[MD] Global dimming part 1a

[Ron Kulp]

Dimming the Sun <http://www.pbs.org/wgbh/nova/sun/> 


PBS Airdate: April 18, 2006
Go to the companion Web site <http://www.pbs.org/wgbh/nova/sun/>  

NARRATOR: He warned us, more than 25 years ago, that human activity was
changing the Earth'sclimate. Since then, the world has gotten hotter,
and NASA scientist James Hansen's warning has been echoed by the vast
majority of climate scientists everywhere.

JAMES HANSEN (NASA Goddard Institute for Space Studies): Global warming
in the past century is about eight-tenths of a degree Celsius, with most
of it occurring in the last 30 years.

NARRATOR: And now the warnings have become more urgent.

JAMES HANSEN: I don't agree that we've passed the point where there's no
hope, but, but, on the other hand, we're darned close.

NARRATOR: Close, because scientists have uncovered a new factor that may
be masking the full impact of global warming. Called global dimming,
it's powerful enough to alter temperatures in a matter of days. It may
have contributed to the world's deadliest drought, and it could mean
that the Earth's climate is about to start heating up as fast as the
most dire predictions.

JAMES HANSEN: I think we have less than a decade to avoid passing what I
call "point of no return."

NARRATOR: What will the future of our planet be, now that we're Dimming
the Sun? Right now on NOVA.

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NARRATOR: September 12th, 2001, the aftermath of tragedy: ironically, as
America mourned, the weather all over the country was unusually clear
and sunny. Eight hundred miles west of New York, in Madison, Wisconsin,
climate scientist David Travis was on his way to work.

DOCTOR DAVID TRAVIS (University of Wisconsin-Whitewater): Around the
12th, later on in the day, when I was driving to work, and I noticed how
bright blue and clear the sky was, and...at first I didn't think about
it, then I realized the sky was unusually clear.

NARRATOR: For 15 years, Travis had been researching a relatively obscure
topic: whether the vapor trails left by aircraft were having a
significant effect on the weather. In the aftermath of 9/11, the entire
U.S. fleet was grounded, and Travis finally had a chance to find out.

DAVID TRAVIS: It was certainly, you know, one of the tiny positives that
may have come out of this-an opportunity to do research-that hopefully
will never happen again.

NARRATOR: Travis suspected the grounding might make a small, but
detectable, change to the weather, but what he observed was both
immediate and dramatic.

DAVID TRAVIS: We found that the change in temperature range during those
three days was just over one degree centigrade. And you have to realize
that from a layman's perspective that doesn't sound like much, but from
a climate perspective that is huge.

NARRATOR: The temperature range is the difference between the highest
and the lowest temperatures in a 24-hour period. Usually, it stays much
the same from day to day, even if the weather changes, but not this
time. Travis had come across a new and powerful phenomenon, one which
would call into question all our predictions about the future of our
planet.

The trail that would lead to this extraordinary discovery of global
dimming began 40 years ago, in Israel, with the work of Gerry Stanhill,
a young English immigrant. Trained as a biologist, Gerry got a job
helping to design irrigation systems. His task was to measure how
strongly the sun shone over Israel.

DOCTOR GERALD STANHILL (Israel Ministry of Agriculture): It was
important, for this work, to measure solar radiation, because that is
the factor that basically determines how much water crops require.

NARRATOR: For a year, Gerry collected data from a network of light
meters. The results were much as expected and were used to help design
the national irrigation system. But, 20 years later, in the 1980s, Gerry
decided to update his measurements. What he found stunned him.

GERALD STANHILL: Well, I was amazed to find that there was a very
serious reduction in sunlight, the amount of sunlight in Israel. In
fact, if we compare those very early measurements, in the 1950s, with
the current measurements, there was a staggering 22 percent drop in the
sunlight, and that really amazed me.

NARRATOR: A 22 percent drop in solar energy was simply massive. If it
were true, surely the effects would be obvious to every Israeli. The
figures were hard for other scientists to take seriously, so when Gerry
published, his results were ignored.

GERALD STANHILL: I must say that the publications had almost no effect
whatsoever on the scientific community.

NARRATOR: But Gerry was not the only scientist who had noticed a decline
in sunlight. In Germany, a young graduate student, Beate Liepert found
that the same thing seemed to be happening over the Bavarian Alps, as
well.

DOCTOR BEATE LIEPERT (Lamont-Doherty Earth Observatory): I was the same;
I was as skeptical as any other climatologist. But then I, I saw the
same results in Germany, so I believed him.

NARRATOR: Germany, Israel, what about the rest of the world? Working
independently of each other, Liepert and Stanhill began searching
through journals and meteorological records from around the world. And
everywhere they looked, they found the same story.

Between the 1950s and the early 1990s, the level of solar energy
reaching the Earth's surface had dropped: nine percent in Antarctica, 10
percent in areas of the U.S.A., by almost 30 percent in one region of
Russia, and by 16 percent in parts of the British Isles. This seemed to
be a global phenomenon, so Gerry gave it a suitable name: "global
dimming."

But again, the response from other scientists was one of disbelief.

GERALD STANHILL: The scientific community was obviously not ready to
deal with the fact that there was a global dimming phenomenon.

NARRATOR: Gerry claimed that, on average, the solar energy reaching
Earth had fallen by two percent to four percent. That should be making
the world significantly cooler, yet scientists knew the Earth was
getting hotter.

As we burn coal, oil and gas, we increase the concentration of carbon
dioxide and other greenhouse gases in the atmosphere. Like a thermal
blanket, they prevent the Sun's heat from radiating back into space,
causing global warming.

BEATE LIEPERT: My friends' reaction, actually, to Gerry's and to my
work-at the same time, too-was, "Oh my god, this is really extreme. You
are contradicting global warming. Do you know how many billions of
dollars was spent on global warming research? And you and this old guy
are contradicting us?"

