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TED2012

James Hansen: Why I must speak out about climate change

February 29, 2012

Top climate scientist James Hansen tells the story of his involvement in the science of and debate over global climate change. In doing so he outlines the overwhelming evidence that change is happening and why that makes him deeply worried about the future.

James Hansen - Climatologist
James Hansen has made key insights into our global climate -- and inspired a generation of activists and scientists. Full bio

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Double-click the English subtitles below to play the video.
What do I know
00:15
that would cause me,
00:17
a reticent, Midwestern scientist,
00:19
to get myself arrested
00:21
in front of the White House protesting?
00:24
And what would you do
00:27
if you knew what I know?
00:29
Let's start with how I got to this point.
00:31
I was lucky to grow up
00:35
at a time when it was not difficult
00:37
for the child of a tenant farmer
00:40
to make his way to the state university.
00:42
And I was really lucky
00:44
to go to the University of Iowa
00:47
where I could study under Professor James Van Allen
00:49
who built instruments
00:52
for the first U.S. satellites.
00:54
Professor Van Allen told me
00:56
about observations of Venus,
00:59
that there was intense microwave radiation.
01:02
Did it mean that Venus had an ionosphere?
01:04
Or was Venus extremely hot?
01:07
The right answer,
01:09
confirmed by the Soviet Venera spacecraft,
01:11
was that Venus was very hot --
01:16
900 degrees Fahrenheit.
01:19
And it was kept hot
01:21
by a thick carbon dioxide atmosphere.
01:23
I was fortunate to join NASA
01:26
and successfully propose
01:28
an experiment to fly to Venus.
01:30
Our instrument took this image
01:32
of the veil of Venus,
01:35
which turned out to be
01:37
a smog of sulfuric acid.
01:39
But while our instrument was being built,
01:42
I became involved in calculations
01:45
of the greenhouse effect
01:47
here on Earth,
01:49
because we realized
01:51
that our atmospheric composition was changing.
01:53
Eventually, I resigned
01:56
as principal investigator
01:58
on our Venus experiment
02:00
because a planet changing before our eyes
02:02
is more interesting and important.
02:05
Its changes will affect all of humanity.
02:07
The greenhouse effect had been well understood
02:10
for more than a century.
02:12
British physicist John Tyndall,
02:14
in the 1850's,
02:16
made laboratory measurements
02:18
of the infrared radiation,
02:20
which is heat.
02:22
And he showed that gasses such as CO2 absorb heat,
02:24
thus acting like a blanket
02:27
warming Earth's surface.
02:30
I worked with other scientists
02:32
to analyze Earth climate observations.
02:34
In 1981,
02:38
we published an article in Science magazine
02:40
concluding that observed warming
02:43
of 0.4 degrees Celsius
02:45
in the prior century
02:47
was consistent with the greenhouse effect
02:49
of increasing CO2.
02:51
That Earth would likely warm in the 1980's,
02:53
and warming would exceed
02:56
the noise level of random weather
02:58
by the end of the century.
03:00
We also said that the 21st century
03:02
would see shifting climate zones,
03:05
creation of drought-prone regions
03:07
in North America and Asia,
03:09
erosion of ice sheets, rising sea levels
03:11
and opening of the fabled Northwest Passage.
03:14
All of these impacts
03:17
have since either happened
03:19
or are now well under way.
03:21
That paper was reported on the front page of the New York Times
03:23
and led to me testifying to Congress
03:27
in the 1980's,
03:29
testimony in which I emphasized
03:31
that global warming increases both extremes
03:34
of the Earth's water cycle.
03:37
Heatwaves and droughts on one hand,
03:40
directly from the warming,
03:42
but also, because a warmer atmosphere
03:44
holds more water vapor
03:46
with its latent energy,
03:48
rainfall will become
03:50
in more extreme events.
03:52
There will be stronger storms and greater flooding.
03:54
Global warming hoopla
03:57
became time-consuming
04:00
and distracted me from doing science --
04:02
partly because I had complained
04:04
that the White House altered my testimony.
04:06
So I decided to go back
04:09
to strictly doing science
04:11
and leave the communication to others.
04:13
By 15 years later,
04:17
evidence of global warming was much stronger.
04:20
