This frozen library, the National Ice Core Lab
in Denver, Colorado, has ice from all over…
kept at minus 35 degrees. The oldest core
here goes back some 400,000 years. Here really ancient ice
from Greenland in the north, and Antarctica
in the south, reveals Earth’s
climate history. Let’s see what cores
like this can tell us. First are those
layers I mentioned in the
New Zealand snow. They’ve turned to ice,
and we can count them, summer, winter,
summer, winter. Like tree-rings,
we can date the core. Other cores
tell other stories. Look at this… it’s the ash of
an Icelandic volcano that blew up to
Greenland 50,000 years ago. Cores hold other and even
more important secrets… look at
these bubbles. They formed as
the snow turned to ice and trapped old air
that’s still in there. Scientists now are working
with cores from Antarctica that go back
even further. They tell us, with a very
high degree of accuracy, how much carbon dioxide
was in the air that far back. Researchers break chunks
of ice in vacuum chambers and carefully analyze
the gases that come off. They’re able to
measure very precisely levels of carbon dioxide
in that ancient air. Looking at the cores, we
see a pattern that repeats… 280 parts per
million of CO2, then 180,
280, 180, 280. By analyzing the chemistry
of the oxygen atoms in the ice you can also
see the pattern of rising and falling
temperature over time. Colder during
the ice ages, warmer during the
interglacial periods. Now put the two
lines together… and you can see
how closely temperature and carbon dioxide
track each other. They’re not
exactly alike. At times the orbits
caused a little
temperature change before the
feedback effects
of CO2 joined in. But, just as we
saw in New Zealand, we can’t explain
the large size of the changes
in temperature without
the effects of CO2. This is the signature
of natural variation, the cycle of
the ice ages driven by changes
in Earth’s orbit, with no
human involvement. But here’s
where we are today. In just 250 years, since
the Industrial Revolution, we’ve blown past 380 with
no sign of slowing down. It’s a level not seen in
more than 400,000 years, forty times longer than the
oldest human civilization.

Author Since: Mar 11, 2019

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