Do we have enough nuclear weapons to wipe out all of humanity?

Question

I have heard several claims that we have enough nuclear weapons to wipe out all of humanity, but has anyone actually done an exact calculation of whether we do?

The claim includes:

• All of the nuclear weapons which are currently built by the whole of humanity (according to available statistics).
• All the direct deaths due to exploding them in the most damaging way (caused by the blast, fallout, radiation poisoning, nuclear winter and whatever other direct consequences that can be accurately predicted)

Answer 1

Yes, the global population would be at very high risk.

Consequences would include:

• Direct thermal damage
• Direct pressure damage
• Direct fallout damage
• Indirect damage when countries stop working (lack of infrastructure/energy/clean water, collapse of civil society)
• Indirect radiation damage
• Indirect damage through nuclear winter, global cooling, ozone depletion, etc.
• Indirect damage through an extended, 10+ years long famine

Good reference for the above breakdown is The Cold and the Dark: The World After Nuclear War, Sagan, Carl et al., Sidgwick & Jackson, 1985 which in turn is based on Sagan's peer-reviewed article Nuclear Winter: Global Consequences of Multiple Nuclear Explosions.

If you look at articles referencing the above, you will find dozens of peer reviewed studies on the subject. They all agree on how deadly this threat is.

The Doomsday clock tracks how close humanity is to self-destruction. Nuclear warfare is the number one threat for our species.

For example, a good, well referenced article on the subject is the following, from Physics today: Environmental consequences of nuclear war, Owen B. Toon, Alan Robock, and Richard P. Turco, Physics Today December 2008, page 37-42

A regional war involving 100 Hiroshima-sized weapons would pose a worldwide threat due to ozone destruction and climate change. A superpower confrontation with a few thousand weapons would be catastrophic

[...]

For any nuclear conflict, nuclear winter would seriously affect non-combatant countries. In a hypothetical SORT war, for example, we estimate that most of the world’s population, including that of the Southern Hemisphere, would be threatened by the indirect effects on global climate. Even a regional war between India and Pakistan, for instance, has the potential to dramatically damage Europe, the US, and other regions through global ozone loss and climate change.

Answer 2

The only plausible mechanism by which nuclear war could cause the extinction of humanity is nuclear winter. The world's present nuclear arsenal is definitely large enough that it would cause a nuclear winter.[Robock 2009] However, climate science is not a high-precision field. All we have are rough estimates. And even if we knew the exact amount by which the world would cool down, we have no reliable way of figuring out what impact it would have on civilization and agriculture, or how many people would die. There is no scientific way of figuring out, for example, whether or not some lucky, powerful, or wealthy group would be able to hoard some large supply of canned food and survive until the nuclear winter was over. As another example, there is no reliable scientific way of figuring out whether some group of people might be able to carry on subsistence agriculture by obtaining appropriate seeds that might grow well enough in some specific area where there was enough light and high enough temperatures. Supposing that some population survived the nuclear winter, there is no scientific way of determining whether they would be able to carry on the human race; e.g., nobody really knows the exact dynamics by which Norse settlements in Greenland died out in the 15th century.[Diamond 2005]

references:

Robock, http://climate.envsci.rutgers.edu/nuclear/RegionalNuclearConsequences24.ppt

Diamond, Collapse: How Societies Choose to Fail or Succeed

Answer 3

Russia has about 12,000, the USA about 9,600 (both figures according to WP). Assuming each warhead is on average the yield of a W76, 100 kt (a total guess), where ground zero (20 psi overpressure) is about 2 miles in diameter, this can only "parking lot" about 0.1% of the earth's land area. Even if the bombs were all 20 Mt, it would only go up to about 4%.

A problem with this figure, is that in order to kill people who are determined to stay alive in well stocked bomb shelters or the like, it is extremely difficult, so you would have to waste several weapons on those areas.

Answer 4

The link that Michael Pryor mentioned:

The smoke would form a stratospheric smoke layer that would block sunlight from reaching the surface of Earth for a period of about ten years.

Probably has a couple inaccuracies.

The U.S and Russia keep more than 2000 strategic nuclear weapons on high-alert

See YouTube: A Time-Lapse Map of Every Nuclear Explosion Since 1945.

There are 2053 nuclear explosions. However, since October 10, 1963 the Limited Test Ban Treaty (LTBT) went into effect, and after this date, every explosion was underground.

You can read about neutron weapons. In their case, nothing would be evaporated into the atmosphere.

You can read about eruption of volcanoes; seems like one volcano makes more dust than 1,000 nuclear bombs.

There was a Great Winter, the year without summer in 535-536 CE.

Looks like Scandinavian Ragnarok is a similar situation. Once Europe has no summer after an eruption, great famine, snow, no greenery, cold...

At the end, see this.

At the time of Berlin's wall, there was much more nuclear weaponry, such as SADM – The Special Atomic Demolition Munition on both sides, USSR and USA. Infantry with such ammunition theoretically can't be stopped or inhibited, only annihilated. The real war of Gods.