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What are catastrophic and existential risks? - Part I: Catastrophic Risks

Updated: Apr 15, 2022

We are currently experiencing an extremely serious global pandemic. The Covid-19 pandemic has been a terrible event that has killed millions of people and has substantially changed the lives of many others. In addition, it has directly or indirectly affected the lives of almost everyone on the planet.

However, in the Effective Altruism movement we consider that there is a probability that should not be ignored that we will experience, in the coming decades or centuries, events that might be much more serious and devastating for humanity. We call these events catastrophic risks and existential risks, depending on their level of severity.

These events are generally ignored as they seem improbable to us. However, we believe that their extreme gravity justifies investing much more in preventing them than what is currently being invested. Furthermore, if we want to protect humanity in the long term, as well as the well-being and prosperity of our future generations, the levels of risk that we are currently taking are, in fact, unsustainably high.

Catastrophic Risks


A catastrophic risk is that event or event on a large scale or world scale that would seriously damage, for a limited amount of time, our well-being, development, and growth at a social and economic level, or our current level of civilization.

Nuclear wars

Nuclear war remains a catastrophic risk to humanity despite the non-aggression and non-proliferation agreements that have been put in place. Our world is still plagued with nuclear weapons that are ready to be detonated.

As Toby Ord relates in his book The Precipice, the decision of a single person in a Soviet submarine not to drop a nuclear bomb saved humanity from a nuclear war between the Soviet Union and the United States in 1962. [i] This means that having made this decision almost certainly saved the lives of millions of people, since nuclear bombs could have fallen on major cities in the United States and the Soviet Union, killing hundreds of millions of people, destroying cities, and ravaging whole regions of the world, what is called mutually assured destruction.

A single nuclear bomb can destroy a city. The Little Boy nuclear bomb that was dropped on Hiroshima in 1945 killed more than 100,000 people in this city of about 350,000 inhabitants and destroyed 70% of the buildings. However, the current situation is much worse than it was then. Little Boy was a 15 Kiloton bomb. The most powerful atomic bomb ever detonated by the Soviet Union, the Tsar's bomb of 1961, was 50,000 Kilotons, that is, more than 3,000 times more powerful than Little Boy. And we must consider that today's nuclear bombs are even more powerful than those of fifty years ago.

If existing nuclear weapons were dropped between countries with this type of weaponry, it would cause a level of destruction never seen before. Because today's nuclear weapons are much more powerful than those of fifty years ago, and since more countries than ever now possess an atomic arsenal, the level of danger from nuclear weapons is similar to that of the Cold War, even though we are not as aware of the danger as we were back then. A nuclear war could change the Earth's temperature by 8-10 degrees Celsius, destroying much of the world's agriculture and affecting billions of people. [ii]

Biological weapons

Nuclear weapons are not the only risk of this kind. As technology advances, we can think of biological weapons created by man that, whether by accident in a research laboratory, by the action of bacteriological warfare, or by bioterrorism, end up decimating the world population by being much more deadly pathogens for humans than any conventional virus. Today, as the world is more connected than ever through airplanes, a pandemic spreads across the globe in a matter of days.

Extreme climate change

Another catastrophic risk is an extreme climate change scenario. We are currently heading for a scenario where the Earth's temperature will be 3 degrees warmer in 2100 than it was in 1900. However, if one of the worst predictions of climate change occurs, or if we do nothing to stop it throughout the next few decades, we could face a rise in global temperatures of 10 degrees or more. This is still considered an unlikely scenario, but it cannot be ruled out, especially if we think in longer timeframes, such as 2200.

A situation of this kind would cause massive migrations of the world population towards the polar regions, and the almost total abandonment of those countries located in islands or close to the equator of the planet, where a large part of the world population lives. Such a crisis would be unprecedented. We would be talking about possible billions of migrants due to droughts, desertification, floods, lack of water and food. In addition, it would lead to an absolute change in the borders of the current countries, which could lead to a very serious crisis or a global migration war.

This is what South Beach (Miami) will look like in 2100 under a normal climate change scenario (3 degrees Celsius global temperature rise). We can hardly imagine what the world would look like under a 7 or 10 degree rise. [iii]

"Dark Age"

There is the possibility that, due to some serious international conflict, a superpower will impose itself with values ​​that lead us to historically regress to a civilizational level much lower than the current one. For example, the rise of fundamentalist or populist regimes could potentially harm our fundamental human rights, which could cause a civilizational stagnation.

Natural disasters

Finally, we must take into consideration natural hazards, such as asteroids, solar flares, massive earthquakes, or supervolcanic eruptions. This can lead us, for example, to the current level of agriculture being unsustainable due to a climate that makes the Earth an inhospitable place. Therefore, the world population would be drastically reduced by a severe hunger crisis.

Unforeseen risks

Since a list is generally not completely exhaustive, it is important to consider that there are other risks that we have not considered, and technologies that do not yet exist. When evaluating risks, it is important not only to consider what we know, but also those risks that we have not thought about, but that nonetheless exist.

From catastrophic to existential risks

In the next article, we will examine existential risks, a category of risks even more serious than catastrophic, as they could lead to the extinction of humanity.

Read Part 2.


[i] Ord, T. (2020). The Precipice: Existential Risk and the Future of Humanity. Hachette Books. The person in question is Vasili Arkhipov.

[ii] A good introduction to the issue of catastrophic risk from nuclear threats is this presentation by Joan Rohlfing, president of the Nuclear Threat Initiative. Many of these statements come from this presentation.

[iii] Image source: The Guardian.

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