10 of the Biggest Threats to Human Existence

Just in case you don't have enough to worry about.

Photo Credit: shutterstock.com

AMC’s “The Walking Dead” is at the top of the cultural zeitgeist these days, one of the most popular television series on the air. In the show, a virus has ravaged the Earth, killing most of humanity, with the dead corpses rising to terrorize the few remaining living souls. While enormously entertaining, it is not a likely scenario for the end of the human race. Dick Cheney notwithstanding, zombies aren’t real. The end of humanity, however, could be. While it is difficult to envision a world without “us,” there are multiple scenarios staring at us, right here, right now, not far-fetched, that could wipe out all or most of humanity, leaving a wasteland for Mother Nature to reclaim. Here are some of the possible ways the reign of man- and womankind might end, no zombies needed.

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1. Global Climate Change

Climate change is the Big Kahuna of all scenarios in which our presence on Earth is ended. Despite what the climate change deniers would have you believe, climate change is real. It is being caused by human beings, with a little help from lots of farting cows emitting methane, plus that giant well of methane lurking under the Arctic ice. As we burn carbon and increase our meat-eating ways, more and more greenhouse gases are building up in the atmosphere. It is pretty easy to see the end game of this scenario. Grab a telescope and look at Venus, a planet with a thick, heat-trapping atmosphere and a surface temperature high enough to, well, melt lead. A few decades ago, climate scientist James Hanson studied Venus, and saw some parallels with what was happening on Earth. What he saw alarmed him, and he testified in Congress in 1988, warning our government that unless we changed our carbon-burning ways, we were on a course for disaster. Hanson got through to a single senator: Al Gore.

Meanwhile, the carbon keeps burning, the CO2 keeps rising, resulting in a slowly rising average Earth temperature despite the occasional freezing cold winter. On average, Earth’s temperature has been rising steadily since the Industrial Revolution unleashed our carbon-burning frenzy, resulting in a slow-moving train wreck. The hottest years in recorded history have occurred in the last decade. Author and environmental activist Bill McKibben outlines the situation:

“The Arctic ice cap is melting [releasing more greenhouse gases], the great glacier above Greenland is thinning, both with disconcerting and unexpected speed. The oceans are distinctly more acid and their level is rising…The greatest storms on our planet, hurricanes and cyclones, have become more powerful… The great rain forest of the Amazon is drying on its margins… The great boreal forest of North America is dying in a matter of years… [This] new planet looks more or less like our own but clearly isn’t."

Many environmentalists think we have already passed the point of no return. Once we pass a certain threshold, Earth will continue warming even if we do manage to cut our CO2 emissions. What we do know is that, if we don’t begin reducing the amount of CO2 we are releasing into the air, and at least minimize the damage, a planet-wide disaster is assured. 

2. Loss of Biodiversity

If we don’t melt ourselves into extinction, another possible route to end times is partly a byproduct of climate change: loss of biodiversity. Human activity is responsible for massive extinctions of countless species on Planet Earth. Environment News Service reported as far back as 1999 that, “the current extinction rate is now approaching 1,000 times the background rate [what would be considered the normal rate of extinction] and may climb to 10,000 times the background rate during the next century, if present trends continue [resulting in] a loss that would easily equal those of past extinctions.” 

The Millennium Ecosystem Assessment, a major environmental report released in 2005, reported 10-30% of mammals, birds and amphibians on the planet are in danger of extinction due to human activity, which includes deforestation (resulting in habitat destruction), CO2 emissions (resulting in acid rain), over-exploitation (such as overfishing the oceans), and invasive species introduction (like boa constrictors in the Florida Everglades). “This rapid extinction is therefore likely to precipitate collapses of ecosystems at a global scale,” said Jann Suurkula, chairman of Physicians and Scientists for Responsible Application of Science and Technology. “This is predicted to create large-scale agricultural problems, threatening food supplies to hundreds of millions of people. This ecological prediction does not take into consideration the effects of global warming which will further aggravate the situation.” 

