Editor’s note: Marshall Brain – futurist, inventor, NCSU professor, writer and creator of “How Stuff Works” is a contributor to WRAL TechWire.  Brain takes a serious as well as entertaining look at a world of possibilities for Earth and the human race.  He’s also author of “The Doomsday Book: The Science Behind Humanity’s Greatest Threats.” Brain has written several posts recently about the threat of climate change. His exclusive columns written for TechWire are published on Fridays.


RALEIGH – If we were to sit down together and create a list of humanity’s biggest existential threats, what would they be? What are the threats that could potentially wipe humanity out or “take us back to the stone age” for a small number of survivors? There are many different doomsday events that have this kind a cataclysmic potential, so let’s take a look at the top 5.

Nuclear War Holocaust

Right now, humanity is in a very strange position when it comes to nuclear warfare. Since the bombings of Hiroshima and Nagasaki in 1945, there has been a quiet understanding amongst the world’s nuclear powers that no one would use nuclear weapons offensively. As long as this idea is true for everyone, then there is no chance of humanity using nuclear weapons.

But now in 2022, Russia is openly threatening to use offensive nuclear weapons in Ukraine. There are plenty of headlines to this effect:

It is easy to imagine how we might get to the point where Russia uses a nuclear bomb in Ukraine. As the cost of Russia’s military failures in Ukraine mount, and as Russia becomes more and more embarrassed on the international stage, Vladimir Putin may decide to quickly end the war with a devastating nuclear strike on a Ukrainian city like Kiev. Now what? If NATO decides to retaliate with a similar strike on a Russian city, then Russia might use a second nuclear weapon, and so on, in an escalating tit-for-tat battle between Russia and NATO. Then a very strange psychology comes into play, as described in this video https://www.youtube.com/watch?v=Z1fvMmkIfSM, where it “makes sense” for both sides to use a large number of nuclear weapons.

The problem with nuclear weapons is that it does not take very many for the specter of global nuclear winter to arise. When a nuclear bomb explodes, it can throw a tremendous amount of dust and debris into the atmosphere, and it also starts fires that create a great deal of smoke and soot. Scientists estimate that it would only take on the order of 100 small or “tactical” nuclear weapons to plunge Planet Earth into a deep freeze. The atmosphere becomes so clogged with particles that it blocks the sun and temperatures drop planet-wide. Global crops fail from both lack of sunlight and falling temperatures. Billions of people could die in this scenario, and civilization as we know it today would collapse.


You may or may not remember the eruption of the Tonga volcano last January. On the one hand, it was the largest volcanic eruption we have seen so far this century. On the other hand, it occurred in a very remote part of the world and was really only witnessed by satellites, as seen in this article . Because it happened in such a remote area, this volcano did little damage, although it did pump a huge amount of water into the stratosphere and this water is having some lasting effects on the planet’s climate.

Or think about the eruption of the Krakatoa volcano in 1883. It created such a loud sound when it exploded that people heard it 3,000 miles away. Imagine a sound so loud in Los Angeles that people can hear the sound in New York City. The Krakatoa eruption blew six cubic miles of debris into the atmosphere and it affected weather around the globe for several years.

However, these eruptions pale in comparison to the eruption of a supervolcano. Supervolcanoes have the potential to devastate an entire continent, and their global impacts would be profound.  This video dramatizes the problem: https://www.youtube.com/watch?v=EFFULferf6U

Take the supervolcano located under Yellowstone national park as an example. Its eruption would be 100X more powerful than Krakatoa, potentially blasting 1,000 cubic miles or more of debris into the atmosphere. All this debris would then rain down upon much of the United States and parts of Canada. It would destroy America’s “breadbasket” region by burying it in ash and dust. This alone would lead to starvation for hundreds of millions of people.

But then the planet is likely to plunge into volcanic winter. The problem is that the eruption of a supervolcano is likely to inject vast quantities of sulfur dioxide into the stratosphere. It will reflect sunlight away and cause temperatures around the globe to plunge. Between this and all the dust in the air, crops will fail around the world and a vast starvation event could kill off billions of people. As is the case with nuclear winter, volcanic winter from a supervolcano is likely to mark the end of civilization as we know it today.

There are 20 known supervolcanoes around the globe. One interesting thing about the supervolcano in Yellowstone is that there is the possibility of neutering this volcano. NASA has suggested that injecting lots of water into the volcano’s magma chamber could cool it down to the point where the eruption threat disappears. This plan would also generate a lot of geothermal electricity.

