to combat climate change, world leaders fail to treat the issue with the urgency it deserves. The Western tendency to treat problems rather than prevent them is what makes this scenario so likely.
Likelihood: 9/10 → It’s already happening, just how much of a temperature rise we’ll see is hard to predict but its effects are pretty much irreversible in the short term.
Destruction factor: 3/10 → In the grand scheme of things, this is not the end of life as we know it, but a large amount of human culture will be lost and more importantly our current biodiversity will suffer a major blow.
An invisible killer against which we have no defences: welcome to the age of antibiotic resistance. A pandemic, defined as the outbreak of a disease on a regional or global scale, can have major consequences for humanity. In the past, pandemics have already plagued us numerous times, with two infamous examples burned into our common memory are the 1918 Spanish Flu and the 14th century Black Plague. The Spanish Flu of 1918 is believed to have infected up to a third of the global population, and with mortality rates of as high as 10-20%, it claimed the lives of some 50 million people. The Black Plague decimated the Old World from 1347 to 1351, wiping out between 75-150 million people at a time when the global population was estimated to be 450 million. In other words 16-33% of the world population was killed by the disease, and between 30-60% of Europe’s population died in only a few years! While all diseases are unique, a pandemic is generally achieved when a disease with high infectivity is able to infect multiple organisms (animals and humans) enabling it to spread rapidly throughout the world before unleashing its lethal mechanisms.
What makes the 21st century particularly vulnerable to pandemics is the combination of a high global urban population with extensive connectivity between all parts of the world. With the advent of globalization: cargo ships, airplanes, trains, trucks and above all people, are constantly crossing borders and carrying microorganisms along with them to the farthest reaches of the planet. Cities are ideal playgrounds for disease given their high population density and the prevalence of rodents and other potential disease vectors. A most disturbing recent discovery is that virus and bacterium are developing a resistance to antibiotics. Penicillin was first used to treat infections in 1942 with huge success, paving the way for the discovery of many more antibiotics. Unfortunately, given how we have come to pump antibiotics in patients and livestock alike, bacteria have increasingly developed mutations making them resistant to antibiotics. As a result, some antibiotics had to be discarded and were replaced by others… until a new resistance inevitably develops. Unfortunately, this cycle cannot go on forever, given how most “easy-to-develop” antibiotics have all been already discovered, few pharmaceutical companies see the multi-billion-dollar development of a new antibiotic as a profitable endeavour. It is estimated that each year, 2 million people in the United States are infected with antibiotic resistant bacterium .
Likelihood: 7/10 → The real question is not “if” but “when”; all the ingredients are there for a major pandemic, all that remains to occur is for a bacteria or virus to develop a set of mutations to induce such an event.
Destruction Factor: 5/10 → While a pandemic might not destroy all human life – there always is an innately immune or resistant minority among us – it could certainly decimate a significant portion of the population and isolate a previously globalised world.
If you have a minute to spare, try out the brilliant mini game Pandemic II, in which you “try to kill everyone in the WORLD”.
3) Nuclear Apocalypse
On the morning of August 6th 1945, Little Boy was dropped on Hiroshima leaving the once great city in ruins in a heartbeat. A second atomic bomb was dropped on Nagasaki on August 9th forcing the Japanese Emperor Hirohito to surrender with a chilling declaration to his people in which he stated that to “continue to fight, not only would it result in an ultimate collapse and obliteration of the Japanese nation, but also it would lead to the total extinction of human civilization.” . As a result, present-day Japan has a strong anti-nuclear weapon policy, but the same cannot be said of the rest of the world. During the Cold War, a number of peculiar phenomena occurred, the most dangerous of which being the nuclear arms race between the two countries involved. In 1985, a staggering 68,000 active nuclear weapons were scattered across the world yet thanks to significant nuclear demilitarization efforts, “only” 4000 active nuclear warheads remain today with approximately 6000 other inactive warheads in existence.
In the event where a great number of nuclear warheads would be launched across the world, the real danger would come from the nuclear fallout and nuclear winter that would follow the initial explosions. While a tremendous number of people would be obliterated from the blasts themselves – assuming major urban centers would be the targets of choice – the aftermath would have far more impact on the global population as a whole. Nuclear fallout – the diffusion of radioactive byproducts of nuclear explosions over great distances – would have serious health implications for the world’s population, from increased risks of cancer due to exposure to contaminated water sources, plants, and animals worldwide. Even more concerning would be the ensuing nuclear winter, during which debris from the bombs would be propelled high up in the atmosphere, preventing sunlight from reaching the surface of the Earth for several years, and ultimately leading to a global drop in temperature. This would destroy existing crops and make life even more difficult for the surviving human population.