Amphibians, such as frogs and salamanders, are considered “marker species," meaning they provide important clues to the health of the ecosystem. Right now, the frog population, as well as other amphibians, has been declining rapidly. In any ecosystem, when one species dies, it affects other species, which depended on the now-extinct species for food and perhaps other necessities. When there is a sudden mass extinction of many species, a chain reaction can cause catastrophic results. There have been five mass extinctions in the history of the Earth, and many scientists are saying we are in the midst of the sixth. "We are entering an unknown territory of marine ecosystem change, and exposing organisms to intolerable evolutionary pressure,” states the International Programme on the State of the Ocean (IPSO), in the biannual State of the Oceans Report. The next mass extinction may have already begun." What would that be like?  Well, in the worst one, 250 million years ago, 96 percent of ocean life and 70 percent of land life perished. What can we expect from mass extinction number six? We probably would prefer not to find out.

3. Bee Decline

Bees are dying—a lot of them, due to CCD, Colony Collapse Disorder. “One of every three bites of food eaten worldwide depends on pollinators, especially bees, for a successful harvest,”  says Elizabeth Grossman, author of Chasing Molecules: Poisonous Products, Human Health. Plants depend on spreading their pollen to produce food. Bees are pollinators. No bees, no food (or at least much less). As many as 50% of the hives in the United States and Europe have collapsed in the past 10 years. The suspect in bee deaths is a class of chemicals called neonicotinoids, pesticides used on a massive scale in commercial farming. It is believed the chemicals impair the bees’ sense of direction, preventing them from returning to the hive.

With reduced pollen in the hive, fewer queen bees are produced, and eventually the colonies collapse. The European Commission has imposed a ban on these pesticides after the European Food Safety Agency concluded that they posed a “high acute risk” to honeybees. The United States, however, has declined to join Europe in banning neonicotinoids, citing other possible causes of CCD, including parasites. Meanwhile, as Nero fiddles, Rome is burning and bees are quickly disappearing. It is not hard to imagine a scenario where resulting acute food shortages bring on mass starvation, war and human extinction. 

4. Bat Decline

Bees aren’t the only pollinators dying off. Bats, too, are dropping like flies. As a result of deforestation, habitat destruction and hunting, combined with a fatal fungal disease spreading among the bat population called White Nose Syndrome, bats are disappearing at an alarming rate. Besides contributing to the pollination crisis, the dwindling bat population brings about another possible human extinction scenario. As their habitats are destroyed, bats are increasingly crossing paths with the human population, in search of food and shelter. With bats come bat viruses. "It's very easy to see how pathogens can jump from animals to humans," says Jon Epstein, at the EcoHealth Alliance, a non-profit agency dedicated to conservation and biodiversity. Every year, on average, five new infectious diseases pop up, and about 75% of these new diseases come from animals. It is already suspected that human killers like Ebola emerged from the bat population. Might some new human-killing pathogen mutate from bats to humans and decimate mankind?

5. Pandemic

Which leads us to a related extinction scenario: a worldwide pandemic. New diseases emerge every year.  Some have the potential to devastate the population. In 1918, a strain of influenza spread worldwide and killed between 20 and 50 million people—more than were killed in all of World War I. In the past several years, diseases like SARS have come close to igniting into worldwide pandemics, and it is not at all inconceivable that, in our airplane-riding, interconnected world, some other virus could arrive on the scene with the virulence and transmissibility to decimate, if not destroy, the human population. “It is not in the interests of a virus to kill all of its hosts, so a virus is unlikely to wipe out the human race,” says Maria Zambon, a virologist with the Health Protection Agency Influenza Laboratory. “But it could cause a serious setback for a number of years. We can never be completely prepared for what nature will do: nature is the ultimate bioterrorist."

6. Biological /Nuclear Terrorism

In the interim, there are plenty of down-and-dirty, run-of-the-mill terrorists and the grand prize they all hope to get their hands on is a weapon of mass destruction like a nuclear bomb or a vial of smallpox virus. “Today's society is more vulnerable to terrorism because it is easier for a malevolent group to get hold of the necessary materials, technology and expertise to make weapons of mass destruction,” says Paul Wilkinson, chairman of the advisory board for the Center for the Study of Terrorism and Political Violence at the University of St. Andrew. “The most likely cause of large scale, mass-casualty terrorism right now is from a chemical or biological weapon.The large-scale release of something like anthrax, the smallpox virus, or the plague, would have a huge effect, and modern communications would quickly make it become a trans-national problem. There is a very high probability that a major attack will occur somewhere in the world, within our lifetimes.” 