Asteroid Strike

NASA has been in the news again because it has managed to crash a satellite into an asteroid with its DART mission. It is an amazing achievement because we are talking about a small satellite the size of a vending machine with a speed of 14,000 miles per hour hitting an object the size of a stadium that is floating in space millions of miles away. This video shows the impact https://www.youtube.com/watch?v=ZuVUrsKkaNI

Why is this event such a big deal? You may recall that 66 million years ago an asteroid crashed into planet Earth. This asteroid was perhaps 25 miles in diameter, and the impact was so devastating that it caused a mass extinction event. This is the event that killed off the dinosaurs and about half of all the life on Earth.

The odds of another asteroid hitting Planet Earth are surprisingly high. We already know about tens of thousands of Near Earth Objects (NEOs) that could potentially hit the planet, and then we are finding about 1,500 new ones each year. In any given year, the chance of an asteroid 100 meters (300 feet) in diameter or larger hitting Earth is about 1-in-10,000. If an asteroid 1,000 meters in diameter or greater were to hit the planet, it would likely mark the end of human civilization as we know it. It would be the same effect as nuclear winter and volcanic winter described above – the asteroid would send so much debris and soot into the atmosphere that all the crops fail.

This is why the NASA DART mission is so exciting. It marks the first step in creating a planetary defense system able to prevent asteroids from hitting our planet. Until a planetary defense system is fully implemented however, the planet is vulnerable to the asteroid threat.

Another Pandemic

The recent Covid-19 pandemic taught humanity three things:

  1. It is possible for a new disease to spontaneously arise in nature, and then…
  2. It is possible for this disease to rapidly spread all over the planet, infecting hundreds of millions of people, and then…
  3. It is possible for millions (about 1%) of those infected people to die.

As of September 2022, approximately 600 million people have been infected by Covid and 6.5 million people have died. This video talks about economic effects: https://www.youtube.com/watch?v=0cGLrSpaf4o

The question then is: what if a more infectious disease were to appear that also happened to be more deadly? A more infectious disease would affect billions of people, and then what if a billion of them died?

In the aftermath of Covid, we have seen how all the Covid deaths plus the long-Covid situation can affect economies by causing worker shortages and disruptions. What if, in the next pandemic, 100X more people die? It has the potential to drive the global economy into a tailspin, leading to mass starvation and potentially the collapse of civilization as we know it.

Climate Change

And then there is climate change. The problem with climate change is that it is actually happening right now, and the effects are getting worse and worse as time goes on. The prior four scenarios are all “maybes” or “mights”:

  • Russia might use nuclear weapons in Ukraine and then the situation might escalate to the point of nuclear winter, destroying civilization as we know it.
  • A supervolcano might erupt somewhere in the world and lead to volcanic winter, destroying civilization as we know it.
  • An asteroid might appear out of nowhere and slam into our planet, causing a mass extinction event and destroying civilization as we know it.
  • A new pandemic that is far more deadly than Covid might arise in nature and spread all over the planet, destroying civilization as we know it.

None of these things are guaranteed.

With climate change, we know that it has started, and we are seeing the early effects. The month of August was surprisingly intense , and it is just the tip of the iceberg compared to what is coming.  But we do not know two things: A) might humanity awaken and start taking serious action to combat climate change? And B) where is the tipping point where climate change becomes so severe that it can destroy civilization as we know it?

The key problem with climate change is that is has so many terrible effects:

  1. Climate change can cause severe heatwaves
  2. These heatwaves can cause severe droughts
  3. Heat and drought can cause severe crop failures, eventually leading to global food shortages
  4. Climate change can also cause severe floods
  5. These floods can impact entire cities or regions – see for example the California megaflood scenario
  6. Climate change can cause significant sea level increases, wiping out coastal cities and turning tens of millions of people into climate refugees.
  7. Climate change can make parts of the planet uninhabitable, and in the process destroy whole ecosystems such as the Amazon rainforest.
  8. Climate change has the potential to destroy the world’s oceans , killing off seafood as a natural resource and putting a billion people at risk of food insecurity.

At some point the crop failures, the number of refugees, the flooding, the heat, and the droughts kill off so many people that we see the collapse of civilization as we know it today. Eventually climate change could cause the sixth mass extinction event for the planet.

