What if a nuclear missile really were headed our way?

For 38 panicked minutes on Jan. 13, Hawaiians prepared for the end. Alarming notifications arrived on cellphones: a ballistic missile was headed their way.

On Jan. 16, the Japanese national broadcaster issued a similar warning, saying North Korea had launched a missile and residents of Japan should seek shelter. The alerts soon proved to be false alarms.

But what if a real nuclear missile was headed for Canada? Public safety officials and experts provided some answers to CBC News.

A ballistic missile aimed at North America would be detected by a series of satellites and warning systems overseen by the U.S. Strategic Command, which would inform North American Aerospace Defence Command, or Norad, which guards the airspace of the United States and Canada.

Canadian military and government decision-makers would be informed by Norad, although a decision about trying to shoot down the missile would be made solely by the U.S. because Canada is not part of the U.S. ballistic missile defence system.

"In general, a missile event anywhere in the world will be detected by Norad within five minutes," says Allen Sens, a professor of international relations at the University of British Columbia.

"Over time, we would become increasingly confident about the approximate impact point of the missile based on its trajectory, course and speed."

If a warhead carried by a missile launched from North Korea were to make impact in Canada, it would be between 20 to 30 minutes from launch.

Cellphone notifications coming

The public would then be alerted through all available channels.

In Canada, emergency alerts are distributed primarily through television, radio and social media. However, cellphone notifications, such as those seen during the false alarm in Hawaii, are coming soon.

A recent CRTC decision has mandated that wireless service providers implement a mobile device alert system on their networks by April.

In addition, emergency alerts are typically issued by provincial or territorial emergency management agencies responsible for the on-the-ground response.

Depending on the number of missiles launched, the accuracy, the explosive power of each warhead and the location hit, the level of destruction would vary greatly.

Given estimates of North Korea's nuclear capabilities, CBC News mapped the potential effects of a nuclear strike in various Canadian cities using Nuke Map — an online tool created by nuclear weapons historian Alex Wellerstein that estimates the impact of a nuclear explosion in a given location.

Those in the immediate blast zone would almost certainly die, says Darryl Culley, president of Emergency Management & Training Inc., which provides emergency preparedness training to governments and other organizations.

Over time, many who survived the initial impact would die from injuries, lack of medical care, asphyxiation or burns and, later, radiation sickness or cancer.

What can you do to survive?

As soon as an alert has been issued, public safety officials advise that people find shelter immediately — such as in basements, subways or in the centre area of middle floors in a high-rise building, away from windows. Public Safety Canada recommends that people keep an emergency kit prepared beforehand for times like this.

According to the U.S. Department of Homeland Security's emergency preparation guide, those who survive the blast should be prepared to stay inside or underground for at least a day to avoid the high radiation levels in the air. People in most areas could be allowed to come out within a few days or evacuate to unaffected areas. Those in areas with the highest radiation levels might need to shelter for up to a month.

Shooting down the missile

In case of a strike against North America, the Americans would first attempt to use their missile defence system, Sens says.

While Canada has not joined the U.S. anti-ballistic missile defence program, he says it would be "utterly implausible" that the Americans would not intercept any missile aimed at North America.

"The Americans are not going to wait around to determine the trajectory of the missile to the point that they are confident that it is going to hit Canada and not the United States before they try to intercept the damn thing," Sens said.

"They're going to want as many shots as they can, and they're going to want to try as early as they can."

Beyond interception, military retaliation against North Korea, if it does attack, would be swift, Sens says.

"Retaliation would include anything from a very significant air attack to destroy its military, its nuclear weapons infrastructure … to create such damage through an air campaign that either the government surrenders or collapses. From that, all the way to an all-out invasion."

The risk of error

Despite recent heated political rhetoric, experts agree the likelihood of a nuclear strike against North America is very low.

"There is no incentive for North Korea to attack because they know a retaliation would destroy them," Sens said.

The bigger risk, he says, is a strike that results from an error or miscalculation.

"The risk of error is greater, especially at times when there's high levels of political distrust and tension and high levels of rhetoric — and that's where we are right now."