Climate change, overpopulation and dwindling resources are some of the big issues currently discussed in the media and they paint a very bleak future for humankind. If you clicked on this article for light-hearted relief, then you’d probably better stop reading right now, as we talk about some of the lesser known terrors that we may face as a species in the future.
It’s traditionally thought that five mass extinctions have occurred in the Earth’s history, though recent evidence suggests a possible sixth. Characterised by their breadth and brevity, each apocalyptic purge spelled extinction for at least 50% of all life. Aptly nicknamed the “Great Dying”, the greatest was the Permian mass extinction (around 250 million years ago) which was virtually all-encompassing: a mere 4% of life endured and all current life descends from these hardy survivors.
For many people, mass extinction summons to mind an image of T. rex and Pterodactyls fleeing a volcanic eruption or an inbound meteorite or asteroid. What exactly happened to cause the Cretaceous-Palaeogene dinosaur extinction 60 million years ago is not entirely known, but both extraterrestrial impact and large-scale volcanic activity have been implicated. A worldwide and abnormally concentrated layer of iridium in the rock strata and a 110 mile-wide crater in Mexico give credence to the theory that the fallout from a celestial body drove the extinction. However, volcanic belches near modern-day Mumbai a whole 5 million years before might have triggered changes in climate drastic enough to elicit the mass extinction, which decimated (among countless others) non-avian dinosaurs.
One unvarnished truth is that everything - from dinosaurs to dandelions - succumbs to death. Earth is a slowly ticking time bomb for life. In about a billion years the Sun will be burning so brightly that Earth’s oceans will boil off. In around seven billion years the Sun will run out of hydrogen in its core, will enter its red giant phase and will roast the Earth with ionised plasma. But human extinction may come much sooner than that.
Our end might not necessarily be part of a wider mass extinction. Nonetheless, let’s take a tour through the existential risks faced by humanity: potential candidates range from nuclear accidents and global tyrannies to supervolcano eruptions, sweeping pandemics and cosmic hazards.
Pandemics have exacted an enormous toll on human life. The outbreak of Spanish influenza in 1918 was more devastating to humanity than the effects of First World War. For a pandemic to wipe out humans entirely it would have to be capable of spreading even to isolated pockets of humanity, requiring a large host range as “carriers” of the disease. According to Seán O'Heigeartaigh of Oxford University’s Future of Humanity Institute (FHI), however, the real threat originates from human activity. Well-intended advances in synthetic biology might backfire in a profound way. Our ability to engineer self-replicating and exponentially destructive pathogens could prove our downfall, especially if used in biological warfare. Furthermore, a chilling artefact of our current exploitation of the natural world could see certain diseases increase in prevalence in the future. A reduction of biodiversity has already been implicated in the increased transmission of several diseases which affect humans.
Nick Bostrom, also of the FHI, says the advancement of human technology within the next century will introduce entirely novel risk factors which as a species we have never encountered. Machine intelligence or molecular nanotechnology could lead to the development of weapon systems which are capable of unthinkable destruction. In a paper, Bostrom wrote that the majority of our short-term extinction threats are speculative scenarios which cannot be given exact probabilities using rigorous statistical methods. He emphasises, however, that just because a threat is unquantifiable, it is not by default negligible. Oh dear.
What about some of the more “natural” extinction threats? Supervolcanoes have been involved in both the extinction of the dinosaurs and the Permian extinction, where massive volcanic eruptions produced enough lava to bury an area the size of the continental United States 305m under. No supervolcano has erupted in recent human history. There are a number (see here) that could cause worldwide devastation by plunging the world into a few years of “volcanic winter”. This has happened in the past when Yellowstone erupted: gases rose into the stratosphere combining with water vapour to produce a sunlight-dimming haze of sulphate aerosols. Asteroid impacts are also capable of causing massive loss of human life. But, the odds are currently fortuitously in our favour. NASA scientists estimate that an object over 400 metres in diameter only collides with Earth once every 160,000 years.
Otherwise, it might be Gamma-ray bursts. These are explosive events sometimes associated with supernovae. As a black hole is being born and matter falls inwards, some of it can accelerate into a particle jet, drill through the star and (if directly pointed our way) could affect Earth from 10,000 light-years away! The closest burst on record so far was 1.3 billion light-years away but who knows what the future holds in store?
Whether human extinction is relatively close or blissfully far away is a question that, despite conjecture, remains elusive. We may perish in a cataclysmic event, or we might die out slowly due to extreme environmental change.