Since the dawn of the nuclear age in the 1940s,
global stability has rested on
a certain set of assumptions.
Most of the world's nuclear capability
was split between the U.S. and Russia,
and the umbrella of American protection meant
that its allies didn't have to develop nukes of their own.
That appears to be changing.
President Trump has famously been less hawkish
about standing up to Russia.
Now, the European Union is reportedly considering
a nuclear deterrent of its own,
in sharing France's weapons
between member countries.
The situation in Asia is even more unsettled.
North Korea is fanatically pursuing its own arsenal
of nuclear-tipped ballistic missiles.
On Monday, it test-launched
four of the rockets into the ocean,
just 200 miles shy of Japan.
And the American President has unconventional ideas
about how Japan should prepare:
— North Korea has nukes.
Japan has a problem with that.
I mean, they have a big problem with that.
Maybe they would in fact be better off
if they defend themselves from North Korea.
— With nukes?
— Including with nukes, yes.
— All of this has experts worried
about an era of renewed nuclear threat,
from jittery states and rogue actors
who might seize on the instability.
Among those sounding the alarm is William Perry,
who served as Secretary of Defense
under President Clinton.
Bill Perry has spent most of his life
watching the world prepare for nuclear war,
and he thinks we aren't
nearly as scared as we should be.
— I think the professionals in the field
have a pretty good understanding of the impact
of the use of nuclear weapons.
But the general public, to me, does not.
And many of our leaders do not.
— Perry is 89-years-old.
He lectures at Stanford,
launched an online seminar last year,
and travels the world two or three months a year
to talk about how close we've come to catastrophe
and how close we still are.
He often talks about his "nightmare scenario,"
where a small amount of enriched uranium
ends up in the hands of a terrorist group.
— If they had maybe 40 kilograms,
they could make an improvised nuclear bomb.
— But what would be the consequences?
— The consequences of a
15-kiloton bomb would be Hiroshima.
And besides the 80,000, 100,000 casualties,
the social, the political, and
the economic consequences
are just really hard to believe.
— How realistic is this, though?
Isn't this just some sci-fi fantasy fear?
— I think, of all of the nuclear 
catastrophes that could happen,
this is the most probable.
I think, I would say it's probably an even chance
this will happen sometime in the next 10 years.
— An even chance?
— Even chance.
Sometime in the next 10 years.
— You may desperately want
to dismiss Perry as an alarmist,
but he's a renowned expert,
often called upon by world leaders.
I met him in Mexico City,
where he was attending the celebration
of a 50-year-old nuclear ban treaty,
and running a closed-door planning meeting
for top nuclear proliferation experts
from around the world,
known as the "Group of Eminent Persons."
They made us turn off the camera.
The truth is, the chance of a nuclear war
is not what it once was.
In the late '80s, there were
70,000 nukes around the world.
Today, there are only about 15,000.
But Perry is not comforted by better odds.
— We have the possibility of a regional nuclear war,
between Pakistan and India, for example.
Even if they used only half of their nuclear arsenal,
those bombs would put enough smoke in the air,
and enough dust in the air,
that'll go up and settle into the stratosphere,
and then distribute itself around the planet.
It would block the rays of the sun for years to come.
There could be millions of people
who die from that alone.
— That's a horrific vision.
Does it keep you up at night?
— The one that really keeps me up at night,
is the one which is not as probable.
And that is that, somehow,
Russia and the United States
blunder into a nuclear war.
An all-out general nuclear war,
between the United States and Russia,
would mean no less than the end of civilization.
That's not being dramatic.
That's a big hyperbolic.
That's just what would happen.
— Today, Russia and the U.S. have 90%
of the world's remaining nukes,
many of them old, and prone to error, and false alarm.
And they're in the hands of leaders who Perry sees
as having cavalier attitudes about their potential.
— Are there things you see with
President Trump that concern you?
— Yes.
I think, unlike President Obama,
he doesn't have a clear understanding of what
the nuclear issues are and
what the nuclear dangers are.
Secondly, I think he's demonstrated
an impulsive temperament.
The first of them is solvable,
we can learn more, if he cares to do it.
The temperament issue, I'm afraid, is... is just there.
— And that's why, at the age of almost 90,
you're here in Mexico City, and not on a golf course.
— Exactly right.
One person can only do so much.
And I think I can do more than most.
— You can scare us better than most.
— I can scare you.
You deserve to be scared.