Which is worse: nuclear Armageddon or climate change? The amazing thing is that both of these are strictly human problems. If a supervolcano erupts, humanity really has very little control over it. But humanity is both the cause and (potentially) the solution to both nuclear bombs and climate change. If humanity could get its act together, it is possible to imagine the elimination of all nuclear bombs on Earth. And if humanity could get its act together, it is possible to imagine a reversal of the worst outcomes of climate change.

The problem therefore is humanity, and in particular humanity’s leaders. If humanity’s leaders could get their act together, we could end two of the biggest threats on this list of five existential threats to humanity. NASA can see a path toward a planetary defense system that would end the asteroid threat, provided that NASA receives sufficient funding from the nation’s or the world’s leaders. It is also possible to imagine a planet where, with enough funding from the world’s leaders, medical advances lead to the end of pandemics as a global threat.

Perhaps the point is: it looks like our planet needs better leaders. We will discuss this possibility in a future article.


  1. https://www.cnn.com/2022/09/26/europe/russia-ukraine-tactical-nuclear-weapons-explainer-intl-hnk-ml/index.html
  2. https://www.politico.com/news/2022/09/27/putin-nuke-russia-ukraine-intel-surveillance-00059020
  3. https://www.businessinsider.com/us-russia-catastrophic-consequences-firing-nuclear-weapons-ukraine-war-2022-9
  4. https://www.reuters.com/world/europe/russias-medvedev-warns-west-that-nuclear-threat-is-not-bluff-2022-09-27/
  5. https://en.wikipedia.org/wiki/Nuclear_winter
  6. https://www.youtube.com/watch?v=Z1fvMmkIfSM – How would the United States Fight a Nuclear War?
  7. https://www.youtube.com/watch?v=2jy3JU-ORpo – Plan A – Our team developed a simulation for a plausible escalating war between the United States and Russia using realistic nuclear force postures, targets and fatality estimates.
  8. https://www.nature.com/articles/d41586-020-00794-y – How a small nuclear war would transform the entire planet
  9. https://www.businessinsider.com/nuclear-explosions-earth-atmosphere-temperature-2017-8
  10. https://www.space.com/tonga-eruption-water-vapor-warm-earth
  11. https://www.dailystar.co.uk/news/world-news/supervolcano-warning-threat-level-raised-28034685
  12. https://interestingengineering.com/science/nasa-has-a-346-billion-plan-to-cool-yellowstone-and-harvest-it-for-energy
  13. https://www.vox.com/2014/9/5/6108169/yellowstone-supervolcano-eruption
  14. https://www.youtube.com/watch?v=EFFULferf6U – Volcanic Hyper Eruption
  15. https://www.youtube.com/watch?v=leU3-1eHnw4 – NASA’s $3.5 Billion Idea To Save Earth From A Supervolcano Apocalypse
  16. https://www.npr.org/2022/09/27/1125314926/nasa-dart-asteroid-photos
  17. https://www.youtube.com/watch?v=ZuVUrsKkaNI – See the moment NASA’s DART spacecraft collides with asteroid
  18. https://www.amnh.org/exhibitions/dinosaurs-ancient-fossils/extinction/mass-extinction
  19. https://en.wikipedia.org/wiki/Chicxulub_crater
  20. https://www.nhm.ac.uk/discover/how-an-asteroid-caused-extinction-of-dinosaurs.html
  21. https://www.axios.com/2022/09/27/asteroid-threat
  22. https://en.wikipedia.org/wiki/Near-Earth_object
  23. https://cneos.jpl.nasa.gov/ – Center for Near Earth Object Studies
  24. https://www.google.com/search?q=covid+dashboard
  25. https://www.thebritishacademy.ac.uk/publications/covid-decade-understanding-the-long-term-societal-impacts-of-covid-19/
  26. https://www.youtube.com/watch?v=0cGLrSpaf4o – Coronavirus outbreak: The impact COVID-19 is having on the global economy
  27. https://wraltechwire.com/2022/09/02/climate-change-catastrophe-august-2022-31-days-of-global-drought-flood/
  28. https://wraltechwire.com/2022/08/19/doomsday-california-megaflood-has-happened-before-it-could-again/
  29. https://wraltechwire.com/2022/09/23/doomsday-warning-its-time-to-start-moving-coastal-cities-to-higher-ground-heres-why/
  30. https://wraltechwire.com/2022/09/16/climate-change-doomsday-irreversible-tipping-points-may-mean-end-of-human-civilization/