North Korea just intimated that it may test a nuclear weapon somewhere above the Pacific Ocean.
If Pyongyang follows through on the threat, it would be the first nuclear weapon detonated in the atmosphere in decades.
The threat risks escalating an already volatile situation, and comes after US President Donald Trump threatened to “totally destroy” North Korea in a speech to the United Nations.
So how would Pyongyang conduct a nuclear test over the Pacific and what impact would it have?
Can they do it?
North Korea has been working tirelessly on developing missiles that can reach the United States and its allies and pair them with a miniaturized nuclear warheads.
After six nuclear tests and a succession of missile tests, the consensus is that Pyongyang is close.
When asked when we’ll know for sure if North Korea has a nuclear-tipped missile, nonproliferation expert Jeffrey Lewis sometimes responds with a bleak joke: “you’ll see a giant bright light.”
Lewis, from the Middlebury Institute of International Studies’ James Martin Center for Nonproliferation Studies, agrees with most experts that we’ll only know for certain when they do it.
The United States military, however, operates under the assumption that North Korea already has the capability.
“I know there’s some debate about the miniaturization advancements made by Pyongyang. But PACOM (US Pacific Command) must be prepared to fight tonight, so I take him at his word. I must assume his (Kim Jong Un’s)claims are true – I know his aspirations certainly are,” Admiral Harry Harris, the head of PACOM, said in a June speech.
How would they do it?
Though the bomb could in theory be dropped from a plane, North Korea analysts say Pyongyang is likely to opt for a missile, as a means of showcasing its newest and most sophisticated technology.
Nuclear-armed missiles have only been tested a handful of times, said Vipin Narang, a professor of political science at MIT and expert on deterrence and nuclear policy.
“The worst-case scenario would be a Juche bird test,” Narang said. “That would be not only provocative, but a lot can go wrong if the missile goes awry.”
The phrase “Juche bird,” used by nonproliferation experts monitoring Pyongyang’s activities, is a play on the 1962 missile test codenamed Frigate Bird. The test involved a nuclear-tipped missile fired from a US submarine toward Christmas Island and detonated over the Pacific Ocean.
North Korean state media often employ the word Juche, the North Korean state ideology of self-reliance, when referring to the country’s nuclear tests.
Will they do it?
When Ri floated the possibility of testing a nuclear weapon over the Pacific, he was careful to say that the final decision was in Kim Jong Un’s hands.
“I think that was clever for them to specify the worst-case test while still leaving room to walk away from it,” Narang told CNN.
Narang thinks that it’s more likely that North Korea would conduct a smaller-scale action first – such as launching another intercontinental ballistic missile (ICBM) test.
“It would be surprising to me if it’s (the Juche bird) their lead-off hitter now,” he said, borrowing from a baseball term.
But Lewis, who described Ri’s comments as in keeping with the country’s broader strategy of “little warnings to be followed by more explicit ones,” believes there’s danger in not taking North Korea seriously.
“We dared the Chinese in 1966 (when they tested a nuclear missile) and they did it. Now we’re daring the North Koreans,” Lewis told CNN.
What if they do it?
Regardless of the geopolitical fallout, the environmental effects could be devastating. Those living near Bikini Atoll, where the US tested many of its nuclear weapons in the mid to late 20th century, are still dealing with a range of health-related issues.
The blast would likely destroy or contaminate fish and marine life, leaving a series of incalculable knock-on effects.
The world hasn’t dealt with an atmospheric test since 1980, when China detonated a weapon over Lop Nur, in the country’s northwest, according to the Stockholm International Peace Research Institute.
Of more than 2,000 tests that have been conducted since the advent of nuclear weapons, more than 100 were detonated in remote locations in the Pacific, according to the CTBTO.
On the Marshall Islands, where the US also tested weapons, the local population suffered from higher rates of cancer, birth defects and thyroid disorders.
In French Polynesia, similar affects were reported, and tests were found to have caused landslides, tsunamis and earthquakes, the CTBTO said.
But the damage to humans could be limited if North Korea picks a particularly isolated spot, analysts say.
“It really depends where they explode the device and what the weather patterns are like at that time,” said Melissa Hanham, a senior researcher also with the Center for Nonproliferation Studies. “That being said, we know from testing over decades that there are persistent environmental effects and impacts on humans.”
CNN’s Begona Blanco Munoz contributed to this report