- Amid mounting evidence today that global temperatures
are on the rise, some scientists have suggested
cooling things down artificially.
They propose trying to manipulate the earth's climate
through a process known as geo-engineering.
- It's a radical idea that comes from a very unlikely place.
Scientific research developed during the 1980s
to study the environmental impact of a nuclear war.
The fear was that nuclear war, most likely between
the United States and the Soviet Union,
could plunge the globe into a civilization ending ice age.
Scientists called it nuclear winter.
- Administration officials from the president on down
have been using hard line rhetoric
against the Soviets all year long.
- The administration's message to Moscow has been
that it's not going to be business as usual anymore.
- Today in virtually every measure of military power,
the Soviet Union enjoys a decided advantage.
The Soviet military buildup must not be ignored.
- If the United States are going to continue their course,
then I am afraid that the world is doomed
to be on the brink of nuclear war.
- It was a real fear in the early '80s
that we were in a more dangerous period
than we had been perhaps since the missile crisis in 1962.
- [Narrator] In the 1980s, tens of thousands
of nuclear warheads already faced off.
But Cold War calculations pushed
the superpowers to build even more.
- It was a balance with tremendous
destructive power on both sides.
So we were in this very, very tenuous situation
right at the edge of a cliff.
- There are 40,000 nuclear warheads
in the inventories of the US and the Soviet Union today.
We must insure it not be used.
- It started quietly, but it is picking up steam,
and maybe gathering strength.
The movement, if that's the right term,
to somehow bring pressure on leaders of both
the United States and the Soviet Union to stop,
just stop the nuclear arms race.
- [Narrator] That movement was called nuclear freeze.
And as its message spread across the nation,
it brought together a wide swath of Americans.
- In order to stop this arms race,
you first gotta freeze it.
- [Narrator] One of those was the astronomer Carl Sagan.
- Imagine a room awash in gasoline.
And there are two implacable enemies in that room.
One of them has 9,000 matches.
The other has 7,000 matches.
Each of them is concerned about who's ahead.
Who's stronger.
Well, that's the kind of situation we are actually in.
- Sagan was a very effective communicator.
I mean, he was a voice for the scientific
community in some sense.
(somber music)
- [Narrator] In 1983, Sagan used that popularity
to draw attention to a troubling
new scientific finding about nuclear war.
- [Journalist] Dr. Carl Sagan and more than 100
other scientists have concluded that the longterm effects
of nuclear war would be much worse
than anyone has predicted so far.
- We studied a range of consequences
of various nuclear war scenarios.
If I may have the first slide.
High yield nuclear weapons explosions.
- [Narrator] Climate scientist Alan Robock
was in the conference audience.
- It was a very new idea that smoke from fires
started by nuclear weapons would go up in the atmosphere,
block out the sun, and make it cold and dark
and dry out the earth's surface,
having impacts on agricultural production.
- [Narrator] As Russian counterparts
weighed in via satellite link,
this view of nuclear war's destructive power took hold.
- For the first time we see that the consequences
of nuclear war might be absolutely devastating for nations
far removed from the conflict.
- The initial splash on this story was profound.
It was kind of selfish or even existential destruction.
Nuclear winter, even the verbiage is portentous.
- [Narrator] To illustrate the point,
Sagan helped produce a short film showing just how
devastating nuclear winter might become.
- [Announcer] Beneath the clouds, virtually all domesticated
and wild sources of food would be destroyed.
Most of the human survivors would starve to death.
The extinction of the human species
would be a real possibility.
- It is known as nuclear winter.
- This is not some peacenik nightmare.
It is a theory supported by at least
40 American scientists of high repute.
- [Reporter] Today, a panel appointed
by the prestigious National Academy
of Sciences agreed with Sagan.
- The Pentagon has accepted as valid
the theory of a nuclear winter.
- The implications of nuclear winter are that we shouldn't
build more, but we should build less.
- It was a combination of everybody's work
that kept making a stronger and stronger case
that this theory was true.
- [Narrator] The fear of nuclear winter soon became
another of the many issues impacting Cold War strategy.
- A great many reputable scientists are telling us
that such a war could just start to end up in no victory
for anyone because we would
wipe out the earth as we know it.