As for the nuclear threat, with increasing numbers of unstable countries like Pakistan and North Korea in possession of atomic weapons, the availability to terrorists seems only a matter of when and not if.

7. Super-Volcanoes

There are volcanoes, and then there are super-volcanoes. "Approximately every 50,000 years the Earth experiences a super-volcano. More than 1,000 square kilometers of land can be obliterated by pyroclastic ash flows, the surrounding continent is coated in ash and sulphur gases are injected into the atmosphere, making a thin veil of sulphuric acid all around the globe and reflecting back sunlight for years to come. Daytime becomes no brighter than a moonlit night.”

This lovely scenario is brought to us by Bill McGuire, director of the Benfield Hazard Research Center at University College London. About 74,000 years ago, the most powerful super-volcano eruption in human history occurred in Indonesia. It was close to the equator, and thus gases quickly passed into both hemispheres. Sunlight was blocked, and temperatures on Earth dropped worldwide for the next five to six years, below freezing even in the tropical regions. A super-volcano eruption is 12 times more likely than an asteroid hitting the Earth. Known super-volcanoes exist in Yellowstone National Park in the U.S. and Toba in Sumatra, Indonesia. And then there are the unknown ones….

8. Asteroid Impact

Recent films like Deep Impact and Armageddon have dramatized this human extinction scenario, an asteroid hitting the Earth. Hollywood is Hollywood, but in 2013, a real-life asteroid appeared without warning in Chelyabinsk, Russia. About 20 meters wide, it hurled into the Earth’s atmosphere at over 40,000 miles per hour. Only the angle it came in at and its relatively small size prevented damage and destruction on a massive scale. But what would happen if a not-at-all uncommon mile-wide asteroid hit the Earth at this speed? Quite probably it would wipe out the human race. The tremendous explosion it would cause upon impact would fling so much dust into the atmosphere that the sun would be completely blocked off, plant life and crops would die, severe acid rain would kill ocean life, and fiery debris would cause firestorms worldwide. 

This has already happened at least once. The likely reason you don’t see any dinosaurs around the neighborhood is that they were wiped out by just such an incident. Donald Yeomans of NASA: “We expect an event of this type every million years on average.”

9. Rise of the Machine

We look to Hollywood again to dramatize our next scenario. The Terminator movies entertained us with killer androids from a future where war was being waged on man by super-intelligent machines. OK, we are not there yet, but as we program more and more intelligence into our computers, exponentially increasing their capabilities every year, it is only a matter of time before they are smarter than we are.  Already we entrust computers to run our stock markets, land our planes, correct our spelling, Google our trivia, and calculate our restaurant tips. In development are robots that look like us, talk like us and recognize our facial movements. How long before they are us, as we download our thoughts and memories into our hard drives, the so-called “singularity”? How long before these machines are self-aware?

Futurist and author Ray Kurzwell believes computers will be as smart as us by 2029, and by 2045 will be billions of times smarter than us. What then? Will they decide we are superfluous? Or maybe we ourselves will decide. Sounds far-fetched, I know, but some very smart people buy into this scenario; people like genius physicist Stephen Hawking: “The danger is real that they [super-computers] could develop intelligence and take over the world.”

10. Zombie Apocalypse

I know. I said zombies aren’t real. But there is a parasite called toxoplasmosa gondii. This terrifying little bug infects rats, but it can only reproduce inside the intestines of a cat, so it evolved a nifty little trick wherein it actually takes over the rat’s brain and compels it to hang out around cats. Naturally, the cat eats the rat. The cat is happy. The parasite is happy because it gets to reproduce in the cat’s intestines. The rat? Not so happy, one would suppose. Why should we care about unhappy rats? Because rats and humans are actually very similar, which is why we conduct so many medical experiments on rats. And humans are infected with the toxoplasmosa gondii parasite. About half the population of the Earth, in fact. Now it so happens that toxoplasmosa gondii  does not affect humans the way it does rats. But what if it did? Viruses mutate. Viruses are manipulated in bio-weapons laboratories. Suddenly half the population would have no instinct for self-preservation. Half the population unable to think in a rational manner. Half the population suddenly very much resembling zombies. Nah. Couldn’t happen. Could it?

Larry Schwartz is a Brooklyn-based freelance writer with a focus on health, science and American history.