Nuclear warfare by North Korea may cause 'ice age' - expert

In the wake of increased tensions between North Korea and its many enemies, an international security expert has warned of the effects nuclear warfare could have on the global climate.

Stanford University's Paul Edwards says plenty is made of the effect nuclear explosions have, and with good reason, but little is said about the effect on the climate.

"The bomb itself can release a lot of dust, but it's not nearly as dangerous as if it was dropped on a forest or a city," he told The AM Show on Tuesday morning.

"In those cases the bomb can set off immense fires, and those fires enter the stratosphere. Once it's up there, it can circle the whole planet, and cause really serious climatic effects."

He said if that should happen, the ozone layer would be damaged "to a degree we've never experienced before, never in human history", and the resulting climate change would be akin to "many volcanoes going off at once".

"The ultraviolet light that would get through the now-damaged ozone layer would burn crops and ecosystems and people," he said.

"The smoke and dust would cool the planet perhaps by as much as two degrees centigrade, which would take us back to where we were in the little ice age of about 700 or 800 years ago.

"These effects would cause widespread failure of crops, there would be killing frosts, the growing season would be shortened by as much as a month in a lot of places. Clearly that would be bad everywhere... it would cause widespread famine all over."

North Korea, the country that perhaps poses the world's biggest nuclear threat, recently warned Australia that it is risking being attacked itself by allying with the US.

But Dr Edwards says North Korea's threats against the nation are likely hollow, as they're still probably years away from actually having the means to carry out a nuclear attack on them.

He says while North Korea could theoretically reach Australia and New Zealand with its current missile system, they don't actually have any weapons small enough to strap on.

"They could definitely reach New Zealand realistically with the weapons they have currently - if they worked," Dr Edwards told host Duncan Garner.

"Right now they don't necessarily have any weapons small enough to fit on one of those missiles, so I think they're still a couple of years away from a convincing test of an intercontinental ballistic missile that could travel to New Zealand, or the United States, or anywhere across the Pacific."

Dr Edwards says while North Korea's arsenal of nuclear weapons is small compared to other world powers, it's rapidly growing.  He says while estimates on the number and scale of North Korea's nuclear weapons cache vary, they only have somewhere between 10 and 60 - and they're not very big.

"The biggest one, the one they tested recently, is about 100 kilotons - that's the equivalent size of TNT that would have to be blown up to equal that bomb," he said.

"Just to put that in perspective, the largest nuclear weapon ever tested was 50 megatons, which is 500 times that size. So they're still relatively small nuclear weapons - but they are nonetheless nuclear weapons, and would destroy cities if they were dropped on them."

Mr Edwards comments come after Japan warned that North Korea's nuclear threat had "grown to the unprecedented, critical and imminent level", and South Korea said their "provocative behaviour is becoming worse and worse".