What are we talking about with a whole
nuclear exchange, a nuclear winter.
- Gorbachev certainly has testified to the fact
that this increased his concern about the consequences
of nuclear war and the arms race.
- Today, I, for the United States,
and the General Secretary for the Soviet Union
have signed the first agreement ever to eliminate
an entire class of US and Soviet nuclear weapons.
We have made history.
- [Narrator] But even before that treaty was signed,
some of the gravest predictions made by nuclear
winter theorists had begun to thaw.
- Those of us who were doing more global models,
we didn't get anything like the result
that Sagan was getting, we got a climatic effect
if you put that much smoke on there.
But we didn't get the kind
of effect they were talking about.
- [Announcer] Nuclear winter, argues one group
of scientists, is what will surely follow nuclear war.
Other scientists, with their own computer calculations
of the doomsday scenario say life after nuclear war
will not be so much nuclear winter as nuclear fall,
severe but survivable.
- Nothing we've seen in our simulations
or in the work going on now leads me to believe
that the extinction of the human race is a real possibility.
- [Narrator] Over time, better modeling caused
many of the original nuclear winter theorists
to agree that nuclear winter's effects
were likely more moderate than they had initially supposed.
- There's a pattern to how some phenomena
and stories play out.
The first idea is very stark.
And then the scientific process is like piranhas
that nibble away at the soft stuff,
and whatever's left is the hard skeleton
of the ideas, the enduring part.
- Even when you get back to the nuclear autumn thing,
you're still having huge environmental effects
that would have agricultural effects.
So it was more a matter of nuance and intensity
rather than a matter of is it real or not.
It didn't have to be quite hyped so much,
but that there were climatic effects was important.
- [Narrator] But as the predicted effects
of nuclear winter became more subtle,
the headlines faded away.
- I think a lot of the public went away with just
the message that this was an exaggerated concern,
they didn't have to worry about it.
- [Narrator] Over the years, another global issue
began to focus the public's concern.
- When I show my results of the climate response
to smoke from nuclear war, inevitably I get a question,
so is that a solution to global warming.
- [Narrator] Nobody's talking about
exploding a nuclear bomb.
But the idea of harnessing a nuclear winter-like effect
to reduce the global temperature has intrigued
policymakers and scientists for some time.
And it is gaining traction.
- The scientific evidence that these technologies
could reduce risk is very strong.
- [Narrator] One technique under consideration involves
dispersing a cloud of sulfate particles
into the stratosphere to partially obscure the sun
and reflect sunlight away from the earth.
- The main benefit is it would cool the climate,
and so it would reduce all the impacts of global warming.
There'd be fewer severe storms,
there would be less sea level rise,
there would be less temperature change,
which might affect agriculture.
So all the negative aspects of global warming
would be reduced, if you could do it.
- [Narrator] The concept is not without controversy.
- This idea of responding to global warming
essentially with nuclear winter-lite,
I guess you could call it,
the science leads to some very worrisome questions.
- The problem is, it's unclear what else
solar geoengineering would do.
- I should mention that I have written a paper
with 26 reasons why geoengineering would be a bad idea.
Anything built by humans and operated by humans can fail.
So would you trust our only planet to this?
- [Narrator] Meanwhile, the Cold War danger
that pushed scientists like Robock to study
these climate effects remains.
In fact, the nuclear landscape
is more complex than ever before.
- There are a lot of weapons out there.
- [Reporter] Rarely has North Korea tested
missiles at this pace.
- I want this nuclear arsenal to be the biggest
and the finest in the world.
- It's important for countries and leaders
to be keeping in mind what nuclear war would do.
Even small exchanges could be absolutely devastating.
You're gonna have first the destruction effects.
You'll have fallout, you may have some
climatic effects that spread.
- Heaven help us if there were a small nuclear exchange.
You could end up with it being on the worse end.
It's like with global warming, you know,
the worst case scenarios can happen.
I guess the good news about nuclear winter
is it remained a theory.
- The global consequences of nuclear war
is not a subject amenable to experimental verification.
Or at least not more than once.
Maybe we've all made some serious mistake
in the calculations, but I wouldn't want
to bet my life on it.
(bright music)