Quirks & Quarks

Explainer: North Korea's nukes, missiles and nuclear winter

Experts think that if North Korea is not yet able to put a powerful warhead on a missile and deliver it to the U.S., they will soon.

North Korea's nuclear threat

4 years ago
Duration 1:00
North Korea's nuclear threat 1:00

On Friday, September 15, at about 7 a.m. local time, a North Korean rocket sailed over Hokkaido, an island in northern Japan.

The launch came one day after North Korea threatened to sink Japan and turn the U.S. into "ashes and darkness".

It's been a heated summer of escalating nuclear tensions between North Korea, its neighbours, and the United States.

First came the intercontinental ballistic missile tests North Korea conducted in July demonstrating it now has the capacity to launch long-range missiles. That was met with U.S. President Donald Trump's "fire and fury" warning to North Korea.

Then on Labour Day weekend, North Korea rocked the world with an underground nuclear test unlike any it had ever tested before.  

Today, we look at North Korea's nuclear threat, and the environmenal threats from different scenarios for nuclear war.

Part 1 - North Korea's bombs

So now that North Korea has this bomb and new long range missiles, what kind of threat does this add up to? Bob McDonald spoke with Dr. David Wright, a physicist and co-director of the Global Security Program at the Union of Concerned Scientists, about calculating the immediate threat of a North Korean attack.

This interview has been edited for length and clarity.

Bob McDonald: What's your estimate for how strong the the bomb was that North Korea tested on Labour Day weekend?

Dr. David Wright: The estimates I've seen suggests it's probably around 150 kilotons, but maybe bigger than that or maybe a little smaller. And that's to be compared to something on the order of 20 to 25 kilotons for the bombs that were dropped on Hiroshima and Nagasaki at the end of World War II. So this is a much bigger bomb than anything that North Korea has tested before, which were on the order of those Hiroshima and Nagasaki bombs.

This undated file photo distributed on Sunday, Sept. 3, 2017, by the North Korean government, shows North Korean leader Kim Jong Un at an undisclosed location in North Korea inspecting a nuclear device. (Korean Central News Agency/Korea News Service via AP)
BM: North Korea says it was a hydrogen bomb. What is that?

DW: There are basically two divisions of bombs, fission and fusion. The early bombs, like those in Hiroshima and Nagasaki, used heavy elements, in particular either plutonium or uranium isotopes. And you can create a chain reaction where those heavy atoms break him the smaller atoms and in the meantime release huge amounts of energy. So that's called a fission bomb because you're fissioning these heavy elements into lighter elements. There are some limits to how big you can make a bomb with that because you just have to have more and more material and the process becomes less efficient.

A hybrid type bomb, for example, is if you have a sphere of plutonium that's being compressed in order to explode and you put some material some lightweight hydrogen isotopes in the middle. Those lightweight atoms under those conditions will actually fuse together and that not only releases energy, but it releases neutrons, which is really the key to the fission and can make the fusion reaction much more effective.

A true hydrogen bomb requires two stages, the fission bomb, which is essentially the igniter, and then you use the energy from that to compress and heat up a bunch of these hydrogen isotopes that then fuse together release information release energy, but also release a tremendous number of neutrons that you can then use to cause another fusion layer. It has essentially unlimited power as you continue to scale it up.

BM: So how convinced are you then that what North Korea detonated was a hydrogen bomb?

DW: A friend who studies China pointed out to me that by China's sixth nuclear test, back in the '60s, they had developed a working hydrogen bomb. So this was North Korea's sixth underground test, which says to me it's not inconceivable that in fact they did exactly what they said they did, which they had managed to figure out how to do this complicated process of a real two-stage hydrogen bomb.

  • What kind of damage could a nuclear weapon do to your region?  NUKEMAP by Alex Wellerstein
In this July 28, 2017, file photo distributed by the North Korean government shows what was said to be the launch of a Hwasong-14 intercontinental ballistic missile (Korean Central News Agency/Korea News Service via AP)
BM: So the other threat that people are worried about is the delivery mechanism to get that hydrogen bomb across the Pacific Ocean potentially to the United States. Tell me about the missile tests North Korea did in July.

DW: North Korea has been launching its tests on unusual trajectories for about the last six months, which is that it shoots them almost directly straight up, so that they come down not very far away from the launch site. When I sat down and calculated how far that same missile could go on sort of a standard trajectory, I got something in excess of ten thousand kilometers. Now that could reach the U.S. west coast, probably reach Chicago, and might even reach Boston.