Most of the things mentioned in our 1981 paper
04:23
were facts.
04:26
I had the privilege to speak twice
04:28
to the president's climate task force.
04:31
But energy policies continued to focus
04:33
on finding more fossil fuels.
04:36
By then we had two grandchildren,
04:39
Sophie and Connor.
04:42
I decided
04:44
that I did not want them in the future
04:46
to say, "Opa understood what was happening,
04:48
but he didn't make it clear."
04:50
So I decided to give a public talk
04:52
criticizing the lack of an appropriate energy policy.
04:55
I gave the talk at the University of Iowa in 2004
04:58
and at the 2005 meeting
05:01
of the American Geophysical Union.
05:04
This led to calls
05:07
from the White House to NASA headquarters
05:09
and I was told that I could not give any talks or speak with the media
05:11
without prior explicit approval
05:14
by NASA headquarters.
05:17
After I informed the New York Times
05:20
about these restrictions,
05:22
NASA was forced to end the censorship.
05:24
But there were consequences.
05:27
I had been using the first line
05:29
of the NASA mission statement,
05:31
"To understand and protect the home planet,"
05:33
to justify my talks.
05:36
Soon the first line of the mission statement
05:38
was deleted, never to appear again.
05:40
Over the next few years
05:44
I was drawn more and more
05:46
into trying to communicate the urgency
05:48
of a change in energy policies,
05:51
while still researching the physics of climate change.
05:54
Let me describe the most important conclusion from the physics --
05:57
first, from Earth's energy balance
06:00
and, second, from Earth's climate history.
06:03
Adding CO2 to the air
06:07
is like throwing another blanket on the bed.
06:09
It reduces Earth's heat radiation to space,
06:12
so there's a temporary energy imbalance.
06:15
More energy is coming in
06:18
than going out,
06:20
until Earth warms up enough
06:22
to again radiate to space
06:24
as much energy as it absorbs from the Sun.
06:26
So the key quantity
06:28
is Earth's energy imbalance.
06:30
Is there more energy coming in
06:33
than going out?
06:35
If so, more warming is in the pipeline.
06:37
It will occur without adding any more greenhouse gasses.
06:40
Now finally,
06:44
we can measure Earth's energy imbalance precisely
06:46
by measuring the heat content
06:50
in Earth's heat reservoirs.
06:52
The biggest reservoir, the ocean, was the least well measured,
06:55
until more than 3,000 Argo floats
06:58
were distributed around the world's ocean.
07:01
These floats reveal
07:04
that the upper half of the ocean
07:06
is gaining heat at a substantial rate.
07:08
The deep ocean is also gaining heat at a smaller rate,
07:11
and energy is going
07:14
into the net melting of ice all around the planet.
07:16
And the land, to depths of tens of meters,
07:19
is also warming.
07:22
The total energy imbalance now
07:24
is about six-tenths of a watt per square meter.
07:27
That may not sound like much,
07:31
but when added up over the whole world, it's enormous.
07:33
It's about 20 times greater
07:36
than the rate of energy use by all of humanity.
07:39
It's equivalent to exploding
07:42
400,000 Hiroshima atomic bombs per day
07:44
365 days per year.
07:50
That's how much extra energy
07:53
Earth is gaining each day.
07:55
This imbalance,
07:57
if we want to stabilize climate,
07:59
means that we must reduce CO2
08:02
from 391 ppm, parts per million,
08:04
back to 350 ppm.
08:07
That is the change needed to restore energy balance
08:10
and prevent further warming.
08:13
Climate change deniers argue
08:15
that the Sun is the main cause of climate change.
08:18
But the measured energy imbalance occurred
08:21
during the deepest solar minimum in the record,
08:24
when the Sun's energy reaching Earth was least.
08:28
Yet, there was more energy coming in than going out.
08:32
This shows that the effect of the Sun's variations on climate
08:35
is overwhelmed by the increasing greenhouse gasses,
08:38
mainly from burning fossil fuels.
08:41
Now consider Earth's climate history.
08:44
These curves for global temperature,
08:47
atmospheric CO2 and sea level
08:49
were derived from ocean cores and Antarctic ice cores,
08:52
from ocean sediments and snowflakes
08:55
that piled up year after year
08:57
over 800,000 years
09:00
forming a two-mile thick ice sheet.
09:02
As you see, there's a high correlation
09:04
between temperature, CO2 and sea level.
09:07
Careful examination shows
09:10
