Narrator: Burning fossil fuel
emits black soot and other pollutants
that fall out of the atmosphere quite quickly.
But it also releases carbon dioxide, which remains
in the air much longer, to influence Earth's climate.
Richard Alley's ice core research shows that sometimes
the Earth experiences abrupt climate changes,
known as tipping points.
And if we keep on burning fossil fuels
without capturing CO2 emissions, we may increase
the risk of pushing Earth's climate over the edge.
It might be wise to Look Before You Leap.
Richard Alley: The Earth's climate system
is usually well-behaved--
a little more Sun, a little more CO2,
and we get a predictable amount of warming.
This is the pattern of natural variability of the climate
our planet has experienced over the past 400 thousand years,
as recorded in the physics and chemistry of ice cores.
The regular ups and downs in temperature are the result
of changes in Earth's orbit around the Sun,
and their subsequent effects on levels of carbon dioxide
and other heat-trapping gases.
You can think of this natural variation
as the Ice Age roller coaster.
As a geologist, I'm at home in the vast expanses of time.
So let's take a ride, cresting hills
and rolling through valleys,
following the more-or-less regular pattern
of changing climate, over hundreds of thousands of years.
Here we're down at 180 parts per million of CO2,
and in an Ice Age.
Now we're climbing to 280 parts per million,
a warmer interglacial period.
Then down to a cold 180 and up again, to a warmer 280.
Then repeating 180-280, the natural cycling
of the climate roller coaster.
But if we look in greater detail at 100,000 years
of Earth history, and specifically
at the ice core record from Greenland,
it's obvious our planet's climate hasn't always
had smooth ups and downs.
Occasionally, we cross some sort
of a tipping point, and the Earth evolves
really rapidly to a new state which is very different.
Over the last 100,000 years of the Ice Age cycling,
we've had a couple of dozen of these large, abrupt,
widespread climate shifts, almost as if the Earth
was bungy-jumping off the climate roller coaster.
Of course, you'd have to be a little nuts
to bungy off a roller coaster.
Which is why I'm leaving this to my computer avatar.
But these abrupt climate changes are real.
Here's one of the largest and most recent.
About 13,000 years ago, as the Earth was climbing out
of the last Ice Age, the North passed a tipping
point and rapidly slid back into a cold millennium--
drying monsoon regions of Asia where huge populations
now rely on rain, and warming the South.
There was weather and climate disruption world-wide.
But then, another tipping point was reached,
and in ten years or so, temperatures in Greenland rose
by about 10 degrees Centigrade, 18 Fahrenheit--
numbers we know with high confidence
from the ice core record.
Today, whatever climate model we use to project the impact
of rising levels of CO2, you see a relatively smooth curve,
heading upward, but in principle
a change we could adapt to.
But Earth's history shows us that Earth's climate
doesn't always work this way.
Sometimes it really does get as crazy and unpredictable
as bungy jumping off the climate roller coaster.
An abrupt climate change could be really bad for people.
We're optimistic that we won't have one, but we're not certain.
And the science suggests that the harder and faster
we turn the CO2 knob, the more likely we are
to cross a tipping point and trigger one.
Yet here we are today, racing up a hill to who knows where.
As burning fossil fuels means we've blown past
390 parts per million, without slowing down.
Will our ascent be smooth and manageable?
Or will our ride come off the rails?
If we wanted to take out insurance
against the possibility of such a change,
we could look at slowing down now before we tip over the edge.
