'A third of the world would die': What would happen if you lived in a nuclear winter?

The reality of even a small-scale nuclear war is unimaginable. Even on the other side of the world you wouldn't be safe.

That's according a scientist who helped pen the book And Then You're Dead: A scientific exploration of the world's most interesting ways to die by Cody Cassidy and Paul Doherty.

"During the Cold War it was widely understood that both the United States and the USSR had the capability to destroy the world with nuclear weapons. What people didn't know was how easily they actually could do it." the book says.

But now, thanks to sophisticated weather models, scientist Paul Doherty learned that even a small nuclear skirmish could lead to devastation.

Should nuclear war break out, Doherty wrote you aren't immune to the devastation even if you are on the other side of the globe, news.com.au reported.

In the event of a nuclear war, the pair penned just what could happen to you.

Your first problem? Radiation.

"When the nukes went off they would irradiate the area and transmute innocuous atoms into dangerous ones. One of the worst of these nuclear bastard children is called strontium-90.

"It's light, so it doesn't take many explosions for it to coat the globe and get deep into the food supply. Once ingested it's so similar to calcium that your body absorbs it into your bones.

"Children born after the open-air nuclear tests of the 1950s have fifty times the natural level of strontium-90 in their teeth. Fortunately, that's still below the threshold for serious danger.

"Unfortunately, unlike a test, a nuclear battle will blow past that threshold.

"Once strontium-90 is in your bones its radioactive decay breaks up the DNA of your cells, leading to bone cancers and leukaemia. So if you survived the initial nuclear exchange, you would have bone cancer to look forward to, but that's only if you could also survive the more serious smoke, ash, and soot problem.

The second issue: Dust

"After the dust has cleared from the initial detonations, is that the dust wouldn't clear.

After a hundred multi-megaton bombs exploded in the air, not only would they directly distribute carbon into the upper atmosphere but they would start enormous forest and urban fires that would release massive amounts of smoke.

"On top of that, the explosions would lift tonnes of fine dust; all of which would be heated by the sun to rise and collect in the stratosphere.

"The smoke from your typical campfire stays below the clouds where it can be wicked away by rain. In the case of nuclear fallout, smoke and ash would be lifted above the clouds where it wouldn't be wicked away by rain, so it would stay parked for years and block sunlight.

"Even conservative environmental simulations show that a hundred nuclear detonations would block enough sunlight to drop the average global temperature by a few degrees. A sudden global drop in temperature of even a couple of degrees would be devastating for the world's food supply, because a single frost kills rice.

"A serious disturbance in rice production would kill as many as 2 billion people around the globe.

"In a hundred-bomb nuclear war nearly a third of the world's population would die from the explosions, starvation, or cancer, but our species would carry on. In larger, multi-thousand exchanges of thermonuclear weapons, like the one that almost occurred in November 1983 between the United States and the USSR, however, we probably wouldn't."

How close the world came to ending

In 1983 The US led NATO into a massive training exercise called Able Archer that mimicked a nuclear strike against the USSR.

However, the USSR mistook the exercise as a cover for an actual strike, forcing the Soviets to mobilise its air force.

Fortunately for the world, the US believed the USSR's mobilisation was a training exercise and so both sides then stood down.

However, Cassidy and Doherty claim if the two world powers went to war that the a large number of the world's population wouldn't live long.

"Even if you didn't live in a large city (basically every city with a population of more than 100,000 in the United States and the USSR was targeted) and, therefore, weren't killed by the initial blasts, you couldn't expect to live long.

"Within two weeks of something like this happening, 180 million tonnes of smoke, soot, and dust would coat our globe like black paint, and there it would stay.

"Light levels would be reduced to a few per cent of what they are today, so high noon would look like predawn. Midsummer highs in North America would be below zero.

"The good news is there would be plenty of dead trees to burn for warmth. The bad news: You would starve. Crops would be wiped out, and those that weren't would suffer from another problem: Bugs.

"Cockroaches and their ilk are quite durable when it comes to radiation, but their predators are not. Without any birds to keep them in check, crop-eating pests would prosper. Pests would decimate any crops that made it through the freeze."

This is an extract from And Then You're Dead: A scientific exploration of the world's most interesting ways to die by Cody Cassidy and Paul Doherty, published by Allen and Unwin and available now.

Paul Doherty is co-director and senior staff scientist at the San Francisco Exploratorium Museum. He received his PhD in solid state physics from Massachusetts Institute of Technology.

Cody Cassidy is a writer and editor.