And so that was a big big step beyond what we'd seen before. Now the caveat is that we don't know how heavy a payload that missile carried. And so the question then is how heavy is a warhead that North Korea can actually mount on a weapon? And that remains a source of a lot of discussion within the expert community. The general consensus is that if North Korea is not to the stage yet that they could put a pretty powerful warhead on a missile and deliver it to the United States, that they will get there soon - within a year or so.
The mushroom cloud from the US "Castle Bravo" nuclear test in 1954. A 15 megaton explosion was set off on Bikini Atoll in the Pacific. (US Department of Energy)

Part 2 - The Environmental Catastrophe of Nuclear War

Any nuclear bomb — whether it be atomic or hydrogen — dropped on a densely populated city, would have catastrophic local effects. But after the fire and fury abate, the cold, darkness, and starvation would set in on a global scale. 

The concept, which Dr. Alan Robock — a climate scientist at Rutgers University has been studying for decades, is known as nuclear winter. "The smoke from the fires get heated and lofted into the stratosphere, which is the atmospheric layer above where we live, which is called the troposphere. The troposphere has rain, which washes particles up at the stratosphere doesn't. And so these tiny particles fall very slowly, get blown around the world, and get heated by the sun and locked into the upper stratosphere, so they just float around for a long time because they're black and the sun keeps them up there."  

Dr. Robock studied what would happen if two nuclear nations, like India and Pakistan, with smaller arsenals got into a nuclear skirmish. If they launched 50 smaller atomic bombs each, it would produce five or six million tons of smoke, which would last in the atmosphere for more than a decade blocking out the sun, making our planet colder and darker.

"It wouldn't be nuclear winter, as in the temperatures wouldn't get below freezing in the summertime in the northern hemisphere, but it would be climate change unprecedented in record human history. There would be huge impacts on agriculture. For example, in Canada, the soybean and corn production would go down by about 30 percent for the first five years and wheat production would go down about 10 percent. So it would have a huge impact on agriculture around the world so there would be a huge threat to the world's food supply." - Dr. Alan Robock

Earthquake and Volcano of the Korea Meteorological Administration Director Lee Mi-seon briefs the media about artificial earthquake in North Korea, in Seoul, South Korea, Sunday, Sept. 3, 2017. (AP Photo/Lee Jin-man)
In the current geopolitical situation, what really concerns Dr. Robock is if North Korea attacks and a nuclear holding nation with even bigger bombs retaliates, potentially leading to a full scale nuclear war. 
We still have enough nuclear weapons to produce nuclear winter even though the total arms are going down. We could have temperatures below freezing and the grain producing regions and that would sentence most of the world to death by famine. So it's a very scary thing.- Dr. Alan Robock

On September 20, 122 nations will be signing a UN Treaty to ban nuclear weapons. "Unfortunately," says Dr. Robock, "the countries with nuclear weapons and some of their allies are boycotting it and are not planning to sign it immediately."

Canada will not be signing the treaty next week. Quirks & Quarks reached out to Global Affairs Canada for comment. Here is the full response from their spokesperson, Brittany Venhola-Fletcher:

We strongly support concrete efforts towards nuclear disarmament. We are taking meaningful steps to achieve nuclear disarmament. That means doing the hard work to deliver real and meaningful results. In 2016, Canada rallied 159 states to support and pass a resolution calling for the Fissile Material Cut-off Treaty. With the support of nuclear and non-nuclear countries, Canada is chairing this high-level group to help phase-out nuclear weapons. This is real action that will have a positive impact towards nuclear disarmament. "We also support Norway's initiative to create a group of governmental experts on nuclear disarmament verification, one of the most challenging obstacles to nuclear disarmament. This type of concerted and inclusive action is necessary to make genuine progress towards the goal of a world free of nuclear weapons.


  • A Fissile Material Cut-off Treaty (FMCT) is the next logical step in our step-by-step approach to nuclear disarmament.
  • In contrast with the Treaty Prohibiting Nuclear Weapons, this 25-member Preparatory Group features the active participation of six states that possess nuclear weapons and therefore has the potential to halt the production of  nuclear weapons."

Paul Meyer, former Canadian diplomat and adjunct professor from Simon Fraser University, says he thinks Canada isn't going far enough. "Set against the current backdrop of geopolitical tensions, I think the failure to come to grips with the threat posed by nuclear weapons is a failure of diplomacy and carries with it grave security risks.

Meyer says he thinks it's a waste of time for Canada to call for the Fissile Material Cut-off Treaty rather than an outright ban of nuclear weapons. "Simply calling for it or engaging in further rounds of study of an issue that's been out there for a half a century, in my mind, is not an adequate the challenges we face." He describes that process as a step by step process held in a UN body that's in constant gridlock because it "operates on the extreme consensus rule where nothing can happen unless all 65 states are in agreement, which is next to impossible to do."