NARRATOR: So Liepert and Stanhill's work was widely dismissed. But
global dimming was not the only phenomenon that didn't seem to fit with
global warming. In Australia, two other biologists, Michael Roderick and
Graham Farquhar, were intrigued by another paradoxical result, the
worldwide decline in something called the "pan evaporation rate."

PROFESSOR GRAHAM FARQUHAR (Australian National University): It's called
pan evaporation rate because it's evaporation rate from a pan. Every
day, all over the world, people come out in the morning and see how much
water they've got to add to a pan to bring it back to the level it was
the same time the morning before. It's that simple.

NARRATOR: In some places, agricultural scientists have been performing
this routine daily task for more than a hundred years.

GRAHAM FARQUHAR: The long-term measurements of pan evaporation are what
gives it its real value.

DOCTOR MICHAEL RODERICK (Australian National University): And the fact
that they're doing the same thing, day in, day out, with the same
instrument.

GRAHAM FARQUHAR: Yeah, they deserve a medal, each of them.

MICHAEL RODERICK: Yeah.

NARRATOR: Nobody outside of agriculture took much notice of the pan
evaporation measurements, but, in the 1990s, scientists spotted
something very strange, the rate of evaporation was falling.

GRAHAM FARQUHAR: There is a paradox here about the fact that the pan
evaporation rate's going down, an apparent paradox, but the global
temperature's going up.

NARRATOR: This was a puzzle. Most scientists reasoned that like a pan on
the stove, turning up the global temperature should increase the rate at
which water evaporated. But Roderick and Farquhar did some calculations
and worked out that temperature was not the most important factor in pan
evaporation.

MICHAEL RODERICK: Well, it turns out, in fact, that the key things for
pan evaporation are the sunlight, the humidity and the wind. But really,
the sunlight is a really dominant term there.

NARRATOR: They found that it was the energy of the photons hitting the
surface-the actual sunlight-that kicks the water molecules out of the
pan and into the atmosphere. And so they, too, reached an extraordinary
conclusion.

MICHAEL RODERICK: You know, if the pan is going down, then maybe that's
the sunlight going down.

NARRATOR: Was the falling pan evaporation, in fact, evidence of global
dimming? Somewhere in the journals, they felt, must be the hard numbers
that could tie the two things together.

MICHAEL RODERICK: And then one day, just by accident, I had to go to the
library to get an article out of Nature. And, as you do, I couldn't find
it, and I just glanced at a...through the thing, and there was an
article called "Evaporation Losing Its Strength," which reported a
decline in pan evaporation over Russia, the United States and Eastern
Europe.

And there, in the measurements, they said that the pans had, on average,
evaporated about a hundred millimeters less of water in the last 30
years.

NARRATOR: Mike knew how much sunlight was needed to evaporate a
millimeter of water, so he put the two sets of figures together, the
drop in evaporation with the drop in sunlight.

MICHAEL RODERICK: So you just do the sum in your head: a hundred
millimeters of water, less a pan evaporation, two and a half mega
joules, so two and a half times a hundred is two hundred and fifty mega
joules. And that was, in fact, what the Russians had measured with the
decline in sunlight in the last 30 years. It was quite amazing.

NARRATOR: It was the same in Europe and the U.S.A. The drop in
evaporation rate matched the decline in sunlight reported by Beate
Liepert and Gerry Stanhill. Two independent sets of observations led to
the same conclusion. Here, at last, was compelling evidence that global
dimming was real.

BEATE LIEPERT: All of a sudden you see, "Oh my god, the world is
dimming." And then you, all of a sudden, you see, "Oh my god, this
really has an im..., tremendous impact.

GRAHAM FARQUHAR: And it had to be dimming in Europe and in America and
in Russia. This is on a global scale. And we thought, "This is really
important," because the amount of dimming was enormous. So this is big
on a, on a global scale.

NARRATOR: But what was causing it? Scientists knew there was nothing
wrong with the sun itself. The culprit had to be somewhere here on
Earth.

The Maldives, a nation of a thousand tiny islands in the middle of the
Indian Ocean: it was here that Veerabhadran Ramanathan, one of the
world's leading climate scientists, began to unravel the mystery of
what's causing global dimming. He had first noticed declining sunlight
over large areas of the Pacific Ocean in the mid-1990s.

PROFESSOR VEERABHADRAN RAMANATHAN (University of California, San Diego):
But we didn't know, at that time, it was part of a much larger global
picture, but I knew we had to find out what was causing that.

NARRATOR: Ramanathan was certain of one thing, the big drop in sunlight
reaching the ground had to be something to do with changes in the
Earth's atmosphere. There was one obvious suspect.

VEERABHADRAN RAMANATHAN: Almost anything we do to create energy causes
pollution.

NARRATOR: Burning fuel doesn't just result in the invisible greenhouse
gases which cause global warming; it also produces visible pollution,
tiny airborne particles of soot and other pollutants. These create the
haze that shrouds many of our cities. So Ramanathan wondered, "Could
this pollution be behind global dimming?" The Maldives were the perfect
place to find out.

The Maldives seem unpolluted, but in fact the northern islands sit in a
stream of dirty air descending from India. Only the southern tip of the
long island chain enjoys clean air, coming all the way from Antarctica.

So, by comparing the northern islands with the southern ones, Ramanathan
and his colleagues would be able to see exactly what difference the
pollution made to the atmosphere and the sunlight.

Project INDOEX, as it was called, was a huge multinational effort. For
four years, every possible technique was used to sample and monitor the
atmosphere over the Maldives. INDOEX cost $25,000,000, but it produced
results; and they surprised everyone.