Why extreme climate scenarios no longer seem so unlikely

AMNA NAWAZ: The United Nations has called
climate change the defining issue of our time.
A U.N. panel estimated the planet’s temperature
will likely rise by at least by 2.7 degrees
Fahrenheit between 2030 and 2052.
That could lead to more extreme weather and
harsher conditions.
But those estimates may be on the more conservative
There are new estimates this week from French
scientists suggesting the temperature rise
between now and 2100 could be much higher.
Business and economics correspondent Paul
Solman looks at the risks from some of the
worst-case scenarios.
His story is part of our Making Sense series
and part of our contribution to Covering Climate
Now, a global collaboration of more than 300
news outlets to enhance coverage of the climate
MARTIN WEITZMAN, Environmental Economist:
So, look, you can start to see erosion along
PAUL SOLMAN: Economist Martin Weitzman four-plus
years ago on the homestead he built on the
North Shore of Massachusetts.
MARTIN WEITZMAN: The water has risen a couple
of inches, at least, in the time, in the 40
years I have been living here.
PAUL SOLMAN: A usually understated math- and
data-driven theorist, Weitzman, who died in
the past few weeks, began as a climate catastrophe
MARTIN WEITZMAN: I was wondering, how could
it be possible that mere human beings could
change the climate in a serious way?
PAUL SOLMAN: But geologic samples of carbon
dioxide going back millennia began to scare
MARTIN WEITZMAN: We were way outside the historical
range for at least 800,000 years, and we’re
climbing very strongly.
At the current trajectory that we’re on, we’re
going to blow right past the doubling of carbon
PAUL SOLMAN: And what might that mean for
homes like Weitzman’s?
His former student, Gernot Wagner.
GERNOT WAGNER, Co-Author, “Climate Shock:
The Economic Consequences of a Hotter Planet”:
Last time concentrations of CO2 were as high
as they are today, we did, in fact, have sea
levels up to 20 meters, 66 feet higher than
Well, 66 feet, and this house is gone.
PAUL SOLMAN: What really shocked Weitzman,
though, and led to his book with Wagner, “Climate
Shock,” was probability math.
MARTIN WEITZMAN: What scared me was how much
probability there was out there in extreme
And it’s worrisome how little we know and
how high the probability is of some catastrophic
PAUL SOLMAN: How much hotter?
GERNOT WAGNER: Six degrees centigrade, 11
degrees Fahrenheit.
That’s a planet, like, nobody would recognize.
PAUL SOLMAN: Wagner is now a professor at
GERNOT WAGNER: Marty’s insight on this was,
he looked back to sort of the consensus science,
hundreds of climate scientists analyzing the
most likely developments.
PAUL SOLMAN: Now, this is the famous bell
curve, Estimated future temperatures increasing
from left to right, the likelihood of any
given temperature indicated by how high the
line is at that point.
Here’s the hump of the curve.
That’s where it’s likely to fall.
Temperature will be between here and here.
But, then, if you keep going…
GERNOT WAGNER: There is this tail.
And there is a small probability of being
all the way out there.
We can’t exclude that.
PAUL SOLMAN: Weitzman’s rigorous estimate
of what’s called the tail risk is what transformed
environmental economics.
MARTIN WEITZMAN: There’s a valid, about almost
a 10 percent chance of an increase of 4.5
degrees Centigrade.
PAUL SOLMAN: But 10 percent, I mean, that
is just one chance in 10.
I have been at the racetrack long enough to
know how rarely a 10-1 shot comes in.
MARTIN WEITZMAN: It’s not that rare.
You buy fire insurance for probabilities that
are much lower than 10 percent.
You buy car insurance for probabilities that
are much lower than one in 10 over a lifetime.
So this is well within the range of things
that we like to insure against.
PAUL SOLMAN: Soon after our time with Wagner
and Weitzman, though, things seemed to be
GERNOT WAGNER: In that we sort of had a handle
of, right, basically growing the global economy,
while not growing CO2 emissions.
PAUL SOLMAN: Because we wouldn’t be using
as much coal, for example.
Alternative energy was replacing fossil fuels.
GERNOT WAGNER: For example, yes.
Well, turns out that happened about three
years ago or so ago.
Last year, we again had more emissions than
the year prior.
This year, we have more emissions than the
year before.
So, yes, temperatures are rising, sea levels
are rising, but what is frightening, frankly,
is, what puts the shock into climate shock,
if you will, year after year, we add more
CO2, and that increase in the increase is
PAUL SOLMAN: One reason the rate is increasing?
The hotter it gets, the more energy we use
to keep cool.
CATHERINE WOLFRAM, University of California,
Berkeley: If the world used as much electricity
for air conditioning as the U.S. currently
does, then we would use as much electricity
for air conditioning as we do for everything
right now.
PAUL SOLMAN: Just look at Southern Asia, says
economist Catherine Wolfram.
CATHERINE WOLFRAM: You look at, like, the
hottest places in the U.S., Miami, it’s not
as hot as the coolest places in India.
And so the potential growth in air conditioning
demand in India is enormous.
PAUL SOLMAN: Now, both Wolfram and Wagner
stress that air conditioning is a blessing,
especially given global warming.
GERNOT WAGNER: Extreme heat simply kills.
PAUL SOLMAN: But to the extent that a country
like China or India becomes wealthier, and
people start putting in air conditioners…
GERNOT WAGNER: Which, for the most part, is
a good thing, right?
GERNOT WAGNER: Fewer people dying because
of heat waves.
PAUL SOLMAN: Yes, but that then is going to
contribute to the acceleration that we’re
talking about.
GERNOT WAGNER: If — right, if the energy
produced is through fossil energy, yes.
PAUL SOLMAN: Was Marty more worried than when
we walked along his property in Gloucester?
GERNOT WAGNER: Yes and no.
More worried because there’s increasingly
more science that tells us things may well
be worse than we had previously thought.
Less worried, hopeful, because there’s a lot
happening too, kids on the streets, millions
of them around the world advocating for the
right policies.
PAUL SOLMAN: The insurance policies Weitzman
and his student were urging in back in 2015.
GERNOT WAGNER: Economics 101, right, price
up, demand down.
Don’t ask economists what they think which
new technologies will come into play.
All we are doing is setting the right price
and getting out of the way.
MARTIN WEITZMAN: That’s right.
Let 1,000 flowers bloom.
We can’t know today what that future technology
is going to bring.
So let’s put a price on carbon that incentivizes
carbon-free technologies, and the winner will
take all.
PAUL SOLMAN: And, says Wagner today, more
countries and states in the U.S. have begun
doing what Weitzman urged.
GERNOT WAGNER: India has a coal tax.
China is experimenting with emissions trading.
States here in this country are experimenting
with the kinds of policies that we ought to
have at the federal level.
We don’t yet, but the emphasis on yet.
There’s only so long we can pretend nothing
is happening and walking in the wrong direction.
MARTIN WEITZMAN: So here is a wooden walkway
that has been lifted up by high tides that
will come over it.
PAUL SOLMAN: You mean this was flat before?
When it was constructed, it was flat.
PAUL SOLMAN: Business and economics correspondent
Paul Solman, stepping ever more carefully
in Massachusetts and New York.

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