How many nuclear warheads would it take to destroy the Earth?
To destroy all of humanity, we can do two things:
Detonate the largest nuclear blasts at a high altitude such that we basically blast all life down and then create firestorms large enough to create a “nuclear winter.”
Detonate large bombs that are “salted,” i.e. contain substances that can cause a radioactive wasteland.
For the first part, we need to understand what’s going on.
“Nuclear winter” is the (faulty) hypothesis that, in a large-scale nuclear war, large numbers of nuclear weapons would detonate in major cities. So many bombs would be dropped, and so many cities would be destroyed, that the resulting firestorms would throw up lots of soot into the atmosphere. This soot would block the Sun’s rays, reducing Earth’s temperatures and screwing with the global climate. These changes would cause changes in weather patterns, crop failures, ecological destruction, and total destruction of much of life on Earth, including humans.
Now, this has some flaws. This mostly stems from the fact that we don’t even have enough nuclear weapons to do this (especially as of 2017), not to mention that they’re not big enough (meaning they can’t throw up enough dust high enough in the air to block the Sun). Plus, many of them would not be hitting cities; they’d be hitting military targets, like missile silos and military bases.
But, let’s say that we ignore all of these quips, and we decide to grab the largest nuclear bomb as of 2017 and detonate it all over the world.
As of 2017, China and Russia have the largest nuclear bombs, with some of these yields packing around five megatons of energy (over 300 times more powerful than the bomb dropped on Japan in 1945).
We’ll use this amazing program called NUKEMAP to calculate what we need, for both scenarios.
So, detonated at an optimum altitude to maximize the 5-PSI blast wave (which would cause most concrete structures to collapse), the 5-PSI blast wave would destroy everything within 7.5 miles (12 km) of the blast zone, or devastating an area of 175 square miles. The 1.5-PSI blast wave, which would shatter glass windows, extends around 18 miles (29 km) from the epicenter, or an area of 950 square miles.
Now, if we spaced out the nuclear weapons to cover all of the Earth’s land masses, this is where the numbers go crazy. Earth has a surface area of around 197 million square miles. One-third of that is land, so that gets cut down to 66 million square miles. If we dispersed the number of nuclear weapons around the world such that 1.5-PSI blast waves “connect” with each other, we’d need close to 70,000 5-megaton bombs to “glass” the surface and cause the firestorms necessary to do this.
In other words, we’d need an impossibly-large number of nuclear weapons, just to blast, burn, and freeze all of humanity.
For the second part, we’d need to modify the bomb so that the radiation left behind would poison large amounts of land for years.
One potential way to do this is to build a “cobalt bomb.” This is a true doomsday weapon, and it’s because of its structure.
Basically, a Cobalt bomb is a nuclear weapon that has Cobalt-59 inside of it. When it detonates, the neutrons released by the explosion, alter the Cobalt-59 so that it becomes Cobalt-60, which is extremely radioactive and long-lasting, having a half-life of 5 years.
To basically cover this planet in radiation (and perhaps, a nuclear winter), we’d need to detonate a lot of nuclear weapons. Again, we’ll use the largest bombs for reference.
Let’s say that, to “destroy” the planet,” we need to drop around 10 rads per hour on an area to irradiate the land and make it poisonous. The program calculates that this “drop” covers an area of around 15,000 square miles. Going by the surface of the Earth, we come to the conclusion that we’d need close to 5,000 nuclear weapons to do the job.