This scenario being entirely driven by erratic human behaviour makes it especially troubling. One would think that after millennia of god-fearing beliefs, we would have more respect for human life and not give ourselves the means to eradicate our own species at the touch of a button. Thankfully, with the end of the Cold War, such a scenario seems unlikely yet given that we’ve already been remarkably close to a nuclear apocalypse during the Cuban Missile Crisis, I am unwilling to rule out its possibility.
Likelihood: 2.5/10 → I would like to rule this one out, but as Murphy’s law states, “anything that can go wrong will go wrong”. Let’s prove it wrong.
Destruction Factor: 8/10 → The resulting post-apocalyptic world would truly be a nightmare. To find yourself surrounded with rampant radiation sickness, reminders of our former glory and scarce food supplies would surely bring out the worse of the surviving population.
If you haven’t already, check out some of the Fallout franchise games where you wander in a post nuclear-apocalypse world listening to some lovely classics of the 30s and 40s.
4) Asteroid Impact
In this scenario, the impact of a large asteroid has destructive potential for practically all life on Earth. It is estimated that any asteroid 1 km in diameter could have catastrophic consequences, and anything larger than 5 km in diameter would have cataclysmic implications. Compared to other scenarios, this one has a pretty solid track record having already wiped out dinosaurs from the planet. In the case of the Cretaceous-Paleogene extinction event that occurred 66 million years ago, an asteroid of approximately 10 km in diameter ushered in a mass extinction, very quickly wiping out 75% of all animal and plant species existing at that time. The massive impact is estimated to have been 6 billion times more powerful than the Hiroshima atom bomb ! The resulting Chicxulub crater in Mexico measures no less than 180 km in diameter and serves as a stark reminder of how fragile life can be.
Interestingly, the real damage of such an event would stem from the worldwide climate disruptions rather than the impact itself. While the resulting shockwave that would follow the immediate impact would be visually impressive and immediately destroy any buildings within dozens of kilometers, the “impact winter” has much more serious implications for what remains of the planet. As the asteroid hits the surface of the earth, an enormous amount of debris is propelled into the atmosphere blocking out the sun’s ray for years, if not decades. Without sunlight, plants would be the first to die being unable to perform the vital process of photosynthesis. The lack of plant-based food would then lead to the extinction of species, gradually moving higher up in the food chain, eventually starving out a portion of humanity. A study estimated the effects on agriculture alone from a ‘medium case’ impact winter could eliminate 25% of the human population . It is fairly certain that an economic crisis would follow given the tremendous shortage of basic food products and their ensuing hyperinflation. There is comfort however, in the fact that many species survived the previous major impact and we are likely to do so as well in the future.
Likelihood: 2/10 → It already happened so it is statistically “likely”, but the fact that it happened 66 million years ago makes it rather unlikely.
Destruction factor: 8/10 → Wiping out 75% of all species is objectively savage and the fact that barely any sun would reach the Earth’s surface for years would make this scenario rather gloomy.
 Chivian, E. and A. Bernstein (eds.) 2008. Sustaining life: How human health depends on biodiversity. Center for Health and the Global Environment. Oxford University Press, New York.
 Ibid. and Thomas, C. D., A. Cameron, R. E. Green, M. Bakkenes, L. J. Beaumont, Y. C. Collingham, B. F. N. Erasmus, M. Ferreira de Siqueira, A. Grainger, Lee Hannah, L. Hughes, Brian Huntley, A. S. van Jaarsveld, G. F. Midgley, L. Miles, M. A. Ortega-Huerta, A. Townsend Peterson, O. L. Phillips, and S. E. Williams. 2004. Extinction risk from climate change. Nature 427: 145–148.
 “Imperial Rescript ending war – What Hirohito really said in his acceptance speech” translated by William Wetherall. Yosha Research.
 Alvarez, L.W.; Alvarez, W.; Asaro, F.; Michel, H. V. (1980). “Extraterrestrial cause for the Cretaceous–Tertiary extinction”. Science. 208 (4448): 1095–1108.
 Engvild, Kjeld C., “A Review of the Risks of Sudden Global Cooling and Its Effects on Agriculture”, Agricultural and Forest Meteorology, 115: 127–137,