that the temperature changes
09:12
slightly lead the CO2 changes
09:14
by a few centuries.
09:16
Climate change deniers like to use this fact
09:19
to confuse and trick the public
09:22
by saying, "Look, the temperature causes CO2 to change,
09:25
not vice versa."
09:28
But that lag
09:30
is exactly what is expected.
09:32
Small changes in Earth's orbit
09:35
that occur over tens to hundreds of thousands of years
09:38
alter the distribution
09:41
of sunlight on Earth.
09:43
When there is more sunlight
09:45
at high latitudes in summer, ice sheets melt.
09:47
Shrinking ice sheets
09:50
make the planet darker,
09:52
so it absorbs more sunlight
09:54
and becomes warmer.
09:56
A warmer ocean releases CO2,
09:58
just as a warm Coca-Cola does.
10:00
And more CO2 causes more warming.
10:03
So CO2, methane, and ice sheets
10:06
were feedbacks
10:09
that amplified global temperature change
10:11
causing these ancient climate oscillations to be huge,
10:14
even though the climate change was initiated
10:17
by a very weak forcing.
10:20
The important point
10:22
is that these same amplifying feedbacks
10:24
will occur today.
10:26
The physics does not change.
10:28
As Earth warms,
10:30
now because of extra CO2 we put in the atmosphere,
10:32
ice will melt,
10:35
and CO2 and methane will be released
10:37
by warming ocean and melting permafrost.
10:39
While we can't say exactly how fast
10:42
these amplifying feedbacks will occur,
10:45
it is certain they will occur,
10:48
unless we stop the warming.
10:51
There is evidence
10:53
that feedbacks are already beginning.
10:55
Precise measurements
10:58
by GRACE, the gravity satellite,
11:00
reveal that both Greenland and Antarctica
11:02
are now losing mass,
11:05
several hundred cubic kilometers per year.
11:07
And the rate has accelerated
11:10
since the measurements began
11:12
nine years ago.
11:14
Methane is also beginning
11:16
to escape from the permafrost.
11:18
What sea level rise
11:21
can we look forward to?
11:23
The last time CO2 was 390 ppm,
11:25
today's value,
11:28
sea level was higher
11:30
by at least 15 meters, 50 feet.
11:32
Where you are sitting now
11:35
would be under water.
11:37
Most estimates are that, this century,
11:39
we will get at least one meter.
11:42
I think it will be more
11:44
if we keep burning fossil fuels,
11:46
perhaps even five meters, which is 18 feet,
11:48
this century or shortly thereafter.
11:51
The important point
11:54
is that we will have started a process
11:56
that is out of humanity's control.
11:59
Ice sheets would continue to disintegrate for centuries.
12:02
There would be no stable shoreline.
12:05
The economic consequences are almost unthinkable.
12:07
Hundreds of New Orleans-like devastations
12:10
around the world.
12:14
What may be more reprehensible,
12:16
if climate denial continues,
12:18
is extermination of species.
12:20
The monarch butterfly
12:22
could be one of the 20 to 50 percent of all species
12:24
that the Intergovernmental Panel on Climate Change estimates
12:29
will be ticketed for extinction
12:32
by the end of the century
12:34
if we stay on business-as-usual fossil fuel use.
12:36
Global warming is already affecting people.
12:40
The Texas, Oklahoma, Mexico
12:43
heatwave and drought last year,
12:45
Moscow the year before
12:48
and Europe in 2003,
12:50
were all exceptional events,
12:52
more than three standard deviations outside the norm.
12:55
Fifty years ago,
12:59
such anomalies
13:01
covered only two- to three-tenths
13:03
of one percent of the land area.
13:05
In recent years,
13:07
because of global warming,
13:09
they now cover about 10 percent --
13:11
an increase by a factor of 25 to 50.
13:13
So we can say with a high degree of confidence
13:16
that the severe Texas and Moscow heatwaves
13:19
were not natural;
13:21
they were caused by global warming.
13:23
An important impact,
13:26
if global warming continues,
13:28
will be on the breadbasket of our nation and the world,
13:30
the Midwest and Great Plains,
13:33
which are expected to become prone to extreme droughts,
13:35
worse than the Dust Bowl,
13:38
within just a few decades,
13:40
if we let global warming continue.
13:42
How did I get dragged deeper and deeper
13:46
into an attempt to communicate,
13:49
giving talks in 10 countries, getting arrested,
13:51
burning up the vacation time
13:54
that I had accumulated over 30 years?
13:56
More grandchildren helped me along.
14:00
Jake is a super-positive,
14:03
enthusiastic boy.
14:05
Here at age two and a half years,
14:08
he thinks he can protect
14:10
his two and a half-day-old little sister.
14:12
It would be immoral
14:15
to leave these young people
14:17
with a climate system
14:19
spiraling out of control.
14:21
Now the tragedy about climate change
14:23
is that we can solve it
14:26
with a simple, honest approach
14:28
of a gradually rising carbon fee
14:30
collected from fossil fuel companies
14:33
and distributed 100 percent electronically
14:35
every month to all legal residents
14:39
on a per capita basis,
14:41
with the government not keeping one dime.
14:43
Most people would get more in the monthly dividend
14:47
than they'd pay in increased prices.
14:50
This fee and dividend
14:52
would stimulate the economy
14:54
and innovations,
14:56
creating millions of jobs.
14:58
It is the principal requirement
15:00
for moving us rapidly
15:02
to a clean energy future.
15:05
Several top economists
15:07
are coauthors on this proposition.
15:09
Jim DiPeso of Republicans for Environmental Protection
15:12
describes it thusly:
15:15
"Transparent. Market-based.
15:17
Does not enlarge government.
15:19
Leaves energy decisions to individual choices.
15:21
Sounds like a conservative climate plan."
15:24
But instead of placing a rising fee on carbon emissions
15:28
to make fossil fuels pay
15:32
their true cost to society,
15:35
our governments are forcing the public
15:37
to subsidize fossil fuels
15:40
by 400 to 500 billion dollars
15:43
per year worldwide,
15:46
thus encouraging extraction of every fossil fuel --
15:48
mountaintop removal,
15:51
longwall mining, fracking,
15:53
tar sands, tar shale,
15:55
deep ocean Arctic drilling.
15:57
This path, if continued,
16:00
guarantees that we will pass tipping points
16:02
leading to ice sheet disintegration
16:05
that will accelerate out of control of future generations.
16:07
A large fraction of species
16:11
will be committed to extinction.
16:13
And increasing intensity of droughts and floods
16:15
will severely impact breadbaskets of the world,
16:17
causing massive famines
16:20
and economic decline.
16:22
Imagine a giant asteroid
16:26
on a direct collision course with Earth.
16:29
That is the equivalent
16:33
of what we face now.
16:35
Yet, we dither,
16:37
taking no action
16:39
to divert the asteroid,
16:41
even though the longer we wait,
16:43
the more difficult and expensive it becomes.
16:45
If we had started in 2005,
16:49
it would have required emission reductions of three percent per year
16:51
to restore planetary energy balance
16:54
and stabilize climate this century.
16:57
If we start next year,
17:00
it is six percent per year.
17:02
If we wait 10 years, it is 15 percent per year --
17:04
extremely difficult and expensive,
17:07
perhaps impossible.
17:09
But we aren't even starting.
17:12
So now you know what I know
17:14
that is moving me to sound this alarm.
17:17
Clearly, I haven't gotten this message across.
17:20
The science is clear.
17:23
I need your help
17:26
to communicate the gravity and the urgency
17:28
of this situation
17:30
and its solutions
17:32
more effectively.
17:34
We owe it to our children and grandchildren.
17:36
Thank you.
17:38
(Applause)
17:40

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James Hansen - Climatologist
James Hansen has made key insights into our global climate -- and inspired a generation of activists and scientists.

Why you should listen

James Hansen is Adjunct Professor of Earth and Environmental Sciences at Columbia University’s Earth Institute. He was trained in physics and astronomy in the space science program of James Van Allen at the University of Iowa. His early research on the clouds of Venus helped identify their composition as sulfuric acid. Since the late 1970s, he has focused his research on Earth's climate, especially human-made climate change. From 1981 to 2013, he headed the NASA Godard Institute for Space Studies. He is also a member of the National Academy of Sciences.

Hansen is known for his testimony on climate change to congressional committees in the 1980s that helped raise broad awareness of the global warming issue. Hansen is recognized for speaking truth to power, for identifying ineffectual policies as greenwash, and for outlining the actions that the public must take to protect the future of young people and the other species on the planet.

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